[John Fields]

On Tue, 25 Jul 2006 08:29:07 -0700, John Larkin
wrote:

On 25 Jul 2006 09:45:40 -0400, (Scott Dorsey) wrote:

John Larkin wrote:
wrote:

The "drag surface" of a variable resistor has to be a couple hundred
times rougher than that. That is going to produce "noise" when
turned, and even when stopped as the contact surface upon the wiper
can and likely will always be different tiny points on the wiper
surface. It is rougher even than basic grain oriented polished
stainless at a certain finish. (maybe a number 4). Pretty rough is
the macro surface quality/texture realm.

But how does that create electrical noise?

When you turn the pot, it bounces up and down across the surface. There
is mechanical noise, and a corresponding change in resistance that causes
electrical noise.

Please explain how a change in resistance creates voltage.


---
You're kidding, right?

E1
|
R1
|
|---+---E2
R2 |
|---+
|
R3
|
0V

R2 is whatever portion of the track the wiper happens to "jump over"
as it's rotated.

If, in one case, the wiper happens to be between R1 and R2, then E2
will be:


E1 (R2 + R3)
E2 = ---------------
R1 + R2 + R3


and in the other, where it jumps to between R2 and R3:


E1 * R3
E2 = ---------------
R1 + R2 + R3


If we let the pot's resistance be 1000 ohms and the jump 100
milliohms wide,


Then we have, for the first case:


10V
|
499.95R
|
+--- 5.0005 V
|
500.05R
|
0V


and, for the second,


10V
|
500.05R
|
+--- 4.9995V
|
499.95R
|
0V

Voila! a difference of 100 milliohms created a change of 100
microvolts.


--
John Fields
Professional Circuit Designer

[John Fields]

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:


OK, new audiophool product: volume controls based on variable
capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesea...=1&render=1&w=
--
John Fields
Professional Circuit Designer

[Bob Quintal]

John Fields wrote in
:

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:


OK, new audiophool product: volume controls based on variable
capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesearch/fsc.jsp?
command=text&at
tr1=H11F1&attr2=&t=0&i=sitemap+id&ia=1&text=H11F1& as=1&render=
1
&w=

Thanks for the memories,
Of candlelight and wine, castles on the Rhine

and old Fairchild compressor/limiters and McCurdy broadcast
consoles.

--
Bob Quintal

PA is y I've altered my email address.

--
Posted via a free Usenet account from http://www.teranews.com

[John Larkin]

On Tue, 25 Jul 2006 13:40:13 -0500, John Fields
wrote:

On Tue, 25 Jul 2006 08:29:07 -0700, John Larkin
wrote:

On 25 Jul 2006 09:45:40 -0400, (Scott Dorsey) wrote:

John Larkin wrote:
wrote:

The "drag surface" of a variable resistor has to be a couple hundred
times rougher than that. That is going to produce "noise" when
turned, and even when stopped as the contact surface upon the wiper
can and likely will always be different tiny points on the wiper
surface. It is rougher even than basic grain oriented polished
stainless at a certain finish. (maybe a number 4). Pretty rough is
the macro surface quality/texture realm.

But how does that create electrical noise?

When you turn the pot, it bounces up and down across the surface. There
is mechanical noise, and a corresponding change in resistance that causes
electrical noise.

Please explain how a change in resistance creates voltage.


---
You're kidding, right?

E1
|
R1
|
|---+---E2
R2 |
|---+
|
R3
|
0V

R2 is whatever portion of the track the wiper happens to "jump over"
as it's rotated.

If, in one case, the wiper happens to be between R1 and R2, then E2
will be:


E1 (R2 + R3)
E2 = ---------------
R1 + R2 + R3


and in the other, where it jumps to between R2 and R3:


E1 * R3
E2 = ---------------
R1 + R2 + R3


If we let the pot's resistance be 1000 ohms and the jump 100
milliohms wide,


Then we have, for the first case:


10V
|
499.95R
|
+--- 5.0005 V
|
500.05R
|
0V


and, for the second,


10V
|
500.05R
|
+--- 4.9995V
|
499.95R
|
0V

Voila! a difference of 100 milliohms created a change of 100
microvolts.



Well, pots don't "jump". And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere. And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots. It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.


John

[Eeyore]

John Larkin wrote:

On Tue, 25 Jul 2006 07:09:55 +0100, Eeyore
wrote:


John Larkin wrote:

On Tue, 25 Jul 2006 05:09:29 GMT, Phat Bytestard
wrote:

On Mon, 24 Jul 2006 20:07:24 -0700, John Larkin
Gave us:

On Tue, 25 Jul 2006 02:28:06 GMT, Phat Bytestard
wrote:

On Mon, 24 Jul 2006 08:24:37 -0700, John Larkin
Gave us:

On 24 Jul 2006 10:41:54 -0400, (Scott Dorsey) wrote:

John Larkin wrote:
On Sun, 23 Jul 2006 04:59:19 GMT, Prune
wrote:

I've tried cermet potentiometers for volume control, and in a blind test
(non-double, used dual switch with my friend) I can't tell the difference
between it and a stepped attenuator; however, in 7/10 trials me and 8/10
trials him heard difference between plastic pot and the cermet, both
preferring the cermet.

Please don't top post.

Agreed. But the problem with cermets is they are noisy as hell when
you turn them. That's fine for trimmers, but no so good for a volume
control on the front panel.

What's the origin of the noise? If the wiper drives a high impedance,
unstable wiper contact resistance will generate no noise.


The surface quality of a first surface mirror is very flat, and very
fine grained in the macroscopic view.

The "drag surface" of a variable resistor has to be a couple hundred
times rougher than that. That is going to produce "noise" when
turned, and even when stopped as the contact surface upon the wiper
can and likely will always be different tiny points on the wiper
surface. It is rougher even than basic grain oriented polished
stainless at a certain finish. (maybe a number 4). Pretty rough is
the macro surface quality/texture realm.

But how does that create electrical noise?

John

While the wiper is still or moving?

While moving, it should be obvious.

Not to me. Noise requires potentials, and resistors don't do that.

But as connections are varying, Vout / Vin also varies. This creates the noise.
Think of the condition with a DC input and it's more immediately obvious.

Graham

That will just result in a tiny amplitude modulation of whatever sound
level is there at that instant,

Which is noise ! I'm talking about sharp step changes, not the 'modulation'
intentionally caused which is vlf.


and the sound level is changing all
the time anyway, especially so as you're turning the pot on purpose
already. That won't be very, whether the pot is cermet, plastic, or
wirewound.

Practice shows otherwise.


The difference with DC is that you can't hear DC, but you can hear the
small variations in DC - real noise - that a bad pot can create.

Those variations may not be so 'small' as you think.

Besides, you should already know that it doesn't matter if the input is ac or dc. Try
doing it with lf ac and you'll hear just as much noise as with dc. Obviously higher
frequencies are more audible and tend to mask the noise but it's still there.

Check out 'zipper noise' for example.

Graham

[Eeyore]

John Larkin wrote:

On 25 Jul 2006 09:45:40 -0400, (Scott Dorsey) wrote:

John Larkin wrote:
wrote:

The "drag surface" of a variable resistor has to be a couple hundred
times rougher than that. That is going to produce "noise" when
turned, and even when stopped as the contact surface upon the wiper
can and likely will always be different tiny points on the wiper
surface. It is rougher even than basic grain oriented polished
stainless at a certain finish. (maybe a number 4). Pretty rough is
the macro surface quality/texture realm.

But how does that create electrical noise?

When you turn the pot, it bounces up and down across the surface. There
is mechanical noise, and a corresponding change in resistance that causes
electrical noise.

Please explain how a change in resistance creates voltage.

Change in Vout / Vin obviously.

Graham

[John Fields]

On Tue, 25 Jul 2006 12:20:07 -0700, John Larkin
wrote:


Well, pots don't "jump".

---
Sure they do, since they've got "stiction" in there, somewhere, and
when you go to crank in that last little bit of resistance you need
to get to 1.234 volts it skips over the spot you needed and now
you're at 1.256 volts and you've got to go back the other way...
---

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

---
That's not true. Depending on the amplitude of the step and how
abruptly it changed, spectral components not present in the program
material (noise, IOW) will be present in the signal leaving the pot
and propagating through the rest of the system.
---

And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

---
So what?
---

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

---
That wasn't the point. The point was that pots can add noise to a
system.
---

It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

---
Sure, but that's a whole 'nother issue.


--
John Fields
Professional Circuit Designer

[Eeyore]

John Fields wrote:

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:

OK, new audiophool product: volume controls based on variable
capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesea...=1&render=1&w=

CdS type photocells have also been used in this application btw.

Graham

[Eeyore]

John Larkin wrote:

Well, pots don't "jump".

Well, they do actually, or they wouldn't make any noise when being rotated ! Of
course the effect varies widely with construction and materials not to mention
age ( cycles of use ).

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

A step change in amplitude is indistinguishable from noise. Remember that those
step changes will be in both directions as the pot as rotated in one direction.


And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

That's because you're not familiar with their use in this respect it seems.


It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

But no 'noise' though. I'm no fan of stepped attenuators btw. The cheaper ones
btw are simply pots with mechanical detents !

Graham

[John Larkin]

On Tue, 25 Jul 2006 20:38:18 +0100, Eeyore
wrote:


John Larkin wrote:

On Tue, 25 Jul 2006 07:09:55 +0100, Eeyore
wrote:


John Larkin wrote:

On Tue, 25 Jul 2006 05:09:29 GMT, Phat Bytestard
wrote:

On Mon, 24 Jul 2006 20:07:24 -0700, John Larkin
Gave us:

On Tue, 25 Jul 2006 02:28:06 GMT, Phat Bytestard
wrote:

On Mon, 24 Jul 2006 08:24:37 -0700, John Larkin
Gave us:

On 24 Jul 2006 10:41:54 -0400, (Scott Dorsey) wrote:

John Larkin wrote:
On Sun, 23 Jul 2006 04:59:19 GMT, Prune
wrote:

I've tried cermet potentiometers for volume control, and in a blind test
(non-double, used dual switch with my friend) I can't tell the difference
between it and a stepped attenuator; however, in 7/10 trials me and 8/10
trials him heard difference between plastic pot and the cermet, both
preferring the cermet.

Please don't top post.

Agreed. But the problem with cermets is they are noisy as hell when
you turn them. That's fine for trimmers, but no so good for a volume
control on the front panel.

What's the origin of the noise? If the wiper drives a high impedance,
unstable wiper contact resistance will generate no noise.


The surface quality of a first surface mirror is very flat, and very
fine grained in the macroscopic view.

The "drag surface" of a variable resistor has to be a couple hundred
times rougher than that. That is going to produce "noise" when
turned, and even when stopped as the contact surface upon the wiper
can and likely will always be different tiny points on the wiper
surface. It is rougher even than basic grain oriented polished
stainless at a certain finish. (maybe a number 4). Pretty rough is
the macro surface quality/texture realm.

But how does that create electrical noise?

John

While the wiper is still or moving?

While moving, it should be obvious.

Not to me. Noise requires potentials, and resistors don't do that.

But as connections are varying, Vout / Vin also varies. This creates the noise.
Think of the condition with a DC input and it's more immediately obvious.

Graham

That will just result in a tiny amplitude modulation of whatever sound
level is there at that instant,

Which is noise ! I'm talking about sharp step changes, not the 'modulation'
intentionally caused which is vlf.


and the sound level is changing all
the time anyway, especially so as you're turning the pot on purpose
already. That won't be very, whether the pot is cermet, plastic, or
wirewound.

Practice shows otherwise.


The difference with DC is that you can't hear DC, but you can hear the
small variations in DC - real noise - that a bad pot can create.

I wasn't considering bad pots; they could cause gross dropouts that
you'd certainly hear.


Those variations may not be so 'small' as you think.

Besides, you should already know that it doesn't matter if the input is ac or dc. Try
doing it with lf ac and you'll hear just as much noise as with dc. Obviously higher
frequencies are more audible and tend to mask the noise but it's still there.

Check out 'zipper noise' for example.

Graham


Well then, I guess you should go to stepped attenuators to avoid the,
err, gain steps.

John

[John Larkin]

On Tue, 25 Jul 2006 20:47:37 +0100, Eeyore
wrote:



John Larkin wrote:

Well, pots don't "jump".

Well, they do actually, or they wouldn't make any noise when being rotated ! Of
course the effect varies widely with construction and materials not to mention
age ( cycles of use ).

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

A step change in amplitude is indistinguishable from noise. Remember that those
step changes will be in both directions as the pot as rotated in one direction.


And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

That's because you're not familiar with their use in this respect it seems.


It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

But no 'noise' though. I'm no fan of stepped attenuators btw. The cheaper ones
btw are simply pots with mechanical detents !

Some wise person once said, "A step change in amplitude is
indistinguishable from noise."


John

[Arny Krueger]

"Eeyore" wrote in
message ...


John Fields wrote:

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:

OK, new audiophool product: volume controls based on variable
capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesea...=1&render=1&w=

CdS type photocells have also been used in this application btw.

Neither are the most linear gain control elements around.

[Bob Quintal]

"Arny Krueger" wrote in
:


"Eeyore"
wrote in message
...


John Fields wrote:

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:

OK, new audiophool product: volume controls based on
variable capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesearch/fsc.jsp?
command=text&
attr1=H11F1&attr2=&t=0&i=sitemap+id&ia=1&text=H11F 1&as=1
&rend
er=1&w=

CdS type photocells have also been used in this application
btw.

Neither are the most linear gain control elements around.

Tell me about it. The McCurdy consoles used an arrangement with
several cells and an incandescent bulb inside a 9-pin tube
envelope (like a 12AX7) painted black. Clockwise rotation of the
potentiometer driving the things always gave an increase of
level at the monitor. That's all they were supposed to control,
though, so you could say that it worked.

--
Bob Quintal

PA is y I've altered my email address.

--
Posted via a free Usenet account from http://www.teranews.com

[Eeyore]

John Larkin wrote:

On Tue, 25 Jul 2006 20:38:18 +0100, Eeyore
wrote:

John Larkin wrote:

The difference with DC is that you can't hear DC, but you can hear the
small variations in DC - real noise - that a bad pot can create.

I wasn't considering bad pots; they could cause gross dropouts that
you'd certainly hear.

Why are you replying to yourself ? It was you who introduced that topic !


Those variations may not be so 'small' as you think.

Besides, you should already know that it doesn't matter if the input is ac or dc. Try
doing it with lf ac and you'll hear just as much noise as with dc. Obviously higher
frequencies are more audible and tend to mask the noise but it's still there.

Check out 'zipper noise' for example.

Graham

Well then, I guess you should go to stepped attenuators to avoid the,
err, gain steps.

Eh ? Zipper noise *is* gain steps. It's different to the rotational noise from a pot
though.

Graham

[Eeyore]

John Larkin wrote:

On Tue, 25 Jul 2006 20:47:37 +0100, Eeyore
wrote:

John Larkin wrote:

Well, pots don't "jump".

Well, they do actually, or they wouldn't make any noise when being rotated ! Of
course the effect varies widely with construction and materials not to mention
age ( cycles of use ).

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

A step change in amplitude is indistinguishable from noise. Remember that those
step changes will be in both directions as the pot as rotated in one direction.


And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

That's because you're not familiar with their use in this respect it seems.


It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

But no 'noise' though. I'm no fan of stepped attenuators btw. The cheaper ones
btw are simply pots with mechanical detents !

Some wise person once said, "A step change in amplitude is
indistinguishable from noise."

More accurately 'normal' noise goes positive and negative randomly, but they are
similar in some ways. A single step doesn't really count as noise though.

I suspect you're trying to obfuscate your way out of the corner you painted yourself
into ! lol !

Graham

[Eeyore]

Arny Krueger wrote:

"Eeyore" wrote in
message ...


John Fields wrote:

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:

OK, new audiophool product: volume controls based on variable
capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesea...=1&render=1&w=

CdS type photocells have also been used in this application btw.

Neither are the most linear gain control elements around.

Perfectly true. I've used CdS cells in a crossfader though ( minimum effect at unity gain and hence very linear at that setting ) . The
only nice, suitably priced VCAs were on 1 yr lead time !

Graham

[Eeyore]

Sander deWaal wrote:

Eeyore said:

You're pathetic. A tribute to audiophoolery.

Al 's a happy tinkerer.
With all respect for your status as a pro designer (so am I, in a
smaller and different way), I'm afraid you've lost that ability
somewhere along the way............

I think you'd be mistaken there !

I love that kind of tinkering that ( for example ) reduces THD to vanishingly
small levels such as 0.00x %. It's a technical and intellectual challenge and I
don't have to use brute force global nfb to do it either !

Of course I don't 'tinker' as such, apart maybe from on the simulation package.
Almost all of it is pure science. Very satisfying it is too to see it work as
per the theory.

It's also nice to hear ppl praise one's products to because they like the way
they sound. :-)

Graham

[Eeyore]

Arny Krueger wrote:

"Eeyore" wrote in
message ...


"Bob H." wrote:

Whoops, I meant 87 db/M
87dbM/m with 4 ohm nominal impedance and who-knows-what impedance dips.

and alnico.
(alinco), Hammer super 12's, and fostex

Good God !

You think that Alnico magnets somehow produce superior sound over other
magnets ? Is that lame or what ?

Yes, there are Alnico gauss and ceramic gauss. The former are more
effective. ;-)

LMAO.

Those Gauss's were so much better than today's Webers.

Graham

[John Larkin]

On Tue, 25 Jul 2006 21:29:22 +0100, Eeyore
wrote:



John Larkin wrote:

On Tue, 25 Jul 2006 20:47:37 +0100, Eeyore
wrote:

John Larkin wrote:

Well, pots don't "jump".

Well, they do actually, or they wouldn't make any noise when being rotated ! Of
course the effect varies widely with construction and materials not to mention
age ( cycles of use ).

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

A step change in amplitude is indistinguishable from noise. Remember that those
step changes will be in both directions as the pot as rotated in one direction.


And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

That's because you're not familiar with their use in this respect it seems.


It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

But no 'noise' though. I'm no fan of stepped attenuators btw. The cheaper ones
btw are simply pots with mechanical detents !

Some wise person once said, "A step change in amplitude is
indistinguishable from noise."

More accurately 'normal' noise goes positive and negative randomly, but they are
similar in some ways. A single step doesn't really count as noise though.

I suspect you're trying to obfuscate your way out of the corner you painted yourself
into ! lol !

Graham


I have no emotional investment in this, other than to understand how a
pot can generate noise, and why a cermet might be worse than a plastic
pot. So far, not much illumination.

John

[Eeyore]

John Larkin wrote:

On Tue, 25 Jul 2006 21:29:22 +0100, Eeyore
wrote:


John Larkin wrote:

On Tue, 25 Jul 2006 20:47:37 +0100, Eeyore
wrote:

John Larkin wrote:

Well, pots don't "jump".

Well, they do actually, or they wouldn't make any noise when being rotated ! Of
course the effect varies widely with construction and materials not to mention
age ( cycles of use ).

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

A step change in amplitude is indistinguishable from noise. Remember that those
step changes will be in both directions as the pot as rotated in one direction.


And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

That's because you're not familiar with their use in this respect it seems.


It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

But no 'noise' though. I'm no fan of stepped attenuators btw. The cheaper ones
btw are simply pots with mechanical detents !

Some wise person once said, "A step change in amplitude is
indistinguishable from noise."

More accurately 'normal' noise goes positive and negative randomly, but they are
similar in some ways. A single step doesn't really count as noise though.

I suspect you're trying to obfuscate your way out of the corner you painted yourself
into ! lol !

Graham

I have no emotional investment in this,

Neither have I. I just like to understand the mechanisms at work.


other than to understand how a
pot can generate noise, and why a cermet might be worse than a plastic
pot. So far, not much illumination.

You're having trouble understanding that when a pot is moved, it moves in 'micro jumps' ?
Those jump sizes vary with the materials used.

Graham

[Rick]

Phil Hobbs wrote:

rick H wrote:

The series expansion gives you (with your formula)
(hf/kT)/(exp(hf/kT)-1) ~= (hf/kT)/(1 + hf/kT -1)
= (hf/kT)/(hf/KT)
= 1
which is an interesting (dimensionless) result!

Right, I'm quoting the Planck *rolloff*. It's normalized to 1 at low
frequency.


Sorry! Having realised that your expression was dimensionless, I really
should have cottoned on you'd normalised with respect to the value at f-0.

Cheers,

--
Rick

[John Larkin]

On Tue, 25 Jul 2006 23:05:08 +0100, Eeyore
wrote:



John Larkin wrote:

On Tue, 25 Jul 2006 21:29:22 +0100, Eeyore
wrote:


John Larkin wrote:

On Tue, 25 Jul 2006 20:47:37 +0100, Eeyore
wrote:

John Larkin wrote:

Well, pots don't "jump".

Well, they do actually, or they wouldn't make any noise when being rotated ! Of
course the effect varies widely with construction and materials not to mention
age ( cycles of use ).

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

A step change in amplitude is indistinguishable from noise. Remember that those
step changes will be in both directions as the pot as rotated in one direction.


And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

That's because you're not familiar with their use in this respect it seems.


It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

But no 'noise' though. I'm no fan of stepped attenuators btw. The cheaper ones
btw are simply pots with mechanical detents !

Some wise person once said, "A step change in amplitude is
indistinguishable from noise."

More accurately 'normal' noise goes positive and negative randomly, but they are
similar in some ways. A single step doesn't really count as noise though.

I suspect you're trying to obfuscate your way out of the corner you painted yourself
into ! lol !

Graham

I have no emotional investment in this,

Neither have I. I just like to understand the mechanisms at work.


other than to understand how a
pot can generate noise, and why a cermet might be worse than a plastic
pot. So far, not much illumination.

You're having trouble understanding that when a pot is moved, it moves in 'micro jumps' ?
Those jump sizes vary with the materials used.

Graham

Of course I understand that; I'm an engineer. And I understand that
the gain of any signal present will be tweaked in a (probably)
monotonic but not necessarily absolutely smooth manner. What I don't
understand, or maybe appreciate, is why this should produce audible
noise. The mechanisms are, probably, gross mechanical static friction
and some sort of micro-granularity in the resistance track itself.
Both should be in the 0.1% range, maybe a lot less. And the 0.1% or
whatever noise is relative to the existing sound level, not absolute
voltage on its own. Of course, a bunch of tube or opamp bias current
dumped into a flakey wiper will generate real noise, a bad part
compounded by bad design.

Really, there are so many myths around audio, it's rational to
question anything that doesn't seem to have a sound physical
foundation.

I think people prefer cp pots because they feel better.

John

[Eeyore]

John Larkin wrote:

On Tue, 25 Jul 2006 23:05:08 +0100, Eeyore
wrote:


John Larkin wrote:

On Tue, 25 Jul 2006 21:29:22 +0100, Eeyore
wrote:


John Larkin wrote:

On Tue, 25 Jul 2006 20:47:37 +0100, Eeyore
wrote:

John Larkin wrote:

Well, pots don't "jump".

Well, they do actually, or they wouldn't make any noise when being rotated ! Of
course the effect varies widely with construction and materials not to mention
age ( cycles of use ).

And all your math indicates is that the
signal gain changed, not that any new "noise" signal was generated
anywhere.

A step change in amplitude is indistinguishable from noise. Remember that those
step changes will be in both directions as the pot as rotated in one direction.


And the signal gain changed because, well, we weren't happy
with the volume and we decided to get off our butts and turn the knob.

I don't think anybody can hear the difference between properly working
cermet and conductive plastic pots.

That's because you're not familiar with their use in this respect it seems.


It is interesting that high-end
golden-ear folks tend to prefer stepped rotary-switch based
attenuators over pots. And stepped attenuators sure do have massive
gain jumps, orders of magnitude more than the case you analyzed.

But no 'noise' though. I'm no fan of stepped attenuators btw. The cheaper ones
btw are simply pots with mechanical detents !

Some wise person once said, "A step change in amplitude is
indistinguishable from noise."

More accurately 'normal' noise goes positive and negative randomly, but they are
similar in some ways. A single step doesn't really count as noise though.

I suspect you're trying to obfuscate your way out of the corner you painted yourself
into ! lol !

Graham

I have no emotional investment in this,

Neither have I. I just like to understand the mechanisms at work.


other than to understand how a
pot can generate noise, and why a cermet might be worse than a plastic
pot. So far, not much illumination.

You're having trouble understanding that when a pot is moved, it moves in 'micro jumps' ?
Those jump sizes vary with the materials used.

Graham

Of course I understand that; I'm an engineer. And I understand that
the gain of any signal present will be tweaked in a (probably)
monotonic but not necessarily absolutely smooth manner.

I think you'll find it's quite non-monotonic actually.


What I don't
understand, or maybe appreciate, is why this should produce audible
noise. The mechanisms are, probably, gross mechanical static friction
and some sort of micro-granularity in the resistance track itself.
Both should be in the 0.1% range, maybe a lot less.

0.1% would be -60dB which is quite good but above the noise floor of good audio.


And the 0.1% or
whatever noise is relative to the existing sound level, not absolute
voltage on its own.

Yes indeed.

Of course, a bunch of tube or opamp bias current
dumped into a flakey wiper will generate real noise, a bad part
compounded by bad design.

That of course is yet another problem. If the wiper goes hi-Z and there's a DC path there'll
be significant trouble ! That's why top end gear usually capacitively couples the wiper
circuit.


Really, there are so many myths around audio, it's rational to
question anything that doesn't seem to have a sound physical
foundation.

I do this too.


I think people prefer cp pots because they feel better.

That's yet another advantage. Their cost is something else though, although Vishay-Sfernice
have some nice parts that aren't too shocking.

Graham

[John Fields]

On Tue, 25 Jul 2006 20:42:48 +0100, Eeyore
wrote:



John Fields wrote:

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:

OK, new audiophool product: volume controls based on variable
capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesea...=1&render=1&w=

CdS type photocells have also been used in this application btw.

---
Yup.

EG&G, early on, had "Vactrols" with incandescents, LED's, and Neons
as the emitters and LDRs as the variable resistance elements.


--
John Fields
Professional Circuit Designer

[Eeyore]

John Fields wrote:

On Tue, 25 Jul 2006 20:42:48 +0100, Eeyore
wrote:



John Fields wrote:

On Tue, 25 Jul 2006 07:05:20 -0700, John Larkin
wrote:

OK, new audiophool product: volume controls based on variable
capacitance.

---
Old pro audio product: volume control based on a photoFET:

http://www.fairchildsemi.com/sitesea...=1&render=1&w=

CdS type photocells have also been used in this application btw.

---
Yup.

EG&G, early on, had "Vactrols" with incandescents, LED's, and Neons
as the emitters and LDRs as the variable resistance elements.

I've had a couple of Vactrols to evaluate in the past but the were pricier than the Silonex parts I used eventually. I've also used the
cheap 'n cheerful 'Eagle' parts from China that are just an led and a little CdS cell in a black plastic box. Perfectly fine actually
but I have had to get some graded for use. Actually the Silonex parts are graded too but you can buy them like that.

The very well known and popular UREI 'levelling amplifiers' used vactrols IIRC incluiding a neon one in an early toob based version.

Graham

[John Fields]

On Tue, 25 Jul 2006 14:52:02 -0700, John Larkin
wrote:


I have no emotional investment in this, other than to understand how a
pot can generate noise, and why a cermet might be worse than a plastic
pot. So far, not much illumination.

---
Come on, John, get real.

You've got a huge emotional investment in this thread since you seem
to want to be one of the gurus here, but you stated, wrongly, that a
step change out of a voltage divider wouldn't generate noise and
you've been proven wrong.

Hey, it happens to the best of us.

Acknowledge your error and get on with your life.

Or spend the rest of your life covering up


--
John Fields
Professional Circuit Designer

[John Larkin]

On Tue, 25 Jul 2006 19:06:06 -0500, John Fields
wrote:

On Tue, 25 Jul 2006 14:52:02 -0700, John Larkin
wrote:


I have no emotional investment in this, other than to understand how a
pot can generate noise, and why a cermet might be worse than a plastic
pot. So far, not much illumination.

---
Come on, John, get real.

You've got a huge emotional investment in this thread

No, really, it's mildly interesting, but since I don't design audio it
doesn't matter much. I do use cermet trimpots and have never been
bothered by their noise during adjustment. If it mattered, I'd do an
experiment and cut through all this expert opinion.

since you seem
to want to be one of the gurus here,

Innocent again. I learn stuff here and sometimes have fun, and might
even find an occasional friend, consultant, or employee, but am not
interested in guru-dom. I find that sort of thing embarassing.

I do admit I sometimes like to mess with the heads of audio types,
such as those heads are. I mean, they do have their own newsgroups
where they can express subjective opinions unemcumbered by physics.


but you stated, wrongly, that a
step change out of a voltage divider wouldn't generate noise and
you've been proven wrong.

Gosh, has anything been proven? I said a pot wouldn't generate voltage
noise on its own, and that it could slightly modulate the amplitude of
any signal present, and questioned whether it was audible or whether
cermet was worse than cp. As far as I'm concerned, the audibility
remains an open question. And I did point out the the function of a
volume control is to modulate amplitude; I sure hope that's not still
being debated.



Hey, it happens to the best of us.

Acknowledge your error and get on with your life.

Or spend the rest of your life covering up

What, carry my shame all the way to the grave?


Listen: this is a newsgroup. It doesn't matter. Good things happened
today that do matter.

John

[John Larkin]

On Sat, 22 Jul 2006 18:29:44 -0400, Phil Hobbs
wrote:

John Larkin wrote:
On Sat, 22 Jul 2006 17:52:39 -0400, Phil Hobbs
wrote:


John Larkin wrote:

On Sat, 22 Jul 2006 19:56:18 GMT, Phat Bytestard
wrote:



On Sat, 22 Jul 2006 11:48:12 +0100, Eeyore
l.com Gave us:



They fail to mention carbon film which is very widely used.

The entire selling point of the sheet was that they are very low
noise compared to other resistor manufacturing mediums.

Noise in a resistor occurs because resistance mediums are actually
heavily diluted semiconductors. The electrons bang around on their
way through. It's a loose lattice.



In a current flow in metals, electron-lattice interactions tend to
space electrons evenly, so their exit from the resistor is more
regular than a random (Poisson) distribution, so current-modulation
noise is far below the shot noise level you'd get for uncorrelated
conduction. The physically longer the resistor, the better the
smoothing effect. This works less well in non-metal conductors, with a
few exceptions.

That doesn't affect Johnson noise of course; that only depends on the
resistance and the temperature, as required by conservation of energy.

John


Oh, man, this old chestnut again. Of course you're perfectly right,
John, but the effort is doomed because half your audience appears to
think that classical thermodynamics is a matter of opinion. Why don't
we all vote on it and find out how resistors *really* behave?

Cheers,

Phil Hobbs


Phil,

Do metal-oxide thickfilm resistors have shot noise? Any idea how much,
as, say, % of full shot?

John


I don't know. The physics is quite a bit more complicated than in
metal, so I can't say from first principles, and I haven't measured it.
Most of my circuits are built from a huge supply of 1% metal film
resistors I bought in about 1989!

It might be quite interesting to measure.

Cheers,

Phil Hobbs


I did a quick hack with available stuff: power supply; grossly
excessive RCRC filter; 100K+100K resistive divider, using various
resistor types; Tek AM502 differential amplifier module (gain 10K)
fronting a Fluke 8842A trms meter.

With 1k-10k bandpass settings (9 KHz net), the Johnson noise should be
around 2.8 uV RMS. The Tek+Fluke setup measures about 8.1 uV with the
power supply off, pure Johnson, and about 7.2 dead shorted. So my
instrument setup can't usefully resolve the Johnson noise.

But on the other hand, I still see 8.1 uv with the power supply at 10
volts, using either RN55 0.1% metal film resistors or cheap 5% carbon
films, when full shot noise should be something like 20 uV.

So it looks like carbon films don't have anything like full shot
noise.

More later, maybe.

John

[Scott Dorsey]

John Fields wrote:

EG&G, early on, had "Vactrols" with incandescents, LED's, and Neons
as the emitters and LDRs as the variable resistance elements.

They still do. The incandescent is slower than the LDR, but the LED and
neons are faster. The LED has a pretty sharp knee, the neons have a
sharper knee, and the incandescent hardly has any knee at all. All good
tools for different jobs.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Eeyore]

Scott Dorsey wrote:

John Fields wrote:

EG&G, early on, had "Vactrols" with incandescents, LED's, and Neons
as the emitters and LDRs as the variable resistance elements.

They still do. The incandescent is slower than the LDR, but the LED and
neons are faster. The LED has a pretty sharp knee, the neons have a
sharper knee, and the incandescent hardly has any knee at all. All good
tools for different jobs.

When you say 'knee' here Scott, which 2 parameters are you comparing ?

Graham

[[email protected]]

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

Please, if you are younger and dumber than G, keep it to yourself.

If you can do that, you are smarter than you know who

Happy Ears!
Al


John Larkin wrote:
So it looks like carbon films don't have anything like full shot
noise.

More later, maybe.

John

[John Larkin]

On 25 Jul 2006 19:32:06 -0700, "
wrote:

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

I just have more test equipment.

John

[Eeyore]

John Larkin wrote:

On 25 Jul 2006 19:32:06 -0700, "
wrote:

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

I just have more test equipment.

But not up to measuring the noise from 50k ohms though !

Graham

[Phat Bytestard]

On 25 Jul 2006 12:49:36 GMT, Bob Quintal Gave
us:

Phat Bytestard wrote in
:

On Mon, 24 Jul 2006 22:51:37 -0700, John Larkin
Gave us:

On Tue, 25 Jul 2006 05:09:29 GMT, Phat Bytestard
wrote:

On Mon, 24 Jul 2006 20:07:24 -0700, John Larkin
Gave us:

On Tue, 25 Jul 2006 02:28:06 GMT, Phat Bytestard
wrote:

On Mon, 24 Jul 2006 08:24:37 -0700, John Larkin
m Gave us:

On 24 Jul 2006 10:41:54 -0400, (Scott
Dorsey) wrote:

John Larkin
m wrote:
On Sun, 23 Jul 2006 04:59:19 GMT, Prune
wrote:

I've tried cermet potentiometers for volume control,
and in a blind test (non-double, used dual switch with
my friend) I can't tell the difference between it and a
stepped attenuator; however, in 7/10 trials me and 8/10
trials him heard difference between plastic pot and the
cermet, both preferring the cermet.

Please don't top post.

Agreed. But the problem with cermets is they are noisy
as hell when you turn them. That's fine for trimmers,
but no so good for a volume control on the front panel.

What's the origin of the noise? If the wiper drives a high
impedance, unstable wiper contact resistance will generate
no noise.


The surface quality of a first surface mirror is very
flat, and very
fine grained in the macroscopic view.

The "drag surface" of a variable resistor has to be a
couple hundred
times rougher than that. That is going to produce "noise"
when turned, and even when stopped as the contact surface
upon the wiper can and likely will always be different tiny
points on the wiper surface. It is rougher even than basic
grain oriented polished stainless at a certain finish.
(maybe a number 4). Pretty rough is the macro surface
quality/texture realm.

But how does that create electrical noise?

John

While the wiper is still or moving?

While moving, it should be obvious.

Not to me. Noise requires potentials, and resistors don't do
that.

The locations where conduction
is taking place are moving all over the wiper surface, and
there are even microscopic arcs taking place

Arcs? At audio signal levels?

You are not thinking in the microscopic level.

Instead of volts per mil, it would be like millivolts per
micron.
If oxides keep a "wiper" from making "intimate" contact, there
will be tiny little breach events that take place as electron
bore through the oxides and the wiper scrapes through.
Generally though it would simply be shot noise magnified by
passage through a smaller surface area of contact. And end
cap has more total surface area of contact than does a pair or
a few wiper noses. Sniff, sniff... Hey... that's it!
Sniffing Noise!

What somebody obviously forgot is that microscopic doesn't apply
to the wiper contact surface area. Each of the locations where
"conduction is taking place" is in parallel with thousands of
other locations where "conduction is taking place". This aso
prevents arcing because of the shunt resistance of the other
contact points.


They are all constantly moving. Even once "set" the wiper location
has to "settle". It can be tracked too. It exhibits more noise until
such settling has taken place. Different resistance mediums have
different settling times. Wiper material cause variances as well.

Wirewound precision potentiometers do not exhibit this "problem".
Only if they get set between two turns of the resistor. The wiper
design typically won't allow this though.

Note that the pot that uses a metal wiper contacting a metal
resistance medium (wire wound) is far less noisy than the metal wiper
contacting a resistance film of "metal" or carbon slurry, etc.

So all of your parallels of thousands of locations don't make as
intimate of contact as does metal on metal. That alone should tell you
that ten thousand tiny pathways are going to be noisier than a few
hundred strong, hard conducting, metal on metal pathways. That is
where the noise comes from. Such tiny pathways are constrictive on an
individual basis, even though there are enough to make "conduction"
"easy", events occur in those pathways that can generate other than
the original signal. We call it noise.

In the metal on metal, the path is not constricted in any way, and
there are less collisions taking place to make noise.

[Phat Bytestard]

On Tue, 25 Jul 2006 14:42:37 -0500, John Fields
Gave us:

On Tue, 25 Jul 2006 12:20:07 -0700, John Larkin
wrote:


Well, pots don't "jump".

---
Sure they do, since they've got "stiction" in there, somewhere, and
when you go to crank in that last little bit of resistance you need
to get to 1.234 volts it skips over the spot you needed and now
you're at 1.256 volts and you've got to go back the other way...
---

I HATE that! :-]

snip

[Phat Bytestard]

On 25 Jul 2006 19:32:06 -0700, "
The top posting dip****, gave us:

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

Please, if you are younger and dumber than G, keep it to yourself.

If you can do that, you are smarter than you know who

You're an idiot. The top post proves that.

[Eeyore]

Phat Bytestard wrote:

On 25 Jul 2006 19:32:06 -0700, "
The top posting dip****, gave us:

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

Please, if you are younger and dumber than G, keep it to yourself.

If you can do that, you are smarter than you know who

You're an idiot. The top post proves that.

He's also a believer in *magic capacitors* ! Notably these ones he's recently
installed.
http://v-cap.com/tefloncapacitors.html

" Now it is possible to get the smooth, liquid, and "musical" presentation of an
oil capacitor, but with even better refinement, transparency and inner detail.
Hear and feel true low frequency extension without any loss of control. Immerse
youself in a holographic soundstage emanating from a velvety black background,
while enjoying the midrange liquidity and bloom coveted by oil capacitor
afficionados. "

Maybe John would like to clarify for him what he thinks of audiophools ?

Graham

[John Larkin]

On Wed, 26 Jul 2006 04:13:29 +0100, Eeyore
wrote:



John Larkin wrote:

On 25 Jul 2006 19:32:06 -0700, "
wrote:

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

I just have more test equipment.

But not up to measuring the noise from 50k ohms though !

Graham

Oh, that hurt. That was cruel and uncalled for. You are Not A Nice
Person.

John

[John Larkin]

On Wed, 26 Jul 2006 04:50:02 +0100, Eeyore
wrote:



Phat Bytestard wrote:

On 25 Jul 2006 19:32:06 -0700, "
The top posting dip****, gave us:

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

Please, if you are younger and dumber than G, keep it to yourself.

If you can do that, you are smarter than you know who

You're an idiot. The top post proves that.

He's also a believer in *magic capacitors* ! Notably these ones he's recently
installed.
http://v-cap.com/tefloncapacitors.html

" Now it is possible to get the smooth, liquid, and "musical" presentation of an
oil capacitor, but with even better refinement, transparency and inner detail.
Hear and feel true low frequency extension without any loss of control. Immerse
youself in a holographic soundstage emanating from a velvety black background,
while enjoying the midrange liquidity and bloom coveted by oil capacitor
afficionados. "

Maybe John would like to clarify for him what he thinks of audiophools ?

Graham


One of my hobbies is collecting audio terms. Additions are welcome.


5N, 6N, 7N (as in 99.99999 pure copper)
acceleration
agressive
air
articulation
bass transient response
blackness
bloom
bright
burnin (cables)
clarity
color
confused
congested
continuousness
crisp
delineation of inner detail
dynamics
effortlessness
etched
extension
fast bass
free-flowing ease
grainy
granularity
hangover
hard
harmonic completeness
hashy
holographic
honesty
impact
jump
layering
liquid
liquidity
liveliness
lush
macrodynamics
microdynamics
musicality
openness
pace
quantum purifier
reference
refinement
relaxed
roundness
reveal
single-crystal copper
slam
slow bass
smear
soundstaging
space
sparkle effect
spatial resolution
speed
stunning (everything is stunning)
thin
tight
tight (bass)
timbre
tipped-up
transparency
truth
unfussiness
wire direction


John

[[email protected]]

Eeyore wrote:
Phat Bytestard wrote:

On 25 Jul 2006 19:32:06 -0700, "
The top posting dip****, gave us:

Hi John,

Since Graham has forced us to this dance, may I say you seem to have
your priorities straight,

Are you smarter than Graham, or simply older? Both?

Please, if you are younger and dumber than G, keep it to yourself.

If you can do that, you are smarter than you know who

You're an idiot. The top post proves that.

He's also a believer in *magic capacitors* ! Notably these ones he's recently
installed.
http://v-cap.com/tefloncapacitors.html

" Now it is possible to get the smooth, liquid, and "musical" presentation of an
oil capacitor, but with even better refinement, transparency and inner detail.
Hear and feel true low frequency extension without any loss of control. Immerse
youself in a holographic soundstage emanating from a velvety black background,
while enjoying the midrange liquidity and bloom coveted by oil capacitor
afficionados. "

Maybe John would like to clarify for him what he thinks of audiophools ?

Graham

OK, is the proper bottom post? You guys are picky, picky, picky.

I like the caps. I did say ignore the mumbo jumbo. Perhaps audiophool
is overly specific. I am an old fool who likes what he hears, whether
or not I really hear it or just think I hear it

Sorry, Graham, I thought maybe you had the best test gear, I get lots
of this technical stuff out of sequence. That's why I don't work, ...
well, that and being horizontal, mostly

Actually, I believe Graham cross posted my thread, so only he needs
admit to any rabid ear bigotry

Happy Ears!
Al