New member, with a vintage PAiA Stringz'n'Thingz

[stefanv]

Just joined this group and wanted to say hello.

I've had an interest in PAiA stuff since I was a teenager, and finally got myself a piece of PAiA gear, a Stringz'n'Things synthesizer in very good condition, both cosmetically and functionally. It does need a little bit of TLC (cleaning the pots, new keyboard bushings, tightening up some connections) but it's basically usable right now. I also plan to change all the electrolytics, since there seem to be some noticeable differences in decay time from one note to the next.

My medium-term plans for it are to build a new "furniture-quality" case (I want to put it on top of my '62 Hammond M-111), drop in a slightly bigger keyboard (44 keys) and extra circuitry to support it, and put all the jacks on the back. I hope no one thinks that's sacrilegious!

[PAiA-Scott]

Welcome Stefan.

I wouldn't say sacrilegious, but maybe ambitious. I suppose we do have some long, cold nights ahead of us in the northern hemisphere though. That'd be some project! Be extra careful when you're 'in there' as it is difficult if at all possible, to obtain some ICs (50240 Top-Octave-Generator used for the tones and the SAD-1024 Analog Delay used on the chorusing board).

--Scott

[stefanv]

Thanks for the feedback Scott. How likely are those chips to get damaged in-circuit, assuming I leave them in place, and don't do anything like get too close with the soldering iron?

It's not that ambitious, is it? After all, someone built the thing in the first place, which would have been a much larger project. I've certainly tackled projects of similar complexity. My most recent is an Analog Drum Machine for My Hammond Organ.

By the way, if I go through with this, it will be fully documented on my web site.

[stefanv]

Just a follow-up to my previous posts. I have not yet completed this project, but am well over half way there. Since my last post, I've done a lot of designing and redesigning of various ideas, and started work.

I've built a board containing eight additional note blocks (to expand the keyboard to 44 keys and implement high C properly), forty-four 12dB/octave RC filters to add a flute voice (i.e. more "Thingz"), and a master clock that can be switched between three crystal-controlled octaves or a variable control as the original had.

I built a second board containing two AD envelope generators, a wave-folder (controlled by one EG and/or the 1550's LFOs), two VCAs (one controlled by the other EG and one by the LFOs), and some additional buffering (for the flutes and also to allow the piano to be split just like the strings).

The new case is finished, and all the electrolytics have been replaced on two of the three boards, and the old ones removed from the third board.

I haven't written the project up yet, since it's not finished, but I have put together a page with some photos of the progress so far:

http://www.stefanv.com/electronics/paia_stringz_n_thingz.html

I found one peculiarity, which was that both voltage regulators were 7805s instead of one each 7805 and 7905. Considering that the pinouts off the two are different, and the 7905 is a negative regulator, I was amazed that the synth worked at all (it seemed to pretty well before I started disassembling it). I sketched up what the schematic would be by wiring in the wrong regulator with the wrong pinout, and came to the conclusion that what I was getting was a nicely regulated +5VDC, but relative to the unregulated -17VDC input (i.e. I was getting an unregulated -12VDC). That explains why it worked, and also why I was getting a fair bit of AC hum on the output.

[PAiA-Cliff]

Completely off topic but my dad has quite the collection of old calculators as well as slide rules. I've forgotten how to use a slide rule but I wish I would have been able to use one for the IEEE design competition a friend and I won this last weekend. Everybody came in with all sorts of books, graphing calculators and were spending most of the competition running simulations. My friend and I walked in with literally nothing and did the entire competition with pen, paper and a simple hand calculator. Funny that we were the only ones to finish the circuit, let alone on time

[stefanv]

Simulation tools are great when used properly, but they can also be the modern equivalent of "prototype until something works". That can find you a solution, but knowing what you're doing (like you and your friend obviously did) is usually faster. It would've been cool if you'd used a slide rule though!

PS. To those wondering what spawned Cliff's OT post, I suspect he found my slide rule and calculator pages when reading my Stringz'n'Thingz "article".

[stefanv]

Just a quick update: Last night I got the new keyboard hooked up to the 1550A and 1550B boards (i.e. the note generator, dividers, and keying circuits), as well as the board with the 8 new note blocks that I constructed to support 7 more keys (and do high C correctly). That board also contains a new crystal-controlled master clock.

I used clip leads to temporarily connect these boards to an external power supply, and connected the audio buses directly into an external amp, and everything works! I now have 44 notes of violin, cello, and piano (all with really long sustain since I left the sustain buses unconnected for now)!

Next task is to hook up the new flute keying circuitry, and if that works, start hooking up the 1550C board and my new effects board (wave folder and envelopes). The panel artwork is all completed; I just have to drill the holes for the pots.

I haven't added it all up, but I think I've spent more on rejuvenating and upgrading this beastie than I paid to buy it. By the way, I thought $249 for a Stringz'n'Thingz was a bargain, but in the last few months, the selling prices for these on eBay have really dropped. One just went a few weeks ago for under $120!

[stefanv]

About a week ago, I completed my Stringz'n'Thingz rejuvenation and expansion project. It certainly took longer than I'd planned, but it's finally done! What I ended up with is:

• 44-key Yamaha keyboard (7 additional notes) in a new case.
  Octave-switchable crystal-controlled master oscillator.
  Separate cello and violin level controls.
  Switchable string chorus modes.
  Split keyboard for the piano.
  Proper circuitry for the high C note block.
  Polyphonic flute voice (almost sine waves).
  Effects section operating on the flute voice:
  • Wave folder to add harmonics (an "unfilter"), modulated by an LFO and/or envelope generator.
    LFO modulated VCA to provide tremolo.
    Envelope generator modulated VCA to provide attack-decay.
  Overall volume control.
  Fused AC voltage and a safer power switch (no AC on 1550C board).

For anyone interested in all the details, including lots of photos, schematics, and some audio samples, the page where I had been recording my progress has become a fairly comprehensive article describing the whole project:

http://www.stefanv.com/electronics/paia ... hingz.html

[toneman]

AWESOME project!!

[stefanv]

Thanks toneman!

I just picked up the September issue of Keyboard Magazine, which has Devo on the front cover, and a quarter-page blurb on page 11 about my project, complete with a link to my article!