Leach Amp bias current (what is yours set to?) - diyAudio
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Old 20th February 2002, 02:13 PM   #1
BrianGT is offline BrianGT  United States
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Default Leach Amp bias current (what is yours set to?)

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.


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Old 21st February 2002, 01:01 AM   #2
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Default 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

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Old 21st February 2002, 06:04 AM   #3
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I set my bias by observing the crossover glitch on my THD meter
(oscilloscope monitoring the THD meter's output) until it just disappears. I've tried arbitrarily higher bias settings but concluded I didn't like the sound or the heat sink temperatures. I'm sure that's a lot less than 200 ma. Ought to check that some time...
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Old 21st February 2002, 08:53 AM   #4
jteef is offline jteef  United States
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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...

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