Vintage Synth Repair

H everyone,
Sorry I´ve been so quiet lately. I´ve been buried in work, writing, 
recording and doing service.
I have just finished service on a Roland VP-330 vocoder/human 
voice/string keyboard, Mark 1, the one with the rocker switches.
Very good machine! But a torture to service and adjust. The schematics 
specify cheap op-amps (4558), but - at the time - state-of-the-art 
op-amps for the final outputs of each board (TL082). However, these 
specified TL082s were not used, it seems, at least not on this stock 
model. They used LM353s all the way, and several of these had failed, 
so that the string was dead, and some of the vocoder filters were not 
working because the op-amps have gone into self-occilation. So after 
debugging and swapping out defected parts, it was down to adjustments. 
For at start, the vocoder sounded dull and unfocused, but somewhat 
right. But the carrier signal was bleeding through a lot. Who would 
have thought that this was among the "best vocoders ever", even used by 
Krafwerk at some point in their carrier?
Well, the vocoder card, with the 10band filters, VCAs and corresponding 
"companders" (compressors + expanders) is neatly laid out, but fiddly 
to adjust. As usual with analog, everything influences each other, so 
there was a roundabout of going back and forth on all the trimmers. I 
feared I would bump into one extreme of any trimmer, so that I would 
have to change resistors as well in order to tune the circuts, but it 
all held together.
After hours of work, I must say that the sonic that this machine now 
creates is amazing. Very distinct vocoder with good sound, the the 
combined human voice and string is indeed very charming.
The machine is full of Roland chips (BA662s etc.), and not to mention 
all the SAD chips for the chorus, so if anything major starts failing 
it will be a nightmare.
But as long as those chips hold, this is a dream machine. And now that 
I have done one and learned it´s secrets, I am sure the next one will 
be a breeze.
Remember to use the right service manual; mark I is significantly 
different from Mk. 2.
Also remember to be patient: every time you adjust a vocoder filter, it 
takes some time to stabilize, so be cool  :-)


Terje Winther
terje.winther@...
http://www.wintherstormer.no/