Liverpool bias (going down!)
Moderators: pompeiisneaks, Colossal
- Reeltarded
- Posts: 9966
- Joined: Sat Feb 14, 2009 4:38 am
- Location: GA USA
Re: Liverpool bias (going down!)
Amp is with 6P14P-EV. I think they need a little less push.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
Re: Liverpool bias (going down!)
You can reduce the 68K resistor to 56K but you lose that craziness. You could try an 12AT7 in the P.I. to reduce drive to the output stage. I’m not sure biasing the valves cooler will result in forward conduction happening significantly later.Reeltarded wrote: ↑Fri Feb 03, 2023 2:48 pm Amp is with 6P14P-EV. I think they need a little less push.
Yours Sincerely
Mark Abbott
Mark Abbott
- Littlewyan
- Posts: 1919
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
1 others liked this
Re: Liverpool bias (going down!)
I now remember! The 55% idle dissipation was to get a similar distortion level to a fixed bias set up and it was with an ultra linear set up.pdf64 wrote: ↑Thu Feb 02, 2023 11:55 pmBear in mind that bias can be tweaked to operate closer to class A. But another approach is to increase the load impedance. Might that align with the 55% example?Littlewyan wrote: ↑Thu Feb 02, 2023 9:57 pm … some cathode biased class AB amps are specced at 80%ish idle bias, some even biased cold at 55% and some at max dissipation. …
It’s about conduction angle, and the change in current from idle to max output, rather than idle dissipation per se.
And you're right, I think in a 5881 datasheet they give examples of both fixed and cathode bias, in the cathode bias they always bump the load impedance up a tad.
- Littlewyan
- Posts: 1919
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
1 others liked this
Re: Liverpool bias (going down!)
If less drive is the intended outcome then I would have an actual voltage divider between stages 2 and 3 to bring it down a tad, whilst adjusting the coupling capacitor at the same time if needed to keep the bass cut the same.