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Old 20th February 2012, 04:26 PM   #1
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Thumbs up Bryston bias setting!!!

I found this interesting information about bias adjustments on most of the Bryston SST series amps that I would like to share with you guys. for all of those proud owners of Bryston amps that would like to check and adjust bias on their units here it is!!!
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Old 20th February 2012, 06:02 PM   #2
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Old 10th October 2016, 07:36 PM   #3
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Hello. Guys can you help to rephras: 25mV means the sum of tp1+tp2?
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Old 11th October 2016, 12:11 PM   #4
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No! Look at the schematics. This would not work for the 4B at all, for example. They want about 6 mV across both pins of TP1 and TP2 each (but measured separately), so that the values numerically add up to about 12 mV.
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Old 11th October 2016, 05:12 PM   #5
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Thank you for the feedback. So means 6mV for TP1 and another 6mV for TP2 12mV in total?
English is not my native, so I am puzzleled.

So meance my bias set 12mV on each TP is twice higher than the spec!? So I need to try if the right adjustment will lower down my DC offcet, which I have 49mV and 72mV across the terminals.

Any sigestion on the possible DC leaking component on the amp board? All the elecelectrolytic caps ( aside of pwr sypply) have been replaced already.
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Old 11th October 2016, 06:00 PM   #6
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Re-adjust bias to the 6.4 and 5.6 per to and tp2 on the channel, and see no influence on DC offset.

So, advice on the possible DC leakage components will be deeply appreciated.
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Old 12th October 2016, 03:37 AM   #7
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You do not say what model Bryston amplifier you are trying to adjust.
DC offset has nothing to do with bias current adjustment, which you are attempting.
Bryston models generally do not have an adjustment control for DC offset so to adjust it,
you would need to calculate and change certain fixed resistor(s), according to the model.
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Old 12th October 2016, 06:17 AM   #8
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I believe resistors value were were calculated by Bryston at the design stage.
I bet some components went loose after 30 year that caused high DC offset, so if someone know what will be the problem, I would appreciate advice.
Ithis is rare 3B with led level indicators, which has 80v in a arm by design
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Old 12th October 2016, 08:52 AM   #9
AndrewT is offline AndrewT  Scotland
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30years ago 5% tolerance resistor were very commonly used (look for the gold stripe).
And some were carbon film.
These loose tolerance and high drift resistors could very easily give output offsets that wander way off specification.
Bryston now do a 20year warranty. Was it 20years back then? If so they must have been pretty confident in the resistors they installed.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 12th October 2016, 09:14 AM   #10
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So, do you mean sine 1988 (which is mine) they moved toward 1% and lowered down DC offset down to 4-6mV that reported by the Bryston 4b-st /sst owners in the forums?

The reason I am trying to find what should I do, as I manage to do basic repair of the non working amp that I bought and recap by my own, but to drawn through the schematic to find the root of high DC offset is above my knowledge level. Shold I send it to the doctor or with some help can manage myself as the good Bryston amp "doctor" is not common in my location.

For example my 2B from 1986 shows DC offset 4mV an 7mV on the channels, so the resistors are from the same age...., but the figures are different.
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