Plain vanilla test harness

[rockola]

Frustrated by the growing pile of not-quite-right projects, I finally built a test harness. Also the perfect excuse to have some ice cream. There's breadboard space for up to 4 pots and any possible resistors/capacitors/etc. attached directly to them. Wires coming from the circuit are connected via speaker terminals.



The all-important gut shot.



The test harness on its maiden voyage, testing Matt Gray's BizNiz: http://graybloomfield.com/guitar/pedals/bizniz/



There's something not quite right with this build of mine (what a surprise), the gain pot seems to work as just another volume pot (didn't have a C10k so chucked in an A10k backwards), and I can't get it to distort. Anyway, the test harness seems to work, signal is going in and coming out, and the pots do something. Well, they started doing something once I remembered to populate the transistor & diode sockets (not the first time I've done this and most certainly not the last time either).

I knew from the start that the ice cream tub would be too flimsy for prolonged use. This is just a prototype for figuring out what the all-new improved version should be like. I already know there should be a bypass switch, it's hard to judge whether a boost is doing anything if there is no way to bypass the circuit.

[EBK]

When you make your improved version, you should label it "URBON VANIL" as a tribute to this one.

A test rig is something I still need to make myself.  I have a handful of enclosures from past endeavors that I should put to use on at least a basic rig.

Nice work!

[antonis]

>didn't have a C10k so chucked in an A10k backwards<

That doesn't turn a Log pot pot into a anti-Log one.. 

Anyway, distortion (due to high gain) in such a circuit is a bit complicated..
It depends on Collector/Emitter resistor ratio but also on Feedback resistor/Input impedance ratio togheter with Feedback/Collector resistor ratio..
(1^st & 3^rd of them are quite satisfactory here..)

Which type of BJT have you used..??

[rockola]

>didn't have a C10k so chucked in an A10k backwards<

That doesn't turn a Log pot pot into a anti-Log one.. 

No. Wasn't too worried about the taper in this test. Backwards because it wouldn't fit otherwise...

Which type of BJT have you used..??

2N3904 and 2N5089, with similar results.

[duck_arse]

reading this:

Also the perfect excuse to have some ice cream.

had me worried about this:

The all-important gut shot.

not sure your pots will withstand multiple insertions into the breadboard [or the breadboard from the pot pins battering], but if you only insert [once] the ones you intend to build with, probably won't damage the pin rivets.

too cold for ice cream here.

[rockola]

Got the BizNiz working. There may have been something else going on at first, but when I finally figured out that a gremlin had swapped IN and OUT on the test rig while I wasn't looking, everything was hunky dory. 

not sure your pots will withstand multiple insertions into the breadboard [or the breadboard from the pot pins battering], but if you only insert [once] the ones you intend to build with, probably won't damage the pin rivets.

Good point. Not sure how to get around this easily.

too cold for ice cream here.

I think you'll find that midwinter Down Under is not entirely unlike midsummer in Helsinki...

[ElectricDruid]

not sure your pots will withstand multiple insertions into the breadboard [or the breadboard from the pot pins battering], but if you only insert [once] the ones you intend to build with, probably won't damage the pin rivets.

Good point. Not sure how to get around this easily.

Use 9mm pots with little pins? The vertical ones are good to use in breadboards if you break off the snap-in tabs that are supposed to hold them into a PCB.

[GGBB]

>didn't have a C10k so chucked in an A10k backwards<

That doesn't turn a Log pot pot into a anti-Log one.. 

Technically no, but it can turn a log control into and anti-log one. Connected backwards (swap pins 1 and 3) and used backwards (counter-clockwise rotation for fuzz increase) will accomplish the same end.

[Fancy Lime]

>didn't have a C10k so chucked in an A10k backwards<

That doesn't turn a Log pot pot into a anti-Log one.. 
...

It doesn't? Assuming by "anti-log" you mean "reverse logarithmic" , the C-taper pots I have do exactly what the A-taper ones do, but in reverse (allowing for the high tolerances that plague most pots). What resistance-vs-travel functions should A-taper and C-taper pots follow? Assuming this is half-decently standardized at all...

Cheers,
Andy

[duck_arse]

one way to beat the pins pounding is to twist the skinny lug-end bits 90^o so the slip between the BB grippers. other way is to solder the pot to header pins, w/ the ones between pulled.

[GGBB]

>didn't have a C10k so chucked in an A10k backwards<

That doesn't turn a Log pot pot into a anti-Log one.. 
...

It doesn't? Assuming by "anti-log" you mean "reverse logarithmic" , the C-taper pots I have do exactly what the A-taper ones do, but in reverse (allowing for the high tolerances that plague most pots). What resistance-vs-travel functions should A-taper and C-taper pots follow? Assuming this is half-decently standardized at all...

Cheers,
Andy

You are correct. Practically speaking it works as desired (see my post above). But technically speaking the "pot" doesn't change its taper when you wire it backwards - it's still either a log pot or a reverse log pot. The "control" changes from being clockwise reverse logarithmic (with a "C" taper) to being counter-clockwise reverse-logarithmic (with an "A" taper) by substituting the pot and wiring and operating it backwards.

For the purposes of this discussion, the point you quoted is moot - we all know what we mean here.

[Fancy Lime]

>didn't have a C10k so chucked in an A10k backwards<

That doesn't turn a Log pot pot into a anti-Log one.. 
...

It doesn't? Assuming by "anti-log" you mean "reverse logarithmic" , the C-taper pots I have do exactly what the A-taper ones do, but in reverse (allowing for the high tolerances that plague most pots). What resistance-vs-travel functions should A-taper and C-taper pots follow? Assuming this is half-decently standardized at all...

Cheers,
Andy

You are correct. Practically speaking it works as desired (see my post above). But technically speaking the "pot" doesn't change its taper when you wire it backwards - it's still either a log pot or a reverse log pot. The "control" changes from being clockwise reverse logarithmic (with a "C" taper) to being counter-clockwise reverse-logarithmic (with an "A" taper) by substituting the pot and wiring and operating it backwards.

For the purposes of this discussion, the quoted point is moot - we all know what we mean here.

'swhat I thought, thanks for the clarification, Gord. I somehow missed your previous post. Sorry bout that.
Andy