Allen amp S-100 input

[CWalchesky]

Hi, first time thread start here.

I'm helping a church move a MOS-2 to a different location. The amps and speakers are in distant chambers and the coaxial cables from the console are not salvageable b/c of the conduit situation. I'm going to need new cables from the console to the amp rack. I planned to use commercial coax upon reinstall but I've since heard about the Allen Jerrold "C-type" ends. Can anyone tell me (based upon the attached photo) which size input these amps use? I don't remember thinking that they seemed smaller than the coax on the back of my cable modem.

FYI I'm several hundred miles away from the organ and why I need the assistance.

Many thanks.

Update: when I removed the threaded part it came off with a 7/16 wrench, not sure if that would tell me?

[jbird604]

I'm pretty sure those are the same as the connectors commonly used for cable TV connections these days. Allen previously used a "mini-Jerrold" connector on remote amps, but switched over to the more common type sometime in the late 70's.

[CWalchesky]

Many thanks, John!

[myorgan]

I'm pretty sure those are the same as the connectors commonly used for cable TV connections these days. Allen previously used a "mini-Jerrold" connector on remote amps, but switched over to the more common type sometime in the late 70's.

John,

That said, can this MOS-2 instrument use those connectors, or will it require coax replacements?

Michael

P.S. What is the length restriction on the length of coax connections from amplifiers to speakers?

[Larrytow]

I'm pretty sure that coax connector style is called type F . And yes, that is what cable TV systems normally use. You could likely use RG58 cable for the new ones. A good hardware store or big box home improvement store should have the cable, connectors, and crimping tool if you don't have one. It looks like there is an RCA connector going to an input also ?

The coax is normally used only from the console to the amps, not the amps to the speakers. That should be conventional speaker wire.

[jbird604]

Yes. All MOS-2 organs were built after the changeover from the mini-Jerrold, so all MOS-2 models will use the type "F" Jerrold screw-on connector at the remote amp rack. (Self-contained organs of course do not have external amp racks, and all the signal cables are ordinary RCA plug/jack.) Regular speaker cable is used from the amps to the speakers, as in all Allen organs.

I suppose there could be some sort of degradation of the signal if the coax were to run for hundreds of feet, but it's unlikely to be noticeable in any kind of common organ setup. RG type coax is designed to handle the very high frequency signals employed in TV (hundreds of megahertz, thousands of times higher than any organ audio frequencies), so it should be a cakewalk for the cable to carry ordinary organ audio for great distances. That is why Allen used coax to put the amps closer to the speakers in their larger models, because there is a lot more danger of signal loss and degradation in long speaker lines than in long coax lines.

[michaelhoddy]

Also should be noted that there are different types of F connectors depending on the cable used. The screw-on mating side is consistent, but the crimp side is different. The major types are RG58/59 and RG6, which is thicker. Every Allen I've seen uses the RG58/59 type. 50-ohm RG58 is somewhat less common than 75-ohm RG59, which is standard shorter-run CATV cable that you can get at your local hardware store, although the F connectors are the same.

I believe Allen installations use RG58. How much the different impedance and UHF handling characteristics of RG59 would make any noticeable difference at audio signal frequencies over the comparatively short distance of an organ installation, I'm not certain.

[CWalchesky]

All of your technical information thus far has been very helpful. Amp inputs are F coax.

I've just hooked up the organ and all is fine EXCEPT stops playing almost inaudible on the Flute & Main Gt/Ch channels. Ive tried using different amps and speakers and no matter what the sound is near silent. Gain hasn't been touched. Thinking it could be something in the console? Tried a different coax out as well to no avail.

Organ is 1405 MOS2

[myorgan]

I've just hooked up the organ and all is fine EXCEPT stops playing almost inaudible on the Flute & Main Gt/Ch channels. Ive tried using different amps and speakers and no matter what the sound is near silent. Gain hasn't been touched. Thinking it could be something in the console? Tried a different coax out as well to no avail.

CWalchesky,

It sounds like you've done everything one would do to troubleshoot. However, I can think of a couple of other possibilities. The gain pot may have developed a dead spot. That will become apparent if you exercise the gain by sweeping it through it's range. Another possibility would be to go from the DAC-3 or DAC-4 card, and switch the RCA inputs between the cards, or between halves of each card to see if the issue switches channels.

Hope this helps.

Michael

[CWalchesky]

Thanks, Michael
Update: moved the output from DAC (both) thru ones I know do work and still an almost inaudible sound. Could the DAC be bad? Not sure where to turn

[CWalchesky]

Update: I swapped the DAC boards on the GT/CH side and still silent. The MOS board coulnt be bad since the other GT/CH is working, right?

[jbird604]

A 1405 would have those impedance-matching/level-boosting boards following the DAC outputs and ahead of the coax outputs. Not sure where they are mounted on that model, but on the 1105 we service, they are on the inside of the kneeboard, above the expression/crescendo area. Follow the audio cables from each DAC output and you will see that they lead to these little boards before the audio goes out to the amps. It is on these boards that expression is applied in the large MOS-2 organs.

I can't recall the name or part number of that board off-hand, but you will know them when you see them. There is one per MOS system. The missing audio is probably due to one of those boards being defective or possibly just disconnected from the power source. If you look at them you should be able to spot the trouble, if it's just a loose connector.

[myorgan]

I can't recall the name or part number of that board off-hand, but you will know them when you see them. There is one per MOS system. The missing audio is probably due to one of those boards being defective or possibly just disconnected from the power source. If you look at them you should be able to spot the trouble, if it's just a loose connector.

John,

Would it be in this thread? https://www.organforum.com/forums/showthread.php?34268 Maybe my organ is too small to have those boards?

Michael

[Admin]

A 1405 would have those impedance-matching/level-boosting boards following the DAC outputs and ahead of the coax outputs. Not sure where they are mounted on that model, but on the 1105 we service, they are on the inside of the kneeboard, above the expression/crescendo area. Follow the audio cables from each DAC output and you will see that they lead to these little boards before the audio goes out to the amps. It is on these boards that expression is applied in the large MOS-2 organs.

I can't recall the name or part number of that board off-hand, but you will know them when you see them. There is one per MOS system. The missing audio is probably due to one of those boards being defective or possibly just disconnected from the power source. If you look at them you should be able to spot the trouble, if it's just a loose connector.

These are the line driver boards, Assm#904-5668, PC board #421-2707. They have two screw terminal barrier strips, one 6 six connection and one 3 connection strip. Each board is two channel, so you should have as many of these line driver boards as computers.

[CWalchesky]

Thanks for all the help everyone. John, you were psychic in your diagnosis. It was the power to the output board. Can't believe I didn't notice.

Now to search for some threads on why the combination action is failing...