A 5 min video of what happens when P3 is adjusted. Enjoy.
https://www.youtube.com/watch?v=CQG2j9fkr9E
https://www.youtube.com/watch?v=CQG2j9fkr9E
Well, you can turn the pot, listen, take notes, and try again...
Do you have a signal generator and a soundcard? You can FFT the signal and see the harmonic spikes.
That is indeed a very informative video. I have watched it over three times. Thanks for making it.
As someone who has just completed building a set of F5TV3 monos(pics to be posted soon) I have a few questions.
Initially before biasing up the amp I set P3 so that the voltage across R3 and R4 were identical. This resulted in P3 being turned clockwise by almost two turns from center. Upon fully biasing the amp I notice that as I turn P3 further clockwise the offset becomes more positive.
Could you give me some indication as to how many turns from the center position you turned to get around the 0.06% distortion you settled for.
Did you notice the same effect on the sound if you turned it the same number of turns anticlockwise as clockwise?
In the video you make no mention about readjusting the offset. So for example if I turn P3 clockwise another 4 turns from center and the offset goes positive, how do you advice bringing it to zero; turning down P1 or turning up P2 or about half of each to get zero offset.
Thanks again. Really nice and helpful work. I intend exploring P3 a lot further.
Nash
As someone who has just completed building a set of F5TV3 monos(pics to be posted soon) I have a few questions.
Initially before biasing up the amp I set P3 so that the voltage across R3 and R4 were identical. This resulted in P3 being turned clockwise by almost two turns from center. Upon fully biasing the amp I notice that as I turn P3 further clockwise the offset becomes more positive.
Could you give me some indication as to how many turns from the center position you turned to get around the 0.06% distortion you settled for.
Did you notice the same effect on the sound if you turned it the same number of turns anticlockwise as clockwise?
In the video you make no mention about readjusting the offset. So for example if I turn P3 clockwise another 4 turns from center and the offset goes positive, how do you advice bringing it to zero; turning down P1 or turning up P2 or about half of each to get zero offset.
Thanks again. Really nice and helpful work. I intend exploring P3 a lot further.
Nash
As many turn as necessary to read that value on your distortion meter. Or FFT of the output with a 1khz signal at about 1 watt output. Esentally that sweet spot, IMO, is still 2nd harmonic dominant, yet with some distortion cancelled.
Kinda, but the absolute phase will change.
Adjust the bias pots as necessary to re-zero it - the 'P3 effect' will not be changed much by the other pots - they do completely different things.
Jim,
I just got some software (faber electroacoustics toolbox) to measure the effect of P3 on my BA-3 based preamp using a USB audio interface (M-audio).
I have never used a scope and the leaning curve is pretty big. I've figured out how to feed it a 1kz signal and do a FFT analysis and convert it to THD+N...all this software assumes you already are familiar with an ocsillascope (which I am not) but I've managed to figure it out. Bless the internet age and youtube tutorials.
Should the outputs of the BA-3 front end be loaded with a resistor when measuring? This is just a preamp, not the whole BA-3 power amp.
I just got some software (faber electroacoustics toolbox) to measure the effect of P3 on my BA-3 based preamp using a USB audio interface (M-audio).
I have never used a scope and the leaning curve is pretty big. I've figured out how to feed it a 1kz signal and do a FFT analysis and convert it to THD+N...all this software assumes you already are familiar with an ocsillascope (which I am not) but I've managed to figure it out. Bless the internet age and youtube tutorials.
Should the outputs of the BA-3 front end be loaded with a resistor when measuring? This is just a preamp, not the whole BA-3 power amp.