Yet another thump problem. ;-)
 

This time, a BBC AM8/16. Basically, a BBC modified Quad 405 to drive the
LS5/8. Has a crossover added to the input to the amps.

One of the two produces a pretty loud squawk on switching off. Not a fault
as such, as plenty early BBC ones in service did the same. But the BBC did
seem to find a cure. The pair I had were ok.

Sadly, the three circuits I've got for the crossover are all the same.

I've only got the one amp here, so can't just look for any differences.

I can post a link to the crossover circuit if it helps. It gets its power
from the + side of the Quad PS and regulates that down to 30 volts.

--
*A cartoonist was found dead in his home. Details are sketchy.*

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

Yet another thump problem. ;-)
 

In article , Dave Plowman (News)
scribeth thus
This time, a BBC AM8/16. Basically, a BBC modified Quad 405 to drive the
LS5/8. Has a crossover added to the input to the amps.

One of the two produces a pretty loud squawk on switching off. Not a fault
as such, as plenty early BBC ones in service did the same. But the BBC did
seem to find a cure. The pair I had were ok.

Sadly, the three circuits I've got for the crossover are all the same.

I've only got the one amp here, so can't just look for any differences.

I can post a link to the crossover circuit if it helps. It gets its power
from the + side of the Quad PS and regulates that down to 30 volts.


Are you saying that one channel squawks whist the other doesn't?.

If this was a problem overall with the 405 I bet QUAD would have done a
mod for it even in the balanced input splitter/driver board

Very much expect its a duff cap or caps somewhere well worth changing at
the age thats likely to be..
--
Tony Sayer

Yet another thump problem. ;-)
 

In article ,
tony sayer wrote:
In article , Dave Plowman (News)
scribeth thus
This time, a BBC AM8/16. Basically, a BBC modified Quad 405 to drive
the LS5/8. Has a crossover added to the input to the amps.

One of the two produces a pretty loud squawk on switching off. Not a
fault as such, as plenty early BBC ones in service did the same. But
the BBC did seem to find a cure. The pair I had were ok.

Sadly, the three circuits I've got for the crossover are all the same.

I've only got the one amp here, so can't just look for any differences.

I can post a link to the crossover circuit if it helps. It gets its
power from the + side of the Quad PS and regulates that down to 30
volts.


Are you saying that one channel squawks whist the other doesn't?.

It seems to be both channels (LF & HF) on the one amp.

If this was a problem overall with the 405 I bet QUAD would have done a
mod for it even in the balanced input splitter/driver board

I don't think it's anything to do with the Quad part.

Very much expect its a duff cap or caps somewhere well worth changing at
the age thats likely to be..

Thing is I well remember new ones doing it at work, when they first came
out. My pair here didn't, but then now no longer have AM8s.

This amp I'm looking at seems to have a later crossover, by my BBC
schematics. But I dunno how many versions there were. And measures just
fine. There are very few electrolytics on this PCB and to change all the
caps on spec would be a very difficult job since many are very odd values.

--
*Why is the word abbreviation so long? *

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

Yet another thump problem. ;-)
 

Dave Plowman (News) wrote:



This time, a BBC AM8/16. Basically, a BBC modified Quad 405 to drive
the LS5/8. Has a crossover added to the input to the amps.

One of the two produces a pretty loud squawk on switching off. Not a
fault as such, as plenty early BBC ones in service did the same. But
the BBC did seem to find a cure. The pair I had were ok.

Sadly, the three circuits I've got for the crossover are all the same.

I've only got the one amp here, so can't just look for any differences.

I can post a link to the crossover circuit if it helps. It gets its
power from the + side of the Quad PS and regulates that down to 30
volts.


Are you saying that one channel squawks whist the other doesn't?.

It seems to be both channels (LF & HF) on the one amp.

If this was a problem overall with the 405 I bet QUAD would have done a
mod for it even in the balanced input splitter/driver board

I don't think it's anything to do with the Quad part.

Very much expect its a duff cap or caps somewhere well worth changing at
the age thats likely to be..

Thing is I well remember new ones doing it at work, when they first came
out. My pair here didn't, but then now no longer have AM8s.

This amp I'm looking at seems to have a later crossover, by my BBC
schematics. But I dunno how many versions there were. And measures just
fine. There are very few electrolytics on this PCB and to change all the
caps on spec would be a very difficult job since many are very odd values.



** The simple solution is to add a DPDT relay to mute both inputs of the 405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by rectified AC from the secondary of the transformer - plus a suitable series resistor.

You can use the contacts to either ground the two signals or open circuit them.



..... Phil

Yet another thump problem. ;-)
 

In article ,
Phil Allison wrote:
** The simple solution is to add a DPDT relay to mute both inputs of the
405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by rectified
AC from the secondary of the transformer - plus a suitable series
resistor.

You can use the contacts to either ground the two signals or open
circuit them.

Snag is this squawk happens immediately at switch off. So the relay would
have to operate extremely quickly.
But I was curious why some do it and some don't.

The DC in the Quad drops off pretty slowly after switching off. The panel
LED takes ages to extinguish. Just why the crossover goes unstable so
quickly, I don't know. The DC from the Quad PS is regulated down to 30v
for the crossover.

--
*If vegetable oil comes from vegetables, where does baby oil come from? *

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

Yet another thump problem. ;-)
 

Dave Plowman (News) wrote:


** The simple solution is to add a DPDT relay to mute both inputs of the
405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by rectified
AC from the secondary of the transformer - plus a suitable series
resistor.

You can use the contacts to either ground the two signals or open
circuit them.

Snag is this squawk happens immediately at switch off. So the relay would
have to operate extremely quickly.



** With the relay powered with rectified AC only, the switch off time is less than 15mS.

That I why I suggested it.

Why not actually try it ?



..... Phil

Yet another thump problem. ;-)
 

In article ,
Phil Allison wrote:
Dave Plowman (News) wrote:


** The simple solution is to add a DPDT relay to mute both inputs of
the 405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by
rectified AC from the secondary of the transformer - plus a suitable
series resistor.

You can use the contacts to either ground the two signals or open
circuit them.

Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.



** With the relay powered with rectified AC only, the switch off time is
less than 15mS.

That I why I suggested it.

Why not actually try it ?


If you'd seen an AM8, you'd know there's not exactly much space inside it.
It could be done, but not easily. It would probably need to be sited on
the far side of the amp from the crossover.

I was more hoping someone could come up with why some of these crossovers
squawk, but some not.

--
*When it rains, why don't sheep shrink? *

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

Yet another thump problem. ;-)
 

In article , Dave Plowman (News)
wrote:

I was more hoping someone could come up with why some of these
crossovers squawk, but some not.

I guess that we can't say much more than the obvious. i.e. that something
is different between examples of amps and crossovers/speakers! Not exactly
news for you. :-/

I've never seen an AM8/16 so have no idea what changes the BBC people may
have made. I can't tell if the 'quawk' is due to a protection circuit
rattling on and off, bursts of RF instability, or what. Might be fixable by
a bigger output inductor or a cap in just the right place. But where?...

Ideally, you'd be best asking in some place were ancient BBC engineers are
listening. But again, I'm not sure where to suggest!

Jim

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

Yet another thump problem. ;-)
 

On 31/05/2016 9:13 PM, Dave Plowman (News) wrote:
In article ,
Phil Allison wrote:
** The simple solution is to add a DPDT relay to mute both inputs of the
405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by rectified
AC from the secondary of the transformer - plus a suitable series
resistor.

You can use the contacts to either ground the two signals or open
circuit them.

Snag is this squawk happens immediately at switch off. So the relay would
have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

Try it.

--
Trevor Wilson
www.rageaudio.com.au

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Yet another thump problem. ;-)
 

Dave Plowman (Nutcase) wrote:


If you'd seen an AM8, you'd know there's not exactly much space inside it.
It could be done, but not easily. It would probably need to be sited on
the far side of the amp from the crossover.


** Miniature DPDT relays measure only 2x1x1cm.

DIL bridges are tiny.



I was more hoping someone could come up with why some of these crossovers
squawk, but some not.

** Same wrong thinking as with all your absurd questions.


.... Phil

Yet another thump problem. ;-)
 

In article , Trevor Wilson
wrote:
On 31/05/2016 9:13 PM, Dave Plowman (News) wrote:
In article ,
Phil Allison wrote:
** The simple solution is to add a DPDT relay to mute both inputs of
the 405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by
rectified AC from the secondary of the transformer - plus a suitable
series resistor.

You can use the contacts to either ground the two signals or open
circuit them.

Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

IIRC The Quad 34 has a circuit that clamps the output to ground as soon as
the rails start to fall when you switch 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/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Yet another thump problem. ;-)
 

In article ,
Jim Lesurf wrote:
I was more hoping someone could come up with why some of these
crossovers squawk, but some not.

I guess that we can't say much more than the obvious. i.e. that
something is different between examples of amps and crossovers/speakers!
Not exactly news for you. :-/

I've never seen an AM8/16 so have no idea what changes the BBC people
may have made. I can't tell if the 'quawk' is due to a protection
circuit rattling on and off, bursts of RF instability, or what. Might be
fixable by a bigger output inductor or a cap in just the right place.
But where?...

Thought I'd made it fairly clear. If you remove the power to the crossover
PCB while leaving the amp powered up, you get the squawk. Leave the power
off that PCB, and the Quad part powers up and off normally.

Ideally, you'd be best asking in some place were ancient BBC engineers
are listening. But again, I'm not sure where to suggest!

Finding one who knows the design intimately is the problem. As an aside,
noticed the Keith Snooks site seems to have disappeared too. Everyone is
getting old.

--
*All those who believe in psychokinesis, raise my hand *

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

Yet another thump problem. ;-)
 

In article ,
Trevor Wilson wrote:
Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.

--
*ONE NICE THING ABOUT EGOTISTS: THEY DON'T TALK ABOUT OTHER PEOPLE.

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

Yet another thump problem. ;-)
 

In article , Dave Plowman (News)
wrote:
I've never seen an AM8/16 so have no idea what changes the BBC people
may have made. I can't tell if the 'quawk' is due to a protection
circuit rattling on and off, bursts of RF instability, or what. Might
be fixable by a bigger output inductor or a cap in just the right
place. But where?...

Thought I'd made it fairly clear. If you remove the power to the
crossover PCB while leaving the amp powered up, you get the squawk.
Leave the power off that PCB, and the Quad part powers up and off
normally.

OK. Then maybe a circuit on the *input* of the 405 that duplicates what it
sees from the output mute on the 34 might help? IIRC this just clamps the
signal line to ground using a bipolar.

Jim

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

Yet another thump problem. ;-)
 

In article , Dave Plowman (News)
scribeth thus
In article ,
Trevor Wilson wrote:
Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.



Seems that this is in the BBC designed bit of the amp?.

Have you got the circuit for that particular variant unit Dave;?..

Phil's idea is a good one but in this instance there is another fault
thats causing a problem that shouldn't be there.

Makes me wonder if thats having an effect on the signal path?

Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

--
Tony Sayer

Yet another thump problem. ;-)
 

Ideally, you'd be best asking in some place were ancient BBC engineers
are listening. But again, I'm not sure where to suggest!




Finding one who knows the design intimately is the problem. As an aside,
noticed the Keith Snooks site seems to have disappeared too. Everyone is
getting old.



His phone number is on here..

As to ageing your bloody right the(...


http://www.dc-daylight.ltd.uk/
--
Tony Sayer

Yet another thump problem. ;-)
 

In article ,
tony sayer wrote:
But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.



Seems that this is in the BBC designed bit of the amp?.

Yes.

Have you got the circuit for that particular variant unit Dave;?..

I think so. I have three versions of the schematic but this amp is a
fairly late one and appears to have the latest of the ones I've seen.
That's not to say there isn't an even later version.

If you'd like it, I'll post a link to it - but you've probably got it
anyway.

Phil's idea is a good one but in this instance there is another fault
thats causing a problem that shouldn't be there.

Quite.

Makes me wonder if thats having an effect on the signal path?

Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)

--
*Caution: I drive like you do.

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

Yet another thump problem. ;-)
 

On 2/06/2016 9:42 AM, Dave Plowman (News) wrote:
In article ,
tony sayer wrote:
But not really an answer to my question, thanks.

It's an fairly obvious 'cure' although might well not be perfect in
practice.



Seems that this is in the BBC designed bit of the amp?.

Yes.

Have you got the circuit for that particular variant unit Dave;?..

I think so. I have three versions of the schematic but this amp is a
fairly late one and appears to have the latest of the ones I've seen.
That's not to say there isn't an even later version.

If you'd like it, I'll post a link to it - but you've probably got it
anyway.

Phil's idea is a good one but in this instance there is another fault
thats causing a problem that shouldn't be there.

Quite.

Makes me wonder if thats having an effect on the signal path?

Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.
Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

--
Trevor Wilson
www.rageaudio.com.au

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Trevor Wilson wrote:



Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.



** Pickering (of the UK) relays are ALL reed types - so have glass encapsulated contacts. They feature Mu-metal shielding and are rated for millions of operations - certainly not a cheap component.

http://www.pickeringrelay.com/


Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

** The non sealed types I have come across develop bad contacts ( high resistance) and cleaning them is PITA.


..... Phil

Yet another thump problem. ;-)
 

On Thu, 2 Jun 2016 04:29:14 -0700 (PDT), Phil Allison
wrote:

Trevor Wilson wrote:



Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.



** Pickering (of the UK) relays are ALL reed types - so have glass encapsulated contacts. They feature Mu-metal shielding and are rated for millions of operations - certainly not a cheap component.

http://www.pickeringrelay.com/


Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

** The non sealed types I have come across develop bad contacts ( high resistance) and cleaning them is PITA.


.... Phil

Mosfets are an excellent alternative to relays these days. On
resistance of a few milliohms in cheap packages.

d

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In article , Don Pearce
wrote:

Mosfets are an excellent alternative to relays these days. On resistance
of a few milliohms in cheap packages.

And should work OK with something like a 405 that has current limiters.

However I must confess that the impression I've gained is that here the
problem may be being injected into the input of the 405. If so, using small
signal devices to clamp that to ground might be cheaper and more effective.

Jim

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

Yet another thump problem. ;-)
 

Don Pearce wrote:



** The non sealed types I have come across develop bad contacts
( high resistance) and cleaning them is PITA.



Mosfets are an excellent alternative to relays these days. On
resistance of a few milliohms in cheap packages.


** Shame about the many drawbacks, like having an *internal diode* in parallel and needing to be driven with a gate voltage to get that low resistance.

Not a practical alternative to a DPDT mini-relay you can by for a couple of dollars.

http://sound.westhost.com/articles/muting.html#s4


..... Phil

Yet another thump problem. ;-)
 

On Thu, 2 Jun 2016 05:14:05 -0700 (PDT), Phil Allison
wrote:

Don Pearce wrote:



** The non sealed types I have come across develop bad contacts
( high resistance) and cleaning them is PITA.



Mosfets are an excellent alternative to relays these days. On
resistance of a few milliohms in cheap packages.


** Shame about the many drawbacks, like having an *internal diode* in parallel and needing to be driven with a gate voltage to get that low resistance.

Not a practical alternative to a DPDT mini-relay you can by for a couple of dollars.

http://sound.westhost.com/articles/muting.html#s4


.... Phil



Just use enhancement mode devices. Gate up at source voltage - the FET
is off. Drag it down by five volts, it is fully on. Pretty much the
same driving method as a five volt relay. And no contacts to get
dirty.

d

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Don Pearce wrote:

Phil Allison

Don Pearce wrote:



** The non sealed types I have come across develop bad contacts
( high resistance) and cleaning them is PITA.



Mosfets are an excellent alternative to relays these days. On
resistance of a few milliohms in cheap packages.


** Shame about the many drawbacks, like having an *internal diode*
in parallel and needing to be driven with a gate voltage to get that
low resistance.

Not a practical alternative to a DPDT mini-relay you can by for a
couple of dollars.

http://sound.westhost.com/articles/muting.html#s4




Just use enhancement mode devices. Gate up at source voltage - the FET
is off. Drag it down by five volts, it is fully on. Pretty much the
same driving method as a five volt relay. And no contacts to get
dirty.


** Same bull**** as before, one mosfet will not do the job for line level signals and having to bias it on makes it almost useless.

The link I quoted has the story right.


..... Phil


d

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On Thu, 2 Jun 2016 05:34:23 -0700 (PDT), Phil Allison
wrote:

Don Pearce wrote:

Phil Allison

Don Pearce wrote:



** The non sealed types I have come across develop bad contacts
( high resistance) and cleaning them is PITA.



Mosfets are an excellent alternative to relays these days. On
resistance of a few milliohms in cheap packages.


** Shame about the many drawbacks, like having an *internal diode*
in parallel and needing to be driven with a gate voltage to get that
low resistance.

Not a practical alternative to a DPDT mini-relay you can by for a
couple of dollars.

http://sound.westhost.com/articles/muting.html#s4




Just use enhancement mode devices. Gate up at source voltage - the FET
is off. Drag it down by five volts, it is fully on. Pretty much the
same driving method as a five volt relay. And no contacts to get
dirty.


** Same bull**** as before, one mosfet will not do the job for line level signals and having to bias it on makes it almost useless.

The link I quoted has the story right.


.... Phil

If you say so. It has always worked for me. How do you operate a relay
without having to "bias" it on?

d

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In article ,
Trevor Wilson wrote:
We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.
Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

I can't remember the exact spec of them - and they certainly did much more
than simply short to ground. They configured the console for track laying,
overdub or mixdown.

--
*What boots up must come down *

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

Yet another thump problem. ;-)
 

On Thu, 02 Jun 2016 13:07:42 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:

Mosfets are an excellent alternative to relays these days. On resistance
of a few milliohms in cheap packages.

And should work OK with something like a 405 that has current limiters.

However I must confess that the impression I've gained is that here the
problem may be being injected into the input of the 405. If so, using small
signal devices to clamp that to ground might be cheaper and more effective.


The Mosfet is ideal for that too. I modelled that on LTSpice, and it
looks perfect. Smaller devices with about 60mOhm channel resistance
are ideal - they have very low gate/channel capacitance and very
little of the operating pulse gets through. My model used a 1k
resistance in series with the signal followed by the Mosfet to ground.

d

---
This email has been checked for viruses by Avast antivirus software.
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Yet another thump problem. ;-)
 

Jim Lesurf wrote:



Mosfets are an excellent alternative to relays these days. On resistance
of a few milliohms in cheap packages.

And should work OK with something like a 405 that has current limiters.


** LOL - no-one here is suggesting shorting the *output* of an amp !!!



However I must confess that the impression I've gained is that here the
problem may be being injected into the input of the 405.


** Duh - you don't say.


If so, using small
signal devices to clamp that to ground might be cheaper and more effective.


** It is actually neither, for many obvious reasons.

Read this link and learn.

http://sound.westhost.com/articles/muting.html#s4



.... Phil

Yet another thump problem. ;-)
 

Don Pearce wrote:



The Mosfet is ideal for that too. I modelled that on LTSpice, and it
looks perfect. Smaller devices with about 60mOhm channel resistance
are ideal - they have very low gate/channel capacitance and very
little of the operating pulse gets through. My model used a 1k
resistance in series with the signal followed by the Mosfet to ground.


** Cleary you have NOT modelled a scheme that mutes switch-on noises OR noises that occur after switch off.

NOR have you worked out how to avoid clipping the audio signal at 0.6V negative.

Read the link I posted and shut up.


..... Phil

Yet another thump problem. ;-)
 

On 2016-06-03 04:40:09 +0000, Phil Allison said:

Don Pearce wrote:



The Mosfet is ideal for that too. I modelled that on LTSpice, and it
looks perfect. Smaller devices with about 60mOhm channel resistance
are ideal - they have very low gate/channel capacitance and very
little of the operating pulse gets through. My model used a 1k
resistance in series with the signal followed by the Mosfet to ground.


** Cleary you have NOT modelled a scheme that mutes switch-on noises OR
noises that occur after switch off.

NOR have you worked out how to avoid clipping the audio signal at 0.6V
negative.

Read the link I posted and shut up.


.... Phil



There are mosfets without the Drain-Source protection diode.

Arthur

--
real email arthur at bellacat dot com

Yet another thump problem. ;-)
 

On Thu, 2 Jun 2016 21:40:09 -0700 (PDT), Phil Allison
wrote:

Don Pearce wrote:



The Mosfet is ideal for that too. I modelled that on LTSpice, and it
looks perfect. Smaller devices with about 60mOhm channel resistance
are ideal - they have very low gate/channel capacitance and very
little of the operating pulse gets through. My model used a 1k
resistance in series with the signal followed by the Mosfet to ground.


** Cleary you have NOT modelled a scheme that mutes switch-on noises OR noises that occur after switch off.

NOR have you worked out how to avoid clipping the audio signal at 0.6V negative.

Read the link I posted and shut up.

These are details of particular designs, not reasons to ignore
Mosfets. If you can't find a circuit location where the signal does
not exceed 0.6V, just use a pedestal voltage. None of this is hard.

d

---
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Yet another thump problem. ;-)
 

Don Pearce = context shifting troll



** Cleary you have NOT modelled a scheme that mutes switch-on noises OR noises that occur after switch off.

NOR have you worked out how to avoid clipping the audio signal at 0.6V negative.

Read the link I posted and shut the **** up.



..... Phil

Yet another thump problem. ;-)
 

In article , Phil
Allison scribeth thus
Trevor Wilson wrote:



Got a sack of mini relays made by Pickering used by Neve and Audix if
you want a few, only problem is there're 24 volt ones....

Got loads of suitable relays here too.

Not a lover of relays in a signal path, though.

We had an inline monitoring 48/4/2 Neve at Thames with thousands of the
bloody things always giving problems. ;-)


**I'll bet they weren't decent, hermetically sealed, gold contact types,
nor were they used to short the signal to earth. If such relays are used
in that type of application, they almost never exhibit problems.



** Pickering (of the UK) relays are ALL reed types - so have glass encapsulated
contacts. They feature Mu-metal shielding and are rated for millions of
operations - certainly not a cheap component.

http://www.pickeringrelay.com/

They aren't, around 5 quid (10 AUS dollars) when i asked last, in small
quantities!..



Whenever I see a product with those clear topped, non-sealed DIL relays,
I know exactly what needs to be done. When the relay is replaced with a
proper one, I never see the job back. There are relays and there are
decent quality relays.

** The non sealed types I have come across develop bad contacts ( high
resistance) and cleaning them is PITA.

Agreed!...



.... Phil

--
Tony Sayer

Yet another thump problem. ;-)
 

Read this link and learn.

http://sound.westhost.com/articles/muting.html#s4

Useful site that:)



... Phil

--
Tony Sayer

Yet another thump problem. ;-)
 

In article ,
tony sayer wrote:

Read this link and learn.

http://sound.westhost.com/articles/muting.html#s4

Useful site that:)


Yes. I'm using their crossover on my modified 5/8s.

--
*WHY IS IT CALLED TOURIST SEASON IF WE CAN'T SHOOT AT THEM?

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

Yet another thump problem. ;-)
 

ponent.

http://www.pickeringrelay.com/

They aren't, around 5 quid (10 AUS dollars) when i asked last, in small
quantities!..


Small word transposition there "Aren't they" of course...

--
Tony Sayer

Yet another thump problem. ;-)
 

In article , Dave Plowman (News)
scribeth thus
In article ,
tony sayer wrote:

Read this link and learn.

http://sound.westhost.com/articles/muting.html#s4

Useful site that:)


Yes. I'm using their crossover on my modified 5/8s.


Ain't 5/8'd anymore then;?....
--
Tony Sayer

Yet another thump problem. ;-)
 

In article ,
tony sayer wrote:
In article , Dave Plowman (News)
scribeth thus
In article ,
tony sayer wrote:

Read this link and learn.

http://sound.westhost.com/articles/muting.html#s4

Useful site that:)


Yes. I'm using their crossover on my modified 5/8s.


Ain't 5/8'd anymore then;?....

Just like they should have been made in the first place. Non of this
nonsense trying to get a 12" unit to work over 6 octaves. ;-)

--
*Microsoft broke Volkswagen's record: They only made 21.4 million bugs.

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