OK this info might get lost in this big thread but it belongs mainly here.Moderators might choose to make it a separate thread if they think it deserves it.
Discussions about the sonic signature of the F1 and F2 (ie preferences for second or third harmonic) made by NP and others as well as recent comments on subjective effects of varying the balance of the push pull pair on the recent PLH suggest that it is possible to design or even ``tune`` an amplifier to have a certain sound more to ones preferences mainly by varying its operating parameters so that its distortion characteristics are altered(theoretical explanation).
Also some others such as Eduardo da Lima of Audiopax(with whom I have had a few discussions) have expounded the very interesting theory- to put it simply- that the aim for very low distortion amps is not the correct path since the speakers are contributing huge amounts of THD to the signal.He claims that the amplifier can be made so that its own THD can cancel some of the (mainly second) THD of the speakers.He also claims that one of the reasons that single ended amps can sound so good on some speakers is that there is some cancellation going on and NOT because we really like to hear huge amounts of the second harmonic.This is the basis of the so called timbre lock patent in his designs- basically a method of altering bias of the output stage and thereby tuning the amp to better fit particular speakers.I have seen this in practice in his factoryand I can attest to the effectiveness of such a system.
So much for the theory.
Now in practice what does that mean for the aleph x?
I have what I think is a pretty good valve dual mono SET amp based on the JElabs circuit but with premium components such as Plitron trafos,oil filled caps only in PS,KR842 VHD output tubes 18 W output,RCA NOS 5692 driver, NOS GZ 37 rectifiers etc etc.Now this amp really excells in the midrange which is where most of the music is anyway.I could never get the AX to sound quite like that in the mids despite the overall great sound it has.It would sound a bit too ``clean`` or slightly lean compared to the very good SET midrange.
But now I have almost managed to address this after a lot of experimentation.
The trick is to slightly unbalance the bias of the two halves of the AX.Let´s say you measure 500mv over the source resistor of the positive half.Try adjusting the negative side bias by about 20 to 40 mv less.
That´s it - now sit back and see how that affects the sound.I know I like it a lot and it has come amazingly close to the sound of my SET.
Some technical purists will say we are losing the benefits of the SUSY etc etc but that´s why I put in the theoretical section on top.They can chew on that for a while.Meanwhile the others can just try it and see if it works for them and if so can enjoy music a little bit more while the techs work up spice models to try and explain what is happening.
Discussions about the sonic signature of the F1 and F2 (ie preferences for second or third harmonic) made by NP and others as well as recent comments on subjective effects of varying the balance of the push pull pair on the recent PLH suggest that it is possible to design or even ``tune`` an amplifier to have a certain sound more to ones preferences mainly by varying its operating parameters so that its distortion characteristics are altered(theoretical explanation).
Also some others such as Eduardo da Lima of Audiopax(with whom I have had a few discussions) have expounded the very interesting theory- to put it simply- that the aim for very low distortion amps is not the correct path since the speakers are contributing huge amounts of THD to the signal.He claims that the amplifier can be made so that its own THD can cancel some of the (mainly second) THD of the speakers.He also claims that one of the reasons that single ended amps can sound so good on some speakers is that there is some cancellation going on and NOT because we really like to hear huge amounts of the second harmonic.This is the basis of the so called timbre lock patent in his designs- basically a method of altering bias of the output stage and thereby tuning the amp to better fit particular speakers.I have seen this in practice in his factoryand I can attest to the effectiveness of such a system.
So much for the theory.
Now in practice what does that mean for the aleph x?
I have what I think is a pretty good valve dual mono SET amp based on the JElabs circuit but with premium components such as Plitron trafos,oil filled caps only in PS,KR842 VHD output tubes 18 W output,RCA NOS 5692 driver, NOS GZ 37 rectifiers etc etc.Now this amp really excells in the midrange which is where most of the music is anyway.I could never get the AX to sound quite like that in the mids despite the overall great sound it has.It would sound a bit too ``clean`` or slightly lean compared to the very good SET midrange.
But now I have almost managed to address this after a lot of experimentation.
The trick is to slightly unbalance the bias of the two halves of the AX.Let´s say you measure 500mv over the source resistor of the positive half.Try adjusting the negative side bias by about 20 to 40 mv less.
That´s it - now sit back and see how that affects the sound.I know I like it a lot and it has come amazingly close to the sound of my SET.
Some technical purists will say we are losing the benefits of the SUSY etc etc but that´s why I put in the theoretical section on top.They can chew on that for a while.Meanwhile the others can just try it and see if it works for them and if so can enjoy music a little bit more while the techs work up spice models to try and explain what is happening.
We spent a lot of time tweaking each Aleph with different
ratios of gain for the positive and negative, much as you
can for the PLH. In fact, there's no reason you can't put a similar
knob on the Aleph.
Referring to the Aleph 3 service manual, the ratio is largely
controlled by R115. You can replace its 1Kohm value with
about a 680 ohm resistor plus a pot ( 1 to 5K maybe) so that
you can adjust from 680 to as high as you like. As the resistance
goes higher, the lower stage starts to own the output. At 680
ohm, the top half will be doing most of the work.
An of course you can do this on an Aleph X.
ratios of gain for the positive and negative, much as you
can for the PLH. In fact, there's no reason you can't put a similar
knob on the Aleph.
Referring to the Aleph 3 service manual, the ratio is largely
controlled by R115. You can replace its 1Kohm value with
about a 680 ohm resistor plus a pot ( 1 to 5K maybe) so that
you can adjust from 680 to as high as you like. As the resistance
goes higher, the lower stage starts to own the output. At 680
ohm, the top half will be doing most of the work.
An of course you can do this on an Aleph X.
Hi,
I´m still not shure what Protos means cause he speaks of (DC?) bias and not ac-current-gain. To change the bias between the positive and negative half you need some absolute offset at the output to divert some current through the resistors from output to ground.
Setting ac-current-gain in an X is not so simple with a pot cause you need to get the two halves the same. So you would need a good stereo pot. I just use resistors placed in ic-feet so they can be changed in seconds.
William
I´m still not shure what Protos means cause he speaks of (DC?) bias and not ac-current-gain. To change the bias between the positive and negative half you need some absolute offset at the output to divert some current through the resistors from output to ground.
Setting ac-current-gain in an X is not so simple with a pot cause you need to get the two halves the same. So you would need a good stereo pot. I just use resistors placed in ic-feet so they can be changed in seconds.
William
Sorry , to simpify things I meant the side of the amp that supplies the negative speaker output.You could as well tweak the positive side to be less biased according to results.There are many settings and variations.
The bias I am talking about is in fact the dc bias you can tweak with the pots provided in the ax.I have not messed with the ac current gain but that is possible too.However the balanced nature of the ax means that there is very little second harmonic which may be something we might in fact want to cancel speaker distortion.The ac current gain will not do this if you have the same gain on both sides.
I did not see any problems with large dc offsets in my amp after adjustment.
Of course you may need to readjust the cental pot which governs the current of the first stage and with which you zero out dc offset to ground.I don´t worry too much about that if it is not in the volts range because the speakers do not see this but only the relative offset between the two outputs.That too might change but as long as it is not more than 100mv as np accepts I would not worry too much about that either.A few mw will absolutely not damage your speakers unless you are connecting earbud headphones to your power amp.
I don´t see any problem with going ahead and giving it a try - no soldering- no extra parts.
I just thought I would share this info because to my ears it did make a noticeable difference for the better.But your mileage may vary.And as I said before for some people it is counterintuitive they will be biased (good pun?) against it.
The bias I am talking about is in fact the dc bias you can tweak with the pots provided in the ax.I have not messed with the ac current gain but that is possible too.However the balanced nature of the ax means that there is very little second harmonic which may be something we might in fact want to cancel speaker distortion.The ac current gain will not do this if you have the same gain on both sides.
I did not see any problems with large dc offsets in my amp after adjustment.
Of course you may need to readjust the cental pot which governs the current of the first stage and with which you zero out dc offset to ground.I don´t worry too much about that if it is not in the volts range because the speakers do not see this but only the relative offset between the two outputs.That too might change but as long as it is not more than 100mv as np accepts I would not worry too much about that either.A few mw will absolutely not damage your speakers unless you are connecting earbud headphones to your power amp.
I don´t see any problem with going ahead and giving it a try - no soldering- no extra parts.
I just thought I would share this info because to my ears it did make a noticeable difference for the better.But your mileage may vary.And as I said before for some people it is counterintuitive they will be biased (good pun?) against it.
Hi
So there no reason this can’t be also be done on the ZEN V2-4?
I was varying the value of R19 (1.5 K) on ZEN V3. It seems that it is possible to connect a 1 k resistor (instead of R19) in series with 1 k pot, which should give a sufficient range of AC-current-gain?
Now I have a switch and R19 is disconnected most of the time (constant current) but sometimes I find that sound too “soft”. With R19 switched on, sound becomes subjectively more “clear” but with a dose of “hardness” added, which is welcomed for Rock Music…
I am curious to know why Nelson didn’t initially include a pot on Aleph current source (both on Alephs and Zens 2-4, so everybody could “adjust” ac-gain….
Now gotta read, there's a lot of homework on passdiy...
Regards,
Vix
Nelson Pass said:We spent a lot of time tweaking each Aleph with different
ratios of gain for the positive and negative, much as you
can for the PLH. In fact, there's no reason you can't put a similar
knob on the Aleph.
So there no reason this can’t be also be done on the ZEN V2-4?
I was varying the value of R19 (1.5 K) on ZEN V3. It seems that it is possible to connect a 1 k resistor (instead of R19) in series with 1 k pot, which should give a sufficient range of AC-current-gain?
Now I have a switch and R19 is disconnected most of the time (constant current) but sometimes I find that sound too “soft”. With R19 switched on, sound becomes subjectively more “clear” but with a dose of “hardness” added, which is welcomed for Rock Music…
I am curious to know why Nelson didn’t initially include a pot on Aleph current source (both on Alephs and Zens 2-4, so everybody could “adjust” ac-gain….
Now gotta read, there's a lot of homework on passdiy...
Regards,
Vix
Hi, Mr.Pass,
What's the difference if the positive : negative is 2:3 or 3:2?
Why is that you (and JLH) found out that bigger portion is better to put on the lower side?
I asked this because in DSelf book, he said it is the same effect between 2:3 or 3:2, but you certainly have the "on-field" experience
What's the difference if the positive : negative is 2:3 or 3:2?
Why is that you (and JLH) found out that bigger portion is better to put on the lower side?
I asked this because in DSelf book, he said it is the same effect between 2:3 or 3:2, but you certainly have the "on-field" experience
Vix said:
You don't need me to think about putting in a pot....
In point of fact, I learned long ago not to give consumers such
adjustments. The typical response is confusion: "Don't YOU
know the best setting?". Also, unscrupulous dealers will set the
knob to disadvantage your product in a demo and sell the
customer something else.
This is less of an issue now that I don't care anyway, and the
unscrupulous dealers are selling Home Theater, and a lot of
the competition has gone away. If you guys want to tweak
the sound to your own taste, then have at it.
lumanauw said:What's the difference if the positive : negative is 2:3 or 3:2?
Why is that you (and JLH) found out that bigger portion is better to put on the lower side?
I asked this because in DSelf book, he said it is the same effect between 2:3 or 3:2, but you certainly have the "on-field" experience
Since we are discussing DSelf, I will set aside subjective
observation. It was JLH's and my experience that they
measure differently in the JLH type circuit, therefore it is
not the same effect. They might be the same in some other
circuit.
Hi Protos,
so you have a 5-10% difference in bias between the two halves. I will try this in the near future (at the moment im still trying different ac-current-gain settings) and see what happens.
Do you have any explanation why setting the bias this way changes the sound?
Did you reduce the bias in one half or did you raise the bias in the other?
What is your ac-current-gain setting at the moment?
William
so you have a 5-10% difference in bias between the two halves. I will try this in the near future (at the moment im still trying different ac-current-gain settings) and see what happens.
Do you have any explanation why setting the bias this way changes the sound?
Did you reduce the bias in one half or did you raise the bias in the other?
What is your ac-current-gain setting at the moment?
William
Wuff waff ,
Have a look at this very interesting article
http://www.milbert.com/articles/DanCheever.pdf?milses
very long but well documented and researched work on psychoacoustics, thd and amp measurement
before that go to www.audiopax.com website and look at the white paper there which is concise and easy to read.
you may also want to look at various famous articles by Jean Hiraga of course which are in the same general vein
Now I don´t have a spectrum analyzer to see how changing the bias changes the distortion spectrum of the amp but I think there is plenty of documentation above to suggest that the type of this spectrum is more important than getting extremely low overall distortion.This may be either because of distortion cancelling at the speaker or because the spectrum better fits the psychoacoustic natural thd of the ear.
Of course theory is important to give you some type of compass bearing on your journey to better sound but in the end does it really matter what some theory says as long as you find something that satisfies your ears.
I also try to listen with my ´´body´´ because the ears per se can deceive when you are trying too hard to listen for something.After some time with an amp let´s say , I try and see how my body is reacting to the music.Is it grooving to the rhythm?Is it a little bit too tense?Am I swaying my head?Is my breathing relaxed?
These things can tell you a lot more if you are going to like a particular component than trying to decide if the cymbals sound more or less realistic or if the bass is too boomy because it is in the recording or because the amp is making it so etc etc.
My ac current gain is over 50% but I don´t remember now exactly how much.I have 4oohm speakers.
Have a look at this very interesting article
http://www.milbert.com/articles/DanCheever.pdf?milses
very long but well documented and researched work on psychoacoustics, thd and amp measurement
before that go to www.audiopax.com website and look at the white paper there which is concise and easy to read.
you may also want to look at various famous articles by Jean Hiraga of course which are in the same general vein
Now I don´t have a spectrum analyzer to see how changing the bias changes the distortion spectrum of the amp but I think there is plenty of documentation above to suggest that the type of this spectrum is more important than getting extremely low overall distortion.This may be either because of distortion cancelling at the speaker or because the spectrum better fits the psychoacoustic natural thd of the ear.
Of course theory is important to give you some type of compass bearing on your journey to better sound but in the end does it really matter what some theory says as long as you find something that satisfies your ears.
I also try to listen with my ´´body´´ because the ears per se can deceive when you are trying too hard to listen for something.After some time with an amp let´s say , I try and see how my body is reacting to the music.Is it grooving to the rhythm?Is it a little bit too tense?Am I swaying my head?Is my breathing relaxed?
These things can tell you a lot more if you are going to like a particular component than trying to decide if the cymbals sound more or less realistic or if the bass is too boomy because it is in the recording or because the amp is making it so etc etc.
My ac current gain is over 50% but I don´t remember now exactly how much.I have 4oohm speakers.
Protos,
I just read the 87page article by Dan Cheever. Very interesting! The audiopax one will have to wait cause my eyes are a bit tired now.......
If your ac-current-gain is above 50% I would suggest lowering it a bit to around 47-50%. I think you will notice another step towards your SET amp.
William
I just read the 87page article by Dan Cheever. Very interesting! The audiopax one will have to wait cause my eyes are a bit tired now.......
If your ac-current-gain is above 50% I would suggest lowering it a bit to around 47-50%. I think you will notice another step towards your SET amp.
William
Interesting observations.
Ages ago I fiddled with the dc bias of the Aleph and also the current gain.
Its like a Red tasting ...what ever you like on the day.
However, siginificant changes in Dc bias will also effect the actual gain and you may need to revise the stability capacitor particularly on the Cs.
In general I found the Passlabs settings agreed with my taste Buds the most. I would suggest Nelson has a nose for a good red based on practical experience!
Heck that was fun..I recall we started off with the Zen...not sure what version, a delightful little amp (his daughters) and on an equally delightful diy speaker and it went on from there to the wee hours.
We should all do this more often.
Ian
Ages ago I fiddled with the dc bias of the Aleph and also the current gain.
Its like a Red tasting ...what ever you like on the day.
However, siginificant changes in Dc bias will also effect the actual gain and you may need to revise the stability capacitor particularly on the Cs.
In general I found the Passlabs settings agreed with my taste Buds the most. I would suggest Nelson has a nose for a good red based on practical experience!
Heck that was fun..I recall we started off with the Zen...not sure what version, a delightful little amp (his daughters) and on an equally delightful diy speaker and it went on from there to the wee hours.
We should all do this more often.
Ian
I am not sure about asymmetrical Dc bias of the X Aleph...kind of defeats the point of the design.
What maybe of interest is that I found that using a stock BOSOZ driving the X Aleph was not as appealing as the X-BOSOZ on the X Aleph.
The X Aleph really made the BOSOZ sound cloudy or woolly. So I figure that its true that certain types of distortions either compliment each other or are perhaps not complimentary..
From what I can gather the BOSOZ is dominated by 2nd harmonic distortion while the X Aleph is possibly dominated by 3rd harmonic distortion. Perhaps the Master can clarify this.
But I have found the X BOSOZ works well driving an Aleph and the stock BOSOZ even more so.
So there we are.....but its all fun.
Ian
What maybe of interest is that I found that using a stock BOSOZ driving the X Aleph was not as appealing as the X-BOSOZ on the X Aleph.
The X Aleph really made the BOSOZ sound cloudy or woolly. So I figure that its true that certain types of distortions either compliment each other or are perhaps not complimentary..
From what I can gather the BOSOZ is dominated by 2nd harmonic distortion while the X Aleph is possibly dominated by 3rd harmonic distortion. Perhaps the Master can clarify this.
But I have found the X BOSOZ works well driving an Aleph and the stock BOSOZ even more so.
So there we are.....but its all fun.
Ian
Protos can maybe clarify a little more because I am not sure about that either. There seem to be two camps here talking about two different things: left and right balance for AX and up and down balance for the Aleph. It has been awhile since I played with the AX but I seem to recall it was all about balancing the two halves to get the 0 VDC at the output. I think in order to bring the DC back to 0 by changing the left and right balance bias one would need to adjust the what Nelson is talking about upper half vs lower half balance to move the DC point of the output. This is for basic operation alone. Or am I totally off base here as usual?
I wouldn't expect different sound from just having different bias in the two halves. Under normal current load the differential would still do it's job of canceling the second harmonic. Any differential circuit will cancel out the second harmonic whether it is an X or not X, I think.
Is there a "finer" circuit that cancels the bulk third harmonic besides the brute force of global NFB? Even the modulated cascode is about getting rid of second harmonic.
Any distortion canceling circuit including NFB, local feedback, longtail pair or whatever, is never going to be perfect, it's always going to leave or to generate some higher order distortion components that don't sound so good.
I wouldn't expect different sound from just having different bias in the two halves. Under normal current load the differential would still do it's job of canceling the second harmonic. Any differential circuit will cancel out the second harmonic whether it is an X or not X, I think.
Is there a "finer" circuit that cancels the bulk third harmonic besides the brute force of global NFB? Even the modulated cascode is about getting rid of second harmonic.
Any distortion canceling circuit including NFB, local feedback, longtail pair or whatever, is never going to be perfect, it's always going to leave or to generate some higher order distortion components that don't sound so good.
Grataku,
two things were spoken of:
1. DC bias imbalance between the two halves of the amp
2. AC gain imbalance between the upper and lower half of the amp (ac-current-gain setting)
The latter has quite an influence on the sound, the first according to Protos also has an influence although I also can´t think of a reason at the moment.
As for getting near 0V relaitve DC at the output with an X you need well matched input pairs. A bit of imbalance in left/right bias is not so important for this (you never get both halve the same as they keep drifting a bit as the amp warms up and you change the settings for bias and abs. dc offset. I also have up to 40mA of difference between the two halves but never thought of this as critical.
William
two things were spoken of:
1. DC bias imbalance between the two halves of the amp
2. AC gain imbalance between the upper and lower half of the amp (ac-current-gain setting)
The latter has quite an influence on the sound, the first according to Protos also has an influence although I also can´t think of a reason at the moment.
As for getting near 0V relaitve DC at the output with an X you need well matched input pairs. A bit of imbalance in left/right bias is not so important for this (you never get both halve the same as they keep drifting a bit as the amp warms up and you change the settings for bias and abs. dc offset. I also have up to 40mA of difference between the two halves but never thought of this as critical.
William
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.