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Modifying 7271 (26-1) kit for sending spinning reverb on an A-100

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  • Modifying 7271 (26-1) kit for sending spinning reverb on an A-100

    My goal is to send a mix of reverb and dry to a 6W type Leslie like the 147, from an A-100. The organ came to me with a 26-1 kit installed. This kit makes no accommodation for reverb.

    The "correct" way to go about doing this is to install an 8444 kit. The gotcha is that this kit has a very complicated M-E-E switch that is hard to find, and I can't find any modern equivalents to it.

    Most organists are fine with making a "mute" switch for their main A-100 speakers. The kit can be set up in such a way that it always sends signal to the Leslie speaker if the Leslie is attached. The problem is that the 26-1 stock M-E-E switch does not have the ability to "mute" both the main and reverb speakers together, but it doesn't have to. It can be set up to mute the main speaker, and leave the reverb speaker always connected. The player can set the reverb volume control as desired. After all, there is nothing wrong with a mixture of spinning reverb coming from the Leslie, and reverb also coming out of the A-100 reverb speaker at the same time.

    With the suggestions of many colleagues and my own pondering, here's a method that allows the stock 26-1 M-E-E switch to function as follows:
    Main: Both A-100 and Leslie speaker active
    Ensemble: Both A-100 and Leslie speaker active
    Echo: A-100 main speakers muted, reverb speaker still active, Leslie speaker active


    Here is a detailed list of steps to modify both the 26-1 (027011) box, and the M-E-E switch to do this:

    1. Disconnect green wire from S3 pin 2
    2. Attach 2 47 ohm half-watt resistors to this bare green wire. Mount them securely.
    3. Attach one of the 47 ohm resistor other end to S3 pin 3.
    4. Attach other 47 ohm resistor end to S3 pin 2.
    5. Jumper S3 pin 2 to S3 pin 5
    6. Attach 8 ohm 10 watt resistor to S3 pin 4.
    7. Attach other end of this resistor to P2 pin 1, or S4 pin 1 (the ground wire).
    On the M-E-E switch:
    8. Jumper the main wafer P3 pin 1 wire to the echo wafer pin that is currently unused.
    9. Detach the echo wafer wire currently attached to P3 pin 2, and attach it to the main wafer that is currently unused.
    10. On P3 connector, move the wire on pin 2 to pin 4.
    11. Attach a wire from the A-100 reverb speaker + lead to P3 pin 3.


    For now, I only plan on doing this if I cannot source an 8444-type (7 wire) M-E-E switch. This seems like a good alternative if one wishes to use the existing 3-wire M-E-E switch to this purpose.

  • #2
    One other thought I just had...

    The stock 8444 kits are set up in such a way that when in Ensemble mode, the speakers, and the two dummy load resistors are in circuit, meaning the amps "sense" them in parallel, 4 ohms.

    This method ensures that the amps always see 8 ohm loads. Could be a benefit.

    Comment


    • #3
      In case one wants to do the same thing but without modifying their 027011 box, you could do this 'outside the box' too, by making modifications to the M-E-E switch, and securely mounting the 3 resistors on a terminal strip outside the box. Alternative steps are:

      1. Splice a wire to the P3 pin 5 wire. Attach this to a 47 ohm 1/2 watt resistor.
      2. Detach the wire from P3 pin 2. Attach an 8 ohm 10 watt resistor to this wire, lengthening the wire if needed. Attach other end of this resistor to ground.
      3. Attach a new wire to P3 pin 2. Attach this to the other end of the 47 ohm 1/2 watt resistor in step 1 above, and add a second 47 ohm 1/2 watt resistor to the same connection.
      4. Attach the other end of this second 47 ohm 1/2 watt resistor to the Reverb speaker + lead.
      On the M-E-E switch:
      5. Jumper the main wafer P3 pin 1 wire to the echo wafer pin that is currently unused.
      6. Detach the echo wafer wire currently attached to the 8 ohm 10 watt resistor, and attach it to the main wafer that is currently unused.


      So it would seem that 6 steps is better than 11 steps, and that this preserves the resell value of the 027011 box.

      Comment


      • #4
        One step I forgot - move the reverb amp input from the main speaker lugs to the output of the AO-39, so that they always get signal.

        Sounds good. I just did the "out-of-box" modification.

        Comment


        • #5
          Just resistively sum the outputs of the two amps, and send this combined signal to the input of the 147.

          Comment


          • #6
            Originally posted by Tim_at_Jonas View Post
            Just resistively sum the outputs of the two amps, and send this combined signal to the input of the 147.

            Yes, I knew that is what was needed, but the question was "how", and how to do this with an existing installed 7271 / 26-1 kit. Now I know.

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