There’s been a few requests for this preamp circuit and I finally got around to it. I based this on a schematic I’m not really sure where I got. I think maybe one of you sent it to me, but anyway. Here’s to hoping it works.

Update (13.12.2011): Built this last night. Had to reverse the wiring on the Presence and Mid pots, and I had the cut count wrong, but it’s working now. Verified!

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11 thoughts on “Request: Modern SLO 100

  1. Tim, if you have plenty JFETs spare you can try swapping them in until you find ones that read close with the given resistor.

  2. Finished building this tonight and it seems nice, but like another person said, some of the JFETs really need a trimmer on there. When i used the stock resistor for Q1, I had a drain voltage of about 2.5V.

    It sounds “ok” but i bet this could sound “awesome” once the transistors are biased properly.

  3. Hi Asgeir,
    Sorry to hear you’re having trouble. If you look a bit further down in the comments you’ll find a link to the schematic; might be of some help. Have you compared your voltages to the ones written out on the layout?
    I hate to say it, but if you had to make radical changes to make it bias right there might be an issue somewhere. I built this one exactly as you see on the layout. I could see slight changes to make it bias right because of transistor variations, but definitely not radical ones. Have you considered debugging using an audio probe? Have a look at the debugging section for some other potentially useful tips.

  4. Hey, I built it but I’m having problems. I’ve checked the board and everything is perfect, no bridges or anything.

    The bass pot doesn’t do anything at all and it’s sounding quite thin. I’ve biased the trannies and I had to do radical changes to the resistors you suggested swapping for biasing. The presence isn’t doing much either.

  5. My Dr. Boogey circuit has been sitting in a drawer for a long time so I couldn’t tell you. I did post the link to the SLO schematic (somewhere in these comments) I based this layout on and on that same site there were some sound clips too.

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