biasing up the mini-crescendo kind of construction..

Mr. Triatic · 29th June 2002, 01:32 PM

will i gain anything except heat?...the bias runs @ 100mA right now...
my output trannies are running hot as is, about 50ºC , should i change them (2sk1058/2sj162) before raising the bias?

any comments or experience are welcome!

wuffwaff · 29th June 2002, 08:19 PM

Hi,

in my experience with the Hitachi fets they gain a lot in sound quality up to 180-200mA per device. I run 3parallel pairs@a bit over 300mA a piece.

Is your heatsink 50° or are the fets this hot? I have run for manny years with heatsinks of 50° without problems.

raising bias from 100 to 180-200 would be asking for trouble though when the sinks are alrasdy 50°.
The best thing would be to change the sinks or leave it as it is.

william

promitheus · 22nd July 2002, 01:06 AM

The higher you bias the output MOSFETS the better it gets.
I tried this before but the heat dissipation is too much.
You need a lot bigger heatsinks if you want to use 200ma or more.

Mr. Triatic · 22nd July 2002, 03:16 PM

Now the amps runs @50ºC stable, measured at the hetsink,
just nearby the transistors.
The bias is now 200mA, and i noticed a slight sonic improvement..
Thank you all for the help!
-another Q, i believe the DC at the output is a little too high, how should i adjust this in a proper way? maybe incorporate a potentiometer at a tactical spot in the circuit? 80mV doesn´t sound very good to me, i´d like it to be much lower, help please!!

Greetings
Ludvig.

29th June 2002, 01:32 PM	#1
Mr. Triatic diyAudio Member Join Date: Feb 2002 Location: SWE EU	biasing up the mini-crescendo kind of construction.. will i gain anything except heat?...the bias runs @ 100mA right now... my output trannies are running hot as is, about 50ºC , should i change them (2sk1058/2sj162) before raising the bias? any comments or experience are welcome!

22nd July 2002, 03:16 PM	#4
Mr. Triatic diyAudio Member Join Date: Feb 2002 Location: SWE EU	ok... Now the amps runs @50ºC stable, measured at the hetsink, just nearby the transistors. The bias is now 200mA, and i noticed a slight sonic improvement.. Thank you all for the help! -another Q, i believe the DC at the output is a little too high, how should i adjust this in a proper way? maybe incorporate a potentiometer at a tactical spot in the circuit? 80mV doesn´t sound very good to me, i´d like it to be much lower, help please!! Greetings Ludvig.

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29th June 2002, 08:19 PM	#2
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	Hi, in my experience with the Hitachi fets they gain a lot in sound quality up to 180-200mA per device. I run 3parallel pairs@a bit over 300mA a piece. Is your heatsink 50° or are the fets this hot? I have run for manny years with heatsinks of 50° without problems. raising bias from 100 to 180-200 would be asking for trouble though when the sinks are alrasdy 50°. The best thing would be to change the sinks or leave it as it is. william

22nd July 2002, 01:06 AM	#3
promitheus diyAudio Member Join Date: Jan 2001 Location: Germany	The higher you bias the output MOSFETS the better it gets. I tried this before but the heat dissipation is too much. You need a lot bigger heatsinks if you want to use 200ma or more.