ADC organ no 12v time delay!

[John Vanderlee]

My Wife's ADC would not turn on today. I found that the 12 volts delayed in the outlet box never came on. Yet the static 12VDC is there from the beginning. I opened it up and learned it has a separate little board with a timer chip 555-type that appears to turn on a transistor that gates the 12 volt to the mutes on the amps. Is my analysis correct? The question is how many have experienced this going bad? and which part is the most likely culprit? The board does also have its own little DC supply which is OK.
Or if anyone had one of these lying around, please PM me. I need to get this going ASAP as we do recordings for virtual service. Yes I know I can work around it by "hot wiring" but she hates the thump! And it scares the dog :(
John

[you795a]

Could you post a photo of that little board with the 555 timer chip? I would think that there may be an electrolytic cap in the circuit somewhere. That could be the culprit. I would probably either check the cap, and transistor or just replace the cap, transistor and the 555 timer IC. All should be inexpensive parts.

[John Vanderlee]

Thanks, I will. I may just take the board out, troubleshoot it and meanwhile jumper the delay out.
John

[you795a]

I am thinking that it should not be a complicated board. If you replace the 555 timer, you can always put a DIP socket on the board and insert the IC in that.

[John Vanderlee]

Its not complicated, but as stated earlier, I'm locked out of our shop and all the good stuff is there, so at home I deal with 2nd rate tools and supplies.

[toodles]

As a temporary fix, wire the regular 12V to the amps delay input via a switch, which you can bring around to the front of the console. Turn on organ, wait a couple of seconds, then turn on the delayed 12V. Turn off the delayed voltage prior to power down to mute the amps.

I think it is pretty common for these to do bad--my MDS Theatre III has the problem. and in addition to the thump, the siren effect goes off during power up!

I believe Allen has used several different circuits to handle this delay over the years; if there is an electrolytic, you might replace it with a tantalum capacitor, as they don't tend to dry out, ubt you probably need to replace the active components.

JBird has used an outboard RC time delay circuit as a substitute, posted here on the forum so search for delayed 12V for details; I've got an industrial timer module I intend to install in my MDS.

[John Vanderlee]

The Siren!! Haha, that explains it going off on the ADC4500 we were working on! We were repairing some audio while the mute was disabled. I had that thought in the back of my mind as it kept happening. Thanks for the confirmation. Definitely needs more than a second delay.

[AllenAnalog]

Well I guess the siren could be considered as a herald for the start of a great performance... or a warning to run for cover!

[John Vanderlee]

Yup, I can do a temp fix. However for my further edification; how exactly does it mute inside the ADC amplifiers? If I were in my shop - but can't because of the virus, grrr - I'd open up a spare one and look. Is it a relay across the input?
The reason I 'd like to know is because I'd like to hook up a separate bass channel with separate amp and speaker. I have the AC relay box and outlet from a MOS organ that I'd like to use to turn the bass amp on. Would that be compatible with that ADC 12v delay system?
Thanks in advance for any info.
John

[you795a]

I am not sure about those but I would think that it would be a Hamlin relay that does short the inputs. Allen used those relays a lot, even into the 2000's before they switched to SMT relays.

[John Vanderlee]

That's why it's a fairly heavy transistor in the delay circuit, I assume, because it would have to switch multiple relays in the larger organs.

[toodles]

The ADC amplifier mute works by using a normally closed reed relay across the input to the amplifier. It shunts the input to signal to ground at all times except when the delayed 12V input energizes the relay, causing the NC contacts to open. A 12VDC reed relay using low coil current (high coil resistance) will work for an outboard bass channel to do the same.

[John Vanderlee]

Thanks Toodles, I 'll find enough parts to build this. I may have some perf board somewhere, and I'll see if I can dig up a relay.
John

[John Vanderlee]

NEWS! I did a close look at the Time delay Circuit; found the output transistor with its side blown off. Apparently something happened that it did not like. Now to find a replacement. Pictures attached

[myorgan]

John,

Could you attach your pictures a different way? This is the 2nd post today where the pictures were broken.

Michael

[jbird604]

Over the years I've come to think that this time delay circuit is one of the first things to blow up when there is a power surge or lightning or whatever that stresses the AC circuitry in an Allen. There have been a few organs where we replaced that little board more than once, especially in rural areas where the electric service tended to be a little erratic and more prone to spikes and such.

That's why I developed my industrial strength heavy-duty indestructible delay unit. That and the cost and bother of getting the little thing from Allen. Here's my hand-drawn schematic. It really doesn't do anything except give you a tiny delay, maybe a second at most, between turning on the power and opening the mutes. That's not much, but is sufficient to cover the turn-on noises. But the most important thing is that the mutes close INSTANTLY when the AC power is turned off. It works perfectly in all Allen digitals that I know of.

Delay Circuit for Allen.pdf

[John Vanderlee]

Thanks John!

[toodles]

The delayed mute circuit as designed by Allen consists of a bridge rectifier across the AC power line, with a single cap filter driving the LED side of an opto isolator. This is just used to tell the 555 when AC has powered on. The phototransistor side of the optoisolator drives the 555 timer circuit input using a 2N3904 as the driver. The output of the 555 drives an obsolete MPSU01 transistor (the one with the heat sink) as an emitter follower; a 1N4004 diode is reverse biased across the emitter to ground to absorb any kickback from relays that are driven by the delayed 12V.

I'd guess that the MPSU01 is the transistor with the blown out side. I suspect Allen used that transistor just because they had it as a standard part, because, as an emitter-follower to drive relays it doesn't need anything special as far as specifications. The heat sink is probably in case other relays other than those in the ADC amp mute circuit are used. The relay in the ADC amp should draw about 13 mA per channel.

The circuit specs the output at 1 amp, but certainly the reed relays in the ADC amplifiers don't need anything like that current. The 555 could probably drive those reed relays directly, as the original Signetics 555 was able to source or sink 200 mA.

For a fix, if you know you are driving ADC amps, you might just bypass the MPSU01 and use the 555 to directly drive the delayed 12V output--be sure to keep the reverse bias diode in the circuit to handle kickback. The output of the 555 is terminal 3; the emitter of the MPSU01 is, of course, the terminal directly connected to the delayed output.

[AllenAnalog]

Probably a beefy output to drive the mechanical power relays in a remote amplifier rack.

[jbird604]

Just use my bullet-proof circuit. Virtually no limit to the current it can deliver (up to the rated amps of the relay contacts). I really don't know why Allen had to reinvent the wheel here. Of course my components do cost more -- a good relay with a 120v AC coil costs a few dollars, and the caps a couple dollars each. But it is utter simplicity. And you only need a half second of turn-on delay, not 4 or 5 seconds like they design into their various versions of delay units.

[John Vanderlee]

Thank you Toodles, I was curious about those details but you saved me a few hours of analysis. I had just re-assembled the organ and put it back in place, and the MPSU01 should be here later today. So I 'll just fixed it then. But more good info to save!

[John Vanderlee]

True in most cases, John, except for the siren effect mentioned earlier.
I'll add that circuit to my collection of useful Allen documents(growing thanks to all of you). I had already ordered the transistor(s), so I might as well keep things native.

[jbird604]

That siren would be a crazy thing to hear when you turn on your organ! I'd probably suspect the neighbors had called the cops to make me stop playing so loud.

[James P]

John B. & all,
Could this be the same part referenced here (MPSU01) that would fix my Allen MDS-45 “blown/shorted out” Mute Relay? Currently I've bypassed the Mute relay by attaching jumper wire crossover on Power Electrical junction box (attached pic).
I can play organ all as normal now, but just hear a slight “pop” in speakers when turning organ “on/off”.
Suggestions how to fix back as designed, OR should I leave well enough alone as is, —& be thankful Organ plays great otherwise?
Thanks!!

[jbird604]

You could use my custom delay circuit instead of simply bypassing the delay. The 3 terminals on the strip provide the connections you need, just wire them to the caps and relays and such using the diagram I posted. That will put an end to the turn-off pop.

[James P]

Thanks John! I'll do that!

[mlaird]

I found this thread interesting, and appreciate John's "bullet-proof" mute circuit. Unfortunately, I don't think it will solve a different but related problem that I would like to solve. I have my R-350 hooked up to a powered subwoofer (SVS PB-2000), which works quite well for the 32's in my instrument. Unfortunately, it makes quite the thump when I turn off the organ, since it has no mute circuit. My mute circuit works just fine for all the Allen amplifiers, but can't mute the thump from the sub because it is getting its signal directly from the computer cage via the line-level audio cables, not the output of the amplifiers (which gets muted properly).

Do you guys have any ideas on how to solve this problem? Basically, I would like to stick some sort of switch inline with the audio-level signal from the computers to the sub and have that switch immediately shut off when I turn the power off. Ideally, I'd also like it to delay turning on the signal to the sub, since that makes an even bigger thump, but usually that doesn't happen because the sub goes to sleep if it sees no signal for more than a certain number of minutes. So as long as I turn the organ on only after having it off for say, fifteen minutes, the sub has gone to sleep and doesn't wake up until after the startup thump is done and over with. The shutdown thump is always a problem, however.

Could I solve this with a simple relay driven by the 12v mute circuit?

[myorgan]

Personally, I'd just opt for the poor man's mute relay-aka a power strip.;-)

Michael