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Old 12th December 2011, 05:18 PM   #531
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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.
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Old 12th December 2011, 07:44 PM   #532
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Maybe you need to have a front panel pot for P3 !
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Old 12th December 2011, 09:13 PM   #533
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Quote:
Originally Posted by Backbones View Post
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.

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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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Old 12th December 2011, 09:23 PM   #534
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Yeah, maybe an attenuator type rotary switch with discrete resistors would be a better option
once things are shaken out..Sweet spot at 12 O'clock! The two channels would match better also

Last edited by Variac; 14th December 2011 at 06:33 AM.
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Old 13th December 2011, 12:22 AM   #535
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Quote:
Originally Posted by Backbones View Post
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.

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Old 13th December 2011, 03:21 PM   #536
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Yeah, maybe an attenuator type rotary switch with discrete resistors would be a better option
once things are shaken out..Sweet spot at 12 O'clock! The two channels would match better also
Good idea.

Last edited by Variac; 14th December 2011 at 06:34 AM.
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Old 14th December 2011, 08:40 PM   #537
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Quote:
Originally Posted by Variac View Post
Yeah, maybe an attenuator type rotary switch with discrete resistors would be a better option
once things are shaken out..Sweet spot at 12 O'clock! The two channels would match better also
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.
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Old 14th December 2011, 09:13 PM   #538
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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.

Last edited by Backbones; 14th December 2011 at 09:16 PM.
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Old 14th December 2011, 09:22 PM   #539
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Originally Posted by Backbones View Post
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.

Last edited by Botte; 14th December 2011 at 09:26 PM.
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Old 14th December 2011, 09:29 PM   #540
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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.

Last edited by Backbones; 14th December 2011 at 09:31 PM.
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