A quick follow about that pedal. Seems like that the CMOS switchings are off although the NAND works good . The output coresponds to the thruth table of the 2 input NAND gate.
Facing the lack of imformations and the zero interest of Dunlop in my request I almost thought that replacing the CMOS chips will save serious time. But that’s not really the proper way of doing it, is it ? it’s what we could call the “guitar shop repair” , replace components until it goes back to work. Quite ridicoulus and expensive.
In such situation you realised that a schematic can save your evenings. I doubt that a repair shop will do it without the schematic. Seriously, what’s the point of hiding that bloody schematic ? No one cared about this when released so why people would bother copying such complex circuit ? (if copying is the matter) that pedal was obviously a commercial dead end so for fuck sake why!!!!
Anyway, in the sake of sharing and helping people who could encounter the same issue, here’s what I’ve came with so far. Fuck Dunlop ! (ho that’s not polite !) And if you don’t know reverse engineering is a MASSIVE pain in the ass !
The 4011 is used to control all the JFET switching (tremolo, volume, bypass). It works as a NAND gate would work (see its truth table). Clever idea although maybe a bit too complex for a simple tremolo pedal. All audio signals are mixed at the end and switched on/off by the CD4011 depending on the logical operation of the inputs. They are all dependent of each others, brain twisted ! Only one at the time. Obviously no “tru bypass” but who cares ? (so sick of that marketing “boobtweak” wank).
The CD4066 switches the control voltages into some “conditioning” circuits and into the VCA’s. I may think that the CD4066 is dead, the B switch isn’t working properly and seems to load down the control voltage when switched for the tremolo part. Maybe a hint !
The Quad-op amp (TL064) is certainly the LFO. Funny enough, I can’t manage the find the traditional integrator cap unless the topology used is different (a square wave oscillator waveshaped into triangle ?). IC4 and POT1 (depth control of the tremolo side) is the end of the LFO part, the wipper of the pot goes into the VC control of the VCA.
I had a look into their newest version of it, the new one, the stereo thingie (already discontinued by the way). A nice guy sent me gut pictures of it (I won’t publish them, they’re not mine) and it seems that the general topology is the same. Although the M5207L01 is not into it, they replaced it with a Quad VCA from analog devices (SSM2164) for the stereo option, that ICs as any other AD devices, is expensive. It’s also interesting to see that they used some unsual parts for a guitar effect (MC33179, 33178 op amps). Op-amps that you don’t usually see in such electronic. Nice!
This Makes me wonder, are (were) there two divisions at Dunlop ? one dealing with the usual guitar crap (signature models, clones and vintage stuff) and the second dealing with new circuits. Or maybe they commisioned a freelancer of some sort because the electronic is those two are so different and so far way for their usual clones/vintage stuff.
Anyway, long post for something that I wanted short. Hope this could help. I’ll complete the schematic later but the audio path is good.