Small Stone Repair

[michael_krell]

I have an old small stone I am trying to get working. It seems that this thing isnt sweeping. it passes signal but it is uneffected. if anyone has sufficient knowledge of these pedals. please reply or IM me or email me.

[puretube]

gez: who`s next?

all others: solution hasn`t been found here yet:
http://diystompboxes.com/sboxforum/viewtopic.php?p=153341&highlight=#153341

:?:

(don`t have a printed schem here,
and jumping pages just makes me mad...)

[gez]

OK, let's shift the thread.  

What exactly should I be looking for in the dry and wet signals? (as far as amplitude and phase and any kind of "dancing").

If you're getting signal at the output then your dry signal from the input buffer is reaching the output (it does occur when you stomp on the switch too doesn't it?)  

From what you've described, your wet signal is working - the phase shift stages are doing their bit.  What isn't happening is the mixing of the two, so check the chain that follows pin6 of the last phase stage to the output.  It's probably just a bad joint.  Edit: I've just checked the schematic and there's only a 27k resistor from wet output to junction of the mixing.  Check with the scope that you're getting a signal at pin 6 (if not get back to us), if you are then redo the joints for this resistor.

also. if i increased the value of that drop down resistor. will i get a higer output? these issues of the small stone seem to have a volume issue

All depends what impedance follows the effect.  That's why I hate passive mixers.  Don't have the schematic in front of me, but if I recall the pull-down is 470k.  This will be loaded by whatever follows - might be slight, might be major.  Increasing it may help, but it could go the other way (too loud) when followed by certain effects/amps...

Op-amp active mixer would be my choice (low output impedance so is consistent) .

[michael_krell]

OK, let's shift the thread.  

What exactly should I be looking for in the dry and wet signals? (as far as amplitude and phase and any kind of "dancing").

If you're getting signal at the output then your dry signal from the input buffer is reaching the output (it does occur when you stomp on the switch too doesn't it?)  

From what you've described, your wet signal is working - the phase shift stages are doing their bit.  What isn't happening is the mixing of the two, so check the chain that follows pin6 of the last phase stage to the output.  It's probably just a bad joint.  Edit: I've just checked the schematic and there's only a 27k resistor from wet output to junction of the mixing.  Check with the scope that you're getting a signal at pin 6 (if not get back to us), if you are then redo the joints for this resistor.

also. if i increased the value of that drop down resistor. will i get a higer output? these issues of the small stone seem to have a volume issue

All depends what impedance follows the effect.  That's why I hate passive mixers.  Don't have the schematic in front of me, but if I recall the pull-down is 470k.  This will be loaded by whatever follows - might be slight, might be major.  Increasing it may help, but it could go the other way (too loud) when followed by certain effects/amps...

Op-amp active mixer would be my choice (low output impedance so is consistent) .

For some odd reason my dry signal is dancing around kind of like the wet one did. Do you think i have a short somewhere and the wet is leaking through to the dry?

[puretube]

As the "dry signal", absolutely only the signal right at the input jack should be regarded.
As the "mix signal", the signal right at the output jack is denoted.
The "wet signal" is at pin 6 of the last stage.

What you describe "the dry signal dancing", IMHO means that indeed the signal is being processed, and a certain amount of it being fed back to the input. (normal in this passive circuit - depending a bit on the "colour" switch position).

What do you hear at the output? (now the input shows the dance, too);
IMO you should be able to hear either vibrato, s.th. wah-like, or the phasing it should do...

PS: wiggle the colour-slideswitch back anf forth quickly a couple of times to clean it - it might be corroded...

[michael_krell]

Quick question:

The problem still has not yet been solved, but i replaced the electrolytic caps. Some of them i used values +-10uF. is this alright???

[puretube]

it`s never wrong to put in fresh caps...
(but that doesn`t seem to be the problem, here);

10µF: I see only 1 in this schem:
http://www.montagar.com/~patj/smlstone.gif
(let`s take this for reference)
the other electrolytics are in the upper left corner for bias-supply
filtering 33µF: lowering this to 10 is not such a good idea (rather 47µF),
but should not be too audible, or stirr up the functioning;
the other 33µF I see is in the LFO-section: lowering that one to 10
will make the speed (rate) 3 times faster, without influence on
the proper functioning of the audio-path.

Another thing: did you have the feeling, when you started debugging
this pedal, that somebody before you already has had some soldering
done in the circuit?
Did you buy the thing secondhand, and it never worked,
or did it suddenly stop functioning while having been in your posession?

[gez]

What do you hear at the output? (now the input shows the dance, too);
IMO you should be able to hear either vibrato, s.th. wah-like, or the phasing it should do...

Michael, answer the question!   :evil:  ( )

[michael_krell]

It looks like someone who had it before me tried to fix it themselves because two of the wires on the switch were in the wrong location so only God knows what else they did. Im sure this thing worked at some point. It does have a bit of rust on it so it was probably neglected for a while. I bought this thing broken.

The output signal has no effect on it. Almost like there is no change when I hit the switch.

what the heck does IMO mean???

[travissk]

IMO = "In My Opinion"

[michael_krell]

thanks travisk. I just noticed that the Current draw for the devices is approximately 4mA. is that normal?

[michael_krell]

What should the amplitudes and DC voltages of the phase stage outputs be? (pin 6 of the IC's)

[travissk]

I don't have a Small Stone (I've been meaning to get one for some time...), but 4mA seems a bit low, with the LED and a modulation effect going on.

I know some modulation pedals come in under 10mA, but my intuition says that just seems too low.

[puretube]

AC vol should be roughly equal @ all stages outputs (=input vol)

check the traces on your PCB, and try to identify the circuit
comparing with the schematic (noted somewhere above);
see if your resistors do have the same values as the schem...

current sounds ok to me

old SS don`t have LED

find the 30k resistor that in the schem goes "south" of the 2nd transistor (2N5087) - lift (disconnect) one end out of the board - what do you get at
the outputjack now? (it should be the same as the input, but moving left to right and back - not "dancing", though).

[michael_krell]

The output of the 4 phasing stages are very very low in output (pin6). That sounds like it could be why i am getting no effected signal at the output when the effect is engaged. What would cause this.

PS. the wave I am driving is a 440 Hertz Sine wave

[puretube]

leave that 30k R lifted;
compare your inputjack voltage with that one appearing directly at the collector of the 2nd trans. (2N5087) (that is the output of the input-stage);
the latter should at least be equal to the input level;
that latter level should stay the same on each pin6 of the subsequent stages (while moving left/right);

oh,yes: set the speedrate slow - it`ll make you mad, when fast!!! -
(but you know that by now, I presume  :wink: ).

edit: see that 30k resistor following the 10µF cap after the 2nd input-transistor right to pin 2 of the first OTA?
That`s probably one that has been played around with... ().
Make sure it really is 30k (or 27k), and not 330k or 270k,
or 3.3k or 2.7k...

[michael_krell]

i tested the output of the input stage and the amplitude seems to close to the amplitude of the input. I looked at the pin6's of each of the phasing stages and it looks like IC1 and 2 have very very low amplitudes ( there is some signal,but not much at all) and 3 and 4 have amplitudes that are about the size of the input amplitude. Is this supposed to be?? I think I might have made a break through in this dumb small stone problem.

I aprreciate your guys's help

[puretube]

all 4 shift ICs should have the same ampl. at their pins6 (=output),
which goes into the next shift-stage thru the following 27k & 68n;
it`s not supposed to be amplified greater in a next stage, when the signal is lost in a previous stage; this means you probably have correct ampl. in the 1st and 2nd stage, but problems in the 3rd and 4th;
(it doesn`t "re-appear" after being lost).

Triple-check all solderpads, R, C values around the 2 malfunctioning ICs.

Gez will tell you next time, how to listen to the 2 seemingly working stages, to at least prove that they are working...
(GEZ???)  

[gez]

I looked at the pin6's of each of the phasing stages and it looks like IC1 and 2 have very very low amplitudes ( there is some signal,but not much at all) and 3 and 4 have amplitudes that are about the size of the input amplitude

Probably a dumb question, but are you sure you've got the stages in the right order? (I've never seen the PCB for the SS, but it might be a little counterintuitive?)  As PT said, there shouldn't be an increase in gain along the chain, so are you sure you haven't got them confused and the low amplitudes are in the final two stages?  Or does it look as though someone has been doing some resoldering in these stages and has got some values wrong?

I outlined earlier on in this thread (or was it the other one?) how you can check aurally to hear what's happening.  Ideally, it would be nice to isolate each stage, but I doubt you could do this here as it would probably involve cutting the traces from each pin6 to the next stage.  You can at least take an output cap from each pin 6 though - might answer a few questions...

[gez]

You can use a test-lead (multi-meter) to take the output from each pin 6.  Just croc-clip another lead to the non-probe end and clip the other end of this second lead to a large value cap (plugged it into a breadboard if possible), then out to your amp.

Strum with one hand, probe with the other...cue Frankie Howerd!