The Organ Forum

Someone mentioned the 555 timer, which is still available in a CMOS version however it lacks the required stability due to component drift with temperature, etc.  The timing on the 555 is set by the R-C time constant.  For a free running oscillator you need a Hartley or Colpits using an Inductor and Capacitor resonant circuit.   Remember, you gotta tune it also so the Inductor must be variable.  Better buy an old analog organ and rebuild it.  The question is your priorities: do you want build and tinker or play.

Al  A&W (Allen & Whistles)

Tinker?  Somebody call me??  Al you make a good point, I'm constantly shifting between the technician and the organist mode.  I do love to collect, learn about and restore these old analogs but it does sometimes get in the way of just sitting down and enjoying the playing experience or working to learn a new song.

I too would recommend picking up an old vintage organ (probably for free or next to nothing) as a treasure trove of assemblies.  Lots of folks strip some very nice Rodgers consoles (Trio's, etc.) to use the cabinets, keyboards, etc. for building VTPO.  The Rodgers stuff is fairly easy to work with except for the size of the circuit board panels.  They work well in the Rodgers "swinging door" consoles giving you easy access but rebuilding them into a smaller enclosure might be some work. I guess you could separate the various boards into smaller enclosures.  Electrically they would be very easy to utilize in a custom design and the tuning stability seems to be great.

I recently picked up a vintage 60's Allen Theatre Deluxe that was heading for the landfill.  It's got three sets of tone generators, each built into a rugged horizontal metal chassis that slides out of the console.  These too are built like a tank, would be easy to use in a custom design and seem to hold their tuning quite well.  Once again the form factor could be a concern since althought he chassis is fairly thin and short it does stretch almost the width of the console.  I see a similar one of these show up a few times a month on Craigslist, ebay, etc.

As a bonus you get some amplifiers, voice filters, speakers, etc. that you could also use.  You sure couldn't build this stuff from scratch any cheaper.

 

 

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Gary
(Rodgers 321B, Gulbransen Theatrum, Hammond H-133, Gulbransen Rialto K with 100GK Isomonic Leslie, Rodgers 322 Trio Deluxe,Rialto K 1135 with 102 and 103 Leslie, Allen Theatre Deluxe with Gyrophonics and other speakers.

Very interesting stuff. Here is another thought. I have a Korg Poly-six that suffered the dreaded leaky NiCad problem. I removed the offending battery and cleaned up the board and it appears that very little trace repair will be needed. One logic chip will also need to be replaced as well. I was planning to convert it to usig a simple flat lithium battery. I wonder if it would be possible to hack into it to allow keying it from a pedal board. That could be fun. The Korg has a bend wheel that could be used for tuning (or even transposing as it has a pretty wide range).

 As to whether I want to play or build I guess I would have to say that I have interest in both. It would be nice to have a portable pedal board but it would also be fun to screw something together in the process. Right now I am in the process of building a cheap opamp based crossover for the PA system involved in the process.

Just for background I have a Peavey XR600 powered mixer that will be used to provide the mixing of a vocal mic or two and the instrument(s). It has a main mix out at line level and direct inputs to both power amps. I am building the speakers that will be used. A two way system will be handling the frequencies above about 100Hz and a 35Hz tapped horn for the lower frequencies. The opamp crossover will split the main out into the two bands which will be fed directly to the power amps. If I need a monitor I will add another external power amp or earphone amp to connect to the monitor out.

 

mike

Hi, I agree with all that has been posted here previously, getting hold of a second hand instrument for parts may be a good idea, and the computer organ approach is also a valid alternative.

but if you do want to pursue the analogue route, then if you could get hold of the Devtronix documentation,  that would help you, as they used to make a oscillator board  236 that used parts that are still available. the earlier tone generators used inductors or ic's which as far as I know you can't get now.

I wrote a response to this last night but it appears to gotten lost.  I think it is perhaps not worthwhile going into more detail until we have some better idea of just what sort of instrument you are wanting to end up with, and how much, if any, building you are willing to do.  Tone generators are available if you know where to look.  I, myself, am a repository for abandoned tone generators from the Schober electronic organs that have been converted by their owners to MIDI technology, along with other parts.  This is a situation I have agreed to accept in order to make those boards available as replacements (and the company went out of business in the 1970s).

For what it's worth, Schober had two different Tone Generator systems:  the original one consisted of 12 identical circuit boards--one for each note--containing discrete transistors and other components to create an oscillator and 7 or 8 divide-by-2 stages to produce the 85 frequencies for the organ; the later version was a single board with a single oscillator (2 MHz) and a Top Octave Generator (TOG) chip to create the 12 high-octave frequencies, with IC divider stages to produce the lower notes.  Although new boards for these systems are not available, I have a nearly complete set of the old multiple-board generators and the schematic for the later single-board version is also available.  In addition, I am in the midst of a modification to my Recital Model that will use a crystal oscillator (2 MHz) and a TOG to create the top octave frequencies and these will be bed into the existing 12 tone generator boards instead of using the individual oscillators on those boards.  To this end I have devised and built a small auxiliary circuit board that contains only the 2 MHz oscillator and TOG chips--it runs on 12 volts.  The schematic for that board is also available.  Anyone skilled with current IC technology would have no problem beginning with that circuit and adding divide-by-2 stages to fill out the frequency spectrum.  (The Schober device used 7-bit binary counters for this purpose--very clever.)

So, what is your desire?

David

Mike,

 Just reading this and thought I'd add my $.02    Building stuff to produce sound is a finnicky and time consuming process, especially if you don't like the sound something makes afterwards (after soldering a boardful of opamps, resistors, caps, etc.).  I'm an inherently cheap, er, frugal, type and what I've learned is to check something out in virtual form before commiting to actual hardware.  For this, I use the FREE PC application, Audacity, which runs on any OS back to ' 98, using a typical sound card.  No need for a laptop or expensive virtual organ Software, just the PC you're reading this reply with.  It's a waveform editor with lots of effects and extensive waveform editing.  It is working at the most basic level of the waveform and thus cannot be a virtual instrument (well, I suppose it can but its a lot of work and non-real-time), but you can learn a great deal about the way any particular waveform sounds.  It a real time saver if you want to find out what a particular tone generator waveform, pushed though various filters and/or modifiers will sound like before commiting to soldering a bunch of parts together. Oh, and did I mention that its free?

 ex-p