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Classic Tube Revealed!! (initial report)

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2/28/2000 4:59 PM

Matthew Springer

Classic Tube Revealed!! (initial report)

There was a thread posted around here a while ago looking for schematics to the DOD FX53 Classic Tube (an absolutely killer cheap OD with huge bass). Seeing as how nobody had one, I have sacrificed one of mine in the name of the science (and good tone).

I don't have the full schemtaic yet, but it looks like the pedal has three (yes, 3) different OD modes. The business part of the pedal looks like a non-inverting op amp with two zener looking diodes in the feedback loop with half a 500k pot for gain control. There's also a cap in parallel with the diode arrangement. So far we have a Tube screamer.

There is also a back to back diode arrangement on the output to clip the output signal ala the blue clipper (I think). Then that whole mess goes through a transistor set up with a diode as the collector load.

That's about as far a I got. There's also some sort of CMOS inverter chip on the board I haven't figure out yet, but I it looks like this does clipping when then gain is set really, really high. So the pedal basically has two signal paths and one only kicks in at high gains. (which is what it sounds like)

More later as I poke aroun da little more.

2/28/2000 7:38 PM

That high gain would account for the boost effect indicated on the front (and as you said certainly audible) I sold mine a few years back because it was just too bass-heavy, This was before I knew how to mod pedals. I do remember a very smooth, touch sensitive and compressed tone for such an inexpensive pedal. But never able to get as much mid and high out of it as I would have liked. Keep us posted, I might try hunting one down and attacking it with my iron.

2/29/2000 1:32 AM

Matthew Springer

I actually really like the bass heavy sound, so I want to build another one with real bypass, better caps, et al.

An alert reader of Ampage was kind enough to send a partial schematic of the FX-52 which is pretty close as far as I can tell. I'll keep everybody posted when I have the thing mostly figured out. It looks like the inverters don't switch in until the last 9/10ths of the gain knob (if that's what's actually going on). I still have to find a multimeter and decode the capacitor code.

2/29/2000 2:18 AM
Cole	FYI, in most DOD pedals, a CMOS inverter (4007 type) is used for the on/off switching.

2/29/2000 7:32 AM
Jim Radmer	Re: Classic Tube layout I've got the FX 52 parts layout and values. The FX 53 and FX 52 are made on the same board with different part values.

2/29/2000 7:29 AM

Re: Classic Tube Revealed!! (initial report)

I am the one with a DOD FX53. I have tried a few cap changes with very little luck. It is too dark for my use (into a Blues deVille) but it has a basically good sound i think. I bought it after sound testing it against a TS-9.

It has a very funny gain setup, where the last 10% og the gain pot increases the gain to a totally wild scream with a large volume boost.

If you find a way to get more highs I would like to know. I think it's worth a mod. It could get very useful.

2/29/2000 7:28 PM
Stuart	Yeah, sorry Jim, I never did get back to you with the full schematic... I think I've been beaten to it now.

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