ALLEN ADC POWER STARTUP

[Guest]

I have a friend that just purchased an Allen ADC8300 organ. He was trying to install it and couldn't figure it all out, no sound. I found that the delayed 12v from the console to the amp shelf was not working. He also didn't have the delayed 12v connected to the rack. But I had no delayed 12v from the console. The next evening when I went there, now there was no switched 12v to turn on the amps, and the capture system stopped operating, but he was trying stuff.</P>


Found the delayed power supply board in the receptacle box, and found the one transistor was shorted. Pulled the board to take it to my shop to attempt a repair. The only thing I could find was the shorted xistor, and replaced it, but still no delay or always 12v. Tried reverse engineering the board to see what was wrong, but can't figure out the circuit. Next step, I thought was to just build a new 12v power supply with a delayed start-up output. Took it up tonight, installed the board, and it came to life. But, there is a bad thump when you turn it off now. Is this a timed both ways supply? It appears that the 12v should come up first, then the delayed 12v to un-mute the amps. On turn off, I guess it should keep the amps powered, with the delayed 12v being the first to disappear so that it mutes the amps before turn off.</P>


Anyone know how that circuit is supposed to work, or have a diagram of it? I have the old board, and haven't given up but really need a schematic. Haven't gotten to the capture system. Thought maybe I would get lucky and the missing delayed 12v had something to do with it, but wasn't the case. </P>


Anyone with any help would be appreciated.</P>


Russ</P>


Allen AP-4 at church, Allen AP-3 at home</P>

[circa1949]

Re: ALLEN ADC POWER STARTUP



I never used my organ's built in amp, but encountered this muting circuit issue when I was prepping the organ to sell it and the future owners wanted to use the internal amp.
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Indeed, I can understand how it works on "switch on", but not how it manages to mute the amp in the split second before the cage "burps". There are big capacitors in the cage power supply...perhaps they slightly delay the cage death long enough for the muting circuit to mute. But in that case your circuit should work, too...
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Some people here have more experience with real repair of these organs and will probably chime in. There's probably a simple explanation.</p>

Interesting that the muting supply circuit was dead...you wonder if a simple thing like that caused the former owner to ditch the organ. At any rate an ADC8300 is a fantastic instrument - presumably just below the Anniversary 8350. Please post some recordings when it's up and running.</p>

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[jbird604]

Re: ALLEN ADC POWER STARTUP



Russ,</P>


Yes indeed, it does have tokill the mute voltage (the "delayed" +12) instantaneously when the power switch is turned off, which releases the mute relays and therebygrounds the inputs to the amps, totally eliminating the turn-off pop.</P>


The circuits Allen has used over the years to do this have been varied. None of them have been extremely reliable, and this circuit is often the first thing to go when there is a power surge.</P>


When I find an organ with the delay-board burned up, I normally replace it with a simple circuit consisting of a very large capacitor (5 to 10,000 mfd) with about a 50 ohm resistor before it and after it. In other words, take the un-delayed (normal) +12, go through a 50 ohm resistor to the + terminal of the big cap (the other end of it is grounded), then on through another 50 ohm resistor to the point where delayed +12 is required (mutes).</P>


This cap with take a couple of seconds to charge up and will therefore delay the opening of the mutes. It doesn't delay the mutes as long as Allen's circuit does, but it is a long enough time to prevent the turn-on noises.</P>


Now to dealwith the turn-off pop --what I've done isplace in series between the above-described delay circuit and the mute relays a normally-openrelay with a 120volt AC coil. I connect the coil to the switched AC of the organ. Now, as soon as the organ is switched off, the coil is de-energized, the contacts of the relay open, and the +12 disappears from the mutes, letting them ground out the amp inputs. This happens quickly enough to silence the amps before you hear any pop.</P>


A resistor of perhaps 2K across the big cap will allow it to fully discharge rather quickly when the organ is turned off, preparing it to delay the turn-on voltage once more at the next flip of the power switch.</P>


Hope this helps.</P>


John</P>
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[Guest]

Re: ALLEN ADC POWER STARTUP



Yesterday, I took the Allen Time Delay Board to another friend of mine, and together we "reverse engineered" it. I now have the parts to shotgun it, and am trying to rebuild it. I kept looking at the board and couldn't figure out how it could make the 12v normal. Didn't make sense. He agreed. The 12v normal must be coming from somewhere else. Where, I ain't sure. Need to search that out. I am sure that I can repair the delay board, but think the problem lays deeper than the board, since I also have no 12v normal feeding it.</P>


Could the missing 12v normal also be the problem with the capture system? I did put a 10,000 mfd cap across the relay coil of the ac power switching and isolated it from the 12v I am supplying with a diode. It now only clicks a little when turned off. My delayed circuit must be holding up a little longer after turn-off than I need, and it is about 16 seconds delay on startup, but I really think I need to find the rest of the source of the problem.</P>


Thanks though for the suggestions, I appreciate them, and am still open to other suggestions. Will keep you informed how this turns out.</P>

[jbird604]

Re: ALLEN ADC POWER STARTUP



The +12 in Allen ADC organs is supplied by a very ordinary unregulated supply that sits in the floor of the console. If you have no +12, perhaps the fuse is blown on that supply.</P>


You'll recognize it by the orange wires soldered to the fanning strip. The fuse is on a removable holder on top of the supply.</P>


John</P>

[jbird604]

Re: ALLEN ADC POWER STARTUP



Maybe I'm not making this clear. The function of the delay board is NOT to create any voltage at all. The un-delayed +12 terminal on the AC distribution box is NOT the source of un-delayed +12. That is where the +12 comes in from the +12 supply that is a completely separate component. The box I referred to above with orange wires coming off the fanning strip.</P>


The delay board does only two things...(1) it waits about 5 seconds after the organ is turned on before passing +12 on to the relays that un-mute the amps. Then (2) at the instant the AC of the organ is switched off it immediately cuts the +12 going to the mutes so that the amps will instantly mute and no turn-off pop will be heard.</P>


That's why I replace that board with the very simply but highly reliable circuit I described above. Believe me, it is much simpler to do that than to fool around with the board you found burned up in the AC dist box!</P>


John</P>
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[Guest]

Re: ALLEN ADC POWER STARTUP



Thanks John, The more I thought about it, that is what I assumed, but the other evening, I checked every power supply that I thought I could find, and they all had proper voltages from them. Glad to know that the delay is only a delay. I am going there today, and will check more thoroughly. By the way, yesterday I had a few minutes, and I did repair the delay board. Replaced the shorted switch xistor which I had tried before to no avail, but now also replaced the 555 timer IC, and feeding an external +12 to the board, and applying power to the 110, it does turn on in about 6 seconds, so I knew that the 12v normal had to come from somewhere else.</P>


Well, got to go, out too late last night, didn't get ready for church today, so I must go pick some music for today.</P>


Will keep you informed.</P>


Russ</P>

[Guest]

Re: ALLEN ADC POWER STARTUP



John, [:)]</P>


Thanks for all your assistance. Got everything working this afternoon. Used a 12vac relay with a wall wart to power the relay, used a 10,000uf cap with a steering diode and a 50 ohm resistor to feed the mute terminals. Wired the relay so that in the off state, it takes the 12v from the cap and drains it to ground through a 2K resistor. Didn't reinstall the delay board, just put it inside the console, just in case.</P>


I had no 12v on Thursday night, today I did. HUMMMM. Found a bad solder joint on the one 12v lead leaving the standalone power supply, and repaired. Also found the problem with the capture system. The smaller (8" X 10") board mounted on the hinged plate above the right card cage, had no 5V. Looking at the plug, the one lead looked like someone had taken it out of the plug and put it back. It was not connected to the pin on the plug, redid the connection, and now that works too.</P>


Being that this is such as large instrument, and the room doesn't allow all those speakers, I Y'd several of the channels together, All the greats together, All the swells together, All the Choirs together, and the high freq's of the pedals together, and fed them to single channels to drive 4 of the main speakers, and another 2 channels for the low of the pedals. Not too bad. Do have to have the amp gains pretty much at max, and some of the voices are low, so we are going to work on balancing out the voicing. Told him he should build a balcony around the room to put all the speakers back, and connect the way it was, but he thought not. There are 17 of the 15" 3-way cabinets, and 2 of those humongous 15" only bass speakers. But he is happy, I liked playing it. </P>


Should work out now. Thanks again.</P>


Russ</P>