Allen MDS-45 Reverb Squeal

[James P]

I usually leave Reverb stop in “on” position and it doesn't turn off w/General Cancel (as designed). As such 3-4 times now when I turn organ on, with no selected stops on, there's a high pitched squeal in speakers. When I flip Reverb to “off”, squeal stops. After awhile I can flip Reverb back on, & usually all's well w/no squeal.
Any ideas what's causing squeal? Or--- if I made a habit of flipping the Reverb tab "off" when I turn organ off, and then flip it "on" after I turn organ on-- would that solve the problem (i.e. no squeal)?
Thanks!

James

[jbird604]

I doesn't seem like this should be happening. According to the schematic, there is no feedback path of any kind involving the reverb system. But then, you are experiencing it, so obviously it's real. You may have to adjust your reverb system in some way. Here are the official instructions from Allen on doing the initial setup of an ADR-4 system. This will produce a very subtle reverb (which is what Allen believes in), but you can get a more dramatic effect by setting the two OUTPUT controls much higher than 1/4. Try going through this and see if it helps. If not, you may have a different kind of problem with the setup

1. Start by setting controls as follows:
   1. Turn input control up to about 3/4
   2. Turn output controls up to about 1/4
   3. Turn Bass controls to mid-position
   4. Set all 4 DIP switches off -- (long reverb--see below)
   5. Turn unmarked control (noise) down all the way (early models only) *
   6. Turn mixer controls up to around 1/2
2. Final Adjustments
   1. Reverb level--Adjust output controls. If output controls are turned up and you start to hear background noise in the audio, back controls down until noise just disappears and increase mixer controls for desired volume level.
   2. Audible background noise (buzz or ringing) after reverb tails off--adjust unmarked control in small increments, key, and repeat adjustment, etc.
   3. Set the DIP switch controls for the length of reverb desired according to the following chart.
      
      IMPORTANT -- WHENEVER THE DIP SWITCHES ARE CHANGED, THE REVERB TAB MUST BE TOGGLED OFF AND ON AGAIN TO TRIGGER THE NEW SETTING.
      

      FUNCTION	DIP SWITCHES
      	1	2	3
      Long	Off	Off	Off
      Med. Long	Off	On	Off
      Medium	Off	Off	On
      Short	Off	On	On
      Shortest	On	On	On

   4. DIP Switch #4 is for changing the delay time to simulate front of auditorium or rear of auditorium reverb. Switch #4 in the "off" position is for front reverb and switch #4 in the "on" position is for rear reverb. If two ADR-4 systems are used (Quadraphonic Reverb), one system would be used for main organ speakers with switch 4 in the "off" position. The second reverb would be attached to antiphonal location speakers with switch 4 in the "on" position. All other controls should be identical for the two system

[regeron]

Should this thread be in the Electronic Organs section?

[myorgan]

Yes, I'll move it, Regeron. Thanks for bringing it up.

Michael

[James P]

John,
Thanks for the info!

James