Rodgers 135M Channel questions

[John Vanderlee]

We dug this 135M with 2 ranks of pipes out this week because some one is looking for a Rodgers with pipes. But the question has to do with the analog Audio. It's been so long since we've had it, I've been trying to recall how it was hooked up. I do think it was set up with only 2 speakers and a dual amplifier. But looking at the output jacks it seems to indicate 4 channels. I looked at the preamp board and it only has one switch, I 'm not quite sure what it does. I have some minimal schematics from another model but they show at least 3 switches for combining channels. I want to offer this unit to this person but not quite sure what to tell him about the sound hookup. I don't think he wants more than a 2 channel system. Although I have more Rodgers amps if he really needs them. I have one M3 type Rodgers "panel" but I'd also supply Allen HC12 or HC15 if he wants all that.
My question is I am not quite sure how to explain his options to him as I have no real reference.
Pictures of Preamp and connectors:

[toodles]

Rodgers typically used the Pedal channel as a "sub-bass" channel, and not a true channel to carry a dedicated pedal system, thus the other channels also carried the bass. If they followed this tradition in the 135, then the audio and mixed channels could carry the organ with just 2 speakers, as long as the speakers were capable of response down to 32 Hz. I'd try using Allen HC-15's on those 2 channels and see if it performs satisfactorily.

Unfortunately, I don't have a 135 technical manual, so I'm making this suggestion based on typical Rodgers approach to audio rather than on specific knowledge of the 135's audio system.

[John Vanderlee]

Thanks toodles, that's more than I know! So which two outputs should I use?

[jbird604]

Looks like they made provision for four separate channels. According to the manual, the mixing switch blends the pedal stops into the diapason channel. In that case, you'd certainly need a hefty speaker on that channel, capable of handling both manual and pedal frequencies. For best results, and if the customer is willing to pay, I'd suggest using the full four-channel setup. Anything else will involve some compromises.

BTW, what are those twisted together wires in that socketed plug? Maybe someone in the past did some "channel mixing" already?

[toodles]

The socketed plug on the output preamp board is for a "practice panel" which would provide reverb along with tape in & out connections.

[John Vanderlee]

Interesting, so technically you could connect 2 amp-speaker channels to the tape output if you did not have the 5 pin plugs available for the 2 channel set up?

[toodles]

It appears that this organ does not have the practice panel installed because it would plug into the large plug on the preamp board, and there isn't a cable connected there. If it were in place, it might be possible, but I would instead, suggest a better solution by adding RCA output jacks connected in parallel to the signal wires on the back of the output panel. It is easy enough to do,

The tape in/out signals are switched (to avoid having both working at once) since feedback could result, and why have that to mess with to ensure speaker audio works?

[John Vanderlee]

You've got a point there. I was thinking of some way to insure that I get a 2 channel signal - which is what the person wants. I guess I could check the 5pin out jacks to see if all divisions are there, out of two jacks.
As an aside, I found a preamp schematic in a "dealer Service manual"(thank you *Bay) that has a few schematics - mostly about updates - that seems to be a generic one like 100 series. I think it might be close to what I have. I could post a copy for the benefit of all.

[jbird604]

To make it simple, just solder an ordinary shielded audio cable to each 5-pin jack. Pin 1 is the ground, pin 5 is the audio signal. Connect the cable shield to pin 1 and the internal conductor to pin 5. Now you have a usable output cable for each of the four channels.

Then you can test each of the four channels to ascertain what they carry. It will probably be as marked. The unit flute will come out the "flute" channel." The 16' pedal stops will come out the "pedal" channel (other pedal stops are just borrowed from the manuals and will come out the appropriate manual channels). The unit diapason will come out the "diapason" channel, and the reeds and the celeste will come out on the "reed/celeste" channel. That channel may also carry the "non-unit" stops on the swell manual, and possibly the harp and carillon.

That pretty much covers it. The Gemshorn (if present on the great manual) is actually just the Principal keyed softly, so it will come out the diapason channel.

The organ should sound quite good if you then connect each of these four channels to a good quality amp and speaker, such as an Allen HC cabinet. Any modern amp will do. I recently bought a little Class D stereo amplifier that claimed it could deliver 160 watts RMS per channel, and used it to replace a failed Rodgers S-100 amp. This little unit cost me all of $50 on Amazon, including a hefty switching power supply. Two of those would serve your needs for this organ quite well. Then you just need four good speaker boxes.

Try flipping the mixing switch. It will blend the pedal 16' stops into the diapason channel, reducing your channel count to three instead of four. If you absolutely must mix down to just two channels, which seems unwise, given the very well planned separation of the stops into these channels, you can of course wire the flute and the reed/celeste outputs together. I wouldn't just twist the two wires together, as that might cause some unwanted interactions in the final pre-amp stages. But you could pass each one through a 4.7K resistor then tie the resistors together at the open ends. That would give you a combined signal suitable to go directly into an amplifier and speaker.