I have a CCS modded Stax SR-006t from Mjolnir Audio that stopped working back in September. For a few weeks I would get no sound until I turned it off and on, but now I get nothing. I've tried multiple sources and cables but no dice. I tested the DC offset between + and - of both channels and between the bias and both channels' - line. After that I tested the AC voltage playing a 1khz signal and followed it from the inputs to the vol control and got nothing.

Spritzer repaired it back in April of 2023. The HV- line wasn't working due to a failed resistor and a capacitor was starting to fail. At the time the left channel was much quieter and had a buzzing noise before I stopped getting sound at all. It had no issues until September or August of last year.

Any thoughts or help are appreciated. I attached some pictures of the amp. Nothing looks obviously amiss to me.

What are the offset voltages?  That's when you measure between each of the 4 outputs and ground.  In theory you can have the balance at 0VDC but one output is stuck at HV+ or HV-

It is also a good idea to measure the rail voltages as the resistors in the power supplies in these love to fail.  Also... is the last cap of the main reservoir caps, closest to the tubes bulging a bit?  Might just be the reflection. 

On 2/23/2025 at 11:36 AM, spritzer said:

What are the offset voltages?  That's when you measure between each of the 4 outputs and ground.  In theory you can have the balance at 0VDC but one output is stuck at HV+ or HV-

It is also a good idea to measure the rail voltages as the resistors in the power supplies in these love to fail.  Also... is the last cap of the main reservoir caps, closest to the tubes bulging a bit?  Might just be the reflection. 

Running a 1 khz signal and measuring AC voltage with the ground lead on the side of the amp and the hot lead on each output pin, I get a brief spike of 0.005 volts before it hits zero. I also noticed the D4 LED is lit while the D3 LED is off or extremely dim.  I don't know if that matters but it caught my eye.

I took another picture of the last main reservoir caps and it doesn't look to be bulging.

Where/how do I measure rail voltages? Will I able to tell visually if those resistors failed? If so, which are they? I try not to open up the amp if I can help it and I haven't done anything with circuits in years so I apologize for the potentially obvious questions.

Does the circled area look like a burned/shorted area?
 

 

It turned out to be the four big caps had failed. I took it to a local hi-fi dealer who recently started carrying Stax and had it repaired.