ElectroTone OrganMate spring reverb - mod suggestions?

fyzygy

Member
2010-07-11 12:51 pm
This thing is designed to be connected *in series* with tube organs, requiring an input signal of between 0.4 and 2.0 volts at the organ's softest stop/setting. It works okay with line levels too, although the reverb effect is subtle and the signal-to-noise ratio appalling (lots of high-frequency hash that can be decimated with a shunt capacitor at output - but that's far from an ideal solution). I am happy to run this thing exclusively tube, at higher signal voltages, but would like to make it more compatible with modern equipment (specifically, to use it as a channel insert or ideally, send/return on a mixing desk).

Please refer attached schematic when considering the following:

1. Would replacing the 12AU7 driver stage with a 12AX7 help drive the springs harder with a more modest input signal?

2. Is there a straightforward way to have this circuit wired fully "wet" - to use with send/return? I don't quite understand the trimmer pot's function - I don't think it's a wet/dry mix as I first assumed. Would simply breaking the "bypass" leg of the circuit at input jack do the trick?

3. I considered replacing the coupling caps (ceramic throughout signal path) with audio types; any suggestions on this? I figured that spring reverb is desired for coloration rather than transparency, so have left the ceramics intact, at least for now.

4. Any other tweaks advisable?

Any ideas, insights or suggestions would be very much appreciated!
 

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1. Would replacing the 12AU7 driver stage with a 12AX7 help drive the springs harder with a more modest input signal?

No. A 12AX7 triode won't be powerful enough as a reverberation tank driver. But you could consider a 12DW7/7247/ECC832 tube, which is half a 12AX7 and half a 12AU7 in one envelope, with the 12AU7 half driving the tank.

2. Is there a straightforward way to have this circuit wired fully "wet" - to use with send/return? I don't quite understand the trimmer pot's function - I don't think it's a wet/dry mix as I first assumed. Would simply breaking the "bypass" leg of the circuit at input jack do the trick?

This circuitry indeed is mentioned as an insert into a Send/Return FX loop. Just connect Send to Input an return to Output. The pot named R20 sets the amplification factor of the regeneration amplifier.[/qoute]

3. I considered replacing the coupling caps (ceramic throughout signal path) with audio types; any suggestions on this? I figured that spring reverb is desired for coloration rather than transparency, so have left the ceramics intact, at least for now.

You'd better leave all capacitors in their original state. Remember, it's just an FX device with no high end ambitions.

4. Any other tweaks advisable?

Sorry, no clues. But you could google for Fisher Space Expander, a similar, but more sophisticated design.

Btw, wrong branch within this board?!?

Best regards!