smallstone issue J clone not working

[nathan Dodd]

Just finished building my first pedal - it's the smallstone on general guitar gadgets. All I’m getting is a low output when the colour is on and nothing when it's off plus a little buzz but no kind of oscillation at all. Any ideas that may save me some time when I get round to fault finding that may make life easier?

Many thanks in advance,

Nathan.

[nathan Dodd]

i am getting a clicking/popping but it may be exterior. all my tracks are fine, my soldering seems... adequate but no more than the avarage level output that's not phasing. any thoughts anyone?

[gez]

i am getting a clicking/popping

If the clicking is rhythmic then at least you know your LFO's working.  Take voltage measurements at all the OTA pins.  Most of my debugging is done with a multimeter and little else - tells you a lot about what's going on.

[nathan Dodd]

ok, update. firstly thanks for the advice! i'll do that - the clicks are rhythmic. i've renewed all my solder joints and they now look top class. my output is now strong and the colour does add colour. the only thing is still no phase!!! aaargh!!! one thing i did do was to put a 30k resistor in place of the 27k marked on R32 on this reference http://www.generalguitargadgets.com/diagrams/smallssc.gif i will replace this with the correct value and see what happens next. if you think this could be the root of the problem say aie! will i need to have my battery in to test my OTAs? and what should i be looking for?

many many thanks,

Nathan

[nathan Dodd]

any ideas? have full output now almost as if the effect is bypassed.

[gez]

one thing i did do was to put a 30k resistor in place of the 27k marked on R32 on this reference

No, it wouldn't be the cause but you should replace it with the correct value.  

I had a similar problem to yours a week ago.  Turned out to be a bridge between a couple of traces.  Couldn't see it but it was there (tracked it down using my multimeter).  Managed to sort it out by scraping between the traces with a scalpel.  I'd also damaged (unbeknown to me) the casing of a resistor which was causing a short with an adjacent component.  This took a little longer to find!

Whenever I etch a board I always go over it with my continuity tester to check for bridges.  From now on though I'll be checking for resistance instead as the continuity tester doesn't show resistances of a few k or more (well, mine doesn't) which is why this 'invisible' bridge wasn't detected before I started soldering.  One whole afternoon of debugging and the lesson has been learnt...

[nathan Dodd]

I took your advice and scraped at any tracks that seemed a little too close for comfort; still I’m getting a lovely clean signal but no phase. I was looking at archived discussions here and started to read about wet n dry signals with the small stone (bare with me here this is alien to me) - so it seems then that what I have is the wet signal?? And no dry signal?? Or sommut like that? Tonight I’m gonna tin all my tracks, re-wire and re-flow all my off board components and get on my knees. It’s gonna be a while before I can get my hands on the correct value resistor though.

Nathan.

[nathan Dodd]

no i got that the rong way round - all i've got is a dry signal. if i had a wet one it'd sound like a vibrato - if i had them both i'd be listening to a shifted phase. am i right or am i left?

[gez]

You've got all dry signal nathan.  What you need to check are the connections between pin6 of IC4 and the output, which is basically R13.  

If still no joy, check connections from C3 to IC1 (plus all connections between the chips used for the 'wet' signal).

Failing that, post voltages for all pins of chips IC1 to IC4.

[nathan Dodd]

I'll be on it tonight. thanks!

[nathan Dodd]

ok my continuity checks out

IC1

1.   0
2.   1.91
3.   1.95
4.   0
5.   0
6.   0.80
7.   9.16
8.   9.16


IC2

1.   0
2.   1.87
3.   1.95
4.   0
5.   0
6.   0.77
7.   9.16
8.   9.16

IC3

1.   0
2.   1.87
3.   1.95
4.   0
5.   0
6.   0.79
7.   9.16
8.   9.16

IC4

1.   0
2.   1.86
3.   1.95
4.   0
5.   0
6.   0.61
7.   9.16
8.   9.16

and just for good measure

IC5

1.   0.39
2.   7.22
3.   7.89
4.   0
5.   0
6.   0
7.   9.16
8.   7.89

does that help?

[gez]

OK, pins 2,3 & 6 should all be at the same voltage (Vref) so there's a problem, and they should bias up higher than they are.  I've had a very quick glance at the schematic for the chip and pin 5 of each chip should be a diode drop above ground so it suggests that there's no input bias current.  Check to see if you've shorted one of the pin5 connections to ground.  Likewise, pin6 of the LFO shouldn't be 0V.  Redo the joints either side of R24 and make sure all the pin 5 connections are sound.

Measure Vbias (junction of R1 & R3) and post.

[gez]

Sorry, I'm right in the middle of etching a board so things are a little sporadic.

pins 4&5 of IC5 (the LFO) shouldn't be 0V.  Are you sure your readings are right? (you said the thing clicks so this does suggest that the LFO is working).  If the readings are right, check everything around R22 & R23.

[nathan Dodd]

sorry, dumb down a bit for me - what do you want me to do between r1 and r3?

[nathan Dodd]

stick with me checking now

[nathan Dodd]

pin 4 is 0 pin 5 is 0.54
ok measuring volts across r23 i've got 1.9v to the left 0v on the right also measuring 0ohms accross it powered 6.38 unpowered

edit i've done some scraping and 5 n 6 are now rising and falling

[nathan Dodd]

my switch and perticularly the wire bottom right going to it are hyper sensative, is this normal - when you go near it or touch it it buzzes like hell.

r 5 is 0.64 solid r 6 is dancing around 0.30 r4 still 0

[gez]

r 5 is 0.64 solid r 6 is dancing around 0.30 r4 still 0

I take it r refers to the pins of the IC rather than a resistor?  I also take it that these measurements are for the LFO (IC5), yes?

Pin4 is the ground connection so you'd expect it to be 0V, and pin 5 (for IC5) should be rock solid (and at around that voltage - one diode drop).  Pin6 of IC5 should 'dance' too.  It sounds as though the LFO is working.

The problem is with the biasing of the chips used for the phase stages.   Measure the voltage at one of the pin5 connections to R24 and post (looks as though there's no Iabc bias current getting to the chips, could be a short to ground).

[nathan Dodd]

yeah you've got it sorry for my lack of clarity.

volts from all pin fives on all other ICs except IC5 = 0v

[gez]

I was just editing my post before you replied (honest guvnor!).  As I said, you've got a short to ground somewhere from one of your pin5s.