Perform Biasing on B&K ST-140

Falcon · 31st January 2010, 04:17 AM

Hi Forum Members:
I have just replaced the pre-drivers and output drivers on both channels of my B&K ST-140 ( early version with only one pair of output transistors per channel ). I would like to know what is the procedure(s) to check and setup the bias on both channels correctly. Also anything else I need to check and adjust to make sure that everything is fine and within specification? I contact B&K but no response so far. Thanks.

Mike

djk · 31st January 2010, 06:50 AM

Pull one fuse on one channel, adjust the bias to about 125mA (100mA per output plus 25mA for the front end). Repeat for the other channel.

jonnymyaudio · 6th February 2010, 04:59 AM

do you know the steps to bias the newer style with 4 outputs per channel

djk · 7th January 2013, 11:55 AM

Same way, 100mA per output P&N output pair, plus 25mA for the front end

jonnymyaudio · 8th January 2013, 05:26 AM

I had a couple problems trying to bias the amp. My readings were all over the map. 1st I was using a cheap multimeter to try and measure ma and 2nd was my 4 100uf 100v caps had a lot of leakage. So I put new caps in and I got a real test meter for measuring ma and now it works like a charm. Thanks djk

tony Ma · 4th March 2013, 05:48 PM

Here what I got from the factory

31st January 2010, 04:17 AM	#1
Falcon diyAudio Member Join Date: Feb 2004 Location: Houston	Perform Biasing on B&K ST-140 Hi Forum Members: I have just replaced the pre-drivers and output drivers on both channels of my B&K ST-140 ( early version with only one pair of output transistors per channel ). I would like to know what is the procedure(s) to check and setup the bias on both channels correctly. Also anything else I need to check and adjust to make sure that everything is fine and within specification? I contact B&K but no response so far. Thanks. Mike

31st January 2010, 06:50 AM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	Pull one fuse on one channel, adjust the bias to about 125mA (100mA per output plus 25mA for the front end). Repeat for the other channel. __________________ Candidates for the Darwin Award should not read this author.

6th February 2010, 04:59 AM	#3
jonnymyaudio diyAudio Member Join Date: Dec 2009	Bias do you know the steps to bias the newer style with 4 outputs per channel

7th January 2013, 11:55 AM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	Same way, 100mA per output P&N output pair, plus 25mA for the front end __________________ Candidates for the Darwin Award should not read this author.

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8th January 2013, 05:26 AM	#5
jonnymyaudio diyAudio Member Join Date: Dec 2009	I had a couple problems trying to bias the amp. My readings were all over the map. 1st I was using a cheap multimeter to try and measure ma and 2nd was my 4 100uf 100v caps had a lot of leakage. So I put new caps in and I got a real test meter for measuring ma and now it works like a charm. Thanks djk

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