Question on connecting Reverb Mix card to Allen 603DK

[Organ John]

Thanks for letting me join the group. (I am a dangerous do it yourselfer.)

The Allen Organ Tech installed an Allen Reverb Mix Board to the amp rack, but the wiring was never completed. My plan is to take the Reverb Mix Board output as an input to a Digital Multi-Effects Processor (Behringer VIRTUALIZER PRO DSP1024P). The output will be connected to two S100 amps and then four small speaker cabinets located in the front and back of the Church building. The organ already has four HC14 speakers in the front and two HC12 antiphonal speakers in the back along with a B40 subwoofer. These seven speakers will be kept “dry” while the reverb will come from the four smaller speakers.

Questions:
• What do I connect to the Allen Reverb Mix Board input connections? Do I tap into the five coaxial cables which are inputs the amplifiers from the organ console or the five speaker outputs from the five amps?
• What power is required (board is labeled -15 G +15)? AC or DC?

Thanks in advance,

John V

[jbird604]

It depends on what model Allen you are dealing with. The power supply required for the reverb mixer board is the Allen 15 volts supply that provides both +15 and -15 volts. The G must be for "ground" which is the power supply common. In most applications, the incoming signals from the organ go to one set of RCA jacks and come out the other side of the board, but you'd need a wiring diagram to see which jack feeds which output. It is not just straight across the board.

However, it might be better for the purposes you indicate to take a simple tap off each amplifier's + speaker terminal and combine all the channels before running into the reverb unit. I have done this in numerous installations. The Allen Reverb Mixer board is only necessary when you want to have both wet and dry signal in the organ's primary speakers. What you propose to do is a much better plan any way.

So, if you want to do it, come off the + terminal of each amplifier with a 10K resistor. (You must obviously solder extensions to the resistors first because the amps won't be close enough together to reach unless you happen to have a one-piece ADC amplifier unit.) Tie the ends together and solder to the inside conductor of a shielded audio cable. At the same solder joint, connect a 1k resistor and connect the other end of that resistor to the shield of your audio cable. Also connect the shield of your audio cable to a ground point such as the "C" or common terminal of one of the amplifiers. This will give you a good line-level mixed signal to feed to the reverb processor and from thence to the amps and speakers you are using for the wet sound.

If you get hum, you can try connecting the ground to the actual chassis of the amplifier instead of the common terminal of the speaker output. Sometimes the common terminal of an Allen amp is not actually ground but floats above it via a small capacitor.

Good luck!

[Organ John]

Hello John,

Thanks for the reply and the information. This is very helpful.

For powering the Reverb Mix board, I recall the Allen Organ Tech suggested I run a pair of wires from the console to the amp rack and that would provide the 15 volt power. This is consistent with your comment.

I tried to keep my original question simple and brief, but I in the process I left out some details and possibly put you at a disadvantage. The Allen Organ REVERB MIX Board PN 904-5600-3 has three sets of screw terminals labeled LEFT, three more labeled RIGHT and a single RCA female connector labeled LINE OUT (see attachment). I believe the original intent was either to use the audio signal from the organ console (using a Y splitter) or the speaker outputs from the amplifiers and connect them to the REVERB MIX board. Then from there split the output into two S100 amps and then the four speaker cabinet.

BTW, my Allen MDS 45 has the ADR-4 mixer board that you mentioned and provides the wet and dry signal using same speakers.

Not sure if it would help, but I attached a picture of the REVERB MIX board. I can get a better picture if needed.

Thank you Sir,

John V
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Church: Allen 603DK
Home: Allen MDS45

[jbird604]

Hmmm.... I've never seen that board before, but I'd guess it takes speaker-level input and all those resistors serve to provide some kind of mixed-down stereo line-level output. And it looks like it needs the +15 and -15 from the console cage. Honestly, I wouldn't fool with it. The simple homemade resistor network I described works perfectly and requires no power.

Let me know how it turns out.

[Organ John]

Hello John,

Thanks for your note. I will give this a try (the KISS version) and by-pass the Reverb Mix board. Off to get the materials, find out how to lay down speaker wire in the Church building, etc. And yes, I will let you know how it turns out.

John V
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Church: Allen 603DK
Home: Allen MDS45

[Organ John]

Hello John,

I have the materials now (wire, resistors, cables, speakers, amps, etc.) and will start installing the reverb system at the Church today.

Since I am using two S100 Allen Organ Amps to drive four speaker cabinets, I will need to connect two speakers to one amp. The speakers are 8 ohm impedance but I cannot find the output impedance of the S100 amps. So I am not sure if I should connect the two speakers in series (adding the speaker impedance to 16 ohms) or in parallel (halving the speaker impedance to 4 ohms).

(BTW, I tested the reverb wiring on my MDS45 at home from one amp running the signal through the Behringer to a S100 amp and then the speaker - it works great!)

Thanks in advance for your help.

John V
--------
Church: Allen 603DK
Home: Allen MDS45

[jbird604]

An S-100 amp can safely drive a 4 ohm load. Just connect the speakers in parallel and you will be fine as long as the amps aren't driven into clipping (which would be at incredibly loud levels).

Good luck and let us know how it works out.

[Organ John]

Hello John,

Thanks for your note and reply. Parallel it is!

We installed about 300 feet of 16 gauge speaker wire and performed a quick test on one amp with the reverb and it worked. We did notice the hum you mentioned when connecting to the C or common terminal of the amp. It was much better but not entirely gone when we changed the chassis of the amp. Not sure if this is important, but dry portion of the amp rack has an S100 amp to drive the Allen subwoofer and two Dual AM-100 amps for the balance of the four HC 14 speaker cabinets.

We hope to finish this Saturday and will let you know the results.

Thanks again.

John V
--------
Church: Allen 603DK
Home: Allen MDS45

[jbird604]

Be sure you are using shielded cable for the audio at all points past the resistors. And you may have to connect everything in the system including the organ itself to a common ground to get rid of all the hum. Try lifting the ground at the amp rack by using a 3-prong to 2-prong adapter on the AC line. Hum is unusual in an Allen, so there must be a cause. The subwoofer crossover, if its the little metal box type they used with MOS organs, is very sensitive to hum pickup if it is placed anywhere near an amplifier or even an AC power cord.