A great source of 70's string sounds the Performer uses the Mostek MK50240N as a top octave synthesizer. 12 TDA1008's are used to create a logical tonal grid according to which keys are being hit on the brass, and 8' and 16' violin mixes. From there on it's a pretty straightforward analog filter/envelope on the brass and EQ and analog delay for the string section. I have a performer version 2 which adds an octave switch in the middle. THIS IS NOT A PERFORMER 2. The performer 2 has that as a push switch on the right. Switch caps look like the Composer so I assume these are made in the early 80's. They dont' have the three band 'eq' for strings but rather a single timbre slider. They add delay for vibrato. I recently got one and set up the filter with the resonance mod and someone had already run the tuning shaft out the front so you don't have to reach around back to tune it. Serials on my units are B04168 (A version 2), B01868 and A320, the latter of which has a totally different Early Brass Board. As you can see there is a ladder filter on that one rather than the SSM unit. So probably it's a typical Crumar thing where they made an initial run of a small number then made some redesigns and punched out a larger number. I couldn't discern other differences except I think they used Tantalum capacitors for the envelopes in the early one like the ARP Omni, then went with regular electrolytics in the later ones I think. (PS 11/23/07 I worked over a beautiful #A840 which also has the ladder filter so apparently the "A" versions all had this? My numerical estimate of how many were made above is based on a statistical evaluation of the serial's I've observed. I figure maybe a thousand to two of the first version. 5 or 6000 of the second version. )
Ok now let's delve a little deeper. The single buss bar carries current to the switches which provides charge for capacitors that open the TDA1008 vca equiv. gradually. (Really it's offsetting the window for the square waves generated in the dividers as I recall, so that their leveles gradually increases as these voltages raise.) On release each discharges either to a fixed bias or to one set by sustain slider. In the stock configuration, when brass isn't selected, the string footages are mixed to bypass a vca that has a crescendo set by the crescendo slider's EG. (With rapid preset sustain decay) When the gate occurs the Strings just crescendo and decay by the EG voltage controlling the TDA1008's. (Pin 7). But on release the caps discharge at the rate set by sustain slider's voltage tap. But when brass is engaged, we need a rapid attack so a preset is sent instead of the string EG crescendo to the TDA1008's. And the string signal is routed through the VCA instead of bypassing it. So that a crescendo is achieved that way. But on release everything dies quickly. The brass would sustain but the EG for the filter has a preset rapid release.
No Brass out main mix? Don't forget there's a shorting jack on the brass out. If it's dirty no brass signal gets to main out. The TOS board is under the keyboard, as are the TDA1008's. I had power supply problems with mine when I got it. Bad regulator or like that. Another with your standard tantalum capacitor shorted before -24V regulator. Also Sliders commonly break off. Using a wire guage bit of appropriate size, I drilled two holes; one near each 'edge' of the plastic face that broke off, and I used JB weld and copper wire to form a 'loop' of metal adhesed into place there. Then I put on a conventional slider cap and it works great!
Try our friend Lorenzo at Vintage synth parts for 6 euro each and qty. discounts
(I see that there are two different types of slider shafts and knobs and they are NOT compatible. The fatter ones will fly off and hit you in the eye if you try to put them on the shaft for the slightly skinnier ones. They look very similar but they aren't compatible. )
Semiconductor and misc. Parts:
Most other parts I have in stock or can be found doing google searches or on ebay etc. The SSM2040 is available rarely on, but here is a engineered SSM2040 replacement Module Contact me if you need anything else.
Contact Sound Doctorin'
I strongly recommend the addition of a 100K trim pot in paralell with the feedback limiting resistance R25 (15K) located near the filter SSM2040. The resonance is really great on these things but no self-resonance from the factory. Enjoy and careful with your speakers!!
Another cool mod that appeared in my early unit was to add a switch for sub-osc! It sounds real nice. They used a bunch of 4066's hooked to the busses on two different boards. I think we could probably get the chip count down some today on that. Now it's hard to let go of any of my units since they are all unique! :-)