Home Forums GuitarPCB Build Support Mini-Me Chorus (solved)

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  • #13625
    Joeri
    Participant

    Hi all, first post here and a beginner pedal builder in general.

    I got the mini-me chorus kit from musikding. It’s the third diy pedal I’m building. I built it according to this document, but it doesn’t produce a chorus effect, instead only the clean channel comes through. I’m using the 3007 IC. I’ve read your crash course and know you need voltages. But since there are so many components, I don’t know where to start.. So just tell which one you want measured and I’ll post it. Note: it does have 2 separate ground planes, GND and G2 (top left corner), so please tell me which one I should use when measuring.

    I’m at a loss here, so any help would be welcome.

    A few images:
    The board. I left out R10 and replaced it with a jumper, because I’m not using the LED on the board. I’ve tried it with the 10K resistor (R10), a jumper wire and without a connection, none of which made any difference. The build doc says I can omit R10, but looking at the schematic, R10 seems rather important to me?


    Underside is also wired for using the 3007. I know it looks bad, but I had to re-solder them to the board after trying it the other way around while troubleshooting, which is stupid, I know.. Anyway that’s why they are sticking out. Before this they were level with the rest of the board, which also did not produce a chorus effect.

    The pots, which I have also rewired twice:

    Thanks in advance!

    #13626
    Billy
    Moderator

    Hi Joeri

    Post some pictures of your offboard wiring to the DC jack, IN and OUT jacks and 3PDT switch so that we can trace the wiring and where it goes to

    Do you get 9v to the pcb

    R10 needs to be in place it is not for the LED

    R34 is the LED current limiting resistor

    #13627
    Joeri
    Participant

    Hi Billy,

    thanks for the quick response. Haven’t included the 3PDT (and board) and the LED yet. Figured I wanted to test the effect before continuing.

    I added R10 to the board again. Following image shows my offboard wiring. The white one is connected to the 9V DC jack ground, which then is connected to a small piece off wire which connects to the board ground and ground 2. The jacks are wired like the example in the document (also tried connecting the in- and out jack grounds directly to the wire with the other grounds, but my setup now follows the wiring diagram in the build doc, just to be sure).

    #13628
    Billy
    Moderator

    Do you get 9v on the pcb +9v and ground pads

    Continuity check all of your grounds making sure your in and out jacks are grounded

    We need a nice clear picture of your DC jack so we can see the lugs

    All of your component values and orientation look correct

    I’m assuming you’ve tested other builds using this method successfully before, I don’t see any reason why it shouldn’t work just trying to make sure you’ve got power to the pcb and your in and out jacks aren’t connected directly together and audio is actually passing through the circuit before we look for circuit errors

    Have you adjusted the trimmer TR1

    These are typical voltages

     

     

    #13631
    Joeri
    Participant

    Here are my measurements. Seems to be lower than yours across the board, which probably explains why the chorus ICs aren’t working as intended. Any ideas on how to fix this?

    #13633
    Billy
    Moderator

    What’s the output of your power supply all your IC power pins are 2 to 3 volts lower

    What are you using to power the pcb

    I take it you mean all your grounds read 0v and you have +9v going into the pcb?

    Check what voltage you get at the junction of R32 and 33 where they join, this is your voltage divider for VB half the power supply voltage so around 4.5v

    #13634
    Joeri
    Participant

    I’m using a 9V jack, connected to a power adapter connected to a wall socket.

    Yes +9V going into the pcb.

    Hard to measure (or to find out where they connect), but I’m getting 3V and 6V, so the voltage divider is working, only it’s getting 3V instead of 4.5V, so the supply is 6V instead of 9V 🙁

    Did check R31 (47R), it drops 3 – 3.3V. Hows that possible? Should the led be connected for this circuit to work?

    Edit: Removed R34 since I’m using the LED on the 3PDT board. Didn’t solve anything though, still 3 – 3.3V drop over R31.

    #13636
    Billy
    Moderator

    Check the colour bands on R31 they should be yellow, purple, black, gold, brown which they look like but it’s not easy to see clearly

    Check the voltage on both sides if you’re saying it goes from 9v one side to 6v the other side of R31 try reflowing the solder joints of R31, C13 and C14

    Use your multimeter continuity check to see where R32 and 33 connect at that point you should get half power supply (VB)

    #13642
    Barry
    Keymaster

    I will take care of the R10 copy and paste typo as it should be the CLR at R34.

     

    #13643
    Joeri
    Participant

    @Billy The color bands are correct. Measured it, it says 47R.

    The voltage between R32 and R33 is 2.9 – 3V. Like I said, the voltage drop over R31 (47R) is 3 – 3.3V down from 9V supply, which leaves 6V remaining and that goes into R32 and R33 and the +9V parts of the circuit. VB reads 3V on my board, which is half of the remaining 6V, so the voltage divider works, R31 just drops too much voltage for being such a small value..

    R31 just shouldn’t drop as much as it is.

    Edit: I replaced C13, C14, R31, R32, R33 just to be sure. Same result. R32 and R33 both read 26.9K instead of 56K, which makes me think there may be something else interfering with the voltage divider. Thoughts?

    #13651
    Billy
    Moderator

    Sounds like something is pulling your voltage down which is obvously having a knock on affect on the rest of the circit

    With power off check resistance between the 9v pad and bottom end of R32 where it meets R33, then check resistance keeping 1 probe on the R32 / 33 resistor junction and the other to ground

    Also with power off check resistance from 9v pad to the bottom end of R31 where it meets C13

    If you’re getting 9v at the top end of R31 then dropping 3v there could be a solder bridge around that area check those solder joints under magnification

    When you look at that part of the circuit and from your description either there’s a bridge on R31 or something possibly C13, 14 or 15 is pulling power to ground

    #13653
    Joeri
    Participant

    Yeah, think so too. Can’t find any (solder) bridges though.

    9V – R32 -> R33: 26.7K
    Ground – R32 -> R33: 26.7K
    R31 -> C13: 0.5R

    Between R31 and C13 there is a tiny amount of resistance, could that be the culprit?

    #13655
    Joeri
    Participant

    Also measured the trim pot. With it turned all the way to the side, it reads 960R (not kilo ohms), when the schematic says it should be a 100K trim pot. Could this make a difference?

    #13657
    Billy
    Moderator

    Trim pot will go from 0 to 100K depending on its tolerance

    What model of multimeter are you using do you know it’s input impedance

    #13659
    Barry
    Keymaster

    The code for the trimpot should be 104. 10 and 4 zeros for 100,000 or 100k.

    Sounds like you may have a 102 which would be 10 and 2 zeros for 1000 or 1k.

    There is no way it would work if that were the case since the preferable setting would be near half rotation or about 1:00.

    #13661
    Billy
    Moderator

    You’d need to know what you get both sides of the trimmer when you said all the way to the side I’d assumed all the way CCW

    With a 100K trimmer across lugs 1 and 3, I get 96.6K turned all the way down I get 1.9R one side and  96.6K the other

    The easiest way to check it if you can’t find a code 104 written on it is to check across the 2 outer lugs for total resistance

    If you’ve done that across the 2 outer lugs and got that reading as Barry says it’s a 1K and would definitely affect the circuit

    #13662
    Joeri
    Participant

    So, the trimpot was indeed the culprit. It’s 1K instead of 100K. Got me one with the right value from a nearby store. It’s a little bigger, so it doesn’t fit, but I soldered some wire to it and taped it to prevent shorts, connected it and lo and behold: a beautiful chorus effect came through my amp!

    So I guess this was an honest mistake by Klaus of Musikding. Will be mailing him.

    Thanks for all the help guys!

    Here’s a picture (it’s very pretty, I know..). Cheers!

Viewing 17 posts - 1 through 17 (of 19 total)
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