Leach Amp bias current (what is yours set to?)


diyAudio Moderator Emeritus
2002-01-21 2:42 pm
near Atlanta, GA
What is a good bias current for the Leach Amp? I currently have mine set to 100 mA, which is what Prof. Leach recommends. I have heard others mention that they had theirs at 150 mA. How would raising the bias current effect the sound of the amplifier. My leach amp runs quite cool now, so the extra heat should not be a problem.




2002-02-05 3:16 am
Leach Bias Current

I am currently running my bias at 230ma and have noticed a giant improvment in bass response. Your milage may vary and it does heat up a good bit more than the 100ma reccomendation but the sound is definitly better. I am using MJ21193/94 so i dont know if the improvment will occur with MJ15003/4's.

Just my 2 cents

Mine is set at 100mA. If i remember correctly, the visible crossover distortion on the scope disappeared well before 100mA. I set it a while ago and was in a rush at the time so I don't remember exactly. I think i finished the amp at about 8pm the day before graduation, I was rushing through all kinds of measurements and last minute tests that night since it was my last chance to use all of the big $ equipment.

I plan on changing the bias though. Leach didn't seem to be much of a hi-fi nut and there are a lot of things in my amp I'd like to change based on what I know now. Unfortunately the only thing i've got to work with is a 5 dollar walmart multi meter. Yes its a piece of junk...I could have built a much better one myself.

Fiddling now is somewhat useless because I'm missing 3 important things needed to tweak. 1. suitable speakers; 2. an accurate multimeter; and 3. an RCA-1/8" adaptor so I can use my PC as a reasonable testing bench. Money is tight(no job..grr) so 1 and 2 might have to wait a while...