Problem with a Transcendent 2000 Synth.

[siranthonytb]

Been restoring a Transcendent 2000 synth and just about getting there but stuck with the following problem. Am getting a percussive thud when playing the keyboard, every key and also when the slow oscillator is pulsing and worse when the ADSR is switched on with the Attack off. Any advice would be greatly appreciated.

[Folderol]

So DC is getting into the signal path.

First off, do you have any schematics? It's hard to suggest test points without them.

Having said that, are the DC rails the correct voltages?
Possibly, broken connections or trackwork unbalancing bias levels.
Also, likely suspects are leaky or short circuit caps.

[Hugh Robjohns]

Scans of the original ETI construction article can be found here:

http://www.pastisch.se/ror/images/t2000.pdf

[N i g e l]

if the VCA isnt nulled, the output will thump.
minimised is probably a better word than nulled but there is probably a whole host of thump oppertunities before that.

Are all your electrolytics renewed & in good condition ? otherwise we are talking 40 years old !

[Wonks]

There aren't that many electrolytics in the T2000. Two larger ones on the PSU board and three smaller ones on the main board, so it doesn't take long to replace them.

[Wonks]

The two aluminium L-shaped bars that the main PCB is bolted to for support aren't really all that stiff, and the PCB is quite flexible when you press it in the middle or use the knobs and switches, which stresses the solder joints.

I've fitted larger/thicker angled aluminium bars to mine and you really can't feel it move at all now. Instead of 6x6mm they are about 8mm x 8mm (IIRC) but the metal is a bit thicker all round and they are a lot more rigid. Well worth doing IMO.

[N i g e l]

yeah the PSU ones are VERY important.

Note that the LFO has 2 electrolytics back to back, nowadays that can be done with a single ceramic cap with no polarity issues.