[sdiy] EKO Stradivarius

Rutger Vlek rutgervlek at gmail.com
Sun Mar 27 19:12:06 CEST 2022

Dear list,

for reasons of knowledge (and instrument) preservation, and out of
enthusiasm I wanted to share some info on my current restoration project. A
few months ago I saw an ad listed on internet for an Eko Stradivarius,
which I didn't know, and by the looks of it assumed it to be a cheap/cheesy
kind of organ. I remember skipping over it, thinking "that's one heck of a
pretentious name for an instrument". Shortly after that I was watching this
documentary on Italian synth industry:
https://www.youtube.com/watch?v=FZ-sVujDlS8 and was amazed at the sounds of
some of the more obscure Italian machines (I owned a few less obscure
Italian instruments but was never impressed with them). It brought me back
to the Stradivarius, and after seeing a short video of it, I realised it
was an amazing sounding string ensemble, easily on par with (and
technically very similar to) the first version of the Solina. Luckily, the
instrument was not yet sold, and I managed to buy it at a very decent
price. Optically, it is in a very good condition, even the original lid was
still there (despite the tolex no longer sticking to some of its corners),
and it was fully functioning!

Arriving back home, I opened it up, wondering what to find inside. The
first, and best surprise was: a service manual with full schematics
stitched to the inside of the case! Since this instrument is so rare and I
could not find any technical info online, I decided to scan and share it
with you (assuming that any legal restrictions are long overdue). EDIT:
attatchment turned out too big for this list, so available on request and
submitted to synfo.nl.

Internally, the instrument seems to be in fully original state, including a
gigantic amount (126!) of electrolytics that are probably several decades
beyond their expected life, but show very little sign of leakage or
bulging. I wondered, since there are so many, if I could leave them in
place, but decided to replace them as I want to give this instrument a much
longer life. Many of them are axial capacitors, by the way, which are much
harder to come by these days (especially when you want a decent brand). I
was wondering how others go about this? Replacing them with radial versions
could mean more physical stress to the legs of the radial ones. Would that
be a problem?

After finishing my shopping list for capacitor values I took a brief glance
at the power inlet, wiring and fuse holder, which generally looked tidy
except for mains insulation that was stripped back a little too far to my
taste, leaving bare copper to be fairly close to the metal casing. I almost
decided to go for lunch, but then thought a quick check of the fuse
couldn't harm, even though the instrument was working fine, so I expected
no problems... well aaaarggh! Glad I checked, because I found an example of
the worst kind of electronics practice: aluminium foil wrapped around a
burned-out fuse, creating a bypass for it without any current limitation
whatsoever. After seeing that I was glad I had decided against using the
instrument much, until at least all PSU electrolytics were replaced. Also,
I'm curious what will happen to a newly inserted fuse at the proper rating,
if there's a hidden malfunction that will trigger it.

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