Vintage Synth Repair

yea, $200 for x-former seemed a little high, but have you seen what
the CMS modules cost? $1300 for a modular VCO. so, im not surprised.
their SMALLEST full system is 7k.

duncan, this other stuff is GREAT news-thanks. ESPECIALLY the
potential of difference in sound w/ digital PSU. resale is not an
issue, as i wont be selling this anytime soon, but i am one of those
kooks who is a firm believer in  the early ARPS being totally distinct
beasts, sonically. if THAT'S the case, then i might as well just try
to source the power transistors, and maybe voltage regulators, and
keep the old PSU. i hate this idea of putting off a potential known
issue(voltage drift), rather just nip it in the bud, but maybe i will
try to get it to behave as such by leaving it on for a few hours.
thanks guys!!


--- In vintagesynthrepair@yahoogroups.com, "duncan" <ferrograph@...>
wrote:
>
> >>previous owner was told by phil it needed a transformer
> > replacement, and would cost $200.<<
> 
> $200 for a transformer?? a tad excessive, even with the price of
> copper being what it is... besides, as we have said earlier, if you're
> getting good 15V rails most of the time & the thing doesn't look or
> smell bad, it's more likely to be something in the regulation that's
> going bad. check for bad solder joints, especially around the large
> power components- the rectifier diodes & the pass-transistors.
> see the posts about the juno 106? same thing, more or less.
> 
> yes, & let the thing drone for a few hours (2600s are supposed to be
> good at this!) into a guitar tuner, see if it drifts any. of course,
> this could all be component breakdown elsewhere in the thing & nothing
> whatever to do with the power supply. 
> 
> e.g. I had a korg monopoly that would not stay in tune- this turned
> out to be the way the thermistors were glued to the oscillator chips;
> the glue went bad & the thing started drifting. the 2600 is full of
> such design quirks, as I recall. mostly in epoxy-potted blocks, right?
> :-/ 
> 
> >>i am now considering another approach:
> > drop an entirely new, linear power-one PSU in as a replacement. the
> > 1.5A unit is only $72, which is relatively very cheap. puts out
> > +/-15V. i have used power-one linear units several times before on
> > other projects, and have always found them to be rock solid, easy to
> > calibrate, and good build quality. is this a horrible idea?<<
> 
> not really so horrible, & it would mean you could use the arp off any
> line voltage/frequency. but it wouldn't be stock any more, & that
> would affect resale value. personally, I don't care about such things-
> to me it just indicates that someone did some restorative work so that
> the instrument had a longer active life. I hate this "museum-grade"
> nonsense... :-)  
> 
> but maybe you can measure the current draw on the existing power
> supply first. 
> the first "gotcha" is likely to be the -15V which, from many
> commercial computer grade SMPSU modules is likely to be capable of
> only a few hundred mA, compared to a couple of amps at 5V or 15V
> positive. your average analogue synth has more or less symmetrical
> current draw....
>  
> the second is going to be radiated HF noise from the power supply. put
> it in a faraday cage (you may have seen this approach inside, say, an
> emu sampler) & fit ferrite rings on the output cables.
> 
> third, it may just affect the sound a little bit... depends how
> "golden-eared" you are, but you'd be replacing an analogue power
> supply with a digital one & this will to a small degree affect the
> behaviour of the synth, sonically.
> 
> let us know how you get on- that's what this list is for! :-)
> 
> duncan.
>