Adding reverb to a Rodgers 840

[John Vanderlee]

Last year an organist acquired this 840. He installed it in his basement as a "classical practice organ" Coincidentally he has a 24 rank Wurlitzer pipe organ in his house, but finds it impractical for serious church work. We should all have such problems!
He finds the 840 to be dry. So thought about adding reverb. It has an unused audio input on the console as part of the MIDI system.
I thought about picking off all the organ audio channels from the preamp board sending them to an audio mixer, and from there to a reverb unit whose output could go into the unused MIDI Audio input? Any thoughts on this?
Thanks in advance!

[toodles]

First, check to see if there is a reverb control on the organ--it would be mounted on the bottom of the keydesk. The organ is supposed to have a spring reverb (optionally a digital reverb), and that's where the volume control for the reverb is mounted. It may just be turned all the way down,.

If the spring reverb is not to his liking (which would not be surprising):
The 840's preamp board includes a bus to sum all the audio channels to drive a reverb system--that's the place to pick up a drive signal. You can always find the cable with the input to the reverb tank (spring reverb) and unplug it from the spring and use it to drive a digital reverb.

Any digital reverb must be set to 100% "wet" (i.e., just the reverberated sound in the output).

You can try mixing the output of the digital reverb back into the original channels using the spring reverb return cable, but the output might distort or be out of tonal balance, as the Rodgers spring reverb recovery preamp has some filtering incorporated. If you want to mix the reverb signal into the main channels, it would be better to feed it back in where the output of the reverb level pot drives back into the preamp--that bypasses the recovery preamp which is not needed.

I'd avoid the MIDI audio input--it might feed back into the reverb mixing bus, resulting in feedback and distortion. The MIDI audio input isn't documented in the 840 technical drawings, so I am not sure of how it feeds into the audio system.

[John Vanderlee]

This organ never came with a reverb tank.Neither does it have any of the controls.

[toodles]

The drive signal and recovery preamp are probably on the output preamp board, even if the tank and control are missing.

Do you or your friend have the 840 technical drawings? The reverb connections are shown on page 11 of 11, right hand side. The reverb drive signal may well be an RCA jack as shown on the drawing. The output from your digital reverb should feed into the connections shown to the left of the reverb level pot--"To RG14 Sheet 7 of 11, location H-4" and "To R861, Sheet 8 of 11, location C-1". This bypasses the recovery preamp (which is not needed with a digital reverb), and avoids the compensating frequency response to match the spring reverb.

Send me a PM with your email address and I can forward the tech drawings if you don't have them.

[John Vanderlee]

Yes toodles I'll PM you. But for the record, that particular organ had the cutout in the circuit board for the RCA jack, but the jack was never installed, neither is any of the circuitry around it related to a reverb.

[toodles]

The drive circuit might be there even if there is no RCA jack on the preamp board; you might check on the output panel--as there was an option to include Reverb sockets there (as well as on the preamp board). I've sent the tech drawings, and you can follow (on the output preamp) the summing into the drive circuit.

You can always populate the components needed for the drive circuit if it is truly missing--it's just a few resistors, capacitors, and one of the single-inline op amps (as used in the rest of the preamp).

[toodles]

An alternative to using the reverb drive signal is to tap off the headphone jack signal.

[John Vanderlee]

great thought. the schematics also show where to re-insert. Thanks