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    Allen organ amplifier codes

    There has been some discussion recently about the differences among the various Allen organ amplifiers built over the decades, and how to determine whether or not a given amp will work in a given organ. I did a little browsing today in my old Allen technical manuals and have some information worth sharing.

    (1) Allen started "coding" amplifiers a long time ago, and their coding system has remained unchanged. So, a T-50 amplifier with a code of 5 will be interchangeable with an S-100 amp or any other model amp that is designated Code 5. Even those AM-100 amps that were specially built to replace MOS amps carry a Code 5 designation. (Note however, that many older amps have the "mini-Jerrold" connector, which is now obsolete.)

    (2) The CODE gives you all the information you need, as to what kind of organ the amp will work with, as it specifies the number and type of connectors and it specifies whether or not there is a pre-amp to handle the very low level/high impedance signals used in the analog and MOS tone generator systems.

    (3) Once you know the secrets of these codes, you can just about glance at any Allen amp and know right away which code it is and therefore what kind of organs it will work with. Here are the codes and the "secret" ways to recognize each one:

    CODE 5 -- Has the preamp circuitry included, so it is designed for MOS and analog organs only. If you connect an ADC organ directly to its input, you will overload the pre-amp and you will get gross distortion. The input connectors are three RCA jacks. Two of them are paralleled, and the third one connects to the expression capacitor, which is normally mounted right on top between two solder terminals. There is a single volume control knob. The three input connectors are for the audio signal, the expression cell, and the mute relay (which is tied to the "voicing" knob on MOS organs). This is the amp normally used in MOS organs with the amps in the console.

    CODE 10A -- Also has the preamp included. Input connectors are one RCA jack and one Jerrold, with the connectors internally jumpered. No expression capacitor on this one, and no place to mount one. One volume knob. This is the amp normally used in MOS organs with amps mounted in a remote rack or inside the speaker cabinets. On most MOS amp racks, the incoming signal is on a Jerrold coax, and there would be a mute relay attached to the RCA jack, if required. (I think there used to be a Code 10 without the "A" and it had just a Jerrold connector without the RCA jack, and was used on analog organs, which required no muting.)

    CODE 12 -- Two SEPARATE Jerrold input connectors, for connecting two separate incoming audio signals. There is a separate pre-amp for each Jerrold input, and two volume control knobs. This was a fairly common configuration in analog days, when some organs were sold with two channels mixed down to one, reeds and flutes mixed together, for example. It was not a common code in MOS days, but Allen would provide this code upon request for replacing amps in old analog organs, or for other unusual applications.

    CODE 13 -- There is no pre-amp in this code, so it was built only for use in ADC organs, as well as in those oddball 80's MDC models. The input connectors will be two RCA jacks and a Jerrold connector, all three of these being in parallel, jumpered inside the chassis. No expression capacitor, and no place to mount one. ADC expression takes place in the cage or on an audio processor board, and in those oddball MDC models, expression was done in a "Catch-all" assembly, which outputted a line level signal for the amp, therefore the amp has nothing to do with expression. You can't use an amp like this for a MOS organ, as there is insufficient gain. You will get a very low level signal and probably no expression.

    So, once you get a grasp of the external physical differences among these amps, you can quickly tell what you are looking at. I also found that there is a "dash number" after the assembly number on the model sticker of most of these amps. But unfortunately the dash number is not the same as the code. MOST of the time, a code 5 amp will have a "-4" after the assembly number. For example, a T-50 may be labeled "905-1000-4."

    And MOST of the time, a "-3" at the end of the assembly number indicates that it is a Code 13 amp. The S-100 used in early ADC models may be labeled 905-1042-3.

    Toward the end of S-100 production, Allen introduced the "universal" S-100 amp, and the dash number after it is "-7." This version is highly configurable, and can be made to work with almost any Allen organ by doing some internal mods. The pre-amp IS present (it is just an extra chip on the pc board), but by unsoldering and moving a wire you can bypass it. However, since MOS amps always have a 5K volume pot and ADC amps need a 100K volume pot, you also have to change the pot. But it is possible to convert a "-7" amp into either a MOS amp or an ADC amp. As to adding expression caps and other details, I'm not sure, but I assume the "-7" amp has provisions for those too, since it was designed to be adaptable to all Allen applications.

    Riveting reading here, I know... but then we're all nerds, aren't we?
    John
    ----------
    Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
    Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
    Shop: Bunch of organs in varying conditions, some good, some not...
    Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches
    https://www.facebook.com/pages/Birds...97551893588434

    #2
    John,

    Thank you so much for this information. Excellent thread! It should be a Sticky.

    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)
    • 9 Pump Organs, 1 Pipe Organ & 4 Pianos

    Comment


      #3
      Interesting. It seems then there are other variations than those originally mentioned.

      My MOS-2 Allen has 6 -7 S-100s and 2 -3 S-100s (for the reverb channels). The -7s have three RCA phono inputs and Jerrold connector. The -3s have 2 RCA inputs and the hole where the Jerrold connector would be is plugged. My MOS-2 has line level outs going to the amplifier rack and the inputs on the -3s for the reverb are also line level inputs.

      Is the amplifier code on the amp or is it inferred from the dash number?
      -Admin

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

      Comment


        #4
        Thanks for the extremely helpful information, John. As always, you are an asset to all of us here on the forum. I've learned so much just from reading your posts!
        Craig

        Hammond L143 with Leslie 760

        Comment


          #5
          Admin, I'm sure Allen built a lot of variations on these basic amp types over the years, and surely customized some of them to suit a buyer's needs. The two types that you have are mentioned in the list above, but with some some slight variations.

          Your six "-7" amps are of the "universal" type that Allen was selling before they discontinued the S-100. These amps were "convertible" and could be modified to suit whatever organ they were to be used in. Someone probably bought those new and had them modified just for your MOS-2 organ. The other two amps you have are "-3" which normally indicates a Code 13 amp, in other words, line level input with no pre-amp and no provisions for expression control on the amp itself. The Code 13 is supposed to have two RCA jacks plus a Jerrold, but apparently the Jerrolds were not installed on yours, possibly because they were ordered specifically for use with your reverb system, which of course does not need the Jerrold connector.

          To answer another question, the "code" is not the same number as the "dash number" on the label. That is unfortunate, as Allen could've made it easier to ID the amps if they'd take that approach. However, the "dash number" at the end of the assembly number DOES tell you something:

          "-3" always means that there is no preamp or "front end" present. In analog and MOS days, the "-3" amps were used for odd applications that did not involve either expression or direct output from the tone generator or DAC. For example, the amps used on their primitive reverb systems back then were "-3", and dash three amps were also used for their "tower carillon" installations, both of these applications being driven by high-level signals not coming straight from a tone generator or DAC.

          "-4" always means that there IS a preamp or front end circuit present. So any -4 amp can theoretically be used with an analog or MOS organ, but remember that not all -4 amps are the same. Some are Code 5 (generally used on remote amp rack models, with the expression capacitors tucked away inside the console, under the metal plate in the floor). And some are Code 10 or 10A, and these are the ones generally used inside the console, where the expression capacitor would be mounted right on top of the amp.

          CRAIG: Please note that your current T-50 amps are both CODE 5, even though they are in your console. That is why I made the statement a long time ago that I suspect your amps were originally mounted inside the gyro cabinets and were later re-located when someone modified the setup. That may or may not be true, but your amps are Code 5, not code 10A, which you would normally see inside a console.

          Finally, a "-7" after the assembly number means "universal" and adaptable to any of the other types. In fact, the pre-amp IS present in -7 amps (it is just an inexpensive chip), but there is a wire jumper that can be moved to either send the incoming signal through it, or else bypass it.

          BTW, when I speak of "assembly numbers" I'm referring to the Allen catalog number that appears on the label of every item in an organ. For amps, the assembly number will start with 905 (at least for T and S series amps), followed by a dash and four more numbers. Then a final dash and a single digit.

          So, the standard MOS S-100 amp is 905-1042-4.

          And the standard ADC S-100 amp is 905-1042-3.
          John
          ----------
          Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
          Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
          Shop: Bunch of organs in varying conditions, some good, some not...
          Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches
          https://www.facebook.com/pages/Birds...97551893588434

          Comment


            #6
            John i have an allen amp that i belive is a s100 amp the schematic i down loaded dose not match the amp i have the circuit board showes the assy no. as 904-5303 and a schematic no. of 081-0381 would you be able to help me find the correct information on this amp thank you
            terry Pokorny

            Comment


              #7
              What you have is not an S-100. It is an old T-50, the amp that Allen used in nearly every organ built from the early 60's to the mid-70's. A marvelous old amp and a workhorse.

              Sadly, they are often not repairable these days, as the output transistors are obsolete. Someone else may chime in and give a source for them, but I don't know any. Also, I have heard that it is possible to replace those old germanium outputs with modern silicon transistors by making certain modifications, but I don't know anything about that myself.

              But if the amp is working and has simply become hummy or noisy, you can replace all the electrolytic caps in it and possibly restore it to like new working order.
              John
              ----------
              Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
              Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
              Shop: Bunch of organs in varying conditions, some good, some not...
              Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches
              https://www.facebook.com/pages/Birds...97551893588434

              Comment


                #8
                i belive the output transistors are ok but i belive it is the input paet that is bad so i need a schematic to trouble shoot it

                Comment


                  #9
                  Try this one:
                  Attached Files
                  John
                  ----------
                  Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
                  Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
                  Shop: Bunch of organs in varying conditions, some good, some not...
                  Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches
                  https://www.facebook.com/pages/Birds...97551893588434

                  Comment


                    #10
                    Hi John. I have gotten very confused with these Amps. We are refurbishing a six channel ADC5000X and when we measured the pots, they read around 79K ohm? Does that seem right? Also can you tell us how exactly the Universal S100 is modified for ADC? We move the input wire on it - which we thought was right - but now the amp is actually much louder than the original ADC 5000 Amps.

                    Thanks!

                    John
                    Can't play an note but love all things "organ" Responsible for 2/10 Wurli pipe organ, Allen 3160(wife's), Allen LL324, Allen GW319EX, ADC4600, many others. E-organ shop to fund free organ lessons for kids.

                    Comment


                      #11
                      I'd guess the 79K you're measuring is somehow affected by the circuit. Best I recall, they are 100K pots, so something in the circuit in parallel with the pot is affecting your measurement. Can you read the info stamped on the housing of the pot? It should tell you for sure. But my notes elsewhere say the pot is supposed to be 100K.

                      To make a universal S-100 work with an ADC organ, you bypass the circuit containing the op-amp chip. So the incoming signal on the RCA jack should go directly to the volume pot instead of passing through the various components related to the op-amp chip.

                      But first you must change the volume pot to a 100K (audio taper, I assume, since it's in an audio circuit). Then you change the wiring of the input area so that the op-amp circuitry is no longer connected in any way to the subsequent stage.

                      At present, you may see that the input terminal of the volume pot is connected to one end of a 5 mfd capacitor, which is the cap that couples the output of the op-amp chip to the volume pot. You don't want that to happen any more, so be sure to clip off the existing connection to the volume pot. The other terminals of the volume pot -- one going to ground, and one (the wiper) going on to the next stage of the amp -- will remain in the same positions on the new 100K pot.

                      Once you've made those mods, the amp should now function exactly like a regular ADC S-100.

                      The situation you describe, with the amp now even hotter than a standard ADC amp, might be due to some feedback into the op-amp, if you haven't yet clipped out the 5 mfd coupling cap.
                      John
                      ----------
                      Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
                      Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
                      Shop: Bunch of organs in varying conditions, some good, some not...
                      Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches
                      https://www.facebook.com/pages/Birds...97551893588434

                      Comment


                        #12
                        There's an S-100 schematic in the Gallery here:
                        http://www.organforum.com/gallery/al...0001/S-100.pdf
                        -Admin

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

                        Comment


                          #13
                          Thanks John ,and Thanks Admin, Between the two of you I should be able to figure it out! But just so I'm sure, I see now that the input to the NEXT stage is through a 10K resistor and a NP 15mf Cap. So the input should just go to that 10 K Resistor, correct?

                          John
                          Can't play an note but love all things "organ" Responsible for 2/10 Wurli pipe organ, Allen 3160(wife's), Allen LL324, Allen GW319EX, ADC4600, many others. E-organ shop to fund free organ lessons for kids.

                          Comment


                            #14
                            John V: you said the magic word - "ADC-5000X" - which was a topic of conversation on a recent thread discussing a free organ. Do you know what the "X" in the model number signifies?

                            P.S. I haven't looked at the schematic but I would think that a 15mF NP cap provides AC coupling to the input - not something I'd want to remove.
                            Larry is my name; Allen is an organ brand name.

                            Main: Allen RMWTHEA.3 with Rocky Mount Electra-Piano, Allen 423-C + Gyro cabinet, Britson Opus OEM38, Saville Series IV Opus 209, Steinway AR Duo-Art, Mills Violano Virtuoso with MIDI
                            Lower Level: Hammond 9812H with roll player, Gulbransen Rialto, Roland E-200, Vintage Moog
                            Shop: Mason&Hamlin AR Ampico piano, Allen ADC-5300-D with 18 speakers and MIDI, 4 Allen theater organ tone cabinets (including 3 Gyros, but don't call me Gyro Gearloose!).

                            Comment


                              #15
                              I was told that it stood for an external Amp rack. I could be wrong.
                              Yes I figured the cap was for input, but there is a 10K resistor ahead of it.
                              Can't play an note but love all things "organ" Responsible for 2/10 Wurli pipe organ, Allen 3160(wife's), Allen LL324, Allen GW319EX, ADC4600, many others. E-organ shop to fund free organ lessons for kids.

                              Comment

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