22-02-2017, 09:47 AM
Had a play with the amp. First I tried taking out the 807's = drive signal was fine. Next put two 807's back in = sine at drivers, IE 12BH7 cathodes distorted as reported before. Changed
470n caps for 100n, aha! = sine distortion has now changed. The "bite" out of the neg going half of the sine now of bigger radius, IE slighter and and higher.
Now I'm on shaky ground, perhaps you can help Trevor. The grid reference R on the OP stage forms a high pass filter, right? So we want all signal's over 50hz say to pass. I have trouble interpreting calculator results in micro farads, but I make 1/ (2.28 x 50 x 150000) = 5.8 -8 or 5n . Nearest value is 4700p or maybe 6n8.
Or have I got this wrong, do I need a a low pass filter here to restrict OP of amp to 20k or maybe 17k? I've seen some transistor amps specs given as f response up to 100khz or something similar, why? Seems reasonable to restrict OP to 17khz or 20khz as this will stop HF instability, yes?
Thanks for taking an interest Trevor, Andy.
470n caps for 100n, aha! = sine distortion has now changed. The "bite" out of the neg going half of the sine now of bigger radius, IE slighter and and higher.
Now I'm on shaky ground, perhaps you can help Trevor. The grid reference R on the OP stage forms a high pass filter, right? So we want all signal's over 50hz say to pass. I have trouble interpreting calculator results in micro farads, but I make 1/ (2.28 x 50 x 150000) = 5.8 -8 or 5n . Nearest value is 4700p or maybe 6n8.
Or have I got this wrong, do I need a a low pass filter here to restrict OP of amp to 20k or maybe 17k? I've seen some transistor amps specs given as f response up to 100khz or something similar, why? Seems reasonable to restrict OP to 17khz or 20khz as this will stop HF instability, yes?
Thanks for taking an interest Trevor, Andy.
