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Thread: Khozmo Attenuator question

  1. #1
    Join Date: Sep 2011

    Location: Kilmarnock, Ayrshire, Scotland

    Posts: 438
    I'm stuart.

    Default Khozmo Attenuator question

    I've built a preamp (DCG3) and currently have a 20k Alps blue fitted - as recommended.

    My usable travel on the pot is around 1/4 - 1/3 of full rotation. Measuring the pot gives 18.4k ohm when fully closed in the 7 o'clock position to 17.8k ohm at the 10 o'clock position and that's getting pretty darn loud.
    Gain is set as 2X and can't be set any lower on the DCG3 although Salas has suggested using a voltage divider on the output to get more travel on the pot.

    The Alps Blue was always just going to be a stop gap for evaluation purposes and the end goal was to use a stepped attenuator. Can any of you guys who have used a Khozmo tell me how many usable steps that would be the equivalent to when using a 25k ohm Khozmo or is it too few to be worthwhile? I'm loathed to buy a Khozmo and find out I've only got about 15 usable steps out of 48!
    Garrard 401, Jelco 750 with Shuggie, Ortofon 2M Black / ZYX Yatra 100, Project Phono RS with Sigma22 Linear PS, RPi3 + DigiOne + Linear PS, RPi3/1Tb SSD with PiCorePlayer + Linear PS, Perreaux Eloquence 250i 40th Anniversary with ES9038Pro DAC, Monitor Audio PL300, Tannoy Mansfield 15" HPD's.

  2. #2
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 4,946
    I'm Alan.

    Default

    Sounds like you need to remove gain from your system to enable you to widen the volume control travel.
    Can't you set the volume control on the Perreaux to a lower level?

  3. #3
    Join Date: Sep 2011

    Location: Kilmarnock, Ayrshire, Scotland

    Posts: 438
    I'm stuart.

    Default

    Quote Originally Posted by Firebottle View Post
    Sounds like you need to remove gain from your system to enable you to widen the volume control travel.
    Can't you set the volume control on the Perreaux to a lower level?
    Not if I bypass the preamp I can't, gain is fixed at 28.8dB for the power amp section. Salas has suggested i replace the output series resistor on the DCG3 with a 470 ohm and then put another 470 ohm across the tip and barrel of the output RCA's, this should effectively half the gain.
    Having said that, my long term plan is to move to a different power amp so maybe in the short term I just run it through the Perreaux preamp as well, setting the Perreaux volume to whatever setting gives me a better travel on the DCG3 pot.

    Other suggestions welcome!
    Garrard 401, Jelco 750 with Shuggie, Ortofon 2M Black / ZYX Yatra 100, Project Phono RS with Sigma22 Linear PS, RPi3 + DigiOne + Linear PS, RPi3/1Tb SSD with PiCorePlayer + Linear PS, Perreaux Eloquence 250i 40th Anniversary with ES9038Pro DAC, Monitor Audio PL300, Tannoy Mansfield 15" HPD's.

  4. #4
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 4,946
    I'm Alan.

    Default

    Don't go with the 470 ohm resistor suggestion, it will load the output with too low an impedance and I guess will kill the dynamics.

    Instead reduce the value of R6 in the circuit to 220 or 150 ohms, that will reduce the gain.

  5. #5
    Join Date: Sep 2011

    Location: Kilmarnock, Ayrshire, Scotland

    Posts: 438
    I'm stuart.

    Default

    I have R6 at 499 ohm, Salas doesn't recommend setting it any lower than this.
    Garrard 401, Jelco 750 with Shuggie, Ortofon 2M Black / ZYX Yatra 100, Project Phono RS with Sigma22 Linear PS, RPi3 + DigiOne + Linear PS, RPi3/1Tb SSD with PiCorePlayer + Linear PS, Perreaux Eloquence 250i 40th Anniversary with ES9038Pro DAC, Monitor Audio PL300, Tannoy Mansfield 15" HPD's.

  6. #6
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 4,946
    I'm Alan.

    Default

    OK

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