BA-3 As Preamp

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#826
Zen Mod said:
everything is making sound

in tube amps - output xformers mostly , then tubes

in sand amps - most singing creatures are old T03 case critters , then ceramic cased ones in much smaller scale

T03 being hollow , act as resonating box

it really depends on voltage swing through critters - greater the swing , greater parasitic s(w)inging
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Zen, I never experienced something like this before. Never heard a transistors or mosfets singing psychically. Sounds like phono cartridge needle noise or listening headphones from 10cm distance.In both cases there is a vibration. There must be a vibration (mechanical) to produce any sound or noise. So, is this means, mosfets are vibrating inside and creates a audible noise?

If I increase volume a little bit, I can listen Bon Jovi's Runaway from the BA-3 pcb itself 😀
 
#833
I spent the weekend playing around w/he BA-3 preamp and a FFT analyzer. The results were pretty interesting.

My measurement setup is pretty bad (Macbook, USB interface, Faber toolbox) and my comprehension of the software is even worse, I've never used an analog scope and it was a pretty steep learning curve. But I made it work.

I think adjusting P3 has a dramatic effect on the sound. With the 2nd harmonic nulled the sound was clean, centered vocals very high and forward. I could only bring the 2nd harmonic to a point where the 2nd and 3rd harmonic were about even.

Going the other direction with the 2nd harmonic dominant the sound was not as clean, vocals were lower and pushed back and soundstage width was greater. Also, bass was not as clean. Less snap but more relaxed.

Another note: With the P3 pot at midpoint it was not "even" channel to channel. I also don't believe the pot at mid setting was an "average" or median setting. It was mostly 2nd harmonic.

My point is...P3 pot at midway sounds good, no problems. But it does not mean the 2 channels have the same harmonic signature or that it is a good "balance" of harmonics. I think the setting is dependent on your fets and probably other variations in the circuit, channel to channel.
 
#835
frankly - I didn't bother calculating ....... because simple one is more than approximate (at least for my liking) , while precise one is too much for my lazy butttt

I just put your values in LTS sim of BA3 FE I already had

in Diyaudio article area - BA3 article - you'll find Papa's explanation , with ooked parts nomenclature;
little lower , you'll find my post/comment with edited parts nomenclature , even if I repeated Papa's ookup with gain calculus - it's upscaled by 2 , comparing to real world
 
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#837
Zen Mod said:
frankly - I didn't bother calculating ....... because simple one is more than approximate (at least for my liking) , while precise one is too much for my lazy butttt

I just put your values in LTS sim of BA3 FE I already had

in Diyaudio article area - BA3 article - you'll find Papa's explanation , with ooked parts nomenclature;
little lower , you'll find my post/comment with edited parts nomenclature , even if I repeated Papa's ookup with gain calculus - it's upscaled by 2 , comparing to real world
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Thanks ZM. I reread the article with your comments of Sept 18, 2011

"The voltage gain of this initial stage is approximately the value of Drain load resistors R6 plus R7 divided by R5. In this case we have roughly unity gain"
"The voltage appearing at the Gate of Q3 is amplified by something less than the ratio of R13 divided by R10, and with the same happening at Q4(R11) and considering the transconductance of the Mosfets, comes out at about 15. Both of them added make a system voltage gain of about 30X, or 30 dB."

So if I wanted to reduce the gain should I not simply reduce the value of R13? So if R13 is 200r then 200/22=9.1; 9.1x2=18.2 which is about 25db Right?

Just trying to wrap my head around this.
 
#840
nashbap said:
Thanks ZM. I reread the article with your comments of Sept 18, 2011

"The voltage gain of this initial stage is approximately the value of Drain load resistors R6 plus R7 divided by R5. In this case we have roughly unity gain"
"The voltage appearing at the Gate of Q3 is amplified by something less than the ratio of R13 divided by R10, and with the same happening at Q4(R11) and considering the transconductance of the Mosfets, comes out at about 15. Both of them added make a system voltage gain of about 30X, or 30 dB."

So if I wanted to reduce the gain should I not simply reduce the value of R13? So if R13 is 200r then 200/22=9.1; 9.1x2=18.2 which is about 25db Right?

Just trying to wrap my head around this.
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I'd be careful here...I built the BA-3 w/stock gain and it was way less than I expected. Feels/sounds more like 15db gain to me, stock. Which is kind of what Zen Mod is saying. I find it perfect w/the F5 at stock gain. Not noisy and when cranked up loud I use 80% of the volume dial.
 
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