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Author Topic: restoring an old Univox Superfuzz  (Read 837 times)
mordechai
Posts: 519


restoring an old Univox Superfuzz
« on: May 30, 2012, 03:42:06 PM »

I have an original (ca. 1968-69) Univox Superfuzz, and it's not performing very well.  It is pretty low gain, and when I switch to the scooped tone, the signal is noisy and sounds like it could cut out. 

Does anybody know a service where I can send this thing to be restored to its original glory?
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R.G.
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Re: restoring an old Univox Superfuzz
« Reply #1 on: May 30, 2012, 07:16:51 PM »

If you build effects, you're qualified to restore this one.

See http://geofex.com/fxdebug/fxdebug.htm and click on the link that is titled "Resuscitating the elderly effect".
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R.G.

It doesn't take a lot of technical chops to understand that such [cryogenic] treatment to a vacuum tube is probably similar to cryogenically treated stove elements.
mordechai
Posts: 519


Re: restoring an old Univox Superfuzz
« Reply #2 on: May 30, 2012, 08:33:28 PM »

Thanks R.G.  From what I described, could these problems stem for electrolytic caps that are just shot?
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R.G.
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Re: restoring an old Univox Superfuzz
« Reply #3 on: May 30, 2012, 09:30:28 PM »

It's possible.

In any case, refurbing that thing will involve replacing the dozen or so electro caps in it. They're over fifty years old, if original.  The resistors, non-electro caps, and semiconductors don't have the same wear-out mechanism that electro caps do. Replacing electros, remelting all the solder joints, and cleaning/replacing all mechanical switch contacts will cure the vast majority of old effects.

Even if that's not all of it, once you get there, you can apply the techniques of "What to do when it doesn't work" and "When good opamps go bad".

Come on, there are only a dozen electros in there, all 1uF and/or 10uF as I (dimly...) remember. How bad could it be?
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R.G.

It doesn't take a lot of technical chops to understand that such [cryogenic] treatment to a vacuum tube is probably similar to cryogenically treated stove elements.
joegagan
Posts: 3082



Re: restoring an old Univox Superfuzz
« Reply #4 on: May 30, 2012, 10:47:25 PM »

I replaced the electros and one transistor on this one four years ago. Without the cap replacements, it hardly made a sound. the trans needed replacing due to a botched earlier repair.
<a href="http://www.youtube.com/watch?v=ChvmvnBYG7Y" target="_blank">http://www.youtube.com/watch?v=ChvmvnBYG7Y</a>
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R.G.
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Re: restoring an old Univox Superfuzz
« Reply #5 on: May 31, 2012, 10:22:11 AM »

While they don't have any built-in wearout mechanism that's perceptible on a human scale, BJTs can be damaged subtly. This was not recognized until the 80s? 90s? and is even today not all that widely known.

If you reverse-break the base-emitter of a BJT even once, it makes it a bit more noisy. It gets noisier as you go, and eventually the gain starts to drop. Early transistor circuits did not take this into account and often had a big emitter capacitor or similar that could reverse-break the emitter junction at power-off. The accumulation over time can make especially the input transistor of a BJT amp get funky. This is one reason that old effects are often noisy. Well, one more reason.  icon_biggrin
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R.G.

It doesn't take a lot of technical chops to understand that such [cryogenic] treatment to a vacuum tube is probably similar to cryogenically treated stove elements.
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