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WERSI SPRING REVERB DRIVER CARDS: PREAMP + EQ



Some years ago I found a Wersi Helios which had been dumped on the street. Already the amp and speakers were removed. I set about dismantling the rest for parts to use myself or sell, stacked it all on my bike and pushed it home (happily around the corner!)


Many Helios models were available with/without options like drum machines etc. They are enormous machines.

I sold most of the parts to Wersi enthusiasts. It is difficult to sell a full Helios even if fully working, hardly anybody wants one these days. The best selling parts were the top octave generator chip, and the bass keying latching chip, both of which sell for 40e a piece these days! TOS chips are used in certain older Korgs, other analogue synths as well as organs.

They create ALL of the tones, the instrument is soundless without one. Some replacements are now produced of course.


Anyhoo I've been working on this driver unit for a while. I had the schematics and all data on it, in German (Wersi are German company) I considered a long time how to implement the rehousing. I also had the two pre-amp cards, and the reverb tank, as well as the complete wiring loom for the entire organ. I never need buy hookup wire again it's great.


I needed a +/-15v supply, and an enclosure. Eventually I found a suitable enclosure, and used a DC to DC converter to turn 12v into +/-15v. Most of the work I did November 2021. I added a 100% wet switch to cut the dry signal. I used ganged pots to bring both L and R cards under single knob control, replacing the PCB mounted VOL, BASS, TREBLE, and REVERB trim pots with panel mounted knobs.


A nice touch about these cards is that they have an LDR (light dependent resistor) input circuit already installed! This is for the footpedal, which raised a curtain in front of a lamp, changed resistance of the LDR, and dropped the VCA (volume) level. It was therefore really simple to add CV input to the VCA in the form of a DIY dual vactrol. Initially I used the same LDRs as came from the footpedal, however at some point they became unresponsive, and I replace them with new devices. You can get classic VCA effects though not super fast because a vactrol can only react fairly slowly - it works well though, dramatically changing the volume (the quiet level [NULL] can be set with a trim pot on the cards)


I have put the final touches to the device, and discuss them and demo the unit in the following video series. Overall I'm really happy with how it looks, and how it sounds, and the fact that it's a long tank, so a nice long reverb tail. Saving it from the street is also a great feeling. I love echoes!! Particularly analogue and grainy digital, they are my favourite effect. I have a DIY cassette tape delay, a modified BBD delay, a digital 10 bit delay with it's own RAM chip, a modified ART digital Multifx box. I would like to get an Oil can delay. (again, I used to have one!)


Enjoy:






Early experiments with the cards mounted in their original extra circuitry (which routed signals to and from different sound generators in the organ) and the HALL 1/2 switches from the organ (reverb amount) This was where a lot of the work was, in figuring out what could be removed and the cards still work as I wanted.







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