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  1. Can’t find the schematic, all known links seem to be dead

  2. No suggestions, sorry. It has been so many years since I last had a look at this circuit.

  3. I tried searching the net, but couldn’t find the schematic I based this on. It’s not my schematic, so I’m not going to post it, but I can send it to you by email if you want.

  4. I found this :

    http://www.diystompboxes.com/smfforum/index.php?topic=74393.0

    I’ve got similar values on all Q, my source is 13V, except Q1 can’t go below 7V (end of trimmer)I’ve tried ad extra resistor so I can get even 3V ( increased gain but lack of adjustment) and Q4 G=-0.55

    Do you have any suggestions ?

    Thanks

  5. Hi

    I made one, the tone is thin, lack of gain and punch, weak…
    Do you have schematic for it?

  6. I guess you could do this, but the general consensus is that these particular JFETs (J201, 2N5457 etc.) sound particularly “tube-ish” compared to other semi-conductors. The other issue, you might have already realized, is that the entire layout would have to be radically redesigned to fit much larger opamps.

  7. Until now, it does make sense. But I have one more question. In terms of electronics, is it possible to swap those JFETs with JFET opamps? I didn´t worked with the draining voltage of JFETs yet and it quite scaries me, so an opamp solution with a simple biasing would be great.

  8. I agree you should keep to effect pedals, at least to begin with. Once you become familiar you can always come back to your idea 🙂

    On the question of biasing the JFETs, yes and no. Although each JFET might be set up with approx. the same drain voltage, because of the great variance between individual JFETs, the resistance needed to get there can be quite different. That’s why you have the trimmers; one JFET might require say 22k while the next one needs 49k.
    If you don’t want to use trimmers you can hook up a temporary potentiometer for each stage, find out what resistance that particular JFET needs, and add the correct resistor in place of that trimmer. The down side to this is you need to keep track of JFETs and you can’t swap them later. Did that make any sense?

  9. I just gave up from the idea of the combo. It is just to hard to design and buildin my electronics knowledge level, for now. It would have been a) a transistor amp. Supposedly it would have some preamps you have here, a 10w power amp, stereo speakers, and some cool other features, like fx loop, line in, and so on. I really enjoyed the idea, I am sure I will get back to it in a couple of years. I will keep it simple, building the preamps as stompboxes, as it is supposed to be.

    But I have one more question. I have read that the voltage at the transistors’ drain lug is very similar (4.59, 4.58, 4.64). For these examples, a simple voltage divider rated at 4.6V (http://www.generalguitargadgets.com/wp-content/uploads/ric_bias2.gif for example) could made any difference in the tone rather than adjusting each Grimm pot one by one?

  10. In theory you could do that, but I don’t see the point. If you’re building an amp and want to incorporate this circuit I assume you:
    a) are building a solid state amp using transistors. Rather than tag this in front, redesign it so it replaces the clean preamp stage.
    b) are building a tube amp. You should definitely go to the source and build the tube preamp that this little circuit is attempting to sound like (the Mesa Boogie MkIIc+).

    If you are building a DIY combo amp with a clean preamp, I suggest you build this circuit as a stand-alone effect pedal that you can place in front of your (or anyone else’s) amp. That’s the whole point of effect pedals, ease and flexibility.

  11. Thanks for the answers.

    But, lets imagine. If I wanted to make a DIY combo amp with this preamp I need to wire it before a clean preamp, and then to the power amp?

  12. Hi Miguel,
    1) Like most guitar effects of this kind, you use it between your guitar output and your amplifier input.
    2) Those trimmers are there to allow for JFET bias adjustment. Check out the “FAQ” section for some info on this.
    3) Feel free to ignore this comment. It means that it is unknown whether each potentiometer should be a linear or logarithmic type.

  13. Thanks for sharing, once I get the parts I will assemble one for myself, but I have some questions:

    1- To where should I connect the output? (mixing desk, amp input, power amp…)
    2- what are those 4 trimmer pots for?
    3- Didn´t understand the mmeaning of the sentence “Pot tappers are only guesses” in the schematic.

  14. Thanks for sharing, Tim! I liked both, but maybe the boogeyman a little bit better. And nice playing 🙂

  15. Forgot to post the comparison vid!

    http://youtu.be/VYu0mfmOYII

  16. I’m dying to hear a demo of it vs a real Mark!

  17. Thanks for sharing, Tim! I’d love to hear a demo, too 🙂

  18. Finished building this pedal today and compared it to my dr. Boogie. Here are my thoughts:

    Dr boogie is scooped and very saturated, like a recto.

    Boogeyman is more middy with less overall gain like a mark series amp (this pedal is still high gain… Don’t kid yourself). I find that it’s easy to get the bass sounding flubby if you have the bass too high and the treble too low (kind of like my mark v amp).The volume/lead volume acts like a level and master volume control.

    I’ll try to get a demo of this vs the mark ii c+ mode on my mark v and see how they compare.

    As a side note, I used smd j201 transistors from mouser and a smd yo through hole adapter from oshpark. The Smd transistors are a lot more consistent, but damn they are small… Soldering them onto the adapter pcb is a test in steady hands…..

  19. I am expecting the parts for this tomorrow. Hopefully I’ll have it built up and a demo of it soon.

  20. I would love to hear a clip of this build! The Mark II got such a great distortion sound.

  21. Nice Ed! I’d like to hear. Not sure where you can post it though, maybe soundcloud or youtube?

  22. I built a 5 stage (thinking of a 6 stage that incorporates the effects loop and master volume with Deep switch, possibly a channel switching model with a charge pump for higher voltages), and I want to post the clip for you somewhere access-able. It sounds a lot like my real Mesa Mark IVB with IIC+ mods!

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