Pass Labs bias settings/adjustments
VR3
Posts: 28,732
So I have been researching this as even after mine was serviced, one side is hotter than the other.
The norm I see is that the amp while idling should be at 50 C which is 122 F and supposedly will only be comfortable to the touch for 5 seconds.
I can pretty much keep my hands on my amplifier forever without any type of discomfort and one side is barely warm to the touch. This is with the amp ON, not in stand by.
I just ordered a temp meter, a 2 pin cable set and some RCA shorting plugs as I intend to check to bias and hopefully adjust as needed.
So my understanding of amp biasing is as follows -
Disconnect amp from power, wait 5 minutes or so.
1) Connect XLR jumper for single ended use (which mine already has)
2) Connect RCA shorting plug
3) Connect 2 x volt meters, requires 2 per channel, connect them outside the amplifier, reinstall the top.
4) Turn on the amplifier, let it sit for a hour, check readings and adjust in very, very small increment on the adjustment pots. Adjust, wait 15 to 20 minutes, adjust, repeat, adjust, repeat...
You are not adjusting to a certain reading, but a certain temperature.
So checking to see if this is on the right path or am I missing variables.
I am not to worried about checking the offsets as that is why my amplifier was in service to begin with. They installed the new UGC6 board and everything.
Side note: I have the X150
The norm I see is that the amp while idling should be at 50 C which is 122 F and supposedly will only be comfortable to the touch for 5 seconds.
I can pretty much keep my hands on my amplifier forever without any type of discomfort and one side is barely warm to the touch. This is with the amp ON, not in stand by.
I just ordered a temp meter, a 2 pin cable set and some RCA shorting plugs as I intend to check to bias and hopefully adjust as needed.
So my understanding of amp biasing is as follows -
Disconnect amp from power, wait 5 minutes or so.
1) Connect XLR jumper for single ended use (which mine already has)
2) Connect RCA shorting plug
3) Connect 2 x volt meters, requires 2 per channel, connect them outside the amplifier, reinstall the top.
4) Turn on the amplifier, let it sit for a hour, check readings and adjust in very, very small increment on the adjustment pots. Adjust, wait 15 to 20 minutes, adjust, repeat, adjust, repeat...
You are not adjusting to a certain reading, but a certain temperature.
So checking to see if this is on the right path or am I missing variables.
I am not to worried about checking the offsets as that is why my amplifier was in service to begin with. They installed the new UGC6 board and everything.
Side note: I have the X150
- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
Comments
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Adjusting to a certain temperature?
That’s a new one for me ....
Where is the temp measured , heat sinks ?
How do you compensate for differing ambient air temperatures?
Bk
PS Audio S300 , WiiM Ultra , Yamaha wxc-50 , Salk SuperCharged Songtowers , Kimber Kable 4TC, Sony 42” - BEDROOM
B&K EX-442 ( it will go in my casket when I die ... ) , PS Audio 4.6 preamp ( old school , but it still jams on ... ) , Eversolo DMP-A6 , Boston Acoustic voyager 7’s - POOL
Parasound A21, Eversolo DMP-A8 , Kimber Kable 4vs , Ascend Acoustics ELX Ribbon Towers , Sony XBR-A8F 65” OLED - DEN , MAIN system
Onkyo TX-nr609 , Polk atrium 7 , Boston acoustic sound ware (4) , Boston acoustic sub , B&W center , Sharp 65” TV - PATIO -
From Nelson Pass himself -
All Pass Labs amplifiers are designed to operate at about 30 deg C. above the ambient temperature, as measured on the top of the heat sinks. One of the reasons that this temperature is chosen is that the sensitivity of human skin to heat is non-linear in this region, and you can fairly reliably tell if the temperature on the heat sink is 50 to 55 deg C. by touch. If you can put your hands on the top of the heat sink for about 5 seconds, then you are close to the correct operating temperature.- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit. -
And from Kent English -
It's actually to a performance metric (Thd + Noise vs Watts) although the temp rise is expected to be about 20 degrees C above ambient At idle the bias pretty much reflects the draw from the AC Mains. By serial we can check that draw from the build records and compare that to the draw from the AC mains at your measured line voltage.
In the average domestic environ 120F - 130F would be pretty normal on sink temp. when fully warmed up,- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit. -
That’s interesting ...
Cool !
BkPS Audio S300 , WiiM Ultra , Yamaha wxc-50 , Salk SuperCharged Songtowers , Kimber Kable 4TC, Sony 42” - BEDROOM
B&K EX-442 ( it will go in my casket when I die ... ) , PS Audio 4.6 preamp ( old school , but it still jams on ... ) , Eversolo DMP-A6 , Boston Acoustic voyager 7’s - POOL
Parasound A21, Eversolo DMP-A8 , Kimber Kable 4vs , Ascend Acoustics ELX Ribbon Towers , Sony XBR-A8F 65” OLED - DEN , MAIN system
Onkyo TX-nr609 , Polk atrium 7 , Boston acoustic sound ware (4) , Boston acoustic sub , B&W center , Sharp 65” TV - PATIO -
So I am doing this right now and my bias was WAY!!!!!!!!!!!!!!!!!!!!!!!!!! off. I dont even think the tech in VA adjusted the bias, I could be wrong but the temperatures were similar from when they left to when they came back.
I adjusted all four bias points at 120 MV.. both heat sinks reading 119 F at this moment! Loving it... just means I have to plug this thing back up after I give the tri vista a spin for a bit to compare since apparently I was listening to a way off amplifier- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit. -
👍
Techs ..... trust but verify!
BkPS Audio S300 , WiiM Ultra , Yamaha wxc-50 , Salk SuperCharged Songtowers , Kimber Kable 4TC, Sony 42” - BEDROOM
B&K EX-442 ( it will go in my casket when I die ... ) , PS Audio 4.6 preamp ( old school , but it still jams on ... ) , Eversolo DMP-A6 , Boston Acoustic voyager 7’s - POOL
Parasound A21, Eversolo DMP-A8 , Kimber Kable 4vs , Ascend Acoustics ELX Ribbon Towers , Sony XBR-A8F 65” OLED - DEN , MAIN system
Onkyo TX-nr609 , Polk atrium 7 , Boston acoustic sound ware (4) , Boston acoustic sub , B&W center , Sharp 65” TV - PATIO -
I'm conversing with Kent at pass labs to verify its on track...
Setting over night each heat sink is at 124 f, 2.05 Amp draw from the wall- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
