Rodgers 840 Questions

[John Vanderlee]

The organ is in my shop! We hooked it up yesterday to some Allen speakers (the owners trashed the originals) and it is an amazing instrument. Then my friend and I spent a couple of honors studying the innards and come up with a few questions and observations.

It has a "gazillion" trim potentiometers! I would expect those on the obvious generator boards but there are many , many more, columns of them in other places. It has some notes out of tune which should not be problem on the generator boards, but should we just leave those other pots alone?

And what is the best place to start tuning, the Principal generators?

It looks like the preamp board has 2 RCA jacks for what we assumed was Reverb, there is even a small Amplifier IC (LMXXX something)in the vicinity. Would that have been to drive a spring reverb? touching those inputs caused no sound response. There is also no reverb tab on the console.

On the inside above the swell pedal assemblies is a board with DIN connectors named for the various divisions. Would that be for the MIDI? It does not say MIDI there although there is a factory installed MIDI box on the gate. Or I thought maybe they were pre amp outs for additional amplifiers?

Finally - for now -There is a big coax connector for the pipe option. Would that be serial data for the pipes? We own a Rodgers 780? that has two ranks of pipes but they seems to be operated from direct drivers from that organ. Did Rodgers use some kind of De- multiplexer to talk to pipes from that coax connector?

Have not decided yet if this is going to be a fun unit or a nightmare.....

[toodles]

The "columns" of potentiometers that you are seeing are probably the Trompette keyer--there is a filter for every 3 notes, and they are on a daughter board, all in a row. Don't mess with those unless you have a few hours to spend revoicing the trompette. There is, however, an overall brightness control on the trompette, and that's usually enough to adjust the trompette for various voicing desires.

As for tuning, the lowest 3 octaves and the celeste oscillators use RC oscillators, and those are tuned with poetniometers on the generator boards. The other oscillators are LC and are tuned by turning the cap on the inductors. I can scan and send you the tuning procedure for the 830 which has the same oscillator setup as the 840. Don't try to tune without the tuning instructions as you need to follow a sequence so that the pipe tuning adjustment will track.

The two RCA jacks on the preamp are for a spring reverb. There is no reverb tab--there should be a pot mounted on the bottom of the keydesk, near the kneeboard. There is also a headphone jack there. Reverb is controlled by adjusting that pot--no on/off control. If you substitute a digital reverb for a spring reverb, be aware that the spring reverb provides a weak signal compared to the digital unit, so keep the adjustment very low. There is also some frequency compensation with the spring preamp, and it would be best to bypass that altogether, which means returning the reverb signal to where the keydesk mounted pot signal returns to the preamp.

The DIN panel above the swell shoes is for external amplifiers (for augmenting the sound) and antiphonal divisions. You won't need to connect anything there is you don't use external amps and speakers.

If the MIDI box is stamped "Factory Installed MIDI" and there are lighted pistons on the bass (left) cheekblock, then look for MIDI In/Out/Thru under the keydesk. The factory MIDI is actually an adapter under the metal panel, and is just a small circuit board. Also under the metal panel is the CPU and the multi-function board.

The coax connector on the output panel is serial data for a glockenspiel and/or pipes. If your 780 is the Asilomar 780 with LED tabs (like the 840) and the pipes are from Rodgers, they should connect to the 780 console via a coax cable just like the type on the 840. If they were done without using Rodgers pipe equipment, I can't advise. If you open up the 780, and open the racks, and find the coax cable connected on a panel just like the one on the 840, you can move the coax to the 840, program the 840 for pipes, and you'll have pipes on it.

If you have the glockenspiel for the 780--it came with one as standard--you can connect it to the 840 if you want, too. Connection is console to glock to pipes--i.e., the glock and pipes are connected in series. If your pipes are connected via your glock, then just move the cable to the 840 and you'll connect both to the 840 instead of the 780. Note you still have to configure the 840 for pipes.

[toodles]

I realized that the 830 tuning instructions are missing some information, so I'm not going to forward that to you as I indicated--without the missing information, they would be extremely confusing. Those instructions also require a Peterson tuner and an oscilloscope--I don't know if you have those.

So, as for tuning, as long as you do not try to tune notes 24 and 36 of the main oscillators, any standard tuning techniques will be fine (counting beats, strobe tuner, pitch reference, etc.). Tuning notes 24 and 36 set up the phase locked loop system to tune the oscillators to the pipes, and if you adjust those tunings you'll mess up the pipe tuning adjustment.

[John Vanderlee]

Thanks for this wealth of info, toodles! It's interesting, but I see NO LC oscillator coils(I know what they look like) Everything I see is RC.
I 'll peruse the beast again tomorrow- much better informed!

[jbird604]

Must be a very late 840, if it has all RC oscillators. I have seen a few Rodgers analogs that must have gone out the door the last year of production with all RC's. There should be a little paper label somewhere that gives instructions relating to the #24 and 36 oscillators, as toodles mentions. Or perhaps not. I seem to recall that the all-RC organs didn't need that phase-locked loop, which functioned to keep the RC and LC sections of the generator synced up.

We tune Rodgers analogs with a cheap or free cell-phone app called "ClearTune" and it is far better and more flexible than the $1000 electro-mechanical device that I bought 40 years ago when I was starting out. A quick search will turn it up for you, if you don't already have a chromatic tuning program of some kind on your phone.

As to the vast numbers of thumb pots all over the organ -- at the Rodgers factory they would've set the organ up for testing and voicing before shipping it out, and they normally marked the pots with a gold or silver Sharpie pen to show the position they arrived at when setting it for standard levels and tone. As good as I think my ear is, I often start out by returning all the pots to this marked factory position, and doing that will frequently solve all kinds of weird voicing anomalies that may have been introduced by some other tinkerer. Then one can always vary from the factory settings very judiciously to address very specific changes you want to make in the voicing. 99% of the time the factory did it best!

The great principal unit probably takes it pitches off the primary rank of oscillators, so tune that first. It goes all the way to the top of a 2' stop. If there is a secondary "ensemble" rank, it may not cover the entire range, might be only 60 notes or less. Most likely the great flute unit is tied to it, so use that stop for tuning it. The celeste rank is tuned of course using the swell celeste stop. (don't use the choir/positiv celeste. best I recall it is not a "real" celeste but a fake one using a bucket brigade effect.)

You must of course tune the 16' octave (notes with a zero as the first digit) using a 16' pedal stop, and the 32' octave (notes with two zeroes) using a 32' pedal stop.

[toodles]

Main oscillators run from 32 ft to the top of the 2 ft stop; ensemble are 61 notes, and celeste are 61 notes, so those cover the 8 ft range only. As JBird indicates, some very late model analog Rodgers used all RC oscillators--I didn't know they carried it into the 840.

If you open the back, the lowest RC oscillators are at the lower left hand corner, and the LC would be the bank just above that--so if those are RC, then it's all RC. I'll have to look for tuning info on an all RC organ--I think I have that in one of my tech manuals.

[John Vanderlee]

Again thanks for all that good info. It appears the organ has never been tinkered with. It was in an original location in Saugerties, NY about 12? years ago, when it was replaced by a new Allen. I was asked to truck it to another church in Poughkeepsie,NY, where a friend of mine played it for the inauguration. Last year the church closed and the private school now owning the building called me to "get rid of it". I happily picked it up. Now the friend I mentioned wants it in his home for a practice instrument. We're doing our best to accommodate him.
It 's nice to get an instrument that you know the history of!

[John Vanderlee]

One more thing we found: It has a small board that looks like an add-on. It has 2 Eproms on it by Walker Technical "MDAG2.1" What did Walker do with Rodgers?
Download address for picture:
https://mail.google.com/mail/u/0/?ui...1&disp=safe&zw

[toodles]

Walker made several enhancement packages for analog Rodgers organs. The two common ones I know of are a jitter circuit--Rodgers used to call this "activity" and an inharmonic chiff. The jitter circuit adds a slight random tuning to the oscillators--like Allen's "Whind" except operating on frequency modulation instead of amplitude. The inharmonic chiff adds a more complicated chiff to the Rodgers flute/principal voices.

Your photo link wants me to sign up for an account--it's better to just post the photo in you posting here.

[John Vanderlee]

sorry still learning!

[toodles]

Aren't we all? :-)

[John Vanderlee]

Walker board

image of board found in Rodgers 840

[toodles]

Definitely an "Inharmonic Articulation" generator--it generates noise at the start of a note, for flutes or principals. One of these is probably on each flute and each principal keyer board--or maybe just on one where a more pipelike chiff was desired.

[John Vanderlee]

Thanks for that explanation. Now back to the reverb. next to the headphone jack is just a hole where a pot. could be. Yet the pre amp has 2 rca jacks soldered in. I tried to inject a signal onto the “in” as well as the “out”. Heard very weak signal out of speakers

[toodles]

Check to see if U59 is installed--it's probably located near the "in" jack. That's the reverb recovery op amp.

Digital reverb was offered as an option on late 1980's analog Rodgers, and if yours had it installed originally, the spring circuitry probably was not installed.

Also, use the "out" and run it to a small amp with speaker to see if you've got the mixed signal to run the reverb spring. If it is there, you can run it into a digital reverb; the signal can be returned at the same locations where the reverb pot signal returned. See pages 7 and 8 of the output preamp schematic.