DOD 680 repair idea

[CheapPedalCollector]

I just realized something with the FX90 and FX96.

The MN3005 usually runs on negative voltage supply, it's cleverly hooking VDD to ground and the chip ground to +v since the supply is single ended with slightly isolated power node.

I wonder if I can fix my 680 using an MN3005 instead of a more complicated daughter board with MN3205 and a regulator using this trick, I guess the only issue would be the clock 4013 clock driver?

Thoughts?

[Rob Strand]

The power supply flip is common you just need to use a big bypass cap. 

There a few details worth looking into:
- The VGG supply, which can be generated with a series diode.
- The DC biasing of the BBD.  If the BBD input DC coupled, it may or may not work as is.
  If all else fails AC couple and add your own bias.

The easiest way forward is to find a pedal with an MN3005.   Try the Pearl stuff, or maybe Electroharmonix.
I have a feeling you will find a version which also uses a 4013.   The  Electroharmonix stuff tends
to use the stronger 4047 drivers.

[CheapPedalCollector]

So going by the DOD R870 Flanger Doubler schematic, looks like they did exactly that. So it should be a relatively simple retrofit with a few part changes and an adapter socket. It would be much simpler and easier to do than the MN3205 solution.



The only issues I'm having is finding a 680 Analog Delay schematic that isn't tiny and is readable. I suppose I'll just have to trace my unit as it doesn't use the NE570 compander chip.