Allen organ problem

[praestant]

Hello, i have a Allen system 120 MOS-1 with internal speakers. Niw if i play it, i hear from all 2 chanels crackles and humm, so as i play , and
if i not play the organ. i have clean the RCA conections on all 2 S-100 AMPLIFIERS , but this crackle and bad humma goes not disappear.
And if i to turn the potnetiometers on the S-100 amplifiers, i hera little crackles, but on both chanels!

I need helf for this problem,

thanks and regards chris

- - - Updated - - -

P.S. I have change the DAC -board, without suddess.

[jbird604]

Your problem is probably in the amplifiers themselves. The potentiometers (volume control knobs) may need to be lubricated with some kind of cleaner such as WD-40. You will have to dismount the amplifiers and turn them upside down to shoot some WD-40 into the pots through the slot next to where the wires are soldered on.

Of course, there are many other things that can be causing your noise. You should examine all the cabling that carries audio. You can try unhooking the expression and muting wires from the amplifiers. These are the other two RCA plugs than connect to each amplifier. It is always possible that there is something wrong with either the expression cells or the muting relays or "voicing" knob that is in parallel with the muting relays.

You may also need to service the power supply. If it has potentiometers for voltage regulation, these could be erratic and sending some noise into the system.

If your organ has a small rotating ("gyro") speaker in the console, the brushes that transfer the signal can also be dirty or worn. You should clean them with WD-40 as well.

With patience, you should be able to find the source of the noise and fix it yourself. Good luck!

[praestant]

Thanks John,
but it is perculiar, that in the swéll the positions from gemshorn 8´ and gedackt 8´, and prinzipal4´ and flute 4´are reversed, instead of gedackt 8´sounds the gemshorn 8
and instead of gemshorn 8´sound gedeckt 8´-and instead of prinzipal 4´sound the flute 4´.

regards chris.

[praestant]

Or to cause this audio problem, the old capacicitors (1000 uF -25V) in the S-100 Allen amps? The organ was built in 1973.
Thanks, Chris

[jbird604]

Old capacitors can be bad, but when they go bad, you get a constant hum, not a crackling noise. I think the problem is not the capacitors, but they might need to be replaced eventually. I would try lubricating the pots first.

The reason for your reversed stops -- someone has put the wrong MOS Board into the system. There are two different types of MOS boards used in the system 120. The original model used Mos Board Code B-1-4-6, but the "dash 3" version of the system 120 used a MOS Board Code B-2-4-6. You should see the code number on a paper sticker at one end of the MOS board.

The two different boards have their stops in different memory slots and different audio channels. If the wrong board is installed, it does no harm, but some of the stops will not have the sound shown on the tab.

[praestant]

Thank you John, i have lubricating the potis and replaced the the big capacitors, but after this replacing, the 2 amps makes distortions in both channels.
now i have use othe s-100 Amps and not distortions to hear.

My organ used MOS board code A-1-4-6 .

If the voices from Flute chanel sounds normaly in HW and Pedal,but the voices from flute chanel amp makes little crackles only in SW, i mean this comes not from the Flute Amp, right? I mean thats the stop board?

Regards Chris.

[jbird604]

Chris,

If you changed the amps and still have a problem, maybe something else is bad. You said you already changed the DAC board, so it could be the MOS board.

Have you tested the power supply? If the -27 volt from the MOS power supply is not very close to exactly 27 volts it can cause distortion in the output. Also, if the capacitors inside the supply are weak there may be some AC ripple on the DC voltages, which might also cause distortion or hum in the sound.

It sounds like you may more than one problem. Best way to find out is to get a complete set of boards from an organ that works properly and try putting in one board at a time to see if anything fixes it. But the power supplies must be very stable before you check anything else. And the amplifiers must be good. Have you tried playing something else through the amplifiers? You could connect a small music player to the input jack. Just be sure to turn down the volume on the player to the lowest level because the amplifiers in a MOS organ have VERY high gain and will distort the sound from an external source unless it is very low level.

The "CODE" on a MOS board indicates several things. The letter A or B concerns the Card Reader function. "A" means the card reader chips are present on the board, "B" means they are not present. If your organ has the card reader, it is supposed to use the "A" board, but it will work just fine with the "B" board, just no card reader voices.

The number "1" in the first position indicates the "original" church organ stoplist. The number "2" in the first position indicates the "second" church stoplist. There are several differences between the two stoplists, most notably in the swell. The "second" list does not contain the Tierce 1-3/5 stop.

Look at the model plate on your organ console. If it says "system 120" you are supposed to have a "1" in the first position. If it says "system 120-3" you are supposed to have a "2" in the second position.

[praestant]

Thank you very much, John for your answer.
Can i replace a A 1 4 6 Mos board with a A 2 4 6 MOS board?

And: can i replace a ALLEN S-100 Amp with other Amps? (American Audio VLP 300)

Thanks and regards, Chris.

[jbird604]

Any MOS board can be used to replace any other MOS board. It won't hurt anything. But if the MOS board is not the same Code as the one designated for your organ model, some of the stops will not sound the correct tone.

If your organ is a System 120, it should have a code A-1-4-6 (or B-1-4-6 if there is no card reader).

If your organ is a System 120-3, it should have a code A-2-4-6 (or B-2-4-6 if there is no card reader).

But if you have a spare board of any code, you can try it in the organ to see if your present MOS board is causing the distortion.

Amplifiers are harder to replace. You can certainly TRY using some other amp, but the S-100 has THREE RCA jacks for a reason. One of the jacks receives the actual audio signal from the DAC. One is connected to the expression shoe. And the other one is connected to the muting relay and "voicing" knob.

You can get some "Y" cables and simply hook all three cables together into one input on the new amp, and it will work, sort of. But you might not have any expression or you might have too much expression. The expression curve is dependent on the input impedance of the amplifier, so if the substitute amp has a different impedance from the Allen S-100, the expression will be affected in some way.

[praestant]

Thanks John, if my S-100 Allen Amplifier of my MOS-1 organ is defective---, my Allen dealer can this Amp, or both Amps, replace with new Allen Amplifiers for
my MOS-1 system 120 organ?

Regards Chris-

[myorgan]

You can get some "Y" cables and simply hook all three cables together into one input on the new amp, and it will work, sort of. But you might not have any expression or you might have too much expression. The expression curve is dependent on the input impedance of the amplifier, so if the substitute amp has a different impedance from the Allen S-100, the expression will be affected in some way.

John,

Another option for Chris would be to just switch the inputs between the amplifiers and see if the issue moves from one set of speakers to another? That could certainly isolate the problem to one particular source or output.

Michael

[jbird604]

Michael, swapping cables between amps is of course the first thing to try always. But I think he's already tried swapping around amps without success. I'm worried that all the amps he has could be bad. But it's hard to diagnose from across the Atlantic!

Chris, Allen CAN sell you new amps, but not S-100 amps any more. They can only sell you a "kit" of stuff to take the place of your old amps. The kit consists of an interface that accepts the present set of RCA plugs plus a modern amplifier. They charge a LOT of money for this kit. It does work perfectly, but it takes up more room in the console than the original amps and requires a lot of relocating of the cables. For a MOS1 organ, I don't think it's really worth spending that kind of money.

[praestant]

hello friends,
all of my problems with my organ are eleminated. The cause of the crackle and diestortion was only the bad old capacitors in both S-100 Amps!!!!
First i changed the large capacitors, however the result was not ok, only after the small capacitors were exchanged, the result was phenomenal, clear and big sound!!!!!!
thanks for all helps, and i konw now, old , 40 years old Amp capacitors was bad in my case.
Thank you John, and now i see so simply capacitors makes a big problem.........
chris ,

[jbird604]

That's wonderful! I hope you can enjoy that Allen for decades to come!

[indianajo]

That's wonderful! I hope you can enjoy that Allen for decades to come!

I can't believe it took 13 posts to get to the obvious usual suspects. And no mention on the root cause from here.
There are other electrolytic caps in the power supplies and possibly on the boards of old MOS Allens. IMHO they are all ****. Once an old electronic system I own has sound problems, out go all the e-caps before I even think about board swapping. Yeah, Allen's have longer lasting caps than the average Conn or Hammond. Nah, they are not epoxy sealed forever caps. I've warned the church where I put the main and power-up-silence caps in the 301 MOS organ S100 amps, "Silent Sunday" might happen again with those old *****y parts still in there. We're trying to finish the pipe organ before that happens.