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Thread: Sovtek green small stone not phasing

  1. #1
    Member Suburbanite's Avatar
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    Sovtek green small stone not phasing

    Hi, Ive acquired an old small stone which has a few issues, namely, it won't phase, opened it up and couldn't see much wrong, a broken lead to the led and a dirty stompswitch so Ive bypassed the switch and re soldered the led, when I put a sound source through theres a small volume drop and when I switch the color switch it takes the treble out,

    also looks possibly like someone has changed the rate pot, not sure but it looks a bit new, its a "a 1m" thought it might need to be a linear rather than an audio

    not sure where to start next and I can't seem to find any schem's for this model

    any help would be gratefully recieved

  2. #2
    Supporting Member Dave Curtis, dB AudioTech's Avatar
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    Here's a stab in the dark: I have an old Bad Stone that didn't work. I tried a bunch of stuff before changing the power supply cap, which fixed it.

  3. #3
    Member Suburbanite's Avatar
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    Would a power cap actually stop the phasing? theres still a signal getting through although there is a volume drop, thought it might of been one of the chips as they're whats responsible for the timing of the sweep?? am I barking up the wrong tree?

    What I'm nearly decided on is changing all the components for new (and better quality) but I'm struggling to identify all the components, I know the pedal isn't worth that much but I quite like the ugly thing

  4. #4
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    Quote Originally Posted by Suburbanite View Post
    ...I know the pedal isn't worth that much but I quite like the ugly thing
    They are cool in an ugly sort of way.

    I would first double check whatever the earlier repair person did, to be be sure that it is not the cause of the problem. I have fixed a couple of these through the years, and the problems are often mechanical and usually related to the switch or the pot.

    I think that it's a very basic 4-stage phase shifter, still based on transconductance op-amps. First check to see if the oscillator is working. Either scope the circuit or look for fluctuating voltages on the osc. chip.

  5. #5
    Old Timer oc disorder's Avatar
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    Here's some links
    http://www.lynx.bc.ca/~jc/moddedSmlStnSchm.gif
    http://www.lynx.bc.ca/~jc/SmallStoneLyt.gif
    http://www.fortunecity.com/tinpan/hu...smallstone.jpg

    The first one has..."mods"
    The layout may be similar in the 2nd link
    The 3rd link the diagram was drawn in '75

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    look for fluctuating voltages on the osc. chip

    Yes if you see fluctuating voltages or a Sinewaveform on the output (pin 6) of the LFO or Pin 5 to any of the CA3094 chips phase shift network stages

    Pin 5 should be the transconductance INPUT to the CA3094 chip

    either than are EH1084 chips or CA3094 datasheets will tell the pinouts also

  7. #7
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    Quote Originally Posted by vincediamond View Post
    Pin 5 should be the transconductance INPUT to the CA3094 chip

    either than are EH1084 chips or CA3094 datasheets will tell the pinouts also
    If this is a green Sovtek version, the chips are not EH1048/CA3094's. Maybe LM13600's?

  8. #8
    Supporting Member Dave Curtis, dB AudioTech's Avatar
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    Quote Originally Posted by Suburbanite View Post
    Would a power cap actually stop the phasing? theres still a signal getting through although there is a volume drop, thought it might of been one of the chips as they're whats responsible for the timing of the sweep?? am I barking up the wrong tree?

    What I'm nearly decided on is changing all the components for new (and better quality) but I'm struggling to identify all the components, I know the pedal isn't worth that much but I quite like the ugly thing
    My Bad Stone was doing the same thing; passing signal, slight difference in volume, etc. I checked the switch, pots and swapped chips to no avail. Changed the 470uF cap (IIRC) and it worked.

  9. #9
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    Quote Originally Posted by 52 Bill View Post
    If this is a green Sovtek version, the chips are not EH1048/CA3094's. Maybe LM13600's?
    I stand corrected, the green ones did use CA3094's. But I did remember correctly, as there was a version that did use the LM13600's.

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    The LM13600's IC chip has a different pin out than the CA3094

    CA3094 is a 8 pin chip
    LM13600 is a 16 pin chip

    The LM13600 is a dual inline chip so maybe to save room and space on the PCB

  11. #11
    Member Suburbanite's Avatar
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    these are the ca3094e chips,

    Newb question would I test earth to pin to check for voltage fluxuations or pin to pin (no scope)

  12. #12
    Member Suburbanite's Avatar
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    heres a pic if it helps
    Attached Thumbnails Attached Thumbnails p10-12-08_15.09.jpg  

  13. #13
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    Yes, earth the black lead of your meter and read the voltages on the pins of the IC's. If you read the voltages on one of the chips in the phase shift circuit, you can compare them with the voltage readings you get on the other three chips. Look for one of the chips to have odd readings from the others. My guess would be that one of your four phase shift circuit chips is bad.

    In the photo, there seems to be a burned resistor on the lower left side (just above the jack). Is it ok and does it read a correct value?

  14. #14
    Member Suburbanite's Avatar
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    resister reads 47 so ok, but good eyes there, I hadn't seen that heat mark before, might swap it out any way

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    i have exactly the same problem with a old small stone (around 1980).

    No phasing, just a loose of volume. Color switch and rate pot do nothing.

    All the traces are ok (checked with multimeter)

    All the resistors are ok (checked on board with multimeter). The 47 ohms on the +9v input was burned but sill fonctionnal. I changed it anyway.

    The 4 transistors are OK (unsoldered and test with the diode test of my multimeter).

    All the condensators seem OK :tested ONBOARD with an softare oscilloscope : I injetct an audio signal (sine 440 hz) in input and i "see" it in output.

    I think that the UC5 (wich "drives" the LFO isn'it ?) is dead.
    How can i test it ?

  16. #16
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    The 47R resistor will be power-supply related. If there are heat marks around it, that does not bode well. Drawing that much current to produce burn marks might be a harbinger of damage elsewhere.

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    Quote Originally Posted by mollotof View Post
    i have exactly the same problem with a old small stone (around 1980).

    No phasing, just a loose of volume. Color switch and rate pot do nothing.

    All the traces are ok (checked with multimeter)

    All the resistors are ok (checked on board with multimeter). The 47 ohms on the +9v input was burned but sill fonctionnal. I changed it anyway.

    The 4 transistors are OK (unsoldered and test with the diode test of my multimeter).

    All the condensators seem OK :tested ONBOARD with an softare oscilloscope : I injetct an audio signal (sine 440 hz) in input and i "see" it in output.

    I think that the UC5 (wich "drives" the LFO isn'it ?) is dead.
    How can i test it ?
    "Poke and Hope" won't fix it. If you don't know what you're doing, and you have no idea how it's meant to work, you'll just break it further. Send it to someone who understands these things, has the right instruments to track the problems, and the spares to repair it. Otherwise, you're just wasting your (and our) time.

  18. #18
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    i have the same phaser
    but the black issue (it has the same board anyways)

    The rate pot is 1M reverse log.

    The LFO might be not oscillating.
    There is a cap in the circuit that when get's bad or unsoldered
    the pedal doesn't have the LFO working that controls the CA3094.

    Check Pot, LFO section for any shorts. Replace CA3094 in LFO section.

  19. #19
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    Angry You also have No Idea!

    Quote Originally Posted by Lee_ranaldo View Post
    i have the same phaser
    but the black issue (it has the same board anyways)

    The rate pot is 1M reverse log.

    The LFO might be not oscillating.
    There is a cap in the circuit that when get's bad or unsoldered
    the pedal doesn't have the LFO working that controls the CA3094.

    Check Pot, LFO section for any shorts. Replace CA3094 in LFO section.
    I have NEVER had any of the ICs fail in a Small Stone, and I've mended dozens of them. The ICs don't even fail if the wrong supply is connected!

    Please stop wasting our time with silly, uninformed conjecture. If you can't actually suggest what's wrong with the thing, don't bother replying.

    Don't waste your time and money just randomly replacing components - you might get lucky and find a faulty component, but it's very unlikely. I'll say it again, but louder this time:

    "POKE AND HOPE" WILL NOT MEND THIS UNIT. If you don't know what you're doing, ship it to somebody who mends equipment like this and get it fixed. It will be cheaper for you in the long run, and will save the world's components for the rest of us who know how to use them!

  20. #20
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    Check the 33uf Capacitor is it's properly soldered and it's ok.
    If now measure with a scope if u're getting an LFO signal. Check the components in the red square.

    The LFO IC is next to a couple of Transistors.





    PD:Posting some info against any kind of help we are trying to give
    sound like a fantastic strategy. either u're a part of the solution or part of the problem, cheers!
    Attached Thumbnails Attached Thumbnails eh_small_stone_phaser.jpg  

  21. #21
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    I've fixed a few of the Sovtek versions, and none have needed a new chip. I have also fixed a lot of the older original EH versions and many have needed new CA3094 chips.

    I thought that we were all here to help one another. If someone asks a reasonable question, then I think that it deserves a reasonable answer.

    The generic answer to the question regarding chip testing is to read the voltages on the pins of the ICs. Get a copy of the data sheet or the schematic and look at the pinout of the chip in question. Check the voltages and see if there are voltages where they should and shouldn't be.

  22. #22
    Noodle of Reality Steve Conner's Avatar
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    Quote Originally Posted by mictester View Post
    Please stop wasting our time with silly, uninformed conjecture. If you can't actually suggest what's wrong with the thing, don't bother replying.
    Chill out, Mr. Grumpy 3 Posts. The entire Internet is a mass of silly, uninformed conjecture designed to waste the time of most of the Western world, you're not going to make a difference.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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