Allen 603DK

[Tom Albrecht]

Hi,

I just acquired an Allen 603DK to use as a practice organ at home. It came with 5 amplifiers and 5 speakers -- two HC15s, two HC14s, and an HC20 subwoofer. I don't think I can make room for all these really big speakers, so I will be looking to use smaller speakers and/or combine channels to reduce the number of speakers.

I see that there are 4 audio lines out of the console:

- A Main
- A Flutes
- B Main
- B Flutes

Can someone tell me what is routed to each? Are there known good methods for combining channels?

One other question. Two stops don't work -- the 1' Siffloete and the 4' Choralbass. Is the most likely cause the drawknob itself, or is the problem likely to be elsewhere?

I'm quite experienced in electronics, so don't refrain from giving me the full scoop technically if you know the answers.

This is really quite an instrument -- a little more elaborate than the one our church has! (We have a similar Allen at church, but a few years older and with a slightly smaller console and few less stops). Looking forward to setting this up in a manner that still leaves some room for living in the living room!

[jbird604]

Tom,

The 600 series MOS organs are indeed quite decent. Even though the technology is 40 years old, I am often amazed at how realistic many of the individual stops are. And the 600 series have two complete MOS systems in the console, so you have rich ensemble on everything and beautiful celestes when you want them. I suppose it has the old sequential combination action (activates the drawknobs in groups rather than all simultaneously for the "clackety-clack" effect), unless it's a late enough 603 to have Double Memory capture. Either system has been quite reliable and should serve you well.

As to your questions -- The "Main" channels of MOS organs normally carry principals, strings, mixtures, and reeds of the manual stops only, with the exception of 16' manual stops which go to the Flute channel. The Main channels also carry the Alterable (card reader) Voices. Since these channels don't need to produce any significant bass, you could downsize by using some small speakers (good quality pro-sound) instead of the big HC-14 or -15 units. BTW, HC-14 and -15 boxes are functionally identical, differing only in the location of the crossover assembly. Allen tweaked the crossover components over the years, so yours may differ in minor details but are fully interchangeable.

The "Flute" channels carry all the manual flute stops plus any 16' manual stops plus all the pedal stops. Obviously, these channels are much heavier in the bass, so large cabinets are pretty essential. However, since you have a B-20 subwoofer, it would be possible to downsize the flute channel speakers as well and let the B-20 do all the heavy lifting in the bass.

(Note: if your 603 happens to be one of the "-3" versions, which would be indicated on the model plate as "System 603-3" you will find that a few manual stops are actually flipped to the opposite channels, but the primary makeup of the stops going to each channel remains the same, with all the bass-heavy stops in the flute channel.)

If you want to try it, you could theoretically mix the organ down to two channels and just use two of the HC cabinets. You might not get a lot of 32' pedal since the HC-14/15 boxes have stiff woofers that can't do much in the 16 Hz range, but unless your room is large you may get all the bass you want.

Important note about mixing: Allen MOS organs do NOT operate at ordinary "line level" audio, but have a rather low level signal at high impedance. Also, the expression system consists of a complex interaction between the LDR cells in the shoes and the input stage of the amplifiers. So, if you decide to mix channels, you can try just using "Y" cables to directly combine the two channels without inserting any intervening electronics between the DAC board and the amp. If you wish to use a real mixer, you'll have to deal with re-designing the expression system. It has been done, but it is not simple. Since you have electronics experience and knowledge, you can probably figure it out.

If mixing channels, there are two ways to do it. One way is to combine the A Main with the A Flute, then combine the B Main with the B Flute. The reasoning here is that the output from each computer (A or B) is locked in tune and will not produce a lot of periodic outphasing if the two channels are mixed. When you draw celeste tuning, the tuning spread between A and B computers is increased, and it will make better celestes if the sharp and flat tones come from different speakers.

On the other hand, it might actually make more sense to combine Main A with Flute B, then combine Main B with Flute A. That way, the bass energy would be equally distributed between both channels and you would still get the separation between channels when you want a celeste. So, try it both ways and see which gives the best effect. Let me know what you think.

For alternative speakers (smaller than the HC's) -- if you decide to keep the B-20 in place and downsize your manual speakers -- take a look at pro-sound boxes with 10" woofers and good quality tweeters. I'd stay away from the cheaper PA boxes with piezo tweeters since they tend to have irregular response and may sound shrill or ragged. I have bought perfectly good pro-sound speaker cabinets with 10" woofers for not much more than $100. Look for units that have a ferro-fluid cooled horn-loaded tweeter.

[jbird604]

Forgot to address the non-working stops question. If both stops are silent in both computer systems, the drawknob itself is the only thing in common. It probably has a reed switch activated by a magnet when the knob is pulled, and the reed switch could be defective or it could just be out of position slightly. You can try re-positioning the switch by gently nudging it or even using a small screwdriver. But be careful because they are fragile and may break. Of course, you may have to replace it anyway, so there's nothing lost if you break it.

[Tom Albrecht]

John,

Thanks very much for the detailed responses! The information on the content of the channels and the mixing will be most useful as I figure out what I'm going to do regarding amp channels and speakers.

Last night I took out the draw knob panel and checked the reed switches. Both are OK on the stops that are not functioning. That would appear to leave the wiring harness or a connector as the most likely culprit, since you have explained that the rest of the system should be separated into two redundant systems, both of which should not have failed simultaneously.

Update: After reseating connectors on the boards, the Choralbass has come back to life, but not the Siffloete. Checking the voltage on the drawknob reed switch, I see the same behavior on the Sif as any other drawknob: 1.6 VDC across the switch when it is off, and zero when it is on. That would suggest that the drawknob reed switch is in fact properly connected to the logic and functioning.

Is there a schematic available somewhere? As you can imagine, once the wire goes into the wiring harness, it is not trivial to figure out which wire it is on the other end. With a little more info on the circuitry, I could probably trace down the issue. Since there is only a single wire from the reed switch into the wiring harness, there must be at least a few components or traces on a board in common before the signal splits between the two computers. Must be a failure at that point.

By the way, mine does seem to activate all the drawknobs simultaneously when using the presets (no "clackity-clack"), so perhaps it has the "double memory capture." Not sure what that is yet.

[Tom Albrecht]

These charts show how my organ is behaving. As you can see, relatively few stops actually play through more than one channel, and two don't play at all (Choralbass stopped working again). Is it possible that this organ is supposed to be configured a bit differently than John's description above? For example, I could possibly imagine it might be intentional that the B Flute channel is dedicated entirely to bright reeds on all three manuals, and nothing else. Or is all this an indication that things are seriously goofed up?

Fortunately, the instrument is quite playable in this condition, but I'm suspecting is not quite right...

[jbird604]

Wow! Your organ has been highly customized, but that is not surprising. If you follow the wires from the drawknobs, you'll see they terminate on a "tone strip" -- a long strip of wood with nails to which the wires are soldered. These nails run down the middle of the strip, and above and below you will see additional rows of nails. There will be diodes or jumpers from the central row to the side rows. One computer system is connected to the top row, the other to the bottom row.

To make a stop play in a given computer system, a diode or jumper is connected from the drawknob (central row) to the corresponding computer. Diodes must be used when a stop is to play from both computers to prevent interaction between the two systems, which could produce undesirable effects.

If you study your tone strip, you'll discover that many diodes have been clipped out (or perhaps were never installed) to give the organ this particular distribution of stops. In the earliest MOS organs, all the stops were duplicated in both computers, but they discovered later that they could build more interesting organs if they doubled some stops (especially those that needed to be more powerful or that needed to be "celestable") while leaving others (such as mixtures and high pitches) undoubled so that they would not create undesirably fast beats in chorus or celeste mode.

So, you have an interesting organ. All my earlier comments still apply, but it looks like the builder intended to put many of the heavy stops into a single channel (A Flute) to make it easier to cross it over to the sub. He reserved the B Flute channel for mostly reeds, possibly positioning that speaker for an en chamade effect. But they left the stops that need to be celestable in both channels. A very clever arrangement!

You can probably follow the wiring with a continuity tester to see which nail is connected to the non-working drawknob. Then follow it to the "stopboard array" (SBA) where it will connect to one of the plugs. If there is continuity all the way from the knob to the SBA but the stop does not sound, you may have a defective SBA board. But I wouldn't fret much about one stop not working with so many that do! You could also move the diode on that stop at the tone strip and cause it to play through the other computer if it will do that.

Keep us informed!

[Tom Albrecht]

John,

Once again your information has been right on the mark and extremely helpful!

I was indeed able to trace the wires from the drawknob panel to the tone strip. Sure enough -- that's where the problem was with the two stops that were not working. Two of the diodes were not properly soldered. They looked like they had been clipped at one time, and then simply touched against the terminal without a good solder connection. After resoldering, both the Choralbass and the Siffloete are working beautifully. Also found one other case of a clipped diode, which I reconnected -- the Mixture III had been channeled only to A, but I reconnected it to B as well. Perhaps the last user didn't like shrill mixtures quite as much as I do. The Celeste on the mixture doesn't bother me, and the Mixture IV on the Great has been connected to both all along, so it's not a big change.

With all those tone strip connections back in place, the organ works 100%, and it appears that everything was intentionally designed to split the stops between A and B this way.

I'll give some more thought to this as I consider combining channels. I may keep all four channels separate with smaller speakers, perhaps using one of the original Allen speakers only for B Flutes where there is need for solid bass. I will try it without a separate subwoofer to save space. My subwoofer is the HC20, not the B20, which I understand from one of the other current postings is not really so special as a subwoofer anyway, compared to the woofer already built into the HC14.

I'm looking at making a "shelf" inside the console near the top for the amps, so that I don't have to have a separate location for the amps. I don't plan to run at particularly high volume, so perhaps heating and ventilation will be satisfactory. Obviously with the shelf in place, the Swell keyboard can't be tilted upward for service, but I'll make the shelf easily removable so the Swell keyboard can still be tilted without a lot of extra effort.

With the amps inside the console, and some smaller speakers, this will make a nice setup for my living room.

[jbird604]

Keep up the good work, Tom!