Hello!
I've had some thoughts on the 2k pot between R51 and R66 on the Aleph P 1.7 pre amp board. (see http://www.passlabs.com/pdf/aleph/apserv17.pdf)
Is it to be considered to be in the signal path, hence call for an expensive pot, or could I just go on and use any regular "found it on the street" pot?
Best,
//magnus
I've had some thoughts on the 2k pot between R51 and R66 on the Aleph P 1.7 pre amp board. (see http://www.passlabs.com/pdf/aleph/apserv17.pdf)
Is it to be considered to be in the signal path, hence call for an expensive pot, or could I just go on and use any regular "found it on the street" pot?
Best,
//magnus
I do not use a pot as a gain resistor.
Actually I replaced R51 and R66 with a 2K2 single resistor.
I get plenty of gain from all my sources, becuase I have modified the input resisitor values for each source. The input resistors are before my selector switch and are sized for each different source to give good volume at about 90% of my attenuator setting.
I maximized the gain resistor, because I assummed like the BZLS the distorion would be the least with the largest resistor value.
I think there is also a reference in the P 1.7 manual about trying to maximize the gain setting for best performance.
I am very pleased with the resulting sound quality.
Actually I replaced R51 and R66 with a 2K2 single resistor.
I get plenty of gain from all my sources, becuase I have modified the input resisitor values for each source. The input resistors are before my selector switch and are sized for each different source to give good volume at about 90% of my attenuator setting.
I maximized the gain resistor, because I assummed like the BZLS the distorion would be the least with the largest resistor value.
I think there is also a reference in the P 1.7 manual about trying to maximize the gain setting for best performance.
I am very pleased with the resulting sound quality.
pot in signal path
I think the pot might be thought of as in the signal path because any fluctuation or noise from the source of Q16 will affect the gain of Q19 and vice versa.
Therefore anything connecting the two sources has an affect on the signal.
Maybe the fact that a larger value gain resistor creates less distortion is because it increases the slight isolation from Q19 to Q16. (This is my guess).
I think the pot might be thought of as in the signal path because any fluctuation or noise from the source of Q16 will affect the gain of Q19 and vice versa.
Therefore anything connecting the two sources has an affect on the signal.
Maybe the fact that a larger value gain resistor creates less distortion is because it increases the slight isolation from Q19 to Q16. (This is my guess).
Evil?
Well...
So are gain devices, if you choose to look at them in terms of the harm they do to the music.
Sooner or later, you're going to need to use a volume device of some kind, whether a pot, rotary switch & resistors, fancy transistor (or chip) array, or whatever. It will either be directly in the signal path, change the operating point of the gain device(s), or change the amount of feedback. Any way you slice it, you're going to have to shake hands with the devil at some point...might as well make up your mind to enjoy the experience.
Go ahead and put it 'in the signal path' (as though there were any other way...) and be done with it.
Grey
Well...
So are gain devices, if you choose to look at them in terms of the harm they do to the music.
Sooner or later, you're going to need to use a volume device of some kind, whether a pot, rotary switch & resistors, fancy transistor (or chip) array, or whatever. It will either be directly in the signal path, change the operating point of the gain device(s), or change the amount of feedback. Any way you slice it, you're going to have to shake hands with the devil at some point...might as well make up your mind to enjoy the experience.
Go ahead and put it 'in the signal path' (as though there were any other way...) and be done with it.
Grey
Aleph P 1.7 pre amp Q:
While discussing the "gain" pots...
Why not use (re-construct) these as volume pot? (when not in need of balance).
What I have heard, in a balanced circuit, it is much better to "cancel out" sound between +/- phase w. even a cheap pot-meter, than having the best pot. in the signal-way.
(Ref.: Electrocompaniet).
Other thaughts?
Arne K
NORWAY
While discussing the "gain" pots...
Why not use (re-construct) these as volume pot? (when not in need of balance).
What I have heard, in a balanced circuit, it is much better to "cancel out" sound between +/- phase w. even a cheap pot-meter, than having the best pot. in the signal-way.
(Ref.: Electrocompaniet).
Other thaughts?
Arne K
NORWAY
HI Grey,
Nice to see you back,
I see the function of R15 in the BOSOZ to be basically the same as the 2K pot in the P1.7
I thought about this and found it easier to use R15 = 450R and parellel with a 2K Pot in series with say 150 - 200 R.
This would appear to make the use of the pot legitimate while keeping the Dale fixed resister in the signal path so it is only shunted by the pot when in use(for higher gain). Hence the effect of the pot on quality is minimised.
This is a bit off topic but I would like your clarification here Grey.
It seems in the Aleph P.17 Preamp the manipulation of the output levels is a bit misunderstood relative to the BOSOZ.
There is no input volume control in the P1.7 , only an internal pad for some 12 db attentuation so to set and forget, the Gain level controls (2Kpots) and and the Master Volume control at the output (a shunt attenuator).
I trying to figure out if the BOSOZ can be set up the same way as the P.17, or does the circuit perform differently in respect the the active use for R15 and of P1 & P2 level controls at the input and its optimum operating point.
In the Pass manual for the P.17 it states for best performance keep the gain level controls counter clock wide (minumum gain) and the Master Volume control as clock wise as possible.
This to me means keep the gain low and it is preferred for best performance not to have the output shunted down too much to enable reasonable voltage swing.
Could this perhaps suggest why there is a tendancy for everyone to use a 5K pot or (or series switched attenuator) rather than the shunt attenuator for the BOZSOZ so the output impediance is constant?
best regards
Ian
Nice to see you back,
I see the function of R15 in the BOSOZ to be basically the same as the 2K pot in the P1.7
I thought about this and found it easier to use R15 = 450R and parellel with a 2K Pot in series with say 150 - 200 R.
This would appear to make the use of the pot legitimate while keeping the Dale fixed resister in the signal path so it is only shunted by the pot when in use(for higher gain). Hence the effect of the pot on quality is minimised.
This is a bit off topic but I would like your clarification here Grey.
It seems in the Aleph P.17 Preamp the manipulation of the output levels is a bit misunderstood relative to the BOSOZ.
There is no input volume control in the P1.7 , only an internal pad for some 12 db attentuation so to set and forget, the Gain level controls (2Kpots) and and the Master Volume control at the output (a shunt attenuator).
I trying to figure out if the BOSOZ can be set up the same way as the P.17, or does the circuit perform differently in respect the the active use for R15 and of P1 & P2 level controls at the input and its optimum operating point.
In the Pass manual for the P.17 it states for best performance keep the gain level controls counter clock wide (minumum gain) and the Master Volume control as clock wise as possible.
This to me means keep the gain low and it is preferred for best performance not to have the output shunted down too much to enable reasonable voltage swing.
Could this perhaps suggest why there is a tendancy for everyone to use a 5K pot or (or series switched attenuator) rather than the shunt attenuator for the BOZSOZ so the output impediance is constant?
best regards
Ian
Arne,
If the positive and negative halves of the output aren't exactly equal, you won't get complete cancellation by using a pot to short them together. That's okay in my book. I don't know anyone who listens at whisper levels. I don't need a lot of control at the bottom of the volume range--just at more-or-less average listening levels. It strikes me as an elegant way to do things.
Ian,
Forgive me, man, but I'm so tired that my eyes are crossed and I'll have to dig to get out the schematics. I'll try to remember to take a whack at it tomorrow.
And I was going to try to get some work done on a story tonight...yeah, right...
G'night, folks.
Grey
If the positive and negative halves of the output aren't exactly equal, you won't get complete cancellation by using a pot to short them together. That's okay in my book. I don't know anyone who listens at whisper levels. I don't need a lot of control at the bottom of the volume range--just at more-or-less average listening levels. It strikes me as an elegant way to do things.
Ian,
Forgive me, man, but I'm so tired that my eyes are crossed and I'll have to dig to get out the schematics. I'll try to remember to take a whack at it tomorrow.
And I was going to try to get some work done on a story tonight...yeah, right...
G'night, folks.
Grey
I have search some more and found an interesting response from Mr Pass regarding R15 :
"It's interesting that R15 does in fact vary the sound
quality. With Aleph P's, there was a consensus among
users that the 1 Kohm pot used in that spot sounded
best at about the 3 o'clock position, which corresponded
to about 200 ohms. With larger resistance values, the
measured distortion and noise was better, but people
didn't prefer that in this particular circuit.
I have a hypothesis that devices have an optimal
working range sonically, and that often you need to
"exercise" them in a larger signal range than is
otherwise necessary in order to get the best sound."
This is rather interesting and I wonder then what the relationship is with the BOSOZ for the use of either a shunt type attenuator for a 5K Pot to acheive the optimum operating point.
The shunt appears to reduce the gain of the circuit and hence attenuate the output while R 15 can increase it.
What I mean is with 1-2 volts output for the optimum working range with P2 & 2 adjusted to do this then will the circuit will still be at the optimum operating range when the shunt is closed down to attenuate the output for nornal volume levels?
If this is not the case then there is a clear advantage for use of a normal pot or precision series switched attenuator when running at less then full volume for the optimum operating point.
Time for some zzz's
Ian
"It's interesting that R15 does in fact vary the sound
quality. With Aleph P's, there was a consensus among
users that the 1 Kohm pot used in that spot sounded
best at about the 3 o'clock position, which corresponded
to about 200 ohms. With larger resistance values, the
measured distortion and noise was better, but people
didn't prefer that in this particular circuit.
I have a hypothesis that devices have an optimal
working range sonically, and that often you need to
"exercise" them in a larger signal range than is
otherwise necessary in order to get the best sound."
This is rather interesting and I wonder then what the relationship is with the BOSOZ for the use of either a shunt type attenuator for a 5K Pot to acheive the optimum operating point.
The shunt appears to reduce the gain of the circuit and hence attenuate the output while R 15 can increase it.
What I mean is with 1-2 volts output for the optimum working range with P2 & 2 adjusted to do this then will the circuit will still be at the optimum operating range when the shunt is closed down to attenuate the output for nornal volume levels?
If this is not the case then there is a clear advantage for use of a normal pot or precision series switched attenuator when running at less then full volume for the optimum operating point.
Time for some zzz's
Ian
Ian,
All other factors being equal, lower gain means lower distortion. That may or may not suit your purposes, depending on your views of distortion.
The BOSOZ has about fifty volume pots. That many choices would drive me crazy. I'd end up deciding that one album sounded better with the input attenuated and gain set to 379 ohms. The next album would sound better with the input wide open, but the pots at the rear turned down. <i>Whew!</i>
Each strategy has advantages and disadvantages. I'm not as worried about noise as others are, so the idea of lower noise at lower volumes with the output pots doesn't really matter to me. I'd probably set the gain as low as I could get away with (the bridge between the Sources of the differential) with a bit to spare, then put a volume control at the inputs.
Unless, of course, I put a pot between the + and - outputs to allow them to cancel each other...
Like I said, this stuff can drive you nuts.
Given that all other factors are never equal, there's usually a "sweet spot" on the volume control. This almost certainly applies to the gain pot, as well.
Experimentation is going to be the key, I expect.
Grey
All other factors being equal, lower gain means lower distortion. That may or may not suit your purposes, depending on your views of distortion.
The BOSOZ has about fifty volume pots. That many choices would drive me crazy. I'd end up deciding that one album sounded better with the input attenuated and gain set to 379 ohms. The next album would sound better with the input wide open, but the pots at the rear turned down. <i>Whew!</i>
Each strategy has advantages and disadvantages. I'm not as worried about noise as others are, so the idea of lower noise at lower volumes with the output pots doesn't really matter to me. I'd probably set the gain as low as I could get away with (the bridge between the Sources of the differential) with a bit to spare, then put a volume control at the inputs.
Unless, of course, I put a pot between the + and - outputs to allow them to cancel each other...
Like I said, this stuff can drive you nuts.
Given that all other factors are never equal, there's usually a "sweet spot" on the volume control. This almost certainly applies to the gain pot, as well.
Experimentation is going to be the key, I expect.
Grey
Volume ! - Aleph P
OK. I will measure "gain"pot & replace w. resistor.
But:
1) Where would it be best to implement the volume-pot?
(I want to use a "common" ALPS pot).
In front of the circuit, "as normal"?
After the pre-amp, as Mr. Pass uses the attenuator?
2) And then, why not use it between +/-phase, as then you can get away with a dual pot in a balanced circuit, and not a 4-gang?
Or would a "conventional" way of use, with a 4-gang, have sonic benefits?
Arne K
NORWAY
OK. I will measure "gain"pot & replace w. resistor.
But:
1) Where would it be best to implement the volume-pot?
(I want to use a "common" ALPS pot).
In front of the circuit, "as normal"?
After the pre-amp, as Mr. Pass uses the attenuator?
2) And then, why not use it between +/-phase, as then you can get away with a dual pot in a balanced circuit, and not a 4-gang?
Or would a "conventional" way of use, with a 4-gang, have sonic benefits?
Arne K
NORWAY
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