Greetings!
I had no luck getting help from Bryston, not sure why they are not responding. I am preparing these Bryston amps for an install at a venue and I need to make sure they are running properly. So, I am reaching out for help here.
I have a working 3B-ST and need some help with the following: where and how do I check and set the "bias" and "offset"?
Also, I have a used 2B-LP and need to confirm the proper "bias" voltage, as it seems to be running hot.
Also, I have a used 3B (non ST), need to confirm the "bias" voltage.
Thanks!
I had no luck getting help from Bryston, not sure why they are not responding. I am preparing these Bryston amps for an install at a venue and I need to make sure they are running properly. So, I am reaching out for help here.
I have a working 3B-ST and need some help with the following: where and how do I check and set the "bias" and "offset"?
Also, I have a used 2B-LP and need to confirm the proper "bias" voltage, as it seems to be running hot.
Also, I have a used 3B (non ST), need to confirm the "bias" voltage.
Thanks!
Acc to service manual (you easy find it just google) you se the name of the pot, find it marked the same on pcb.
Dc is servo cotrolled. If you have dc more than-20mv with dc servo, then worry.
BTW you mean bias current or ?
Why al thise worries, uless amps have been opened for service? Then i'd wurry much more abt replaced components. and why.
Dc is servo cotrolled. If you have dc more than-20mv with dc servo, then worry.
BTW you mean bias current or ?
Why al thise worries, uless amps have been opened for service? Then i'd wurry much more abt replaced components. and why.
Dijk,
I mean bias current.
The reality is when I install them in the amp rack room, no one from the venue staff will turn them off or want to service them for the next two years. So I am just trying to make sure they are running as good as possible.
For 3BST, there is schematics but no values given for biased current. Unless I cannot find it and it’s there.
I mean bias current.
The reality is when I install them in the amp rack room, no one from the venue staff will turn them off or want to service them for the next two years. So I am just trying to make sure they are running as good as possible.
For 3BST, there is schematics but no values given for biased current. Unless I cannot find it and it’s there.
Unlesss there is som sort of trasmitter iterference that can make som strange effekts.. Bias do not have to be adjusted in a amp's lifetime.
Unless its tube.
And bias should be set after runnng the amp with load for som time.
It's like you'r caling for someone to watch, or watch you.
God luck.
Unless its tube.
And bias should be set after runnng the amp with load for som time.
It's like you'r caling for someone to watch, or watch you.
God luck.
but I have no idea and who and how service was performed on these Bryston amps. I don’t know their history. So I will attempt to get them to the best performance possible, per Specifications
I hope this may be helpful, to share my recent experience repairing an early series of the Bryston 2B power amplifier, serial number 2930.
Report, “Bryston 2B Power Amplifier repair - Hints and Lessons Learned” is posted over at the Audio Circle site in their Vintage audio category.
https://www.audiocircle.com/index.php?topic=184949.0
Brief text extract on setting output stage bias in an early series of 2B:
Measurements after repairs:
Thank you,
John
Report, “Bryston 2B Power Amplifier repair - Hints and Lessons Learned” is posted over at the Audio Circle site in their Vintage audio category.
https://www.audiocircle.com/index.php?topic=184949.0
Brief text extract on setting output stage bias in an early series of 2B:
Measurements after repairs:
- Whenever replacing the bias potentiometer and/or the power transistors it requires a resetting of the bias current. The instructions for setting the bias level are well documented in Bryston’s 2B Technical Data sheet “Burn-in Procedure”.
- Ensure the AC supply voltage is stable before performing this measurement.
- With the amplifier fully warmed up after a few hours operating, I set both channel’s bias values to between 9 ~ 10 mV, measured between the V+ red terminal of the bridge rectifier and the 100-ohm resistor. This setting proved to be the most stable, even when driven at the highest output power level.
- Hint, patience is required for the bias adjustment. While changing the bias potentiometer setting induces an immediate electrical change, with thermal lag it may take a few minutes for the temperature feedback sensing to fully respond. Suggest when changing the bias current setting, to do it a small step at a time, then wait for the system to stabilize and re-check the measurement. When I first set the bias, I didn’t pay attention to this and as a result the amplifier became very hot after a few hours of playing music.
- As a general guideline, if you place your hand on the 2B’s top panel after a few hours of playing music and it’s warm to the touch, the bias current is likely okay. But if the surface is hot to the touch and/or the power supply is overloaded causing the chassis to hum then the bias current is likely running too high.
- Last check, with the analog inputs shorted to ground, the DC offset measured across the output terminals was 4mV left channel and 6 mV right channel (should be less than 50mV).
Thank you,
John