Stax SRM-1/Mk2 Bias Modification

Step 5: Bias Setting
Now is the time to set up the pro-bias module.
• Prepare a multimeter, set into DC volts.
• Turn VR1 on the pro-bias module counter clockwise till you reach a stop.
• Place the red probe of the multimeter at the test point, and the black probe at the ground/chassis.
• Turn on the amplifier
• Turn VR1 clockwise until the multimeter shows 580V (for Stax Pro bias)
• Wait until the amplifier has reached operating temperature, then re-check the voltage at the test point, and re-adjust VR1 if necessary.
• For Koss ESP950 you can set the voltage to 620V.



Step 6: Testing
If the bias has been properly set, then you can test using the headphone connected.
The modded SRM-1/Mk2 now has a normal bias and a pro bias socket.


Enjoy, and click on that Facebook-Like icon if you enjoy the article!

Thanks to Psychaudio for sharing this modification technique.

5/5 - (1 vote)

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8 Comments

  • Reply July 13, 2013

    M H

    Would this design work with SRD-6/7?

    • Reply July 13, 2013

      Mike

      Aren’t the SRD transformer boxes?

      • Reply July 13, 2013

        M H

        Yes.

        • Reply July 13, 2013

          Mike

          I think you should be able to, it’s based on the same principles and basically you just want to up the bias voltage right? However I’m not quite an expert in this and so I can’t make any guarantees.

          • Reply July 13, 2013

            M H

            That’s what I think as well, though I am not an expert on the issue either.

  • Reply May 22, 2018

    Mai Buhaul

    Doesnt the srd already have a board? Would you just need to add a resistor?

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