Home Forums GuitarPCB Build Support Mini-Me: no effect

Viewing 15 posts - 1 through 15 (of 15 total)
  • Author
  • #1239


    Thanks for any help in advance! First post…

    I’ve built a Mini-Me chorus. I get signal through in bypass and switched on – the signal/audio path seems to be OK (using an audio probe and following an annotated circuit diagram from the GuitarPCB forums). But I get no effect. I’ve double checked all resistor and capacitor values, reflowed all joints, and given a good visual check a few times. Tried two MN3007 chips, both from SmallBear.


    Source: 9.46v

    IC1 – 4558

    1 – 4.53

    2 – 4.53

    3 – 4.43

    4 – 0.00

    5 – 4.50

    6 – 4.51

    7 – 4.50

    8 – 9.03

    IC2 – MN3007 (SmallBear)

    1 – 8.43

    2 – 0.00

    3 – 5.83

    4 – 0.00

    5 – 0.00

    6 – 8.43

    7 – 7.86

    8 – 7.85

    IC3 – CD4047BE

    1 – 8.42

    2 – 0.00

    3 – 7.93

    4 – 8.43

    5 – 8.42

    6 – 8.42

    7 – 0.00

    8 – 0.00

    9 – 0.00

    10 – 0.01

    11 – 8.42

    12 – 0.00

    13 – 8.42

    14 – 8.42

    IC4 – LM358P

    1 – 7.71*

    2 – 0.00

    3 – 4.07

    4 – 0.00

    5 – 7.65*

    6 – 2.23

    7 – 7.76*

    8 – 9.02

    Q1 – 2N5087

    E – 5.31

    B – 4.70

    C – 0.00

    Q2 – 2N5088

    E – 5.84

    B – 6.39

    C – 9.02

    Q3 – 2N5088

    E – 8.42

    B – 9.00

    C – 9.02



    It may seem simple but the trimmer usually dials in the Chorus at around 1:00 position for most MN3007 chips. While some slightly off spec chips may yield different results the current position of your trimmer would not normally yield the chorus effect. I have personally hand tested 100’s of chips and 90% dial in at around 1:00.

    Additionally the range of rotation which will yield the chorus effect is very small. We need the full range of the trimmer however to account for chips that have a poor tolerance.

    I cannot see from the photo very well but make sure both grounds are hooked up securely as well.


    Your voltages are off on several Ics.  See the document below for typical voltages and a signal path.


    Thanks Barry and Wilkie for having a look.

    Both grounds are in continuity.

    I set the pedal up behind a looper so I could have a simple guitar signal to try to adjust the trimmer. I got no variation. There is a very slight volume decrease, but no effect, throughout the entire trimmer range.

    I can see the voltage differences, but I don’t know how they translate to which part of the circuit I should be checking. For example, having 0.00v at pin 2 on IC2 but 8.42v at pin 11 on IC3 – on the circuit diagram they look connected, shouldn’t they be the same? Any suggestions?

    Significant voltages differences are at pins 2,6,7,8 on IC2 (MN3007); 10,11 on IC3 (CD4047BE); and pin 2 on IC4 (LM358P – assuming some of the other variations here are due to oscillations).


    Back-side photo below: I made an error in the original post, thought I had put this in. I’ve double checked all resister values, capacitors and diode/electrolytic cap directions, and reflowed all joints, and scratched between solder joints to remove any bridges, all before posting. The backside of the potentiometers have caps. I’ll follow all suggestions above when I get the chance – thanks for again for the help.


    SInce the voltages at the 358 are oscillating, the LFO section is working.  This should be giving a changing voltage at pin 1 of the 4047 and at pin 1 of the 3007.  The voltage at pins 10 and 11 of the 4047 should match the voltages at pins 6 and 2 respectively of the 3007.

    I suspect bad solder joints.  I suggest removing power and all ICs and resoldering all joints particularly around the sockets for the 3007 and the 4047.  Also resolder P1, C19, R29, C18 and D2.  Also check for solder bridges that may be causing shorts.  Photos of the back side would help to locate bad joints and bridges.


    Hi this is Jens from Germany 🙂

    I’ve assembled the Mini-Me, but the P1 (Depth) works halfway. P2 (rate) is without function. Also, there is generally no oscillation. But at least sound comes through when the effect is activated. Trim Poti is about halfway up. Below are my volt measurements.

    1          4,16                 8          8,24
    2          4,16                 7          4,09
    3          4,06                 6          4,13
    4          0                      5          4,12

    1          7,58                 8          5,15
    2          3,75                 7          5,15
    3          5,01                 6          3,74
    4          0                      5          0

    1          7,4                   14        7,58
    2          0,11                 13        7,42
    3          6,65                 12        0
    4          7,58                 11        3,75
    5          7,58                 10        3,74
    6          7,58                 9          0
    7          0                      8          0


    1          6,88                 8          8,24
    2          5,31                 7          7,61
    3          5,49                 6          7,44
    4          0                      5          6,94

    Q1                              Q2                              Q3
    E         4,49                 E         4,48                 E         7,58
    B         3,87                 B         3,87                 B         8,20
    C         0                      C         8,24                 C         8,24

    I see that the values deviate at IC4? So what could be my mistake?

    Here is a picture from the inside.


    The trim pot is usually active more near 1:00 did you try to dial it in by ear?

    I have never had one work set at 12:00 exactly.

    Some of the intermittence errors sound like cold solder joints so I would re-flow the entire project including all off-board wiring as well.

    If any of the above doesn’t help where did you get your MN3007? If you got it from Musikding you should be fine but if you got it from eBay it is probably a fake.


    Thanks Barry,

    Yes, I’ve adjusted it by ear. The most effect is strangely enough at 12:00 … not at 01:00.

    Thanks in any case for the hint. I’ll do another one tomorrow. The MN3007 came in the set of Musikding. The Mini-Me is not my first kit. Built by GuitarPCB I have the Black Dog, Sunn-T … and the ones running splendidly 🙂

    I still wonder the deviating values ​​in IC4? If I turn P1 manually (between 7:00 and 12:00 o’clock) I have these typical chorus sounds during the rotation. if the regulator stops, the sound stays, but without modulation. If I turn P1 further than 12:00, then the chorus sounds go off at the rest of the way. If I turn P2 (rate), it still has no effect?

    Yeah let’s see what’s tomorrow … maybe it’s really something banal like a cold soldering tin? I have just got another idea. The poti underside is protected by a small round rubber that came from Musikding. Maybe this one has conductive properties? I’ll work on the pots … we’ll see 🙂


    Yes something is definitely going wrong at IC4. I would check values against board photo locations and also re-flow. A bad potis is possible. Especially these areas:

    If you have an audio probe that would be helpful to trace the audio path and hear where it goes wrong.


    No, unfortunately not … I do not have an audio sample. But … I can record the Mini-Me. Maybe that’s also a clue to a diagnosis? Now it is unfortunately too late here for me. Otherwise my wife will be angry with me … Hahaha 🙂

    Thank you so far Barry


    I was meaning an Audio Probe (not an audio sample). A device to test the audio path.

    See our Guides Page for more. Subject Audio Probe


    Patrick Garland

    I’ve actually got a Mini-Me right here with the same problem – signal when engaged but not Chorus, been racking my brain trying to figure out what the problem is – wonder if I have bad chips? I checked the Trim, checked orientation, flow, etc. I’ll resolder the joints and see what happens. I am using 5089 instead of 5088, but I checked all orientation both ways and it did the same thing. Im careful about what chips I buy, so I probably just have an error somewhere. I’m going to replace my diodes and check and see if I can get some voltages for a troubleshoot.


    @Patrick your problem is different than the one above. If you closely read his thread he is getting chorus. I would not want others to think their is a common board design issue by suggesting it is the same problem.

    If you have an audio probe it could lead you to the area with the problem rather quickly.

    Also he has a verified source for his MN3007 and since he does get chorus through part of the rotation I would have to still ask where did you get your MN3007 chip? I have no longer been able to find “real” chips on eBay for well over two years now.

    I have hundreds in my possession from 10 or more retailers and all are Fake. I only kept them so I could potentially recognize the “Fake Stamps” on them. Testing proved also that none of them worked at all in a verified working circuit. I always left bad feedback for reference. The feedback I left would be at least 1 year old by now and many even older. I had to quit trying at that point. Small Bear have “REAL” MN3007 chips – 80 left: http://www.smallbear-electronics.mybigcommerce.com/ic-mn3007/

    Make sure both grounds are hooked up per the document which is another common error. The board has two isolated planes for noise reduction.



    I haven’t jumped into this thread sooner because I’m getting confused.  It seems we now have three (3) different builds that have problems (the first one dating back to July).  Can we please put these into separate threads so we can tackle them one at a time?  I doubt that all three have exactly the same problems.  After all, Barry has been selling this board for years.  I recall building it several years ago with no problem.  So, I am sure that there is nothing wrong with the board itself.

Viewing 15 posts - 1 through 15 (of 15 total)
  • You must be logged in to reply to this topic.