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Old 28th April 2007, 02:09 PM   #1
Barry1 is offline Barry1  United States
diyAudio Member
Join Date: Apr 2007
Location: Philadelphia
Unhappy Threshold S/550e Bias advice

Iím an amateur and need some help with setting the bias on a newly acquired Threshold S/550e. I have a manual & related info for Threshold amplifiers with the same topology, but no specifics for this one.

Iím guessing the amp needs biasing because the heat sinks are running at 31 Ė 35C even after an all night warm-up and Ĺ hour of playing time. The operating manual I have is for all the Stasis amps, S/350e to 1600e, class A/AB, as well as the pure class A, S/4e through S/12e. It gives no S/550e biasing instructions. However, in another manual posted on NPís website it says, Ďthe E series amps are designed to run at 45 -50 degreesí, but the amps referenced are the Class A varieties & the bigger A/AB 1600e.

The schematic for the SA12e shows only one variable resistor, P1, a 10K trimpot, in the front end circuitry (which I hope I attached). That must set the bias, right?

Iím assuming I would use standard procedures adjusting that trimpot and taking my readings across one of the 1 ohm emitter resistor on the final output stage rechecking again in another 5 minutes or so.

I only have bias voltages for an S/500, the earlier model, which are 100mV cold and 75mV hot. Do these values sound right? Any other related advice?

If you have something to e-mail related to this Iím at:

Thanks for your help! Barry
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