Transistor DOD 250?

[boy howdy]

Hi,

I have an old 70s yellow 250 which I've changed the input cap to a .01 and removed the cap that smooths out the clipping diodes (for maximum treble). I use it as a booster - the gain up about 1/4 and the volume up about 3/4. I love the tone of it. But its distortion is awful. I once removed the diodes to use it just as a clean boost and discovered that the IC actually clips fairly early, and sounds horrible when it does.

I was wondering - in my infinite ignorance - if it would be possible to use a transistor instead. They are said to distort in a more musical manner (don't know, I don't have any boxes that don't use ICs). I imagine that an entirely new pedal would result which is not really what I'm after. Like I said, I really love the *tone* of the 250 as it is.

Is there a way to make this work? I'm getting ready to build a 250 with a few mods (like switchable input caps, for instance).

[Kipper4]

Are you sure they didn't mean use a transistor in the place of the clipping diode?
Welcome to the forum.

[nocentelli]

http://www.diystompboxes.com/smfforum/index.php?topic=103671.0

The "transistor gain stage" DOD 250 has been done before: Note though that the intention behind this design seems to have been to simplify the design somewhat, not to improve the clipping sound of the gain stage alone - Joe has left the diodes in place, and the clipping they impart upon the boosted signal will likely mask the clipping deliverd within the earlier gain stage itself.

I made a stock-ish MXR D+ years ago (similar to the DOD: Mine was made with Si, not Ge diodes), and it was ok - A roughly overdriven sound at mid gain, increasing to a fuzz-type sound as the gain is wound up.

If you're not too keen on the sound beause it's not a very convincing amp-like overdrive, I'd look eleswhere for a different circuit to fulfil that function: Replacing the opamp with a transistor stage and also removing the diodes are unlikely to help much. I haven't come across many low gain convincing "overdrive" circuits using BJTs (please chip in with links if i've overlloked something obvious) - JFETs and mosfets, on the other hand, can do a decent low gain amp sound, see runoff groove and catalinbread's many amp-in-a-box offering for examples. Also, opamps with clipping diodes in the feedback loop tend to be more subtle and less fuzzy, more "amp-like" - e.g. Paul Cochrane's Timmy is amazing for what you might call a "transparent" overdrive, if such a thing can exist.

[boy howdy]

Yeah, I have the Dano version of the Timmy and it works really well - its distortion is certainly a LOT nicer (though again, I use that as a booster as well) - but really for me the DOD kicks it's butt. It's just that huge, fat, bright tone that does it for me. I am planning to try some diodes in the feedback loop (ala Timmy) as well, when I get to building one. But really I use just a touch of clipping anyway, so it's not likely to have much affect.

There are just times when I'd like to turn the distortion up without that ugly IC distortion. Oh well, you can't have everything.

I'll check out the other thread.

[bool]

Just try to stick a couple of LEDs in the nfb loop.

LEDs and a 741 like each other imho.