[sdiy] LM566, SAD1024 and a Paia String synthesizer

[Tim Heffield]

There are two separate SAD-1024 BBD delay lines, each with it's own 566 high
freq clock.  These two 566 clocks are modulated with the other two 566's
running at low frequencies and are set by the modulation rate control.  They
purposely are kept separate and not synced so that there will be phase and
time differences between the delay lines. I would almost be willing to bet
that the electrolytics are killing this section as well.  I doubt that the
ICs are bad unless someone applied the wrong voltage to the unit.  I don't
know where PAIA got those electolytics but they were a real problem.  This
synth is over twenty years old and it would be good practice to replace the
electrolytics anyway, even if they didn't have such a bad reputation.  I
wouldn't be so quick to blame the ICs and the chorus section worked pretty
well for it's time.

Regards,

Tim

-----Original Message-----
From: Karl Ekdahl [mailto:elektrodwarf at yahoo.se]
Sent: Sunday, July 01, 2007 10:26 PM
To: Tim Heffield; Synth-Diy
Subject: SV: RE: [sdiy] LM566, SAD1024 and a Paia String synthesizer


Tim

> If that is the Stringz 'n' Things (1550) I built one
> of the those many years
> ago.  The one thing I remember is that about 10 of
> the electolytic
> capacitors were bad right out of the box. If I

Ouch, yeah i was almost thinking it was something like
that. I'm gonna desolder the rest of 566's and try
them on a breadboard.

> recall there was no sound at
> all on the notes connected with these capacitors.
> Once I changed the caps
> out it worked fine.  If I were you I would change
> ALL of the electrolytics
> in the thing.  I have schematics for the unit that I
> can scan if you need
> them.  Does the top octave chip (MK50240) work?

I do got the schematic, thanks though! Everything
works except the chorus and one of the keys is a
little funky, looking closer on the board someone's
already replaced two of the caps on that notes section
so you're probably right...

I'm still thinking that i could totally diss the whole
internal SAD-driver and just do something simpler
myself, i don't really understand the complexity of
the 566's - in my mind one should be enough, why four?

Karl


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