Burning Amp BA-3

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#321
Backbones said:
Generg,
Did you see my earlier post? Just wanted your observations on how the BA3 sounded on various P3 settings (or anyone else for that matter).
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I have played with various settings of P3. The character of the sound changes from lean to full based on the amount of second harmonic but the ambient characteristic of the no feedback design stays either way. The one thing you have to watch out for is having the second harmonic out of phase with the test tone. It gives a very strange sound like an over damped room, you hear the primary but the bloom is gone, this really stands out with percussion instruments. Currently I have the second harmonic 3dB over the third. It’s a nice balance. I’m sill playing around with the output follower bias so things could change. It’s a fun amp to experiment with.

🙂
 
#322
Thanks Botte, very interesting.....!

The phase you mentioned is the same aspect Nelson mentioned in the manual I suppose and he suggested to do it in a certain way, something with imitating air, I did not really understand it ........

Now I am eager to hear Backbones comments when he comes out of his garage after 36 hours.....🙂😀
 
#323
generg said:
The phase you mentioned is the same aspect Nelson mentioned in the manual I suppose and he suggested to do it in a certain way, something with imitating air, I did not really understand it ........
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It helps to take Nelson's recent BA-3 article in context with his many previous articles, particularly the ones discussing single-ended amplifier output stages.

The comment about air is not related to distortion, per se, so much as the analogous asymmetrical nature of single-ended amplifiers. In earlier articles, Nelson pointed out that all sounds traveling through the air are limited by the single-ended nature of the atmosphere. He says that air pressure can increase, but it cannot go below zero; that particular function is single-ended because it affects the "bottom" of the waveform differently than the "top." I can neither confirm nor deny the physics, but it sure seems to make some sense to me offhand.

So, when he says in the BA-3 article that "favoring the positive going waveform is possibly preferred - with proper speaker polarity, this mimics the acoustic character of air," he's referring again to the single-ended nature of our natural atmosphere, where the opposite extremes of vibrations have different constraints. It would make sense that giving a slight boost to the positive going waveform peaks would have an approximately equivalent effect as the shortage experienced in negative going waveform excursions when sound travels through the air.
 
#324
rsdio said:
So, when he says in the BA-3 article that "favoring the positive going waveform is possibly preferred - with proper speaker polarity, this mimics the acoustic character of air," he's referring again to the single-ended nature of our natural atmosphere, where the opposite extremes of vibrations have different constraints. It would make sense that giving a slight boost to the positive going waveform peaks would have an approximately equivalent effect as the shortage experienced in negative going waveform excursions when sound travels through the air.
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Very interesting explanation. My take on this was to interpret it in the light of past experiments with interconnects.
Take two sets of twisted wire pair interconnects. One pair twist loosely and the other double or treble the number of turns per unit length.
One finds that the loose twist sounds as though there is great space around the instruments with a great sense of 'air' but instruments seem to occupy more of the soundstage. The highly twisted lacks this sense of space and 'air' by comparison but instruments are more discrete and seem a little further away. I prefer that sense of 'air' and it is probably related to lower capacitance and higher inductance.
Chris
 
#325
Botte said:
Currently I have the second harmonic 3dB over the third. It’s a nice balance. I’m sill playing around with the output follower bias so things could change. It’s a fun amp to experiment with.

🙂
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Botte,
In terms of resistance of P3 where do you reckon you are with the above findings? Ten ohms one way or 20ohms or even more subtle?
Chris
 
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#326
Backbones said:
Very interesting explanation. My take on this was to interpret it in the light of past experiments with interconnects.
Take two sets of twisted wire pair interconnects. One pair twist loosely and the other double or treble the number of turns per unit length.
One finds that the loose twist sounds as though there is great space around the instruments with a great sense of 'air' but instruments seem to occupy more of the soundstage. The highly twisted lacks this sense of space and 'air' by comparison but instruments are more discrete and seem a little further away. I prefer that sense of 'air' and it is probably related to lower capacitance and higher inductance.
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If you've ever seen Nelson Pass write about such things, then please provide a reference.

I searched through his articles that discuss single-ended circuits, and found the following in the very first Zen article:
Nelson Pass said:
Simplicity is not the only reason for the use of the single-ended topology. The characteristic of a single-ended gain stage is the most musically natural. Its asymmetry is similar to the compression / rarefaction characteristic of air, where for a given displacement slightly higher pressure is observed on a positive (compression) than on a negative (rarefaction). Air itself is observed to be a single-ended medium, where the pressure can become very high, but never go below 0. The harmonic distortion of such a medium is second harmonic, the least offensive variety.
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I think that the above quote fully explains what he was referring to in the latest BA-3 article.
 
#327
rsdio said:
" this mimics the acoustic character of air," .
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Hi RSDIO,
this is similar to an explanation made by Peter van Willenswaard in around 2000, when he also claimed that boxed cone speakers do sound more natural [than flat diafragm electrostats; my addition] because they compress and decompress the air in a natural way.
I immediately, when reading NP's article, saw that connection too.
albert
 
#330
Backbones said:
Botte,
In terms of resistance of P3 where do you reckon you are with the above findings? Ten ohms one way or 20ohms or even more subtle?
Chris
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Unfortunately this is all based on the match of the jfets. So it’s different for every pair. I would just center the dial until you can put it on a spectrum analyzer.
Speaking of analyzers, compared to the price of building an amplifier getting an old laptop and some free software should be no problem. I’m sure there will be more discussion of this on the Forum.
🙂
 
#332
Backbones said:
Thanks Botte.
I'm just going to have to do this by ear. I can't see myself getting a frequency analyser (then again I wasn't going to build my own amps a few years back). I've set P3 on both boards mid-way and I'll just see what happens.
Chris
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Here’s the thing, you can use just about any old computer with a sound card for this. You just need to be careful about not overloading the input of the sound card. You can just put a couple of diodes across the input or build a pad. Look at this link for more info. Once you have this tool you will wonder how you got by without it. 🙂
 
#333
And if you are too lazy to build it yourself.......like me
Look for this

"VIRTINS Sound Card Oscilloscope Probe Kits- the world's first"*********************************

Virtins Technology: Turn a PC into Virtual Instrument - Products

scroll down the page...


By the way ....... Good old Aleph P looks very well concerning distortion......

K2 in my build is a bit lower than k3 and both values are very low..... At medium volume

And also an easy build....

Also no feedback, even SUSY on board .......😀
 
#334
Botte said:
Here’s the thing, you can use just about any old computer with a sound card for this. You just need to be careful about not overloading the input of the sound card. You can just put a couple of diodes across the input or build a pad.
Click to expand...
The diodes are a great idea in terms of protecting the sound card input (provided that they're wired correctly), but if they actually conduct then they will create distortion that you might falsely attribute to your amplifier under test. It seems to me that a passive pad would be a superior choice since it shouldn't introduce significant distortion. Then again, an insufficient pad wouldn't protect your sound card, so perhaps both are needed. I guess it depends upon your exact situation and the amount of gain in your amplifier.

The link you provided seems to have good suggestions.
 
#338
Oh what a pity.......,

I also stopp sometimes my work too late and I produce faults....mostly with the second channel, less concentrated, already a bit eager to have a result, euphorized from the working first channel .....

But I learn ... Do you have to wait a long time for your replacements?
 
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