Request: Hiwatt DR103 preamp emulator

Update (16.12.14): Now verified as working, thanks to jay 🙂

JFET version of the Hiwatt DR103 preamp, with a few extra components to (hopefully) make it work. I added R14, C9, C10 and D1; not sure if C9 is big enough, but it’s probably fine. You can assemble it either as “normal” or “bright”. I’m not sure which one would sound better.


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28 thoughts on “Request: Hiwatt DR103 preamp emulator

  1. I know this thread is kind of old but I’m hoping you can help me out…

    I’ve built this circuit twice now, and in both circuits, I’m not getting any low-end from the output. Turning the Mid knob makes very little audible difference, and the bass control does nothing. I’ve been over the layout a number of times with my MM to make sure nothing is bridged that shouldn’t be. I used J201s, and they are all biased properly.

    Using an audio probe, I’ve found that the signal at R9 is pretty much all treble (everything after this seems to be working correctly tho). If I turn the treble all the way down, I start to get some more play in the Mid control and a little bit on the Bass (but it never sounds good). Once the Treble is even just at 12 o’clock, it’s shrill and nasty.

    If I touch my probe to the lugs on the Mid and Bass pots, it sounds exactly like you’d expect. But once it hits the treble part of the circuit, the low end is all sucked out.

    Any ideas on what could be causing it or what I should try doing to fix it? thanks!

  2. Carlos,
    Since it’s not my schematic (I didn’t draw it or modify it) I don’t want to host it. Sorry.
    But it should be easy to find on the Internet.

  3. Hey guys, is there an actual schematic for this circuit?
    Approximating the layout or comparing this to an original DR103 schem only goes so far!

  4. Clay, This build is based on the original Hiwatt DR103 that I gave to Harald for the conversion. Check out the schematics page.

  5. I’m interested in this build as I have a friend that wants a hiwatt in a box but doesnt like the catalinbread WHO at all. Where did this circuit come from? do you have a schematic?

  6. This works great. Nice clean tones. Worked first try.This thing is loud. Running it at 15 volts. Couldn’t get q3 to go below 9v so I just set all my drain voltage at 9v.Should be verified. Is there a way to add a gain knob like the catalinbread rah?

  7. Hi,

    Just build that one, everything fine except that volume is really low at output, I have to turn Volume and Master all the way up to get a little sound (which is thin). Could someone give me a hint please on what to look for to add volume ? I would appreciate.


  8. Arik, well, all of my builds have been done with J201, I never tried anything else so, if you can give them a try. And by the way, for various reasons I have not finished it yet, even though I already have everything including the board built with all of the components.
    Harald I think you should put it as verified since some folks reported it as working.

  9. George, At one point of debugging my build I shielded every wire. I even tried bumping c10 to 100 uf and adding a resistor from 9v to help power filtering, but the noise remain. I used 2N5457 that seem good in my bsiab2. Other than that I used 3PDT to switch between the bright and normal modes. For the moment I left it alone, maybe I should try It with J201?

  10. Not sure I’m going to be of much help, Arik. Can you describe the noise a bit more? Is it static/white noise, oscillation of some sort, high pitch or low pitch, varying, background noise etc.? Since it’s also present when there’s no signal I’m thinking it could be either noise from your power supply or one (or more) of your JFETs being damaged.

  11. Hi Harald, yesterday I built this preamp emulator and it sound really good, but there is a constant noise in the background that is very noticeable, a specially when I stop playing. the weird thing is that even when the guitar lead is not connected the noise is the same. any suggestions?
    By the way the circuit is inside 1590BB box.

  12. I got finally what I needed, so hopefully I’ll be able to finish it tomorrow.

  13. I have not been able to finish it, been extremely busy this last month or so, on Monday I’ll jump on it right away if the parts needed arrive.

  14. Harald,

    I may have just answered my own question – i put it in an old box roughly and it seems to have fixed the problem.

    Thanks for the posts.

  15. Harold,

    I am having a problem with excess radio interference with this pedal. I haven’t boxed it yet – would this help or do you have any other suggestions.


  16. Much appreciated, Glenn. I’m happy you were able to correct it and I’ll tag it as verified right away.
    (Haven’t played the new amp yet as it needs a proper enclosure first).

  17. Hi again Harald:
    never mind, I re-flowed the solder and I found the first component i put down (a jumper) was the problem. I did put a small cap across lug 2 an3 on the volume pot, this might not be needed but, I’m gonna leave it (I’m lazy).
    I do like the tone section and especially the bass. You get the thumpiness you hear on Hiwatt’s…sound good. So its verified.
    Take care…

  18. Hi Harald, hope all is well and hope your enjoying your new amp.
    I built this and it sounds great all the controls work….. except for a huge hiss and radio noise.I never had this problem before with my builds, I tried putting a resistor in series with input but that didn’t help. I will play around with it, but if you have any advice, that would be great. Cheers bro.

  19. Uuuuuuuuh !!!!! Niiiice!!! I thank you infinitely, Harald. Thank you very much indeed.

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