Identify & comment on this Allen organ?

[zuulmusic]

I'm looking for an upgrade from my Rodgers 750B for home practice and this is Allen is available.
Can anyone identify it and comment if its any good? Approx era? Things to check for if/when I visit it?
It does have an "Allen Digital Computer Organ" label.
Much thanks!

[Organkeys Jones]

MOS 1 (1st generation of digital organs), 600 series, dual computer, 4-channel with possible bass channel, mid 1970's, has new amps. I would consider this an upgrade from a Rodgers 750B.

[jbird604]

Looks super clean, and the amps have been replaced with modern types, presumably by an Allen dealer or tech. While MOS organs are sometimes criticized for the granular sound when heard up close (as in a small home organ room), they can sound marvelous if there is room for the sound to bloom a bit. Also, the 600 and larger series, with more than one computer, definitely sound better, even up close, due to the subtle chorusing produced by the double computer arrangement. That one has the Double Memory capture action as well, which ought to be a large improvement over the capture action in an older Rodgers console.

Be aware that there COULD be numerous issues with an organ of that age, such as speakers needed re-coning, battery damage on the capture board (if batteries were not changed regularly and/or moved off the board), and of course just general maintenance. However, that one does look exceptionally clean, and the fact that the amps were updated in recent years leads me to think that someone took pretty good care of it.

[AllenAnalog]

So here I go again about things on the bottom shelf! LOL What are those three boards with terminal strips on the left and eight vertical posts on the right? Are they a new style of UNIVREL board or something totally unrelated to the organ?

Also, I see a +/- 15VDC power supply on the top shelf that one would not normally need in a MOS-1 organ (unless it had been upgraded to DAC4 boards, in which case the power supply would presumably be inside the console, not in an amp rack).

[myorgan]

Thank you, John, for the details on the amplifiers and their iterations.

Michael

[jbird604]

Larry,

Those boards on the bottom shelf are the "adapter" boards that Allen provided with the M5 amps to accept the low-level high-impedance DAC board outputs and match them to the line-level inputs of the M5 amps. They also have speaker output terminal strips to allow speaker wires with spade lugs to be connected, as the M5 amp's speaker outputs are just pins on a plug.

[AllenAnalog]

Just ran across this recent YT video of someone playing what looks like this same model organ. Nice celeste sounds. There are pics of his custom speaker and amp rack enclosures on the Allen Owner's Group Facebook page.

[toodles]

Perhaps the only "downgrade" from the 750B is that there is a single expression shoe on this model--the 750B had 2. Note that this organ has no native percussion stops like chimes or harp; you had to execute those via the tone cards, and I don't know if this series had a good chimes card (or even one at all).

[myorgan]

There were at least 2 different chimes cards for the MOS series organs that I know of. Neither were spectacular, but when used over an accompaniment, they are passable.

Michael

[davidecasteel]

Chimes, or tubular bells, don't actually "play" the pitches that we "hear". They have partials with the ratios of 81:121:169, which are very close to being 2:3:4 -- close enough that we "hear" a virtual pitch about an octave lower than the lowest partial. I used my spreadsheet to see what the waveform would look like with the 2nd harmonic at level 1 and the 3rd and 4th harmonics at level 0.5; as it happens that copy of the spreadsheet had a waveform from a card image also within it, and the 2 waveforms were very similar. Unfortunately, I have not been able to identify just what card I had used for the last "save" of the spreadsheet.

You might find that some of the 4' flute stops might produce interesting bell tones when used with percussion.

David

[jbird604]

David makes a good point about using the percussion. While authentic-sounding chimes were not the forte of the MOS series, many folks find simpler percussion tones just as satisfying. The good old Chrysoglott card (with percussion) makes a lovely bell-like sound, and has the advantage that it doesn't sound bad even if you play "chords" on it. Same goes for turning on various combinations of flutes with percussion. You'll get numerous "music box" effects, depending on the pitches and where in the manual compass you play. Just don't set the sustain length too high so that the notes run together unattractively.

I've made this pitch to a customer more than once when trying to sell a MOS organ. True, the chimes card is pretty bad. (And the cheaper MOS models don't even have a card reader.) But a skillful player can make some interesting and appealing bell-like sounds using nothing but flutes and percussion.

[myorgan]

To be fair, however, Allen did make several harmonics cards available for the purpose of making the chimes sound more realistic. Unfortunately, I've never found documentation regarding exactly which cards to add to the chimes to make them sound more realistic.

Michael

[Admin]

I found the Tubular Chimes card to be the most chime-like. The one I have is octave sounding and was best played an octave lower. Two basic problems for percussions with MOS series Allens is the lack of upper harmonic development and lack of polyphony. The long sustain required by chimes eats polyphony and the older notes in a sequence drop out suddenly. Playing a melody with chimes on a MOS organ is not satisfying for this reason. Single note chime accents were passable, but in addition to the polyphony and harmonic issues, Allen didn't manage to get the decay of their percussions quite right on MOS instruments. I'm not sure if it had to with the linearity of the decay, the limitations of a 7 bit resolution, or some other factor, but the decay always seemed to end abruptly, like a damped string, rather than a smooth tail to silence.

[AllenAnalog]

I haven't seen any response from the OP about whether the instrument was purchased. Curiosity runs deep here.

[zuulmusic]

I haven't seen any response from the OP about whether the instrument was purchased. Curiosity runs deep here.

Sorry to say that somebody snatched this up before I had a chance to set up a visit! But thanks everyone for the info.