Burning Amp BA-3

Before I realized BA2 front end was already obsoleted by BA3,
I had thrown a few of my zany ideas at the older topology...
Shunt regulated tail, etc etc...
250130d1321681891-burning-amp-ba-3-srba2.gif


I totally goofed the negative end of C207, obviously bootstrap
has to be wired as Nelson originally showed it, driven from off
board. Otherwise, has anyone tried the shunt tail pair trick yet?

The points of merit theoretically are: Twice open loop gain
compared to the series high impedance tail. And automagic
offset cancellation maybe good enough to get rid coupling
cap at C203?

We are holding both halves of Q201 at same current and
drain voltage, one might expect offset to be improved?

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There was some misunderstanding earlier about Q204 as
a high impedance tail, it is a low impedance active tail.
Intended to shunt away all but a constant tail current.

Also improves the gain of Q201b to unity, up from 1/2.
Thats where the doubling of open loop gain comes from...

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I gotta fix a McIntosh 2100 with almost this same front
end topology. Turned upside down, and BJT's for FET's,
and no bootstrap, but otherwise unmistakably similar.
Tempted to try a BJT-ishy version of the shunt tail.

It too has a 10uF output cap, might be getting rid of...
 
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Just to update on that grounding debate several pages back. The Salas voltage reg grounds (one for left and one for right) were connected to the star ground of the power board supply (see Nelson's BA-2 design for this). One ground wire is connected from this star ground to the BA-3 ground. One wire also connects this star ground to the -ve loudspeaker output.
No hums, just as quiet as the grave.:xmastree:
 
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After reading all the accounts of those out there using BA-3 FE as a stand alone gain stage behind a passive volume knob and in front of an F-4 I got to wondering.......when using my F-5 with speakers of lesser efficiency I have replaced the B-1 with another preamp I have (Audio by Vanalstein Super Pass III) which has gain to get a little more volume out......

....then I wondered if I could just put a BA-3 FE behind the B-1, the have the BA-3 (with all its gain, up to 30 dB I understand) feed into the F-5 solving the gain problem....BUT..I assume there is a reason no one else has mentioned this yet? (Not to mention upcoming F-5 turbo) Any thought on this would be appreciated!!! (Iam building a BA-3 both in a complete amp as well as one of these front end versions for a future F-4 build....for which I am also building Pumpkin....does it ever stop? I hope not.

The setup with B-1. BA-3 FE to F-5 would also give me "P3" adjustment capability without building "R-1" version of F-5 I am hoping...

thanks for any info,

Russellc
 
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Lots of gain happens everyday among some of the biggest names in Audio. That is exactly what Nelson is addressing in his B1 writeup. Its not that its wrong, but often wasted. Why not get rid of some of that gain for more linearity and lower distortion. Using F5 as output may not reveal true character of Ba3 FE. Just guessing though. Hopefully more experienced members will chime in.
 
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Lots of gain happens everyday among some of the biggest names in Audio. That is exactly what Nelson is addressing in his B1 writeup. Its not that its wrong, but often wasted. Why not get rid of some of that gain for more linearity and lower distortion. Using F5 as output may not reveal true character of Ba3 FE. Just guessing though. Hopefully more experienced members will chime in.

This is kind of what I thought. But, I am building them and I do have an F-5.........Probably nothing revolutionary but I could try.

There is No wasted gain with the particular set of speakers, about 83-84dB efficiency, it needs more....not 30dB more but that's likely adjustable.

While the F-4's frontend may be more transparent than the F-5, the F-5 is no slouch at letting the character of front ends come through. I understand there is a different relationship with the F-4, which has no gain than it would be with the F-5 which does. but if you look at it in combination with the B-1 it wouldnt be that different from any pre with gain, so I thought it might be interesting to try together with the F-5.

Unless, like Buzzforb says some more experienced member can see a reason NOT to try it, instability, etc?
on so on. Thanks for the response!

Russellc
 
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Many thanks.
I have had some time now to play around with P3 and some general characteristics seem to be manifesting. I can't relate these to distortions of second and third harmonics and the like because of an absence of equipment, however, in order to explain what I am hearing I will use a photographic analogy. As P3 moves towards R4 it is like decreasing the focal length of a zoom lens, i.e., the musical images move away somewhat from the listener and appear more precise in their outline, better focussed. Mid and upper frequencies become sharper and more highlighted but do not become hard. The opposite seems true as P3 is turned towards R3: musical images become larger as though one was zooming in on them but they are less well difined in terms of outline. Upper and mid frequencies seem a little softer and yes there is a general sense that images are less pinned down, have more air and space around them. I must admit to preferring the latter setting but I know many who will go for the former; everything just seems beautifully arranged. With the setting towards R3 the BA-3 starts to sound like the BA-2 in this regard but more of that later when I can compare the two properly.
 
Many thanks.
I have had some time now to play around with P3 and some general characteristics seem to be manifesting. I can't relate these to distortions of second and third harmonics and the like because of an absence of equipment, however, in order to explain what I am hearing I will use a photographic analogy. As P3 moves towards R4 it is like decreasing the focal length of a zoom lens, i.e., the musical images move away somewhat from the listener and appear more precise in their outline, better focussed. Mid and upper frequencies become sharper and more highlighted but do not become hard. The opposite seems true as P3 is turned towards R3: musical images become larger as though one was zooming in on them but they are less well difined in terms of outline. Upper and mid frequencies seem a little softer and yes there is a general sense that images are less pinned down, have more air and space around them. I must admit to preferring the latter setting but I know many who will go for the former; everything just seems beautifully arranged. With the setting towards R3 the BA-3 starts to sound like the BA-2 in this regard but more of that later when I can compare the two properly.

I tend to agree with some exceptions. I found that with higher bias on the output stage and the resulting distortion reduction , which i believe is audible(not proven with numbers yet), seems to merge the two natures of this amp with emphasis going to retaining the sense of presence and air while still maintaining detail and good imaging. I am running two pairs of outputs at about 750mA each for a total bias around 3A. Total bias is not much higher, but individual bias is up substantially, being almost double standard setting. I would like to try 3 output pairs, but don't know if I have the heatsink for it.

Maybe you need to have a front panel pot for P3 !

I think this could be a great idea, assuming that you have limited the range of the pot to settings that truly pit the two natures against each other, with a possible middle road setting. I personally like this setup more than the AJ, F5 (Juma style), and Linn stuff I have heard. I have yet to listen to BA-2 FE.
 
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As P3 moves towards R4 it is like decreasing the focal length of a zoom lens, i.e., the musical images move away somewhat from the listener and appear more precise in their outline, better focussed. Mid and upper frequencies become sharper and more highlighted but do not become hard. The opposite seems true as P3 is turned towards R3: musical images become larger as though one was zooming in on them but they are less well difined in terms of outline. Upper and mid frequencies seem a little softer and yes there is a general sense that images are less pinned down, have more air and space around them.

Welcome to rolling your own harmonics.

:cool:
 
Every time you change this you need to adjust the bias on Q3 and Q4. So it's not quite as easy as a switch. :(

True but at least if we all moved P3 by the same resistor value it might make comparisons easier. I haven't found the overall sound picture changes much anyway when altering P1 and P2 to reset the DC offset. The big sound difference comes from P3.
It is possible to twiddle P3 and listen and then alter it again without rushing to reset the DC offset each time. The amp doesn't blow up but obviously when the ideal setting has been achieved P1 and P2 need adjusting.
I now have the voltage reg in place on the right channel, which is the BA-2 configuration. Let the comparisons begin.:)
 
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True but at least if we all moved P3 by the same resistor value it might make comparisons easier. I haven't found the overall sound picture changes much anyway when altering P1 and P2 to reset the DC offset. The big difference comes from P3.

I now have the voltage reg in place on the right channel, which is the BA-2 configuration. Let the comparisons begin.:)

The amount and level of second harmonic can only be specified in dB with an analyzer because having P3 centered is not necessarily the null of the stage. Any reference to voltage or resistance is only valid for that set of FETs.

Sorry.

All the comments about what you hear are very valid; it's just that we can't say that a certain setting is correct for everyone unless it’s specified in dB.
 
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The amount and level of second harmonic can only be specified in dB with an analyzer because having P3 centered is not necessarily the null of the stage. Any reference to voltage or resistance is only valid for that set of FETs.

Sorry.

All the comments about what you hear are very valid it's just that we can't say that a certain setting is correct for everyone.

Point taken. I take it you do have an analyzer and I would be interested to know what happens when P3 is turned let us say from the null point. If P3 is turned so as to increase second harmonic distortion, does that distortion increase in a linear manner as P3 is moved further?
Certainly the sound differences when moving in a certain direction have a linear feel to them, i.e., they don't change erratically.
 
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