stax bias voltages on SRD 7 modified for pro and normal bias measurements?
May 22, 2012 at 2:45 PM Thread Starter Post #1 of 3

cjfrbw

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I have had some balance problems with my Stax 507 with the right channel being scratchy and low compared to the left.  I don't have an amplifier, but use one of the SRD 7 transformers with the pro and normal bias boards added.
 
I was wondering if the bias voltage was down, because the efficiency also seemed weak.
 
I measure 240V at the bias pin output jack to ground, and 360V in front of the last resistor (2.2M?)  for the pro bias.
 
I measure about 120v at the normal bias pin to ground, and 160V in front of the last resistor (2.2M?) for the normal bias.
 
Is the board correct, or do I need a repair?  Could it be the Zener diode? Where else should I measure?
 
Thanks.
 
May 23, 2012 at 1:19 PM Post #3 of 3

spritzer

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With the super high impedance of those boards you need a VTVM (vacuum tube voltage meter) to measure as the 10M input impedance of even the best DMM's is just far too low.  This overloads the voltage multiplier and you can't get accurate readings. 
 
With only one channel affected then the bias supply is not the culprit but that particular Stax driver. 
 

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