[sdiy] Jupiter-8 'selected' op-amp replacement

[Harry Bissell Jr]

Hi Tony.

Selected opamps are usually chosen for
low offset voltage... or matched offset
voltage.

I don;t know about the Jupiter-8 case. You should
be able to wire a socket as a voltage follower with
the non-inverting input grounded. Measure the output
voltage.

If they need to be matched, choose two with similar
voltages. If they are selected for 'low'... use those
that are 'low enough'.

I'd wonder if you're looking in the wrong place...
Have you checked the S/H outputs for the VCO CVs ?
This is a usual spot on most synths for problems
common
to several VCOs

How about power supply voltages ???

H^) harry

--- Tony Kalomiris <tonyk38 at sympatico.ca> wrote:

> Hi,I've been working on this JP-8 and several
> oscillators are 
> unsteady (vibrato like effect) and
> when I scoped around the VCO the problem seems to be
> pointing to the 
> TL080CP as the culprit.
> 
> My question is how do I go about matching these - a
> pair is needed in 
> each current controlled oscillator- without any
> special test rig ?
> 
> I'm also concerned about the thermistors epoxied
> onto the CA3046, 
> what if I have to change those as well,: how do I
> remove them without 
> damaging them , they look very fragile (BTW where
> can I buy 
> replacements just in case I need them ?)
> 
> Sorry for all the questions it's been a while since
> I've worked on 
> one of these beasts and I'm a little gun shy.
> 
> Thanks for the help with the Strobe tuner as well I
> ended up using 
> the Lissajous technique suggested in the service
> notes
> it's more fun to watch the funky patterns than a
> spinning disc ;)
> 
> Oh isn't concert A 440 Hz? Why does the manual
> suggest 442 hz,884hz etc ?
> 
> Tony K
> 
> P.S. I still have the EMS circuit cards if anyone is
> still interested 
> on this list.I've received alot of inquiries but no
> takers yet. 
> 
> 
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