[sdiy] Kenton TB-303 sockets schematic?

rburnett at richieburnett.co.uk rburnett at richieburnett.co.uk
Tue Apr 11 13:00:20 CEST 2023

Thanks Roman.  You are right that there is a transistor of some sort in 
there, and a bunch of resistors and that's it I think.

I know that it should never break, but I worry that one of the wires 
will fall off somewhere and I won't know where to reconnect it to.  I 
guess the only solution is to open it up carefully and take some hi-res 
digital photographs documenting where the wires go on the PCB now while 
it is still working :-)

The FILTER CV input definitely alters the sound if you insert a jack and 
feed it from 0 volts (shorted jack plug).  The voltage input required on 
this jack for "no change" seems to be about 3.1 volts.  As you hinted I 
think it is fed into a summing node like where the VCF envelope sweep 
and the accent envelope sweep get combined in the exponential converter 
at the bottom of the ladder.


On 2023-04-11 11:51, Roman Sowa wrote:
> Based on what I could see in Kenton's page photo this is very minimal
> kit, with maybe 3 resistors and a transistor. CV for pitch and filter
> are probably just resistors going to summing nodes of VCO and VCF
> respectively, probably directly to the base of 2SC1583, so without any
> voltage at their sockets, there's no difference from un-modded TB303.
> The other 3 are just on/off switching signals.
> All I'm saying is, the kit does not change anything when nothing is
> connected and is so simple that has no chance of ever needing a
> repair.
> Roman
> W dniu 2023-04-10 o 21:37, Richie Burnett pisze:
>> The TB-303 that I got second-hand many years ago has a set of 3.5mm 
>> jack sockets along the back of the enclosure marked SLIDE, ACCENT, 
>> FILTER, GATE and CV.  I believe these are a mod for use with a Kenton 
>> MIDI-to-CV interface?
>> Does anyone know the details of how these sockets connect into the 
>> rest of the TB-303 schematic?  Last time I had the 303 open to replace 
>> the tact switches I noticed that there were various resistors and 
>> transistors inside bits of heat-shrink tubing soldered to the copper 
>> side of the PCB.  I'm trying to find a schematic of the connections 
>> for a couple of reasons:
>> 1. I want to know how to fix them if a wire should fall off at some 
>> time in the future.
>> 2. I'd like to make a judgement on whether these mods affect the sound 
>> in any way compared to a standard production TB-303, even when nothing 
>> is connected to the jack sockets.
>> Before anyone says "open it up and trace out what wires go where", I 
>> had thought of that!  I'm not being lazy, I'm just trying to minimise 
>> the number of times I open up the unit as the old plastic enclosure 
>> and PCBs are quite fragile.  There's also the risk of human error if I 
>> trace out the connections vs working from a schematic if one exists 
>> somewhere?
>> Has anyone ever fitted one of these kits?  It looks like Kenton 
>> Electronics still do them...
>> https://kentonuk.com/product/roland-tb-303/
>> ...but the PDF docs at the bottom of that page don't tell you how to 
>> install the kit.
>> -Richie,
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