Allen S100 amp issues

[samibe]

My mom has an Allen MOS-2 (282) organ. It has two S100 amps in it that each drive an HC-11 speaker. The amp that handles the flute and pedal stops keeps flipping the breaker. I'm never there when the breaker flips (even if I play it daily over the course of a long weekend) so I don't know what might be causing the breaker to flip.

Here is what I've checked or noticed.
- The speaker wire runs are 10ft max.
- The flute channel amp/speaker thumps fairly loud when the organ is turned on but not when the organ is turned off.
- The other amp/speaker does not thump when the organ is turned on or off.
- If stops on both channels are selected before the organ is turned on and keys are held down when (or right after) the organ is turned on, the organ thumps when it is turned on but nothing plays for a few seconds until the amps unmute.
- There doesn't appear to be any visible damage to the amplifier.
- There is an odd capacitor screwed to the outside of the amp housing.

What have I missed? What should I check? and what might the culprit be? Thanks.

p.s. Each amp appears to have two audio inputs (and an expression signal input). I haven't traced the wires yet, but is this organ a four channel organ that gets mixed down to two channels at the amplifier? or is the second input something totally different?

[myorgan]

My mom has an Allen MOS-2 (282) organ. It has two S100 amps in it that each drive an HC-11 speaker. The amp that handles the flute and pedal stops keeps flipping the breaker. I'm never there when the breaker flips (even if I play it daily over the course of a long weekend) so I don't know what might be causing the breaker to flip.

Here is what I've checked or noticed.
- The flute channel amp/speaker thumps fairly loud when the organ is turned on but not when the organ is turned off.
- The other amp/speaker does not thump when the organ is turned on or off.
[snip]
- There is an odd capacitor screwed to the outside of the amp housing.
[snip]
p.s. Each amp appears to have two audio inputs (and an expression signal input). I haven't traced the wires yet, but is this organ a four channel organ that gets mixed down to two channels at the amplifier? or is the second input something totally different?

Sam,

First things first. A MOS-2 organ has different requirements from the amplifiers than the MOS-1 or ADC organs-even though they use the same amplifier on the outside, the innards are quite different. John has started a thread regarding Allen amplifiers here: https://organforum.com/forums/forum/...mplifier-codes.

When I got my 505B, half of the organ wasn't working, and the same issue was presenting itself. It turned out to be a slo-blo fuse in the +/- 12v power supply. I purchased a few-just in case, but never needed them once I moved (& eventually replaced) the AM-100 amplifier which was causing the problem, with two S-100 amplifiers I found online.

You have correctly identified that in one amplifier, the mute relay has probably failed. I seem to remember somewhere on the Forum in the last year, there has been a discussion of repairing the mute relay on a S-100 amplifier. I believe the S-100 schematic was also provided at that time.

The capacitor on the outside of the amplifier is part of the pre-amp circuit and is normally on the inside of the amplifier. It may have been modified, therefore being outside the chassis, but it does belong.

I checked my MOS-2 manuals and couldn't find any reference to a Model 282 organ there, but the Model 453/456 (3-manual) is a 2-channel organ. For that reason, I think your Model 282 is probably also a 2-channel organ.

Regarding the connections on the amplifier, the MOS-2 S-100 amplifiers had 2 inputs, and I don't believe it matters which you use. The other RCA input connector is for Expression. Whereas in the ADC the expression takes place in the cage, in the MOS-2 organs, it takes place between the Expression pedal and amplifier.

Finally, some years ago I created a MOS-2 reference thread which can be found here: https://organforum.com/forums/forum/...os-2-reference. I hope this helps begin to answer all your questions for now.

John is definitely the guru on the topic, but if you need basic information, I can help somewhat. Best of luck with the repair.

Michael

[Organkeys Jones]

Some random thoughts ... I think the 282 was an LDS model, sold directly by the factory to LDS stakes. Makes sense with your Utah location! And it would be a 2-channel organ. Your problem probably is the mute circuit, or maybe a delay circuit since there seems to be some audio muting happening. I disagree with Michael about MOS 1 and 2 S-100 amps - I thought they are the same. It was the S-100's on the early ADC organs that looked the same but had no pre-amp built in. About that odd capacitor on top - I've seen a lot of S-100's with that special feature! At the moment I can't remember why there are 2 audio inputs.

Have you switched audio inputs between amps to see if the thump moves or stays in the same amp? Would be worth a try if the cables are long enough.

[samibe]

I looked through the pictures I took over the weekend again. I think I found the mute relay box (1st picture) unless it is just the box that alters the tone to simulate the swell box effects. I don't have a good picture of where the two other audio cables come from although it looks like they might come from the voicing knob on the left key cheek (2nd picture). The two cables that leave the upper left corner of picture 1 seem to head in that direction. I'm guessing it is two channels and the signal is just split into treble and bass (no idea where that happens) with the treble getting sent to the voicing knob and then both sent to the amp. I'm guessing the amp can use the expression signal to change the volume and alter the treble/bass mix. The DAC seems to only have bass control (3rd picture). Where should I look for a mute relay (if it is not the box in picture 1)? I don't see anything in the amp that looks like a relay (4th picture). The part that has me confused is that the mute seems to be working for both channels (as far as the audio is concerned), but the thump in one of the channels gets missed. Or is the audio always delayed a few seconds while the system starts regardless of the mute?

The 282 is a a 200-series organ. I think it is a standard 200 with a stoplist that the Church of Jesus Christ specified.
I will try switching the audio inputs between amps to see if that changes anything the next time I visit my mom. Thanks for the help.

[AllenAnalog]

I don't know about MOS-2 instruments but my MOS-1 organ did not have the +/- 15VDC power supply to support DAC-3 and DAC-4 boards. So I had to add one and install new wiring when I upgraded from the original DAC-2 to the new DAC-4.

[samibe]

Michael, I thought I responded but it looks like I only thought about it. I saw the mute relays in the other topic. I haven't found anything in this organ that looks like that. I'm wondering if they might be located under the check blocks and not in the main console. From John's advice in the amp topic, it seems that mute relay might be up by the voicing knob. I'll look a little harder for it the next time I visit.

[myorgan]

Sam,

In looking at the Series 200 models, it appears the mute relays were not separate until the Series 500 MOS-2 organs. I'll do some more reading to see if I can find where it actually is (i.e. Power Supply or Amplifier).

Michael

[Admin]

Tripping breakers may be due to ultrasonic oscillations. One cause of this is using multi-conductor speaker cable rather than individual pairs for each speaker. The only way of identifying if the oscillations are present is by viewing the output. on a scope. The oscillations may be intermittent.

If you don't have a scope, I'd swap inputs between the two amps. If the same amp keeps popping the breaker, you've eliminated that channel as the possible cause of the problem and limited to the amp itself or its speaker connections.

[samibe]

I don't have a scope so I'll try switching inputs and see what happens.