Welson Gypsy organ restoration and modification

This is the only piece of information I found on this organ on the web.

It’s an Italian made combo organ with 7 preset solo sounds, a few pre programmed beats, and an accompaniment section with bass and chords elements. I found it in the Haifa flee market and paid about $20 for it.

It had problem with the C key, which didn’t work in any of the octaves.

Organs work different than analog synthesizers in that they use what’s called a top octave generator. Instead of using voltage control to determine the oscillator’s pitch, a chip puts out all the frequencies in the top octave range of the organ, and each of these frequencies is then divided down creating the rest of the octaves. Also, instead of using a VCA to turn the notes on and off, the keyboard acts as a set of switches, where each key allows the corresponding note to be mixed in.

Having that in mind the prime suspects for the missing Cs were the divider ICs. To test this I switched them around and sure enough a different key was missing in all the octaves. Switching out the defective IC with another one fixed the problem. The frequency divider used in this organ is the SAA1005P. I just checked ebay, and the only one currently for sale is $50.. jesus.. lucky I had one lying around in my ICs box.

For a while the organ rested in my closet as I have an Oberheim OB-3 which I always use when I need organ sounds. But reading more about organ architecture and realizing that all the old string machines were based on organ technology I decided to add a few mods to the solo section and make it a little more useful.

The modifications are: external control for the original internal vibrato, separate outputs for the ‘rhythm/accompaniment’ section and the ‘solo’ section, a fully controllable variable mode filter section (Thomas Henry’s VCF-1), and an LFO (with both square and triangle waves) to modulate the filter.

TH’s VCF works very nicely with organ sounds apparently! The LFO wide range makes it possible to come up with some seriously modulated sounds – it’s an altogether different instrument now, and I can still get all the original sounds out of a separate output. I’m considering adding a similar mod to the accompaniment section and adding control to the on-board drum sounds. But maybe that’s going overboard.. dunno.

Here is a short demonstration of the mods in action. I wish I had a section in the video with the original sounds and drums/accompaniments in it. If I mod it further I’ll make sure to include those as well!

4 thoughts on “Welson Gypsy organ restoration and modification

  1. Disciple

    Very interesting mod ! What a sound !
    Could you tell us more about these mods ? (waht are the points on the pcb,and the components etc….)
    Nice job !

  2. admin Post author

    Hey! Thanks!
    The excellent Thomas Henry VCF can be found on the link I posted.
    In all honesty I can’t remember which LFO circuit I used but I do remember I dug it up in the Electro-Music forums. A search there will give you quite a few options to choose from.
    As for the points on the PCB – unfortunately I couldn’t find the schematics for this specific organ so I had to trace the sound around the board until I located the unfiltered wave (just as it enters the preset filters available on the organ). Takes a little bit of patience but is easily done. Use an oscilloscope or a probe connected to a test speaker and start testing points around the preset buttons circuitry. The output comes straight out of the filter. The benefit being a separate output for the bass notes on this particular model.
    Good luck and happy tinkering! đŸ™‚

  3. TILMAN André

    Hello,

    I own an old Welson Gipsy organ. But it does not ork anymore. I thought it was the fuse and I have replaced it by a new on. It makes a sound, but not the good one : brroooh….. and the keyboard does not work at all. Do you know eventually if it looks like a serious problem ? All the lights are working but no sounf from the keyboard, just “brrooh”.

    Thanks if you reed my message.

    Best regards.
    André TILMAN
    4219 MEEFFE
    BELGIUM

  4. admin Post author

    Hi Andre. Well, many things could cause the problem, starting with a bad connection and ending with a burnt out TOG (the chip responsible for generating the sound).
    I suggest you open it up, take a look inside. Is the volume fader connected on the inside? Are the wires leading to the speaker well connected? If you use the output plug, does it work then?
    When you try to produce sounds, does any of the preset sounds work? When you activate the rhythm section, do you hear the drums and accompaniment?
    Checking all of the above will give us some clues as to what might be wrong with it.

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