In article , Arny Krueger
wrote:

"Jim Lesurf" wrote in message
...

Electolytic caps come to mind here. However I would hope that a decent
design would be built to avoid this. Indeed, apart from power
reservoirs, my understanding is that electrolytics are generally
avoided these days in equipment with 'audiophile' aspirations.

Let's talk about the part of every stereo system that has strong effects
on sound quality but is totally out of the control of audiophiles - the
recording and production equipment. If you peruse the schematics of
typical audio production equipment, there are many electrolytics in the
signal path. Ironically, a production facility might use high end mic
preamps with lotsa film caps or servos or both, but you'll find plenty
of them in the mixing console, mastering facility, etc.

Indeed. This was why I referred to "...equipment with 'audiophile'
aspirations." ;-

FWIW One of the 'criticisms' that was aimed by a reviewer at the amps I
designed years ago was that I dared to use electrolytic caps in various
stages. I still seem to lack any sense of shame or embarassment about doing
this, and probably would do so again if the results sounded and measured
fine to me. :-) This is despite being aware of various 'problems' with
electrolytic, and various other types of cap.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Maybe, what is being burnt-in is not
the hardware, but one's appreciation of the sound.

Very possible. Except that after mods I make that sound 'better' , the most
likely denoument is that the honeymoon period will wear off and I tend to think
the sound gets worse - not better.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

On Tue, 15 Jul 2003 08:42:20 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Mon, 14 Jul 2003 09:12:51 +0100, Jim Lesurf
wrote:

Do people still use electrolytics as signal path coupling caps these
days in 'audiophile' equipment? I know that other types show charge
storage effects, but this should, I hope, not be audible with decent
designs handling musical signal patterns.

Plot the AC signal path of an amplifier's output stage and you will find
that the supply decoupling electroloytics are in series with the speaker
- they function as speaker coupling caps. I am not aware of any design
that has done away with this topology yet.

I don't really agree that the above is an adequate description of what is
happening, since it is only a part of the story in this context. Indeed, I
tend to by slightly wary of terms like "signal path" even though I have to
use it at times as my impression is that it is used in a misleading way by
reviewers at times. I'll try to outline why I feel this...

Consider three uses of caps (nominally electrolytic).

1) As a d.c. break (decoupling capacitor) between amplifier stages with no
feedback from one stage to the other.

2) As a d.c. isolation at the 'foot' of a resistive feedback network to
ensure the amplifier gain falls to unit or zero at low frequency.

3) As reservoir caps in a power amp.

In conventional audio equipment the signal pattern is conveyed as a
*voltage* pattern, with whatever current may be required to assert this
voltage being provided. In such circumstances I tend to apply the following
'test' for deciding if something is "on the signal path".

I consider adding a fictitious voltage generator in series with the
relevant component to add a small 'error signal' (be it noise, distortion,
or whatever). I then ask if this then simply adds to the intended signal
with the rest of the system having no way to identify and reject this
addition.

In (1) and (2) any such error signal become part of the signal, and are not
rejected or ignored by the amplifier system. Hence any injected noise or
distortion at such component locations can be regarded as having been
injected into the signal path.

However with (3) the amplifier should have been designed to reject or
ignore any voltage fluctuations on the power rail voltages. My experience
is that well-designed amps do this fairly well. Hence case (3) seems to me
to be different to (1) and (2) *unless* the amplifier design has
effectively no ability to reject fluctuations on the rails due to
imperfections of limitations of the PSU (reservoirs, etc).

I certainly agree that the charge which passes through the loudspeaker was
previously stored in the reservoir capacitors. However I have my doubts
that this means we should regard the reservoir caps as part of the signal
path due to the behaviour of the amplifier in rejecting these fluctuations.
This may not be perfect, but is somewhat different to (1) and (2) were no
rejection may take place.

Makers and reviewers often mention that a given amp uses a side-chain of
some kind for d.c. offset removal, hence moving any caps 'out of the signal
path'. I have my doubts about this since, by the above argument, any error
voltages produced by the cap may still end up being added to the signal.
Hence I am not currently convinced these methods are all 'better' than the
old fashioned d.c. break cap at the foot of a resistive feedback network.
:-)

Slainte,

Jim

I appreciate all this reasoning, Jim, but the way I see it is this:

ALL of the AC signal current that goes through the speakers must pass
through these electrolytics as series elements. That puts them in the
signal path. Whether they are at the "cold" or "hot" end of the
speaker is really neither here nor there.

Actually my use of the word "ALL" above may seem contentious, but any
current that doesn't go through the caps must go instead through the
rest of the power supply - including the diodes - where it will be
chopped and modulated by the mains. Another good reason for big, fat,
low ESR electrolytics.

Just another view.

d

_____________________________

http://www.pearce.uk.com

In article , Don Pearce
wrote:
On Tue, 15 Jul 2003 08:42:20 +0100, Jim Lesurf
wrote:
[snip loads to avoid repetition]

I appreciate all this reasoning, Jim, but the way I see it is this:

ALL of the AC signal current that goes through the speakers must pass
through these electrolytics as series elements.

Agreed. ;-)

That puts them in the signal path.

This is what I find unsatisfactory as a description for the reasons I
outlined. - i.e. the amp should be drawing the current, but rejecting or
ignoring any resulting voltage variations of the rail voltage from which it
is drawing the current. Thus provided the available current and voltage are
'sufficient', the rail variations should have little or no effect upon the
output signal pattern.

In effect, the rail rejection of the amp seeks to isolate imperfections of
the reservoir caps from the 'signal path' in terms of their having any
effect upon the output. This is not so for the other cap locations I
mentioned. Hence the distinction I make.

There *are* (or can be) problems in these areas, of course. For example,
where some form of 'common mode' impedance due to shared power
arrangements in a stereo/multichannel amp causes distorted cross-talk. The
problem with things like this, though, is that unless we take care we end
up regarding *everything* as being in the signal path. It is possible to
argue this, but my worry is that the term may end up being so broad as to
cease to have any value.

My concern here is perhaps analogous to the way some people tend to use
'distortion' to mean *any* change in waveform shape (e.g. due to linear
filtering) whereas others limit it to effects due to non-linearities.
Problems then arise when we try to use the term to discuss specific issues
as the term ends up meaning different things to different people and they
may not notice they are arguing/discussing at cross-puposes as they are
making different assumptions as to the meanings of the terms. As an
academic I tend to prefer fairly limited and specific definitions where
possible to avoid the risk of this.

Whether they are at the "cold" or "hot" end of the speaker is really
neither here nor there.

Agreed. :-) Not the point I was making, though.

Actually my use of the word "ALL" above may seem contentious, but any
current that doesn't go through the caps must go instead through the
rest of the power supply - including the diodes - where it will be
chopped and modulated by the mains. Another good reason for big, fat,
low ESR electrolytics.

I'd agree that good electrolytics with adequate values, low ESR, etc, are
desirable. However I also feel it is the task of the amp to then reject any
remaining fluctuations on the rail. I's also agree that no amp can be
expected to do this perfectly. But I contrast this with the other cases I
mentioned where the amp can't really do anything at all about any cap
imperfections.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Don Pearce" wrote in message

On Mon, 14 Jul 2003 09:12:51 +0100, Jim Lesurf
wrote:

Do people still use electrolytics as signal path coupling caps these
days in 'audiophile' equipment? I know that other types show charge
storage effects, but this should, I hope, not be audible with decent
designs handling musical signal patterns.

Plot the AC signal path of an amplifier's output stage and you will
find that the supply decoupling electroloytics are in series with the
speaker - they function as speaker coupling caps. I am not aware of
any design that has done away with this topology yet.

It makes a big difference whether the caps are inside or outside the
feedback loop.

On Tue, 15 Jul 2003 21:26:05 -0400, "Arny Krueger"
wrote:

"Don Pearce" wrote in message

On Mon, 14 Jul 2003 09:12:51 +0100, Jim Lesurf
wrote:

Do people still use electrolytics as signal path coupling caps these
days in 'audiophile' equipment? I know that other types show charge
storage effects, but this should, I hope, not be audible with decent
designs handling musical signal patterns.

Plot the AC signal path of an amplifier's output stage and you will
find that the supply decoupling electroloytics are in series with the
speaker - they function as speaker coupling caps. I am not aware of
any design that has done away with this topology yet.

It makes a big difference whether the caps are inside or outside the
feedback loop.

Doesn't change the fact that they couple current into the speakers.
And of course everything, including the speakers themselves, is inside
the feedback loop.

d

_____________________________

http://www.pearce.uk.com

On Tue, 15 Jul 2003 17:03:39 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Tue, 15 Jul 2003 08:42:20 +0100, Jim Lesurf
wrote:
[snip loads to avoid repetition]

I appreciate all this reasoning, Jim, but the way I see it is this:

ALL of the AC signal current that goes through the speakers must pass
through these electrolytics as series elements.

Agreed. ;-)

That puts them in the signal path.

This is what I find unsatisfactory as a description for the reasons I
outlined. - i.e. the amp should be drawing the current, but rejecting or
ignoring any resulting voltage variations of the rail voltage from which it
is drawing the current. Thus provided the available current and voltage are
'sufficient', the rail variations should have little or no effect upon the
output signal pattern.

In effect, the rail rejection of the amp seeks to isolate imperfections of
the reservoir caps from the 'signal path' in terms of their having any
effect upon the output. This is not so for the other cap locations I
mentioned. Hence the distinction I make.

There *are* (or can be) problems in these areas, of course. For example,
where some form of 'common mode' impedance due to shared power
arrangements in a stereo/multichannel amp causes distorted cross-talk. The
problem with things like this, though, is that unless we take care we end
up regarding *everything* as being in the signal path. It is possible to
argue this, but my worry is that the term may end up being so broad as to
cease to have any value.

My concern here is perhaps analogous to the way some people tend to use
'distortion' to mean *any* change in waveform shape (e.g. due to linear
filtering) whereas others limit it to effects due to non-linearities.
Problems then arise when we try to use the term to discuss specific issues
as the term ends up meaning different things to different people and they
may not notice they are arguing/discussing at cross-puposes as they are
making different assumptions as to the meanings of the terms. As an
academic I tend to prefer fairly limited and specific definitions where
possible to avoid the risk of this.

Whether they are at the "cold" or "hot" end of the speaker is really
neither here nor there.

Agreed. :-) Not the point I was making, though.

Actually my use of the word "ALL" above may seem contentious, but any
current that doesn't go through the caps must go instead through the
rest of the power supply - including the diodes - where it will be
chopped and modulated by the mains. Another good reason for big, fat,
low ESR electrolytics.

I'd agree that good electrolytics with adequate values, low ESR, etc, are
desirable. However I also feel it is the task of the amp to then reject any
remaining fluctuations on the rail. I's also agree that no amp can be
expected to do this perfectly. But I contrast this with the other cases I
mentioned where the amp can't really do anything at all about any cap
imperfections.

Slainte,

Jim

All true, JIm. But it is the task of the amp - or more specifically
the feedback loop - to reject or at least minimise the imperfections
of all signal path components. The fact that the control path that
sorts out these caps is slightly different really doesn't change that
case.

d

_____________________________

http://www.pearce.uk.com

"Don Pearce" wrote in message

On Tue, 15 Jul 2003 21:26:05 -0400, "Arny Krueger"
wrote:

"Don Pearce" wrote in message

On Mon, 14 Jul 2003 09:12:51 +0100, Jim Lesurf
wrote:

Do people still use electrolytics as signal path coupling caps
these days in 'audiophile' equipment? I know that other types show
charge storage effects, but this should, I hope, not be audible
with decent designs handling musical signal patterns.

Plot the AC signal path of an amplifier's output stage and you will
find that the supply decoupling electroloytics are in series with
the speaker - they function as speaker coupling caps. I am not
aware of any design that has done away with this topology yet.

It makes a big difference whether the caps are inside or outside the
feedback loop.

Doesn't change the fact that they couple current into the speakers.

Which is another way of saying that feedback doesn't do much for dynamic
range.

But feedback does improve the accuracy within the dynamic range limitations.

And of course everything, including the speakers themselves, is inside
the feedback loop.

Say what? To put speakers inside a feedback loop you have to accurately
sense their acoustical output in a timely fashion, and that has always been
a problem.

On Wed, 16 Jul 2003 06:57:55 -0400, "Arny Krueger"
wrote:

And of course everything, including the speakers themselves, is inside
the feedback loop.

Say what? To put speakers inside a feedback loop you have to accurately
sense their acoustical output in a timely fashion, and that has always been
a problem.

I'm talking about the speakers as electronic components. I don't mean
that the feedback includes the acoustic output - although to a limited
extent it does. The speaker terminals of an amplifier are within the
feedback loop, and anything connected there is within that loop.

That is why some designs are capable (hah!) of bursting into
oscillation if an inappropriate impedance is connected there.

d

_____________________________

http://www.pearce.uk.com

"Don Pearce" wrote in message

On Wed, 16 Jul 2003 06:57:55 -0400, "Arny Krueger"
wrote:

And of course everything, including the speakers themselves, is
inside the feedback loop.

Say what? To put speakers inside a feedback loop you have to
accurately sense their acoustical output in a timely fashion, and
that has always been a problem.

I'm talking about the speakers as electronic components. I don't mean
that the feedback includes the acoustic output - although to a limited
extent it does. The speaker terminals of an amplifier are within the
feedback loop, and anything connected there is within that loop.

I guess I was taught a narrow view of what is inside the loop. Clearly the
source and load impedance affect the operation of the loop, but the way I
was taught, they are not inside the loop.

That is why some designs are capable (hah!) of bursting into
oscillation if an inappropriate impedance is connected there.

The way I was taught, those would be called influences outside the loop that
affect how the loop operates. Other influences include EMI and the power
source.