Home › Forums › Help/Technical Questions › Small Stone rev. L repair

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  • September 16, 2010 at 5:49 pm #80742
    almost enough
    Participant

    My Small Stone is not working correctly. In bypass (Prior to my true bypass mod…I did this despite the effect issue. I have done this in the past, so I know this isn’t the issue.) it was cutting off all the highs, and making a very noticeable volume drop. Effect engaged and color off has no change, and then with color on it makes slight phasing sounds in the background, but with more guitar coming through than the effect. Still has a volume drop/high roll off that’s unbearable.

    I’ve read online that sometimes the ICs will fail on it. Is there a way I can test these with a digital multimeter before I go ordering replacements? If I DO need to order replacements, are the IC CA3080E from Small Bear the correct ones?

    I’ve looked through past threads in the forum on this, and didn’t see one specifically for rev. L, and also didn’t read anyone explain what the problem small stones sounded like before replacing the ICs.

    Any help would be much obliged. Thanks.

    September 20, 2010 at 7:31 pm #111543
    almost enough
    Participant

    Does anybody have any input that I could use to at least get a little further on this problem?

    I tried all the ICs in different sockets to see if it affected the sound at all and it did not.

    I’m beginning to think that the problem isn’t in the ICs. I can hear FAINT phasing on the effect, but the effect volume drop is HUGE and there isn’t even a lot of background noise. Could the problem be in the voltage being sent through the pedal? Maybe a bad resistor?

    I’ve searched for a schematic for this pedal but to no avail. The values are written right on the PCB, so I can use that to an extent.

    If anybody has ANY ideas, maybe drop me a line?

    September 23, 2010 at 6:52 pm #111611
    The EH Man
    Moderator

    Have you verified the footswitch is fine? Try shorting the lug going to the output jack to the lug going to the effect output and see if that helps.
    Could also be a bad cap on the output. Just fixed an MXR Delay that did that. It had echo, but it was very faint.

    September 24, 2010 at 3:29 pm #111642
    Kekke466
    Member

    I have seen a whole series of bad Small Stones Rev. L that didn’t work.

    I can tell you that the CA3080 won’t work, because I tried it myself. In the past I have repaired many Small Stones from this series. Most likely you have a bad opamp if the LED and bypass still work.

    Have you tried to measure the voltage on the output legs?

    Regards

    Kekke466

    September 24, 2010 at 3:42 pm #111644
    Kekke466
    Member

    I believe in REV.L there were CA3094 used. Probably one of them are bad.

    October 4, 2010 at 10:53 pm #111817
    almost enough
    Participant

    I tested the op amps. I’m hoping I did it right. I measured with the ground on pin 4 and then the measurements on pins 6 and 8. Pin 8 was consistently 4.96 on all 5 of the op amps. Pin 6 was consistently ~2v, except for U5 which constantly changing. I’m not really familiar with op amps, but if I understand them correctly, it looks like this is about correct, right?

    I don’t have a capacitance meter, so I don’t know how I can test the output capacitors yet. I’ll probably be picking one up soon. C7 is the capacitor closest to the output…0.1uf. I’ll probably just try and replace that, since I can pick that up at the local Rat Shack.

    Thanks for the pointers so far. Still collecting dust, but I feel like I’m making head way on it.

    October 4, 2010 at 11:15 pm #111818
    The EH Man
    Moderator

    You really need to audio probe the circuit.

    October 5, 2010 at 1:00 am #111819
    almost enough
    Participant

    K.

    I’m going to really dive in on that when I can get some alligator clips. I started doing a little bit of probing today, and I know there’s SOMETHING wrong, but can’t quite figure it out yet. I’ll double check over a schematic tonight and see if I can follow the signal path. I get lost on the board pretty easy. It almost looks like the signal splits and goes to a phasing section, then rejoins with the dry and gets sent to the output…and I get a dry signal through a lot of it, but the signal grows REALLY faint once it starts getting to the op amps, then it just pretty much disappears by the end of it.

    Is the board I have really close or the same as another revision that I’ve seen schematics for? I haven’t found one for this model, but there’s others.

    Again, thanks for the help. I’m learning a lot.

    October 5, 2010 at 1:53 am #111821
    The EH Man
    Moderator
    Quote:
    K.
    It almost looks like the signal splits and goes to a phasing section, then rejoins with the dry and gets sent to the output

    That’s exactly what happens. If your signal is weak going into the first op-amp, it’s may be the transistors on the input.

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