Speaker level adjustment
 

On 28/01/2014 10:24, Chris J Dixon wrote:
John Williamson wrote:

On 27/01/2014 16:41, Chris J Dixon wrote:
I boxed up an L-pad
http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544
and installed it a while ago, but it doesn't really seem to have
sufficient adjustment.

I find that odd, as if it's wired correctly, an L-pad should give an
adjustment range from 0- 100% of full power.

Well, AFAUK I have done it right, but I suppose that is a bit of
a circular argument. ;-)

Indeed. Obviously, you'd not deliberately or knowingly do it
incorrectly. :-)

Another alternative would be to install a 100 volt speaker system with
independent volume controls in each room, but that would mean buying a
new amplifier,and some matching transformers and volume controls.

So, significant expense, compare with my proposal which you
snipped. Just for the record, what would its advantages be?

Completely independent control of levels on all speakers. Only one
amplifier to go wrong, and 100 volt line amplifiers tend to be designed
and built to last for ever even when abused. The downside is that the
transformers can degrade the sound quality slightly, which may obviously
be an issue.


--
Tciao for Now!

John.

Speaker level adjustment
 

In article ,
John Williamson wrote:
Another alternative would be to install a 100 volt speaker system with
independent volume controls in each room, but that would mean buying a
new amplifier,and some matching transformers and volume controls.

I've used a 100 v line transformer I had lying around to adjust the level
of a speaker fed from a normal low impedance amp. It worked rather better
than a pad. It had five level taps on it - but it would be a bit of luck
if it gave the amount of attenuation wanted. Pads always seem to upset the
bass end - even on speakers which aren't exactly Hi-Fi.

--
*Procrastination is the art of keeping up with yesterday.

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

Speaker level adjustment
 

On 28/01/2014 10:24, Chris J Dixon wrote:
John Williamson wrote:

On 27/01/2014 16:41, Chris J Dixon wrote:
I boxed up an L-pad
http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544
and installed it a while ago, but it doesn't really seem to have
sufficient adjustment.

I find that odd, as if it's wired correctly, an L-pad should give an
adjustment range from 0- 100% of full power.

Well, AFAUK I have done it right, but I suppose that is a bit of
a circular argument. ;-)

There are only three terminals on a potentiometer.

The amplifier should go to the outer pair and see 8R load. The speaker
should go to the centre tap and one end (the low end). If you choose the
correct end then you will get a logarithmic adjustment and if you choose
the wrong end you will get a sort of all or nothing behaviour.

Rotation 0 1 2 3 4 5
r (correct) 0 0.5 1 2 4 8 (correct)
r'(wrong) 0 4 6 7 7.5 8

Swap the end you connect the speaker to and you might be surprised.

You still lose some bass damping this way but it may not bother you.

--
Regards,
Martin Brown

Speaker level adjustment
 

On 28/01/14 10:51, John Williamson wrote:
On 28/01/2014 10:24, Chris J Dixon wrote:
John Williamson wrote:

On 27/01/2014 16:41, Chris J Dixon wrote:
I boxed up an L-pad
http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544

and installed it a while ago, but it doesn't really seem to have
sufficient adjustment.

I find that odd, as if it's wired correctly, an L-pad should give an
adjustment range from 0- 100% of full power.

Well, AFAUK I have done it right, but I suppose that is a bit of
a circular argument. ;-)

Indeed. Obviously, you'd not deliberately or knowingly do it
incorrectly. :-)

Another alternative would be to install a 100 volt speaker system with
independent volume controls in each room, but that would mean buying a
new amplifier,and some matching transformers and volume controls.

So, significant expense, compare with my proposal which you
snipped. Just for the record, what would its advantages be?

Completely independent control of levels on all speakers. Only one
amplifier to go wrong, and 100 volt line amplifiers tend to be designed
and built to last for ever even when abused. The downside is that the
transformers can degrade the sound quality slightly, which may obviously
be an issue.


as can ANY form of passive attenuation to a loudspeaker designed to be
driven from a 0.1 ohm source. 100V line or not.

100V line is merely a way to transmit audio POWER over long distances
using less than arm sized cabling.

The fact that it is in general more robust is not inherent in the
100V-ness of it, but more because such systems tend to be deployed out
doors or in large buildings where the integrity of cabling and its
immunity from lightning strikes or induced surges or shorts cannot be
guaranteed, and into professional applications where a lack of
robustness is not tolerable either.

A better way in domestic situations is to deploy active loudspeakers fed
from e.g a 1V line source, preferably balanced 600 ohm., and possibly
with power being fed to them via the wires, and then attenuate that and
feed it to a local low output impedance amplifier.

In short pretty much what a pair of 'computer speakers' already does.


--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

Speaker level adjustment
 

On 28/01/14 10:56, Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
Another alternative would be to install a 100 volt speaker system with
independent volume controls in each room, but that would mean buying a
new amplifier,and some matching transformers and volume controls.

I've used a 100 v line transformer I had lying around to adjust the level
of a speaker fed from a normal low impedance amp. It worked rather better
than a pad. It had five level taps on it - but it would be a bit of luck
if it gave the amount of attenuation wanted. Pads always seem to upset the
bass end - even on speakers which aren't exactly Hi-Fi.

+1

You can use a transformer to adjust power output via taps without
upsetting the impedance - but resistive pads are not good for bass units.

As part of my essays into reproducing 'valve sound' for guitar
amplifiers, artificially raising the output impedance of the power
amplifier was routine.

The good old Vox A30 amplifier has an output impedance of some 80 ohms.
Driving an 8ohm pair of loudspeakers, the effects are dramatic.

Massive bass resonance, about the bottom A on a guitar, plus overall
treble boost as the rising impedance of the speaker voice coil (a lot of
leakage inductance in a voice coil) is no longer a significant effect in
reducing treble output. Boom an chink we used to call it.

Also all other resonances in the paper cones and cabinets are much less
well damped, so the sound comes 'alive' with the sound of - well wood
and paper!

The amplifier loudspeaker and cabinet are the 'sound box' of an electric
guitar and give it an interest and colour it otherwise lacks. Hifi it
aint. But it isn't intended to be, either.



--

Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

Speaker level adjustment
 

On Tue, 28 Jan 2014 10:56:29 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
John Williamson wrote:
Another alternative would be to install a 100 volt speaker system with
independent volume controls in each room, but that would mean buying a
new amplifier,and some matching transformers and volume controls.

I've used a 100 v line transformer I had lying around to adjust the level
of a speaker fed from a normal low impedance amp. It worked rather better
than a pad. It had five level taps on it - but it would be a bit of luck
if it gave the amount of attenuation wanted. Pads always seem to upset the
bass end - even on speakers which aren't exactly Hi-Fi.

I'm not familiar with the design of attenuator pads used in 100v and
70v line driver setups but presumably it must be raising the 'source'
impedance as seen by the speaker.

I suppose the reduction of "Damping Factor"[1] is allowing the bass
cone resonance to more prominently dominate the frequency response.

[1] Forty years ago, "Damping Factor" was an oft quoted figure of
merit for amplifiers which was derived from the output impedance
(ideally, zero ohms) of the amplifier versus the impedance of the
speaker loads it was designed to drive. Figures of 400:1 for 8 ohm
loads being not uncommon (implying an output Z of 0.02 ohms).

Since over 90% of the typical bass driver's "Voice Coil Impedance"
was made up of its ohmic resistance, the actual "Damping Factor" was
more like 1:1 using such an amplifier (the voice coil resistance being
effectively in series with the amplifier's output impedance).

In practice, the damping effect was only of importance at the
resonant frequency of the drive unit which is reflected as an increase
of impedance which, for an 8 ohm driver, could climb to as high a
value as 30 or more ohms.

In the case of a 32 ohm impedance at resonance, the actual damping
factor applied by our "400:1 Damping Factor" amplifier would actually
be a mere 4:1, just 1% of the claimed 'figure of merit' implied.

It's been a good 30 years or more since I last looked at such Hi Fi
advertising 'blurb' so I don't know whether this misleading practice
has stopped and the more useful "Output Impedance" figures are being
quoted instead (e.g. "Output Z = 20 milli ohms", rather than "DF=400:1
for 8 ohm loads"). Quite frankly, the difference between 500 milli
ohms and 20 milli ohms output impedance would be barely measurable let
alone audible.
--
Regards, J B Good

Speaker level adjustment
 

And QED used to make resistive speaker controls with wirewound pots. OK
they could get a bit warm and crackly, but the seemed to work.

Brian

--
From the Sofa of Brian Gaff Reply address is active
"Johny B Good" wrote in message
...
On Tue, 28 Jan 2014 10:56:29 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
John Williamson wrote:
Another alternative would be to install a 100 volt speaker system with
independent volume controls in each room, but that would mean buying a
new amplifier,and some matching transformers and volume controls.

I've used a 100 v line transformer I had lying around to adjust the level
of a speaker fed from a normal low impedance amp. It worked rather better
than a pad. It had five level taps on it - but it would be a bit of luck
if it gave the amount of attenuation wanted. Pads always seem to upset the
bass end - even on speakers which aren't exactly Hi-Fi.

I'm not familiar with the design of attenuator pads used in 100v and
70v line driver setups but presumably it must be raising the 'source'
impedance as seen by the speaker.

I suppose the reduction of "Damping Factor"[1] is allowing the bass
cone resonance to more prominently dominate the frequency response.

[1] Forty years ago, "Damping Factor" was an oft quoted figure of
merit for amplifiers which was derived from the output impedance
(ideally, zero ohms) of the amplifier versus the impedance of the
speaker loads it was designed to drive. Figures of 400:1 for 8 ohm
loads being not uncommon (implying an output Z of 0.02 ohms).

Since over 90% of the typical bass driver's "Voice Coil Impedance"
was made up of its ohmic resistance, the actual "Damping Factor" was
more like 1:1 using such an amplifier (the voice coil resistance being
effectively in series with the amplifier's output impedance).

In practice, the damping effect was only of importance at the
resonant frequency of the drive unit which is reflected as an increase
of impedance which, for an 8 ohm driver, could climb to as high a
value as 30 or more ohms.

In the case of a 32 ohm impedance at resonance, the actual damping
factor applied by our "400:1 Damping Factor" amplifier would actually
be a mere 4:1, just 1% of the claimed 'figure of merit' implied.

It's been a good 30 years or more since I last looked at such Hi Fi
advertising 'blurb' so I don't know whether this misleading practice
has stopped and the more useful "Output Impedance" figures are being
quoted instead (e.g. "Output Z = 20 milli ohms", rather than "DF=400:1
for 8 ohm loads"). Quite frankly, the difference between 500 milli
ohms and 20 milli ohms output impedance would be barely measurable let
alone audible.
--
Regards, J B Good

Speaker level adjustment
 

John Williamson wrote:

On 28/01/2014 10:24, Chris J Dixon wrote:
John Williamson wrote:

On 27/01/2014 16:41, Chris J Dixon wrote:
I boxed up an L-pad
http://cpc.farnell.com/_/lp-200-8/speaker-l-pad-stereo/dp/LS00544?Ntt=LS00544
and installed it a while ago, but it doesn't really seem to have
sufficient adjustment.

Actually, that isn't quite correct, see below, I had forgotten
what I actually did.

I find that odd, as if it's wired correctly, an L-pad should give an
adjustment range from 0- 100% of full power.

Well, AFAUK I have done it right, but I suppose that is a bit of
a circular argument. ;-)

Indeed. Obviously, you'd not deliberately or knowingly do it
incorrectly. :-)

Looking again at what I have done, if you remember my original
problem:

[My amplifier has two outputs. One is switched, and used for the
speakers in the living room. The other is taken via a separate
switch box to speakers in the dining room and kitchen. The
kitchen is too quiet.]

I used the L-pad to reduce the volume in the dining room, which
closer examination shows is actually working. However, to get the
kitchen loud enough, the living room would be too loud, and I
don't really want to mess with that output, since that is the
best set of speakers.

Chris
--
Chris J Dixon Nottingham UK


Plant amazing Acers.

Speaker level adjustment
 

"The Natural Philosopher"

You can use a transformer to adjust power output via taps without
upsetting the impedance

** Very dodgy connecting a matching transformer to any old SS amp. Many
output stages cannot cope with the very low primary resistance and
propensity to core saturation at low frequencies.

- but resistive pads are not good for bass units.


** Perfectly OK for the purpose of an extension speaker.


As part of my essays into reproducing 'valve sound' for guitar amplifiers,
artificially raising the output impedance of the power amplifier was
routine.

** By adding a 0.1ohm 5W resistor to the ground in the feedback loop and
returning the speaker to it - right ?


The good old Vox A30 amplifier has an output impedance of some 80 ohms.
Driving an 8ohm pair of loudspeakers, the effects are dramatic.

** The speakers in an AC30 are series connected, giving a nominal 16 ohms.
At bass resonance, that will rise to about 60 ohms - so the amp's output
will rise by 4 times giving a 12dB peak at about 75Hz.


Massive bass resonance, about the bottom A on a guitar, plus overall
treble boost as the rising impedance of the speaker voice coil (a lot of
leakage inductance in a voice coil) is no longer a significant effect in
reducing treble output. Boom an chink we used to call it.

** That is the sound of an AC30 - despite the amp testing almost flat with
a dummy load.

Lotsa valve guitar amps use PP output pentodes with little or no NFB, just
like the AC30.


..... Phil

Speaker level adjustment
 

"The Natural Philosopher"

Phil Allison wrote:

You can use a transformer to adjust power output via taps without
upsetting the impedance

** Very dodgy connecting a matching transformer to any old SS amp. Many
output stages cannot cope with the very low primary resistance and
propensity to core saturation at low frequencies.

Never had any problems with any of my designs attaching 100V transformers
to em.

** ROTFL - so ****ing what ?


LF response is pre tail;rerd to get rid of serious 'rumble' on most amps
anyway

** Saturation may easily well ocurr at 50Hz or higher.

You have no clue - do you ?

and SOAR protection mens teh worst that can happen is serious distortion
if you end up wit DC bias..

** You have even less than no clue.

FYI:

A great many hi-fi amps have no or useless SOA limiting and a mere switch on
thump will cause instant output stage destruction if a transformer is
connected to the output.


- but resistive pads are not good for bass units.


** Perfectly OK for the purpose of an extension speaker.


No not perfectly good. Acceptable. Barely.

** Yawnnnnnnnnnnn...

You a professional bull**** artist or what ?


The good old Vox A30 amplifier has an output impedance of some 80 ohms.
Driving an 8ohm pair of loudspeakers, the effects are dramatic.

** The speakers in an AC30 are series connected, giving a nominal 16
ohms.
At bass resonance, that will rise to about 60 ohms - so the amp's output
will rise by 4 times giving a 12dB peak at about 75Hz.


Are they? Been too long..but your figures are as I recall from tests in
terms of ferquency and gain..

** I overestimated the boost, with 80 ohms driving 60 ohms max boost is more
like 8dB.


Lotsa valve guitar amps use PP output pentodes with little or no NFB,
just
like the AC30.

Actually you would be surprised.

** No I wouldn't.

I make my living repairing valve guitar amps - among others.

Since 1973.

They do NOT.


Only the AC 30 (EL84) was in any way seriously high impedance.

** Oh, there are lots of others with impedances in the 50 to 200 ohms range.

All those with pentodes and no feedback.


Most EL34 naps had some feedback - Marshalls come out around 8 ohms and
the US amps (tetrodes) were much more 'hi fi' at less than an ohm.

** Nonsense.

Only one maker of valve "guitar amps" had such low output impedances -
Dynachord.


I concluded that Fender, being an ex radio engineer, designed decent
amplifiers.

** Fender amps vary a lot, but most have output impedances over 4 ohms even
with a 4 ohm nominal load rating.

1950s models ( SE and PP) had no NFB at all.


Whoever did the Vox was a post war penny pinching scoundrel,

** Huh ??

The main reason Vox used no NFB was that being class A, it was simply not
needed to reduce crossover distortion - as was the case with all Fender's
class AB designs.


and Jim Marshall was a carpenter,

** Fact he was a drummer and music shop owner who employed techs to do his
amp building.

They just copied a popular Fender design at first - then stuffed it up.


IN short the British 'valve' sound was entirely due to a serendipitous
coincidence of parsimony and incompetence.

** Describes Marshall to a T.

Swapping Fender's 5881s and 6L6s for EL34s was a master stroke of
incompetence.


Then of course both Jim Marshall and the Vox boys were chasing decibels at
low cost, so both employed ultra lightweight speaker cones that had vile
coloration and zero stiffness. But louder. One imagines Celestion were
glad to unload these at any price.

** ROTFLMAO !!

Celestion made their guitar ( and radio ) speakers to be as efficient as
possible plus suitable for open back enclosures.

Low cone mass and fairly high resonant frequencies are the name of the game,
plus limited VC excursion for safety.

Rest of your tripe snipped.



..... Phil