So I just pulled my old DEM out of the crate of currently unused effects. I tweaked a couple of the trimpots (bias & clock) by ear, which had been messed with, replaced the 4558 input opamp with a TL072, true-bypassed it, and replaced the DPDT with a 3PDT for no reason other than my congenital inability to solder to an X-wing Carling without destroying it. I plugged her in and fell in love all over again (don't tell my wife). So I gets to thinking--would you mind thinking with me? Here's a schematic linky. There's plenty of room for a small daughter-board on the side of the main board, and for extra pots along the top. An easy mod is bringing the mix control out to the panel. But here are some other thoughts, half-gestated.
1) One reason I haven't been using her has been the annoyance of the AC power, especially now that I have moved from the US to 220V-land. However, just now I realized that all the power it really needs is enough to drive the 12VDC regulator, and in fact the export models took a 24VAC wallwart--which could have been as little as 14VDC. So, priority no. 1 is getting rid of the transformer and making this work with my pedalboard. Currently, I'm running everything off a 1-Spot, and I'd rather not have a separate wallwart for one pedal if it can be avoided. However, a quick search tells me that folks have not been too successful trying to feed these with a charge pump due to heterodyning issues. Would massive filtering help with this? Hey, I'm ditching a power transformer, I ought to be able to squeeze a couple of electrolytics and a choke in, if it would help, and there are volts to spare. Has anybody successfully pulled this off, or have a recipe for doing so?
2) If I feed this puppy 18VDC (through the connection in the Euro/Japanese version of the schematic, i.e. J4), can I just ignore the rectifier diodes, or do I have to take them out?
3) Among the other wonders of this thing are the lovely vibe/near-rotating speaker effect it can produce. So I think a LERA or similar would be grand, but the LERA as drafted by RG has two connecting points and replaces a 25k-250k pot, whereas the rate pot on the DEM is 10k, and connects to the circuit (not ground) at three points. Is there a way to hook a LERA into a DEM? And, is there a very low profile DPDT anyone can point me to that will fit between the pcb and the casing?
4) I also think that the rotating speaker effect would be enhanced by a light trem in sync with the flanger. What do you think about tapping the LFO at E10 (the filter matrix switch) and using it to control a switchable simple dual opamp plus optocoupler affair at the output?
Enough for now. TIA,