MOSFET amp thump.

[Dave Plowman (News)]

Pretty basic MOSFET power amp.

I'm used to it thumping at switch on. No speaker relay in this basic
design.

But one of them as taken to thumping at switch off. Not always, which
makes fault finding more tricky.

Most likely cause?

--
*Change is inevitable, except from a vending machine*

Dave Plowman London SW
To e-mail, change noise into sound.

[Jim Lesurf[_2_]]

In article >, Dave Plowman (News)
> wrote:
> Pretty basic MOSFET power amp.

> I'm used to it thumping at switch on. No speaker relay in this basic
> design.

> But one of them as taken to thumping at switch off. Not always, which
> makes fault finding more tricky.

> Most likely cause?

Circuit diagram might help diagnosis. I'm also not clear if the "switch
off" thump is at the instant you switch off, or a short time later.

My first guess is that something is adding a dc offset that now causes the
thump as the amp bias collapses and it is abruptly removed. However I can
only guess due to lack of detailed info.

Jim

--
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Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

[Brian Gaff]

Some kind of imbalance in the discharge of something?
I was wondering, if I take out a relay in the speaker feed of a mosfet amp
made by Denon, whether it will just thump or could it cause damage to the
amp or speakers?
Its nice not to have it but the number of times I need to clean the relay
contacts is getting stupid.

Brian

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"Dave Plowman (News)" > wrote in message
...
> Pretty basic MOSFET power amp.
>
> I'm used to it thumping at switch on. No speaker relay in this basic
> design.
>
> But one of them as taken to thumping at switch off. Not always, which
> makes fault finding more tricky.
>
> Most likely cause?
>
> --
> *Change is inevitable, except from a vending machine*
>
> Dave Plowman London SW
> To e-mail, change noise into sound.

[Trevor Wilson]

On 27/04/2016 11:06 PM, Dave Plowman (News) wrote:
> Pretty basic MOSFET power amp.
>
> I'm used to it thumping at switch on. No speaker relay in this basic
> design.
>
> But one of them as taken to thumping at switch off. Not always, which
> makes fault finding more tricky.
>
> Most likely cause?
>

**Cosmic rays? Who knows? Without a GREAT DEAL more information, no one
can help you. Brand and model numbers would be helpful at the very
least. A schematic would be better.

Do you REALLY expect useful advice with so little information?

--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison[_3_]]

Dave Plowman (Nutcase) wrote:
>
> Pretty basic MOSFET power amp.
>
> I'm used to it thumping at switch on. No speaker relay in this basic
> design.
>

** You posted the same here in December last year.


> But one of them as taken to thumping at switch off. Not always, which
> makes fault finding more tricky.
>
> Most likely cause?


** Old and bad electros are the cause of almost everything.


BTW; anyone familiar with the famous Crown DC300A ?

Both channels would emit a long squeal about 10 seconds after switch off - it sounded much like a party balloon being let down while squeezing the neck.

There was a note inserted in later service manuals that *no attempt* should be made to fix the problem, as any possible fix would render the amp unstable.




..... Phil

[Jim Lesurf[_2_]]

In article >, Phil
Allison > wrote:

> BTW; anyone familiar with the famous Crown DC300A ?

> Both channels would emit a long squeal about 10 seconds after switch off
> - it sounded much like a party balloon being let down while squeezing
> the neck.

Sounds like the amp was blowing a raspberry at the user for daring to turn
it off! :-)

Jim

--
Please use the address on the audiomisc page if you wish to email me.
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[Eiron[_3_]]

On 28/04/2016 02:44, Phil Allison wrote:

> BTW; anyone familiar with the famous Crown DC300A ?
>
> Both channels would emit a long squeal about 10 seconds after switch off - it sounded much like a party balloon being let down while squeezing the neck.
>
> There was a note inserted in later service manuals that *no attempt* should be made to fix the problem, as any possible fix would render the amp unstable.


My preamplifier did that.
http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1977/Distortion%20in%20low-noise%20amplifiers.pdf

It wasn't enough to damage the tweeters so I didn't worry about it.

--
Eiron.

[Don Pearce[_3_]]

On Wed, 27 Apr 2016 18:44:59 -0700 (PDT), Phil Allison
> wrote:

>Dave Plowman (Nutcase) wrote:
>>
>> Pretty basic MOSFET power amp.
>>
>> I'm used to it thumping at switch on. No speaker relay in this basic
>> design.
>>
>
> ** You posted the same here in December last year.
>
>
>> But one of them as taken to thumping at switch off. Not always, which
>> makes fault finding more tricky.
>>
>> Most likely cause?
>
>
>** Old and bad electros are the cause of almost everything.
>
>
>BTW; anyone familiar with the famous Crown DC300A ?
>
>Both channels would emit a long squeal about 10 seconds after switch off - it sounded much like a party balloon being let down while squeezing the neck.
>
>There was a note inserted in later service manuals that *no attempt* should be made to fix the problem, as any possible fix would render the amp unstable.
>
>
>
>
>.... Phil

So they had an instability they couldn't fix, but sales took it off
the engineers and put it in the market anyway? Why am I not
surprised?

I don't know the design, but assuming it is an op-amp (as most audio
amps are) it shouldn't be beyond the wit of man to get a dominant pole
into the loop.

d

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[Brian Gaff]

I recall an old Onkyo did something similar to that. It was not a mosfet one
though.
Brian

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"Jim Lesurf" > wrote in message
...
> In article >, Phil
> Allison > wrote:
>
>> BTW; anyone familiar with the famous Crown DC300A ?
>
>> Both channels would emit a long squeal about 10 seconds after switch off
>> - it sounded much like a party balloon being let down while squeezing
>> the neck.
>
> Sounds like the amp was blowing a raspberry at the user for daring to turn
> it off! :-)
>
> Jim
>
> --
> Please use the address on the audiomisc page if you wish to email me.
> Electronics
> http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
> Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
> Audio Misc http://www.audiomisc.co.uk/index.html
>

[Phil Allison[_3_]]

Don Pearce wrote:
>
> >
> >BTW; anyone familiar with the famous Crown DC300A ?
> >
> >Both channels would emit a long squeal about 10 seconds after switch off
> > - it sounded much like a party balloon being let down while squeezing
> > the neck.
> >
> >There was a note inserted in later service manuals that *no attempt*
> should be made to fix the problem, as any possible fix would render the
> amp unstable.
> >
> >
> >
>
> So they had an instability they couldn't fix, but sales took it off
> the engineers and put it in the market anyway? Why am I not
> surprised?
>

** The DC300A is perfectly stable with any load and all frequencies.

When the AC supply is removed, an internal +10V boost rail above the main positive rail quickly dies removing current from the class A driver stage - which pretty much disables the output stage.

When the DC rails to the input op-amp ( a uA739 ) drop below a working level, the squealing sound arrives. Its not particularly loud and does not depends on load conditions. The frequency is a few kHz, falling in pitch until there is almost no charge left in the main filter caps.

I know about it since I was asked to fix the noise by a customer who owned a DC300A. The solution was to fit a speaker relay with switch on delay and fast off.

I only mentioned this as an example of how trying to fix a small problem can lead to creating a much worse one. I suspect trying to fix inbuilt turn on/off transients in power amps are mostly like this.

IOW - " leave good enough alone ".



.... Phil

[Dave Plowman (News)]

In article >,
Phil Allison > wrote:
> Dave Plowman (Nutcase) wrote:
> >
> > Pretty basic MOSFET power amp.
> >
> > I'm used to it thumping at switch on. No speaker relay in this basic
> > design.
> >

> ** You posted the same here in December last year.

About switch on thump. This is at switch off, and a fault.

> > But one of them as taken to thumping at switch off. Not always, which
> > makes fault finding more tricky.
> >
> > Most likely cause?


> ** Old and bad electros are the cause of almost everything.

They are all relatively new, and good quality. Not to say one can't have
failed. There are only 4 electros in this pretty basic design. Two are
across the supply rails, one on the input, and the most likely one a low
ESR type which is part of a RC network across the speaker output.

But the fault hasn't occurred again.


> BTW; anyone familiar with the famous Crown DC300A ?

> Both channels would emit a long squeal about 10 seconds after switch off
> - it sounded much like a party balloon being let down while squeezing
> the neck.

> There was a note inserted in later service manuals that *no attempt*
> should be made to fix the problem, as any possible fix would render the
> amp unstable.




> .... Phil

--
*HOW DO THEY GET DEER TO CROSS THE ROAD ONLY AT THOSE YELLOW ROAD SIGNS?

Dave Plowman London SW
To e-mail, change noise into sound.

[Don Pearce[_3_]]

On Fri, 29 Apr 2016 19:17:55 -0700 (PDT), Phil Allison
> wrote:

>Don Pearce wrote:
>>
>> >
>> >BTW; anyone familiar with the famous Crown DC300A ?
>> >
>> >Both channels would emit a long squeal about 10 seconds after switch off
>> > - it sounded much like a party balloon being let down while squeezing
>> > the neck.
>> >
>> >There was a note inserted in later service manuals that *no attempt*
>> should be made to fix the problem, as any possible fix would render the
>> amp unstable.
>> >
>> >
>> >
>>
>> So they had an instability they couldn't fix, but sales took it off
>> the engineers and put it in the market anyway? Why am I not
>> surprised?
>>
>
>** The DC300A is perfectly stable with any load and all frequencies.
>
>When the AC supply is removed, an internal +10V boost rail above the main positive rail quickly dies removing current from the class A driver stage - which pretty much disables the output stage.
>
>When the DC rails to the input op-amp ( a uA739 ) drop below a working level, the squealing sound arrives. Its not particularly loud and does not depends on load conditions. The frequency is a few kHz, falling in pitch until there is almost no charge left in the main filter caps.
>
>I know about it since I was asked to fix the noise by a customer who owned a DC300A. The solution was to fit a speaker relay with switch on delay and fast off.
>
>I only mentioned this as an example of how trying to fix a small problem can lead to creating a much worse one. I suspect trying to fix inbuilt turn on/off transients in power amps are mostly like this.
>
>IOW - " leave good enough alone ".
>
>
>
>... Phil

I certainly agree that there is very little point for the end user to
try and fix this. But it is a design flaw and should have been fixed
by the original engineers.

Speaker relay? Yes, that will stop you hearing it, but it doesn't fix
the problem.

d

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[Jim Lesurf[_2_]]

In article >, Don Pearce
> wrote:
> I certainly agree that there is very little point for the end user to
> try and fix this. But it is a design flaw and should have been fixed by
> the original engineers.

> Speaker relay? Yes, that will stop you hearing it, but it doesn't fix
> the problem.

FWIW When designing the 730/732 amps the development *preamp* design at
one point tended to give bursts of about 1MHz about ten secs after being
turned off. It was coming from ICs being used to regulate and stabilise the
rails.

I solved it by not using ICs in the PSU.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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[Don Pearce[_3_]]

On Sat, 30 Apr 2016 12:44:07 +0100, Jim Lesurf >
wrote:

>In article >, Don Pearce
> wrote:
>> I certainly agree that there is very little point for the end user to
>> try and fix this. But it is a design flaw and should have been fixed by
>> the original engineers.
>
>> Speaker relay? Yes, that will stop you hearing it, but it doesn't fix
>> the problem.
>
>FWIW When designing the 730/732 amps the development *preamp* design at
>one point tended to give bursts of about 1MHz about ten secs after being
>turned off. It was coming from ICs being used to regulate and stabilise the
>rails.
>
>I solved it by not using ICs in the PSU.
>
>Jim

Fair enough. Why were you regulating the rails - couldn't get the kind
of CMRR you were after from the preamp?

d

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[Jim Lesurf[_2_]]

In article >, Don Pearce
> wrote:

> Fair enough. Why were you regulating the rails - couldn't get the kind
> of CMRR you were after from the preamp?

So far as I recall, it was purely because I started off assuming I might as
well. At the time the 'conventional wisdom' was to use ICs to regulate
rails, and discrete devices for the amp stages.

But I eventually concluded that making a 'smooth' PSU was simpler and
worked nicely. FWIW The stages had decent rejection, and I added per-stage
rail decoupling anyway. So I ended up with some transistors in the PSU
(essentially capacitance multipliers) and ICs for the gain stages. Simply
found it worked nicely.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

[Phil Allison[_3_]]

Don Pearce wrote:

> Phil Allison
>
> >>
> >> So they had an instability they couldn't fix, but sales took it off
> >> the engineers and put it in the market anyway? Why am I not
> >> surprised?
> >>
> >
> >** The DC300A is perfectly stable with any load and all frequencies.
> >
> >When the AC supply is removed, an internal +10V boost rail above the
> >main positive rail quickly dies removing current from the class A
> >driver stage - which pretty much disables the output stage.
> >
> >When the DC rails to the input op-amp ( a uA739 ) drop below a working
> > level, the squealing sound arrives. Its not particularly loud and does
> > not depends on load conditions. The frequency is a few kHz, falling
> >in pitch until there is almost no charge left in the main filter caps.
> >
> >I know about it since I was asked to fix the noise by a customer who
> >owned a DC300A. The solution was to fit a speaker relay with switch on
> >delay and fast off.
> >
> >I only mentioned this as an example of how trying to fix a small problem
> >can lead to creating a much worse one. I suspect trying to fix inbuilt
> >turn on/off transients in power amps are mostly like this.
> >
> >IOW - " leave good enough alone ".
> >
> >
>
> I certainly agree that there is very little point for the end user to
> try and fix this. But it is a design flaw and should have been fixed
> by the original engineers.
>

** It was not a problem that needed fixing.

The DC300A was marketed as a laboratory & professional use amplifier - not a home audio one.


> Speaker relay? Yes, that will stop you hearing it, but it doesn't fix
> the problem.
>

** Speaker muting relays have been standard features in countless home and professional audio amplifiers for decades. Their main purpose is to stop transients at switch on/off from being heard.

The last Onkyo 7.2 channel receiver I serviced had 9 chunky relays, one for each power amp, one in the AC supply and one in the main AC secondary for standby.

They are very much the solution to the problem.



..... Phil

[Don Pearce[_3_]]

On Sat, 30 Apr 2016 18:01:30 +0100, Jim Lesurf >
wrote:

>In article >, Don Pearce
> wrote:
>
>> Fair enough. Why were you regulating the rails - couldn't get the kind
>> of CMRR you were after from the preamp?
>
>So far as I recall, it was purely because I started off assuming I might as
>well. At the time the 'conventional wisdom' was to use ICs to regulate
>rails, and discrete devices for the amp stages.
>
>But I eventually concluded that making a 'smooth' PSU was simpler and
>worked nicely. FWIW The stages had decent rejection, and I added per-stage
>rail decoupling anyway. So I ended up with some transistors in the PSU
>(essentially capacitance multipliers) and ICs for the gain stages. Simply
>found it worked nicely.
>
>Jim

And back then regulators, as I remember, were incredibly noisy at
their outputs. You could kill that with a series resistor plus big
electrolytic, but that kind of destroyed the regulation. As you say,
for the kind of current drawn by a preamp, smoothing the PSU is really
no problem.

d

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[Dave Plowman (News)]

In article >,
Phil Allison > wrote:
> > Speaker relay? Yes, that will stop you hearing it, but it doesn't fix
> > the problem.
> >

> ** Speaker muting relays have been standard features in countless home
> and professional audio amplifiers for decades. Their main purpose is to
> stop transients at switch on/off from being heard.

They can also include a circuit to make them drop out if they detect a
large DC offset. Very good way of protecting speakers in event of a fault.

--
*Cleaned by Stevie Wonder, checked by David Blunkett*

Dave Plowman London SW
To e-mail, change noise into sound.

[Phil Allison[_3_]]

Dave Plowman (News) wrote:

>
>
> > ** Speaker muting relays have been standard features in countless home
> > and professional audio amplifiers for decades. Their main purpose is to
> > stop transients at switch on/off from being heard.
>
>
> They can also include a circuit to make them drop out if they detect a
> large DC offset. Very good way of protecting speakers in event of a fault.
>
>

** Few speaker relay systems provide reliable protection if that happens - nor do they claim to.

The simple fact being that the kind of relays used are only capable of switching *off* DC voltages to a maximum of 30V at rated current. IOW, their current breaking capacity is very limited for DC voltages.

What happens instead is a continuous arc forms between the contacts as they open and persists until the relay is destroyed along with the speaker voice coil as well.

Amplifiers with DC supply rails under 50V may allow the arc to break, but any higher and there is practically no chance.



.... Phil

[Dave Plowman (News)]

In article >,
Phil Allison > wrote:
> > They can also include a circuit to make them drop out if they detect a
> > large DC offset. Very good way of protecting speakers in event of a
> > fault.
> >
> >

> ** Few speaker relay systems provide reliable protection if that happens
> - nor do they claim to.

I'm talking about those which do.

> The simple fact being that the kind of relays used are only capable of
> switching *off* DC voltages to a maximum of 30V at rated current. IOW,
> their current breaking capacity is very limited for DC voltages.

Then use a relay fit for purpose. Fraction of the cost of a speaker repair.

--
*Why don't sheep shrink when it rains?

Dave Plowman London SW
To e-mail, change noise into sound.

[Trevor Wilson]

On 1/05/2016 11:18 PM, Dave Plowman (News) wrote:
> In article >,
> Phil Allison > wrote:
>>> They can also include a circuit to make them drop out if they detect a
>>> large DC offset. Very good way of protecting speakers in event of a
>>> fault.
>>>
>>>
>
>> ** Few speaker relay systems provide reliable protection if that happens
>> - nor do they claim to.
>
> I'm talking about those which do.
>
>> The simple fact being that the kind of relays used are only capable of
>> switching *off* DC voltages to a maximum of 30V at rated current. IOW,
>> their current breaking capacity is very limited for DC voltages.
>
> Then use a relay fit for purpose. Fraction of the cost of a speaker repair.
>

**High Voltage (>30 VDC) DC relays are quite expensive. Certainly more
expensive than mid-range bass drivers.

http://uk.farnell.com/te-connectivity-potter-brumfield/prd-11dh0-24/relay-dpdt-125vdc-20a/dp/1386559

You STILL haven't told us the brand and model of the amplifier. Failing
that, you could point us to a schematic.

--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison[_3_]]

Dave Plowman (News) wrote:
>
>
>
> > ** Few speaker relay systems provide reliable protection if that happens
> > - nor do they claim to.
>
> I'm talking about those which do.
>

** Bet you have never seen one.



.... Phil

[Phil Allison[_3_]]

Trevor Wilson wrote:

>
> >
> > Then use a relay fit for purpose. Fraction of the cost of a speaker repair.
> >
>
> **High Voltage (>30 VDC) DC relays are quite expensive. Certainly more
> expensive than mid-range bass drivers.
>

http://uk.farnell.com/te-connectivity-potter-brumfield/prd-11dh0-24/relay-dpdt-125vdc-20a/dp/1386559


** Such a large and expensive relay is quite impractical for use in a domestic hi-fi amplifier - also note that it needs powerful magnets for "magnetic blow out" of the arc to meet the 125V spec with DC.

A simple triac "crow bar" gives low cost, very effective DC protection for speakers - but surprisingly few amps have them fitted, the Quad 405 being an exception.


..... Phil

[Iain Churches[_2_]]

> In article >, Phil
> Allison > wrote:
>
>> BTW; anyone familiar with the famous Crown DC300A ?
>
>> Both channels would emit a long squeal about 10 seconds after switch off
>> - it sounded much like a party balloon being let down while squeezing
>> the neck.
>

Yes.- I remember it well.

The Crown DC 300A was a ubiquitous studio workhorse in the UK.
I still have a copy of the manual:

Laboratory amplifier. 155W pc minimum RMS 1Hz to 20kHz.
FR +/- 0.1dB DC - 20kHz at 1W into 8 Ohms
FR +/- 1 dB DC - 100Khz
HD < 0.001% 20Hz to 400 Hz increasing linbearly to 0.05% ar
20kHz at 150W RMS pc into 8 Ohms.
Output impedance <7 mOhms in series with < 3uHenries

Unconditionally stable with any load including completely
reactive.

The IM and THD charts that come with the manual are blank
and marked "Disclosure prohibited 4.11.1974"

Our chief of maintenance described it as "a good amp,
incredibly reliable and clean as a whistle DC to daylight!" :-)

It was frequenty partnered with the Lockwood Major Monitor, a
studio speaker with a Tannoy 15" Gold. A very impressive
combination.

The Crown (Amcron in some territories) was also used as a vinyl
cutting amp, driven from a inverse RIAA preamp. It gave very
good results. Recorded Productions Ltd in London W1 had such
a set up.



Iain

[Jim Lesurf[_2_]]

In article >,
Iain Churches > wrote:

[snip amp details]

> The IM and THD charts that come with the manual are blank
> and marked "Disclosure prohibited 4.11.1974"

I must confess I burst out laughing when I read that! Did they think the
detailed distortion performance of their amp was a 'trade secret' and that
no-one should be allowed either to know the spec or measure it for
themselves?!

8-]

Jim

--
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[Phil Allison[_3_]]

Jim Lesurf wrote:

>
>
> > The IM and THD charts that come with the manual are blank
> > and marked "Disclosure prohibited 4.11.1974"
>
>
> I must confess I burst out laughing when I read that! Did they think the
> detailed distortion performance of their amp was a 'trade secret' and that
> no-one should be allowed either to know the spec or measure it for
> themselves?!
>

** The word "prohibited" ought to tell you there was an FCC law in the USA that prevented making such disclosures.

The same FFC law allowed only continuous RMS power specs and then after a 1/3 power pre-conditioning session for 30 minutes.

The original law was Draconian and eventually became relaxed.



..... Phil

[Dave Plowman (News)]

In article >,
Jim Lesurf > wrote:
> In article >,
> Iain Churches > wrote:

> [snip amp details]

> > The IM and THD charts that come with the manual are blank
> > and marked "Disclosure prohibited 4.11.1974"

> I must confess I burst out laughing when I read that! Did they think the
> detailed distortion performance of their amp was a 'trade secret' and
> that no-one should be allowed either to know the spec or measure it for
> themselves?!

Possibly because the results were so bad? The Crown amp was loved by the
pop boys because it was loud and brash. But when used at normal levels for
GP stuff, bettered by many others.

--
*7up is good for you, signed snow white*

Dave Plowman London SW
To e-mail, change noise into sound.

[Iain Churches[_2_]]

"Dave Plowman (News)" > wrote in message
...
> In article >,
> Jim Lesurf > wrote:
>> In article >,
>> Iain Churches > wrote:
>
>> [snip amp details]
>
>> > The IM and THD charts that come with the manual are blank
>> > and marked "Disclosure prohibited 4.11.1974"
>
>> I must confess I burst out laughing when I read that! Did they think the
>> detailed distortion performance of their amp was a 'trade secret' and
>> that no-one should be allowed either to know the spec or measure it for
>> themselves?!
>
> Possibly because the results were so bad?

You snipped the figures I gave. They are excellent.


<z The Crown amp was loved by the
> pop boys because it was loud and brash. But when used at normal levels for
> GP stuff, bettered by many others.
>

The Crown amp was popular everywhere, it had the power to be loud
but not brash. Driving large Tannoys or Lockwoods it made a very
impressive monitor system. A good vinyl cutting amp also.

Iain

[Jim Lesurf[_2_]]

In article >, Phil
Allison > wrote:
> Jim Lesurf wrote:

> >
> >
> > > The IM and THD charts that come with the manual are blank and
> > > marked "Disclosure prohibited 4.11.1974"
> >
> >
> > I must confess I burst out laughing when I read that! Did they think
> > the detailed distortion performance of their amp was a 'trade secret'
> > and that no-one should be allowed either to know the spec or measure
> > it for themselves?!
> >

> ** The word "prohibited" ought to tell you there was an FCC law in the
> USA that prevented making such disclosures.

Why would the Federal Communications Commission prohibit a manufacturer of
audio amplifiers from publishing measurement charts of audio IM/THD?

> The same FFC law allowed only continuous RMS power specs and then after
> a 1/3 power pre-conditioning session for 30 minutes.

I can recall that the IHFA laid down IHFA-707 specs that required this. Had
to ensure the 700 power amps passed it to keep magazine reviewers happy.
But I don't recall it being mandated by the *FCC*. And the results weren't
then 'prohibited' from being published.

Do you mean FTC? I think the 1/3rd power malarky was their idea to stop all
the American claims for wildly overstated 'output powers'. But I can't
recall any FTC documentation I ever saw that made IM curves 'secret'.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
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[Dave Plowman (News)]

In article >,
Iain Churches > wrote:

> "Dave Plowman (News)" > wrote in message
> ...
> > In article >,
> > Jim Lesurf > wrote:
> >> In article >,
> >> Iain Churches > wrote:
> >
> >> [snip amp details]
> >
> >> > The IM and THD charts that come with the manual are blank
> >> > and marked "Disclosure prohibited 4.11.1974"
> >
> >> I must confess I burst out laughing when I read that! Did they think
> >> the detailed distortion performance of their amp was a 'trade secret'
> >> and that no-one should be allowed either to know the spec or measure
> >> it for themselves?!
> >
> > Possibly because the results were so bad?

> You snipped the figures I gave.

No I didn't.

> They are excellent.


> <z The Crown amp was loved by the
> > pop boys because it was loud and brash. But when used at normal levels
> > for GP stuff, bettered by many others.
> >

> The Crown amp was popular everywhere,

No it wasn't. ;-)

> it had the power to be loud
> but not brash.

Not on the tests I heard.


> Driving large Tannoys or Lockwoods it made a very
> impressive monitor system.

Tannoys never were the most critical of speaker chassis. Merely loud.

> A good vinyl cutting amp also.

No idea about that. But then some types of distortion isn't going to be
critical for that application anyway.

--
*If at first you don't succeed, try management *

Dave Plowman London SW
To e-mail, change noise into sound.

[Phil Allison[_3_]]

Jim Lesurf wrote:

> > >
> > >
> > > > The IM and THD charts that come with the manual are blank and
> > > > marked "Disclosure prohibited 4.11.1974"
> > >
> > >
> > > I must confess I burst out laughing when I read that! Did they think
> > > the detailed distortion performance of their amp was a 'trade secret'
> > > and that no-one should be allowed either to know the spec or measure
> > > it for themselves?!
> > >
>
> > ** The word "prohibited" ought to tell you there was an FCC law in the
> > USA that prevented making such disclosures.
>
> Why would the Federal Communications Commission prohibit a manufacturer of
> audio amplifiers from publishing measurement charts of audio IM/THD?


** In 1974, the FTC ( Federal Trade Commission ) specified a set of rules for quoting amplifier power output specs and banned all others.


>
> > The same FFC law allowed only continuous RMS power specs and then after
> > a 1/3 power pre-conditioning session for 30 minutes.
>
> Do you mean FTC?

** Yes.


> I think the 1/3rd power malarky was their idea to stop all
> the American claims for wildly overstated 'output powers'. But I can't
> recall any FTC documentation I ever saw that made IM curves 'secret'.
>

** The 30 minute, 1/3 power pre-conditioning test was to eliminate amplifiers with inadequate heat sinks claiming max power outputs that could not be sustained continuously with music program. It was a very tough test that caught a lot of good amplifiers out since it is the exact level that produces max self heating in a class B or low bias AB stage.

Crown's instruction manuals at the time contained curves that showed power response with one channel driven, THD and IM for various impedances and frequencies plus a VI limiting graph.

This broke the FTC rule that published power specs be for 8 ohm loads only with both channels driven and with a specified THD limit over a 20 to 20kHz band.

I have contemporary manuals on hand for the Crown D60 and D150 models - the former with all graphs included and the latter with the offending ones obscured.

BTW:

What you cannot recall is hardly worth a mention.



..... Phil

[Jim Lesurf[_2_]]

In article >, Phil
Allison > wrote:

> This broke the FTC rule that published power specs be for 8 ohm loads
> only with both channels driven and with a specified THD limit over a 20
> to 20kHz band.

Now we've clarified that it was FTC: Yes, I knew they mandated that and
that the power 'rating' had to be given for 8 Ohms under the accumulated
1/3rd power for an hour 'preconditioning'. What I didn't know, or have
forgotten, is that they also forbade any other mention of IM versus
power/frequency *along with* the 8 Ohm 'rated' values. Seems weird
to prevent people knowing what happens *in addition* to the standardised
'power rating' value.

Would have made choosing an amp rather difficult given that most speakers
aren't 8 Ohm resistors. I'll see if I can find my old IHFA-707 leaflet.

Occurs to me that it might not have helped Crown sell the amps for
the purpose of driving cutters, either!

Jim

--
Please use the address on the audiomisc page if you wish to email me.
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Audio Misc http://www.audiomisc.co.uk/index.html

[Don Pearce[_3_]]

On Wed, 04 May 2016 14:59:40 +0100, Jim Lesurf >
wrote:

>In article >, Phil
>Allison > wrote:
>
>> This broke the FTC rule that published power specs be for 8 ohm loads
>> only with both channels driven and with a specified THD limit over a 20
>> to 20kHz band.
>
>Now we've clarified that it was FTC: Yes, I knew they mandated that and
>that the power 'rating' had to be given for 8 Ohms under the accumulated
>1/3rd power for an hour 'preconditioning'. What I didn't know, or have
>forgotten, is that they also forbade any other mention of IM versus
>power/frequency *along with* the 8 Ohm 'rated' values. Seems weird
>to prevent people knowing what happens *in addition* to the standardised
>'power rating' value.
>
>Would have made choosing an amp rather difficult given that most speakers
>aren't 8 Ohm resistors. I'll see if I can find my old IHFA-707 leaflet.
>
>Occurs to me that it might not have helped Crown sell the amps for
>the purpose of driving cutters, either!
>
>Jim

Particularly strange given that they are quite happy to give a total
distortion rating. IM is relatively closely related, and it wouldn't
be hard to make a decent estimate.

What is not discussed is distortion at low output power - crossover
distortion, of course. FET amplifiers tend to be particularly poor
performers in this regard as the curves don't meet at all tidily.

d

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[Jim Lesurf[_2_]]

In article >, Don Pearce
> wrote:

> Particularly strange given that they are quite happy to give a total
> distortion rating. IM is relatively closely related, and it wouldn't be
> hard to make a decent estimate.

I think I may have some old Crown amp spec sheets somewhere. These would
be ones issued in the UK. If I can find them I'll see if they have the same
'prohibition' applied. The FTC had mo jurisdiction here, so Crown need not
have been concerned.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

[Dave Plowman (News)]

In article >,
Don Pearce > wrote:
> What is not discussed is distortion at low output power - crossover
> distortion, of course. FET amplifiers tend to be particularly poor
> performers in this regard as the curves don't meet at all tidily.

That may have been the problem in the tests I heard. For use in a TV
studio control room. You don't tend to drive a speaker hard for drama
monitoring. So what might suit the 'pop' boys may not be good for
everything.

--
*Whatever kind of look you were going for, you missed.

Dave Plowman London SW
To e-mail, change noise into sound.

[Phil Allison[_3_]]

Jim Lesurf wrote:
>
>
> > This broke the FTC rule that published power specs be for 8 ohm loads
> > only with both channels driven and with a specified THD limit over a 20
> > to 20kHz band.
>
> Now we've clarified that it was FTC:
>

** Small victories intrigue small minds.


> Yes, I knew they mandated that and
> that the power 'rating' had to be given for 8 Ohms under the accumulated
> 1/3rd power for an hour 'preconditioning'. What I didn't know, or have
> forgotten, is that they also forbade any other mention of IM versus
> power/frequency *along with* the 8 Ohm 'rated' values. Seems weird
> to prevent people knowing what happens *in addition* to the standardised
> 'power rating' value.
>

** The purpose was to prevent abominations like "PMPO into a 1ohm load" being mentioned. Having only one, industry accepted way seemed like a good idea at he time - as it levelled the playing field.


> Would have made choosing an amp rather difficult given that most speakers
> aren't 8 Ohm resistors.

** Yes, reactive load and low impedance behaviour is often important to know - but to this day requires test results that very few makers publish.

Using only published information, can you say which modern amps are safe to use with a Quad ESL57 or 63?


..... Phil

[Trevor Wilson]

On 5/05/2016 12:16 PM, Phil Allison wrote:
> Jim Lesurf wrote:
>>
>>
>>> This broke the FTC rule that published power specs be for 8 ohm loads
>>> only with both channels driven and with a specified THD limit over a 20
>>> to 20kHz band.
>>
>> Now we've clarified that it was FTC:
>>
>
> ** Small victories intrigue small minds.
>
>
>> Yes, I knew they mandated that and
>> that the power 'rating' had to be given for 8 Ohms under the accumulated
>> 1/3rd power for an hour 'preconditioning'. What I didn't know, or have
>> forgotten, is that they also forbade any other mention of IM versus
>> power/frequency *along with* the 8 Ohm 'rated' values. Seems weird
>> to prevent people knowing what happens *in addition* to the standardised
>> 'power rating' value.
>>
>
> ** The purpose was to prevent abominations like "PMPO into a 1ohm load" being mentioned. Having only one, industry accepted way seemed like a good idea at he time - as it levelled the playing field.
>
>
>> Would have made choosing an amp rather difficult given that most speakers
>> aren't 8 Ohm resistors.
>
> ** Yes, reactive load and low impedance behaviour is often important to know - but to this day requires test results that very few makers publish.
>
> Using only published information, can you say which modern amps are safe to use with a Quad ESL57 or 63?
>

**This one:

http://me-au.com/me850data2.jpg

It will even survive the crowbar protection system (until that
protection system is destroyed).


--
Trevor Wilson
www.rageaudio.com.au

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[Don Pearce[_3_]]

On Thu, 5 May 2016 15:12:49 +1000, Trevor Wilson
> wrote:

>On 5/05/2016 12:16 PM, Phil Allison wrote:
>> Jim Lesurf wrote:
>>>
>>>
>>>> This broke the FTC rule that published power specs be for 8 ohm loads
>>>> only with both channels driven and with a specified THD limit over a 20
>>>> to 20kHz band.
>>>
>>> Now we've clarified that it was FTC:
>>>
>>
>> ** Small victories intrigue small minds.
>>
>>
>>> Yes, I knew they mandated that and
>>> that the power 'rating' had to be given for 8 Ohms under the accumulated
>>> 1/3rd power for an hour 'preconditioning'. What I didn't know, or have
>>> forgotten, is that they also forbade any other mention of IM versus
>>> power/frequency *along with* the 8 Ohm 'rated' values. Seems weird
>>> to prevent people knowing what happens *in addition* to the standardised
>>> 'power rating' value.
>>>
>>
>> ** The purpose was to prevent abominations like "PMPO into a 1ohm load" being mentioned. Having only one, industry accepted way seemed like a good idea at he time - as it levelled the playing field.
>>
>>
>>> Would have made choosing an amp rather difficult given that most speakers
>>> aren't 8 Ohm resistors.
>>
>> ** Yes, reactive load and low impedance behaviour is often important to know - but to this day requires test results that very few makers publish.
>>
>> Using only published information, can you say which modern amps are safe to use with a Quad ESL57 or 63?
>>
>
>**This one:
>
>http://me-au.com/me850data2.jpg
>
>It will even survive the crowbar protection system (until that
>protection system is destroyed).

Why would anyone design that amplifier and say it is for music? One of
the most pointless specs I've ever read. You're just ****ing your
money away if you buy that.

d

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[Eiron[_3_]]

On 05/05/2016 07:17, Don Pearce wrote:
> On Thu, 5 May 2016 15:12:49 +1000, Trevor Wilson
> > wrote:


>> http://me-au.com/me850data2.jpg
>>
>> It will even survive the crowbar protection system (until that
>> protection system is destroyed).
>
> Why would anyone design that amplifier and say it is for music? One of
> the most pointless specs I've ever read. You're just ****ing your
> money away if you buy that.

Because of the Australian fashion for designing speakers with impedances
that drop to zero at the crossover frequencies.

--
Eiron.

[Phil Allison[_3_]]

Trevor Wilson wrote:

Phil Allison wrote:

>
> >
> > ** Yes, reactive load and low impedance behaviour is often important
> > to know - but to this day requires test results that very few makers
> > publish.
> >
> > Using only published information, can you say which modern amps are
> > safe to use with a Quad ESL57 or 63?
> >
>
> **This one:
>
> http://me-au.com/me850data2.jpg
>
> It will even survive the crowbar protection system (until that
> protection system is destroyed).
>

** Using the advice published by Quad, that old ME model is not suitable for use with either Quad ESL. Too many volts for the '57 and too many amps for the '63.

Quad advise the '57 is safe up to 33V peak ( 68 watts at 8 ohms) and the '63 should only be use with amplifiers that have VI limiting.

In both cases, the amplifier should also have good sub-sonic filtering - not flat response down to DC !!!



..... Phil

[Phil Allison[_3_]]

Eiron wrote:

>
>
> Because of the Australian fashion for designing speakers with impedances
> that drop to zero at the crossover frequencies.
>
>

** Not afraid of making a gross overstatement - are you ?

FYI:

There are far more examples of bad loudspeaker x-over design from the USA.

How about the once popular Acoustic Research AR11 model ??

http://www.classicspeakerpages.net/IP.Board/uploads/monthly_08_2009/post-103158-1251408626.jpg

All three drivers used are 4 ohms types with the dome mid and tweeter operating in *parallel* over the range above 2kHz - making the impedance 2 to 2.5 ohms in that range.



..... Phil

[Jim Lesurf[_2_]]

In article >, Trevor Wilson
> wrote:

> **This one:

> http://me-au.com/me850data2.jpg

> It will even survive the crowbar protection system (until that
> protection system is destroyed).

FWIW The Armstrong 732 is also "safe" for this... in the sense that the
amplifier will survive driving the 63/57 beyond their limits. Afraid I did
once set fire to a 57 when testing the 732. The amp was fine, but Quad were
somewhat surprised by the state of the 57 when I sent it for repair.

But I do agree with Phil's general point. It can often be quite hard to use
published specs for such matters. That's why "prohibiting" giving details
seems a really weird idea. It made sense to mandate how the 'rated' power
should be measured and specified. But it doesn't make sense to try and
'ban' any further details being given in addition.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

[Jim Lesurf[_2_]]

In article >, Don Pearce
> wrote:

> Why would anyone design that amplifier and say it is for music? One of
> the most pointless specs I've ever read. You're just ****ing your money
> away if you buy that.

Remember that some of us had to design amps in the era of some really
'demanding' speaker loadings like the old maggies. The problem became that
some speakers needed very high outputs into nastly loadings whilst others
were vulnerable. Some people using some speakers will want an amp that
would destroy another speaker. In the end, you have to choose what is
appropriate. This is why detailed info for users is important.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

[Trevor Wilson]

On 5/05/2016 5:37 PM, Phil Allison wrote:
> Eiron wrote:
>
>>
>>
>> Because of the Australian fashion for designing speakers with impedances
>> that drop to zero at the crossover frequencies.
>>
>>
>
> ** Not afraid of making a gross overstatement - are you ?
>
> FYI:
>
> There are far more examples of bad loudspeaker x-over design from the USA.
>
> How about the once popular Acoustic Research AR11 model ??
>
> http://www.classicspeakerpages.net/IP.Board/uploads/monthly_08_2009/post-103158-1251408626.jpg
>
> All three drivers used are 4 ohms types with the dome mid and tweeter operating in *parallel* over the range above 2kHz - making the impedance 2 to 2.5 ohms in that range.
>

**Or the Infinty 4.5. Two 4 Ohm voice coils in parallel, with another
pair of 2 Ohm voice coils operating in the low bass in parallel with
them. Back in the late 1970s, I was called in to investigate why the
speakers were destroying so many big amplifiers. I guess the 0.75 Ohm
load in the bass region had a lot to do with it. Even Peter Stein's
ME100 only lasted a few weeks (which is a lot longer than any Phase
Linear did), causing him to revise the VI limiting in that model to
cope. Apparently, the current limiting transistors over-dissipated, then
failed, leading to the eventual destruction of the output devices. Peter
always ensured his big amps could deal with such loads from that time on.


--
Trevor Wilson
www.rageaudio.com.au

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[Trevor Wilson]

On 5/05/2016 5:13 PM, Phil Allison wrote:
> Trevor Wilson wrote:
>
> Phil Allison wrote:
>
>>
>>>
>>> ** Yes, reactive load and low impedance behaviour is often important
>>> to know - but to this day requires test results that very few makers
>>> publish.
>>>
>>> Using only published information, can you say which modern amps are
>>> safe to use with a Quad ESL57 or 63?
>>>
>>
>> **This one:
>>
>> http://me-au.com/me850data2.jpg
>>
>> It will even survive the crowbar protection system (until that
>> protection system is destroyed).
>>
>
> ** Using the advice published by Quad, that old ME model is not suitable for use with either Quad ESL. Too many volts for the '57 and too many amps for the '63.
>
> Quad advise the '57 is safe up to 33V peak ( 68 watts at 8 ohms) and the '63 should only be use with amplifiers that have VI limiting.
>
> In both cases, the amplifier should also have good sub-sonic filtering - not flat response down to DC !!!
>


**Ah, I misinterpreted the term: "safe". I thought you indicated that
the amplifier could be damaged. That said, sub-sonic filtering can
easily be placed on the preamp and the ME850 has excellent VI limiting.
It is quite difficult to damage. But yes, I would never use the ME850
with the ESL57, but it sounds astonishingly good on the ESL63. I've
never damaged a pair, nor triggered the protection system (on the
speakers) using the pairing and I've done so many times (I used to sell
the ESL63).


--
Trevor Wilson
www.rageaudio.com.au

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[Trevor Wilson]

On 5/05/2016 4:44 PM, Eiron wrote:
> On 05/05/2016 07:17, Don Pearce wrote:
>> On Thu, 5 May 2016 15:12:49 +1000, Trevor Wilson
>> > wrote:
>
>
>>> http://me-au.com/me850data2.jpg
>>>
>>> It will even survive the crowbar protection system (until that
>>> protection system is destroyed).
>>
>> Why would anyone design that amplifier and say it is for music? One of
>> the most pointless specs I've ever read. You're just ****ing your
>> money away if you buy that.
>
> Because of the Australian fashion for designing speakers with impedances
> that drop to zero at the crossover frequencies.
>

**As PA has indicated, that type of speaker is commonly manufactured by
Americans, not Australians. Here are the impedance plots of two old
American speakers:

Infinity Kappa 9:

http://www.rageaudio.com.au/modules/gallery/view.php?a=Kappa9&image=090801082656_kappa9.jpg

Acoustat (I can't recall the model - Spectra something-or-other):

http://www.rageaudio.com.au/modules/gallery/view.php?a=Accustat&image=091027105452_accu.jpg

I ran the impedance curve of the infamous Infinity 4.5 many years ago,
but it was long before computerised test equipment and the curve
(primitive that it was) has long since vanished. The impedance fell to
around 0.75 Ohms in the bass region. I'll dig out the crossover
schematic provide a link. Be very careful when you examine it. Make
certain you are sitting down with a nice cool beverage (alcoholic). It
is a truly scary stuff.


--
Trevor Wilson
www.rageaudio.com.au

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[Jim Lesurf[_2_]]

In article >, Trevor Wilson
> wrote:
> **Ah, I misinterpreted the term: "safe". I thought you indicated that
> the amplifier could be damaged. That said, sub-sonic filtering can
> easily be placed on the preamp and the ME850 has excellent VI limiting.
> It is quite difficult to damage. But yes, I would never use the ME850
> with the ESL57, but it sounds astonishingly good on the ESL63. I've
> never damaged a pair, nor triggered the protection system (on the
> speakers) using the pairing and I've done so many times (I used to sell
> the ESL63).

The above was alwas a dilemma for me. I've happily used 732s for decades
without any harm to a succession of ESLs or the amps. And I think the
combination sounds better than using a quad amp limited as relevant. But
I've been far from sure the combination would be 'safe' for others unless
they knew what they were doing and could avoid driving the speakers too
hard.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
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[Jim Lesurf[_2_]]

In article >, Trevor Wilson
> wrote:
> I ran the impedance curve of the infamous Infinity 4.5 many years ago,
> but it was long before computerised test equipment and the curve
> (primitive that it was) has long since vanished. The impedance fell to
> around 0.75 Ohms in the bass region. I'll dig out the crossover
> schematic provide a link. Be very careful when you examine it. Make
> certain you are sitting down with a nice cool beverage (alcoholic). It
> is a truly scary stuff.

This was the kind of dilemma faced by amp designers of the period. A
variety of highly regarded ( or at least highly hyped! ;-> ) 'super
speakers' appeared. Some needed a hell of an amplifier to drive them
because they were inefficient had awful impedance behaviour. Yet others
could be toasted by an amp designed to drive the awkward squad. Limiting
the amp then limited its use.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
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[Don Pearce[_3_]]

On Thu, 05 May 2016 09:14:27 +0100, Jim Lesurf >
wrote:

>In article >, Don Pearce
> wrote:
>
>> Why would anyone design that amplifier and say it is for music? One of
>> the most pointless specs I've ever read. You're just ****ing your money
>> away if you buy that.
>
>Remember that some of us had to design amps in the era of some really
>'demanding' speaker loadings like the old maggies. The problem became that
>some speakers needed very high outputs into nastly loadings whilst others
>were vulnerable. Some people using some speakers will want an amp that
>would destroy another speaker. In the end, you have to choose what is
>appropriate. This is why detailed info for users is important.
>
>Jim

It isn't just the basic spec, but things like the power supply,
designed clearly to permit full power sine wave drive, ignoring the
peaky nature of music (then at any rate - maybe they anticipated the
highly-compressed pop of today).

d

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[Jim Lesurf[_2_]]

In article >, Don Pearce
> wrote:

> It isn't just the basic spec, but things like the power supply, designed
> clearly to permit full power sine wave drive, ignoring the peaky nature
> of music (then at any rate - maybe they anticipated the
> highly-compressed pop of today).

Agreed. FWIW being able to deliver high peaks was why I avoided using a
stabilised PSU for a power amp. And - coming back to the idea of
'prohibiting' anything other than the sinewave rated power - that mean an
amp that had to be 'rated' as 200wpc but could play much bigger peaks Some
measure of 'dynamic headroom' is clearly useful, therefore.

Jim

--
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[Trevor Wilson]

On 5/05/2016 4:44 PM, Eiron wrote:
> On 05/05/2016 07:17, Don Pearce wrote:
>> On Thu, 5 May 2016 15:12:49 +1000, Trevor Wilson
>> > wrote:
>
>
>>> http://me-au.com/me850data2.jpg
>>>
>>> It will even survive the crowbar protection system (until that
>>> protection system is destroyed).
>>
>> Why would anyone design that amplifier and say it is for music? One of
>> the most pointless specs I've ever read. You're just ****ing your
>> money away if you buy that.
>
> Because of the Australian fashion for designing speakers with impedances
> that drop to zero at the crossover frequencies.
>

**I should also mention the (in)famous Gale 401 speaker. UK designed and
built, with an impedance curve dipping to around 1.8 Ohms in the
mid-bass region. In fact, the designer of the above-mentioned amplifier
owned a pair of Gale 401s back when they were first released and was
part of the reason why he designed his amplifiers with such prodigious
current ability.

--
Trevor Wilson
www.rageaudio.com.au

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[Don Pearce[_3_]]

On Fri, 6 May 2016 06:48:59 +1000, Trevor Wilson
> wrote:

>On 5/05/2016 4:44 PM, Eiron wrote:
>> On 05/05/2016 07:17, Don Pearce wrote:
>>> On Thu, 5 May 2016 15:12:49 +1000, Trevor Wilson
>>> > wrote:
>>
>>
>>>> http://me-au.com/me850data2.jpg
>>>>
>>>> It will even survive the crowbar protection system (until that
>>>> protection system is destroyed).
>>>
>>> Why would anyone design that amplifier and say it is for music? One of
>>> the most pointless specs I've ever read. You're just ****ing your
>>> money away if you buy that.
>>
>> Because of the Australian fashion for designing speakers with impedances
>> that drop to zero at the crossover frequencies.
>>
>
>**I should also mention the (in)famous Gale 401 speaker. UK designed and
>built, with an impedance curve dipping to around 1.8 Ohms in the
>mid-bass region. In fact, the designer of the above-mentioned amplifier
>owned a pair of Gale 401s back when they were first released and was
>part of the reason why he designed his amplifiers with such prodigious
>current ability.

Gale never made much of a mark here. They pretty quickly got taken
over and became an own-brand label for Richer Sounds.

d

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[Trevor Wilson]

On 6/05/2016 8:05 AM, Don Pearce wrote:
> On Fri, 6 May 2016 06:48:59 +1000, Trevor Wilson
> > wrote:
>
>> On 5/05/2016 4:44 PM, Eiron wrote:
>>> On 05/05/2016 07:17, Don Pearce wrote:
>>>> On Thu, 5 May 2016 15:12:49 +1000, Trevor Wilson
>>>> > wrote:
>>>
>>>
>>>>> http://me-au.com/me850data2.jpg
>>>>>
>>>>> It will even survive the crowbar protection system (until that
>>>>> protection system is destroyed).
>>>>
>>>> Why would anyone design that amplifier and say it is for music? One of
>>>> the most pointless specs I've ever read. You're just ****ing your
>>>> money away if you buy that.
>>>
>>> Because of the Australian fashion for designing speakers with impedances
>>> that drop to zero at the crossover frequencies.
>>>
>>
>> **I should also mention the (in)famous Gale 401 speaker. UK designed and
>> built, with an impedance curve dipping to around 1.8 Ohms in the
>> mid-bass region. In fact, the designer of the above-mentioned amplifier
>> owned a pair of Gale 401s back when they were first released and was
>> part of the reason why he designed his amplifiers with such prodigious
>> current ability.
>
> Gale never made much of a mark here. They pretty quickly got taken
> over and became an own-brand label for Richer Sounds.
>

**Funny about that. The Gales have acquired something of a cult status
over here. 40 year old examples command quite respectable prices.


--
Trevor Wilson
www.rageaudio.com.au

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[Trevor Wilson]

On 5/05/2016 4:44 PM, Eiron wrote:
> On 05/05/2016 07:17, Don Pearce wrote:
>> On Thu, 5 May 2016 15:12:49 +1000, Trevor Wilson
>> > wrote:
>
>
>>> http://me-au.com/me850data2.jpg
>>>
>>> It will even survive the crowbar protection system (until that
>>> protection system is destroyed).
>>
>> Why would anyone design that amplifier and say it is for music? One of
>> the most pointless specs I've ever read. You're just ****ing your
>> money away if you buy that.
>
> Because of the Australian fashion for designing speakers with impedances
> that drop to zero at the crossover frequencies.
>

**I have scanned and uploaded three crossover diagrams from several
Infinity models:

Quantum Line Source (QLS):

The QLS used a VERY heavy, mica coated, clay loaded, 30cm paper cone
'Watkins' bass driver in a large, sealed enclosure. The driver employed
two voice coils. VC1 is a 4 Ohm rated coil and VC2 is a 2 Ohm rated
coil. Very tough to drive, but fabulous sounding system, with, arguably
the best bass of any Infinity speaker.

RS2.5:

The RS2.5 used a single polypropylene, 30cm 'Watkins' bass driver in a
large, sealed enclosure. A ******* of a speaker to driver, with a flabby
bottom end, likely due to the poor piston properties of the bass driver.

RS4.5:

The RS4.5 used two 'Watkins' bass drivers in a very large, sealed
enclosure. Possibly the worst speaker load I've ever encountered. Just
horrible. Destroyer of amplifiers and requiring HUGE gobs of current in
the bottom end. Prodigious, if quite flabby and ill-defined bass. The
mids and highs were easier, being substantially resistive in nature, but
still hovered around 3 Ohms for most of the range.

Crossover schematics:

http://postimg.org/gallery/29r95sbwy/


--
Trevor Wilson
www.rageaudio.com.au

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[Trevor Wilson]

On 6/05/2016 9:25 AM, Trevor Wilson wrote:

>
> Crossover schematics:
>

**Let's try again:

http://www.pdf-archive.com/2016/05/06/infinity-xovers/




--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison[_3_]]

Trevor Wilson wrote:

>
>
> **I should also mention the (in)famous Gale 401 speaker. UK designed and
> built, with an impedance curve dipping to around 1.8 Ohms in the
> mid-bass region.

** Not true at all.

The Gale 401 used two nominal 8 ohm woofers ( 5.6ohms DC ) in parallel, with a 3.3mH inductor in series. The box was sealed so the impedance of the woofers rose to a maximum at resonance and fell to a minimum around 250Hz.

http://0339436.netsolhost.com/WordPress/wp-content/uploads/2011/09/Copy-2-of-GS401-Speaker-Crossover-Schematic-4.jpg

The minimum *possible* impedance at 250 Hz calculates to 6.3 ohms.

Warm the voice coils up a bit with bass and you will see 8 ohms or more.

Reviews said the speaker's impedance averaged 8 ohms - as claimed.


> In fact, the designer of the above-mentioned amplifier
> owned a pair of Gale 401s back when they were first released and was
> part of the reason why he designed his amplifiers with such prodigious
> current ability.
>

** Really ??

That would have been a big mistake for Mr Stein.



...... Phil