[sdiy] TB-303 servicing questions

Robin Whittle rw at firstpr.com.au
Tue Dec 3 09:24:15 CET 2013

Hi Damien,

You wrote, in part:

> My 303's knobs are all easy to turn except for the res knob. The
> potentiometer is a dual type - the rest are single gang. Is this normal? If
> yes, are there any good repkacements? If it's not normal - should I replace
> the pot? Spray it with a specific lube? Open it up and clean it out inside?

You can dismantle it, clean the tracks and wiper with isopropyl alcohol,
remove the friction grease and replace it with lighter silicone grease.
 Also, watch out for signs of track cutting:


Replacement pot sets can be purchased from
http://www.technologytransplant.com .  The sets I got from them recently
have shafts which are about 2.5 to 3mm too long, so you would need to
use a fine hacksaw and file on them.  I take out the friction grease and
use a lighter silicone grease, but you don't really need to do this.
With the two sets I got the resonance pots had a stain on the silver
metal tracks of the resonance pot.  This looks bad but some of it came
off with methylated spirits (ethyl alcohol) and the rest of it wore off
really quickly with a few wipes of the wiper, so I think it is nothing
to worry about.

The pots which are used in the Bass Bot are similar (but no stain in any
of them), but have a shaft which is the correct length, considering
their somewhat higher mounting base.  As far as I know Cyclone Analogic
doesn't sell them.

> The volume pot is crackly. Is there a good replacement? Or is there
> something I can do to the existing one?

Dismantle it and clean it with isopropyl alcohol.  I do this routinely.
 These pots are fine - I think they will work for many decades to come,
but they might occasionally need cleaning like this, or perhaps just a
spray of isopropyl alcohol or some special DeoxIt fluid (I haven't used
any yet) and a few turns without pulling it apart.

> The waveform switch is flaky on the square side. Should I replace it? Open
> it up? Is it a standard type?

I know of no replacement.  You can probably open it and clean it, but I
would be inclined to use isopropyl alcohol without desoldering it from
the PCB or opening it up.  Give it a spray and then flick it back and
forth a hundred times or so.

> I could use a new case. Mostly for a few mods I'd like to perform; I'm
> reluctant to drill in the original case. Does anyone make plastic
> replacements? There was a post in 2010 by David Bulog that Technology
> Transplant were making a group buy, but their site doesn't list it and
> there is no other info. I've put David on CC, maybe he knows anything more.
> If they don't have TB-303 cases I wonder if they have ones for the
> TT-303.  Those seem like they would fit as well - does anyone know
> for sure?

I don't know of Technology Transplant selling any.  The Cyclone Analogic
Bass Bot case is different in that it has a polycarbonate label, which
is expecting to get light from SMD LEDs, not the 3mm LEDS which are part
of the TB-303.  I am not sure they would mount well together and be thin
enough even if that was not a problem, since it has the plastic case
rather than the thin aluminium metal switch plate of the TB-303.

You can probably find a TR-606 case, move the metal switch panel to it
(dissolve the contact adhesive slowly with Shellite = petrol), and
forget about the different markings.  Alternatively, you could get
someone to spray it or do a fancy spray and screen print job such as the
black and orange one (which I have only seen photos of) at:


This is the work of Jeff Toman in the UK: http://www.customsynth.co.uk .

 - Robin

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