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  • Allen S-100 AMP

    So I went to Radio Shack and picked up supplies to fix my S-100 Amp on my Allen 120-C. Then I realized, that after spending $60 for this stuff, perhaps there is a place I could just send it to to get fixed that wouldn't cost much more than what I spent on these returnable items. There are also two of these sold as a pair on e-bay which maybe I should just purchase when I get some extra money so that I can continue to practice, even with the increasing "audio irregularities," shall we say... it is getting worse...

    I noticed that those amps on e-bay appear to have both a coaxial input and RCA inputs, would that work with my Allen 120-C?

    Sorry for the constant questions... this is bordering on Aspergers. I just want to practice on my baby....
    Buuuuuuuuuuuuzy.

  • #2
    I quit buying from Radio Shack 25 years ago. They sell absolute reject components in some cases, and their electrolytic capacitors are the **** grade, good for a couple of years maybe. The last two Radio Shack soldering irons worked a couple of joints before they corroded up and wouldn't transfer heat anymore. If you're going to spend all that labor, buy a WP35 Weller iron with an accessory screwdriver tip, and some >3000 hour service life capactors that are sealed with silicon seal instead of gum rubber.
    As far as e-bay, any Allen amp you buy will probably also have 30+ year old capacitors and be good for a couple of months unless you luck out and get one that has already been re-e-capped.
    Allen MOS organs have the swell pedal linked into the op amp feedback circuit, and require a modification to work with PA or hifi type amps. Many consumer grade hifi or home theater amps don't have heat sinks big enough to produce their rated wattage for an hour at a time without melting transistors. Quality PA amps do have adequiate heat sinks, and the sign of quality is more brand name than any number they quote. Known durable PA amp brands are Peavey, Crown, QSC, Yamaha. In these, if road weary they will need in addition to e-caps if over 20 years old, they will need input and output connectors and probably some potentiometers.
    So if it were me, I would order some capacitors and a soldering iron from newark.com, or out west mouser.com, and fix the S-100. Fishing department cutters and pliers are sometimes adequate, although if you want hand tools for sure that are good, buy sears craftsman, cooper tools, diamond tools, or xcelite tools. Don't forget safety glasses for de-soldering, and a roll of 60-40 tin lead rosin core solder. RS solder has been okay, newark sells by the pound. The other thing RS sells that is okay is the clip leads.
    When ordering from newark, look at the service life column in the selector table and buy the good parts. Newark will sell you 500 hour caps too, if you really want to do the job again in two years. Mouser does not have the service life in the selector table, they make you download the datasheet and read it. Don't buy any e-caps from xicor or CDE. they are made in the country that lies on QC paperwork for baby formula and chicken. I've been getting caps from more disciplined countries from Panasonic, Nichicon, Rubicon, and Vishay Sprague.
    Last edited by indianajo; 09-08-2013, 03:59 AM.
    city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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    • #3
      Allen S-100 amps came in more than one version, and were used on MOS1, MOS2, and ADC organs, some with internal speakers, some with external, so you have to be sure you're getting the right type or else you'll be in for some modifications that aren't easy without technical skills. If your amps have the expression capacitors mounted on top (small round waxy-feeling caps mounted between two small terminals right above the input jacks) you need to find amps that also have these caps, otherwise your expression will not work and there could be other mismatch problems.

      Post pictures of your amps and I'll tell you what kind your have.

      I've seen and serviced a lot of old Allen amps, and they seem to be holding up remarkably well, especially the S-100 type, so a used one might be just fine, or it might have problems too. But they are a pretty good bet if that were working when removed from service. The old T-50 amps seem to have a lot of leaky caps, but maybe that's because some of these amps are approaching 50 years old.

      I-Joe, I have had better luck than you buying from Radio Shack. I rarely do that any more because online prices are so much better, but in a pinch I've bought caps, resistors, diodes, etc., and paid maybe 2 or 3 times what I should have, but haven't seen any defective parts. The caps are usually Nichicon or Illinois or other standard brand. Not "premium" quality but the same type found in most consumer electronics products. Not defending Radio Shack, but they are nice to have around when you need something and don't have time to order!
      John
      ----------
      *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

      https://www.facebook.com/pages/Birds...97551893588434

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      • #4
        Originally posted by indianajo View Post
        Allen MOS organs have the swell pedal linked into the op amp feedback circuit, and require a modification to work with PA or hifi type amps.
        No, that's not the case. The LDR in the expression pedals is a simple shunt to ground. In the MOS 1 series the DAC output is typically shunted by the expression pedal. For this to work the output impedance of the DAC is relatively high so if you feed this output to a conventional input the input impedance of that device becomes the primary path to ground dropping the output and causing the expression pedal not to work. MOS-2 instruments have line amps following the expression pedal so that's not a problem with these models.

        The impedance matching device sold by Harrison Labs is simply a series resistor that can be used to raise the output impedance of a device inserted between the DAC and the pedal or to raise the input impedance of any devices following the pedal.
        -Admin

        Allen 965
        Zuma Group Midi Keyboard Encoder
        Zuma Group DM Midi Stop Controller
        Hauptwerk 4.2

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        • #5
          Buzzy,

          Believe John & Admin on this one. I have had a MOS2 for about 10 years now, and everything works great. To my knowledge, they're original to the organ. Can't say the same for my ADC, though. One amp needs to be rebuilt due to a popping sound that sounds like moisture buildup. In a nod to Joe, for the first time in my life I'll say it may be a cap, but I'll need to wait for some performances to pass before I send it away for repair.

          The S-100s currently listed on eBay appear to be for MOS-1 instruments, but I haven't looked closely at the pictures. I've just noticed that they don't have the capacitor on the top of the case, and they only have 2 inputs on the back (MOS2 usually have 3). Buy from someone you know and/or trust, and that way you can be sure.

          John, can an AM100 be used on MOS-1 instruments? I'm using it as the MIDI amp for my Ensemble presently, but I'm thinking of changing that. I am thinking of adding it to power the antiphonal of my ADC-4300, but want to be careful with that because of the different levels.

          Best of luck with your project, Buzzy!

          Michael
          Way too many organs to list, but I do have 5 Allens:
          • MOS-2 Model 505-B / ADC-4300-DK / ADC-5400 / ADC-6000 (Symphony) / ADC-8000DKC
          • Lowrey Heritage (DSO-1)
          • 11 Pump Organs, 1 Pipe Organ & 7 Pianos

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          • #6
            Michael,

            The AM100 was the general purpose amp during the MDS era, the 1990's. So the input level and other characteristics are the same as for ADC amplifiers, which means line level. Therefore, they are not usable with MOS organs. However, I believe Allen sold a specially modified version of the AM100 as a replacement amp for MOS organs, and it had the expression, mute, and signal inputs (3 RCA jacks) that you need on the amp in a MOS organ with amps in console, and also had the pre-amp and impedance matching circuitry built in to accomodate the lower signal levels of MOS organs.

            (The AM100 you have is of course perfect for giving your Ensemble its own audio, and it could be used with the 4300 as well.)

            Nowadays, if you want to buy a new amp from Allen for a MOS organ, you have to get a "replacement kit" which includes an interface panel with jacks for all the cables along with a volume knob and the necessary level-matching circuits, and this interface panel connects to one of their current amplifiers used in Quantum organs. Needless to say, this is a pricey solution and also takes up more space than there is inside some MOS consoles.

            Best solution for MOS owners is to have one's existing amps rebuilt. Allen amps are generally built to last forever, at least the "hard parts" such as the transformers, output transistors, and hardware. Replacing the capacitors in a 40-year-old amp might make it work for another 40 years!
            John
            ----------
            *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

            https://www.facebook.com/pages/Birds...97551893588434

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            • #7
              Well, I've retyped this so many times, the words, themselves, are staring to loose meaning, so let's hope that the website doesn't shut me out again..

              1. Here are pics of the amps.
              2. I think I know why I couldn't get the reverb to work because I was hooking up to the wrong chords perhaps.
              3. How does one adjust the two amps correctly. There is no 'dial' or measure of how far you've turned the damn things.
              4. How can I install headphone on this thing so I can practice with normal registrations?
              5. Do I need to replace any of the orange ceramic caps?
              6. Do I need exact cap values if I replace the electrolytics?
              7. What is the purpose of the 'waxy' caps on the amps, why are they waxy and where would I have ever seen waxy caps before?
              8. Could the ebay amps work on this MOS organ?
              9. Why did I not have any problems adding reverb to my other MOS organ (even the swell pedal works, even without any impedance corrector, etc. )

              Uff!
              berrrrtz.
              Attached Files

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              • #8
                Buzzy,

                That is of course an S-100, not an old T-50 or other previous model. I rarely see an S-100 that needs rebuilding because they are so much newer and used more durable components. The old T-50 amps have capacitors underneath that start leaking, but the caps in that S-100 all look perfectly good to me, from this distance anyway. I really doubt that you need new amps. The noise in your audio might be coming from a defective pre-amp IC (the 14-pin chip in the first pic), or perhaps one of the small signal transistors. Almost any electronic tech should be able to spot the trouble and replace the part for a relatively small charge. And you wouldn't have to worry about making an incompatible amp work. The ones I've seen on ebay do NOT have expression caps on them, so they would have to be extensively modified to work in your Allen.

                The reason your reverb worked on the model 600 MOS is that the expression and muting take place inside the console on that organ, before the audio signal exits the console on those four coaxial cables, so the external amplifier is just an amp and nothing else. It was just a lucky coincidence that the reverb unit didn't happen to mess with the impedances or levels enough to keep it from working. This smaller Allen, with amps and speakers in the console, is wired differently. That is why you have three RCA plugs going into each amp. One is the audio signal for that channel, a second one is for the muting relay, and a third one comes from the expression pedal. The expression connection goes through that little waxy capacitor right above the inputs, and then connects to the signal input. So the expression only works correctly when routed through that capacitor, and that is why there is a little problem wiring the reverb unit straight into the signal. The expression cell in the pedal and the expression capacitor are specifically configured to work in a high impedance circuit, and the output impedance of a modern device like a digital reverb is very low, so the expression unit cannot work with it. However, I still don't understand why you get almost no signal at all if you have the input and output levels on the reverb correctly set.

                The isolators sold by Harrison Labs are probably just resistors (around 100K perhaps) that are inserted into the signal path following the reverb unit to "fool" the expression circuit into thinking that the signal is still coming from the high impedance (100K ohms more or less) of the DAC board output. Evidently they do the job, so you may have little choice but to get a pair of those. They should completely solve the expression and volume level issues with your small organ.

                Bottom line: Get a local radio/TV shop or the repair guy at some sound system store to fix the Allen amp. Then get the isolators from HL and connect the reverb as they recommend.
                John
                ----------
                *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

                https://www.facebook.com/pages/Birds...97551893588434

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                • #9
                  So I managed to find the only electronics shop left in South Eastern Minnesota that still uses a soldering iron and dropped off my S-100 AMP at a nice place in "Med City." I can only hope that the miracles that the Mayo Brothers did for tertiary medical care can be replicated on my poor little amp. He estimated it will be a couple of weeks and cost at least $100. It still beats the price that an Allen rep would charge to drive down here.

                  So my question is this. Would I do any harm to my organ or its components by hooked up the other channels and speakers to the remaining amp so that I can practice until the other amp is back?

                  Also, I was monkeying around with the choke on the swell pedal and wonder if I can do any harm by doing that? I managed to get the organ quiet enough so that I can practice with full registrations in my apartment without anyone hearing it but me.

                  Also, also.. is there an easy way to hook in a set of headphones to my organ so that I can just practice without anyone else in my sleepy little apartment building hearing me?

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                  • #10
                    You can use an RCA Y-cable to play both channels into the same amp. If the amp still left in the organ is the one that drives the 15" speaker and its related 8" and tweeter, you can safely play all your stops. If the remaining amp is the one that drives only a pair of 8" and a pair of tweeters, the pedal stops will be quite weak, but you won't do any harm because there is a blocking capacitor to keep the bass out of the smaller speakers. If you want to try hooking up the other speakers to the one remaining amp, it won't do any harm since your S-100 amps are plenty sturdy to drive a four-ohm load. Just be sure to hook them up with the correct polarity -- black wire on both amp speaker outputs is the "common" and should remain on the common terminal. The other wire, which might be yellow or green, is the + wire and should be on the + terminal.

                    The choke on the expression pedal is actually a variable wire-wound resistor used to vary the brightness of the expression lamp. Turning the lamp brightness way up will decrease the organ volume, but at the risk of burning out the lamp before its time. Your best way to turn down the volume is to turn it down with the potentiometer shaft sticking out the back of the amplifier near the input jacks. It probably doesn't have a knob on it and it may be marked with red paint to show the default factory volume level. You can turn it down as much as you like.

                    Adding a headphone jack that works as expected and automatically silences the internal speakers is not easy. But there are inexpensive headphone amplifiers on the market that might be used if you removed the input signal from the amplifiers and ran them to the headphone amp. You wouldn't have any expression, but that might not matter.
                    John
                    ----------
                    *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

                    https://www.facebook.com/pages/Birds...97551893588434

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