This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Thursday, September 20, 2018

MXR Micro Chorus

The originals used a now nearly unobtainable SAD512D chip, but the wizards on FSB converted it to work with an MN3007. Now that those are also hard to get a hold of, I've laid this out for an MN 3207–which is almost the same as the 3007, just with a slightly different pinout for power and ground. But if you want to use a 3007, I've included a daughter board that will let you use it (it will also work to use a 3207 in place of a 3007). This will best fit in a 125B and the schematic can be found here.




71 comments:

  1. I'll try to verify it as soon as I can. I have a few 3207 lying around and absolutely love the micro chorus. Thanks for the layouts!

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  2. Looks interesting? Any ideas on a depth mod?

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    1. https://goo.gl/images/mupTSj
      I assume that I can put a Pot between C17 and R28 y R34 ass a voltage divider. Maybe it's wrong, I don't know.

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  3. Justo venía a preguntar lo mismo. (I just came to ask the same)

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  4. Hello, thank you very much for your work.
    Where Rate 1 should go connected ???
    Thank you very much!!

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    1. As I understand it, Rate 1 is not connected. You could connect it to Rate 2. It is just the resistance between Rate 2 & 3 that matters.

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  5. Unfortunately, I didn't manage to get my circuit working properly. I only get clean signal out of the circuit. I'm still looking for my wiring mistakes. The thing that bothers me though is the voltage divider around pin4 of the MN unit. The datasheet says that typical voltage for that pin is ~14/15 of supply voltage and as it is, it is much lower than that. I checked the schematic and it gives the values used here, but shouldn't they be reversed?

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    1. BTW I decided to do so, but I'll be able to chceck the results tomorrow in the morning as it's 11pm at my place :)

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    2. There could be an error on the schematic, or it could have to do with swapping the 3007 for the 3207. Might be worth swapping those 2 resistors.

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    3. I tried swapping them and I also checked several MN units, but I did not manage to get chorus sound, only the clean sound of my guitar... I'm still looking for some mistakes in my wiring. I'll let you know if I get it working properly :)

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    4. Czcibor Hejwowski
      I have not done this yet, but it seems to me that there is a mistake. In the case of MN3207 pin 7 and 8, the 47 K resistor should go on ground and not on power

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    5. There are two 47K resistors in the schematic and layout, one is connected to the ground and the other one to VCC. Isn't that supposed to be a voltage divider/biasing for the circuit?

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  6. There is hope to see here Catalinbread Topanga(FV-1)? thank you for your work!!!!!!

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  7. If you are using the 3207 chip you may need to swap the resistors going to pin 4 of the 3207 around. As is the Vgg (pin 4) voltage seems to suit the MN3007.

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  8. I compared several schemes with MN3007 and MN3207, and I found the same situation as Slowpoke101, pin4 VGG needs to be fed with less 1volt than the VCC(pin1 MN3007-pin5 MN3207) as the power of the 3007 is negative we need to add + 1V to get more positive. in the 3207 we have to subtract, so we have to swap the resistors of the voltage divider R37 / R38.
    The ideal voltage for the 3207, which recommend on several blogs will be between 7 and 8v, some use a voltage regulator, others speak in a 8.2V zener, because 9V seems excessive and can cause distortion. This last situation do not know how applies.ūüėĘ

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  9. Verified! Crystal clear chorus, the rate button produces a very analogous oscillation.
    Since I had soldered all the components I made a small adapter plate to apply the corrections, it is necessary to swap the resistors, and I ended up also trying out other values ​​R37 1.2K and R38 15K, the capacitor C21 in the circuits that is applied the MN3207 has the value of 4.7uF.
    My power supply for the pedals has 10V, and the MN is not advisable to reach more than 8V, so I applied a 8.2V zener with a capacitor to stabilize. I also advise to use a more precise Multi Turn Pot for the Vbias setting because the chorus range is smaller in the MN3207 than in the 3007, I found in 2 different IC's the effect within the 5.40V and 6V (PIN3) .
    The ideal would be to use a voltage regulator like the 78L08, with an individual track for the MN, and the rest of the circuit at 9V.
    I send a link with the adapter plate, so if you want to try it.
    https://imgur.com/Jh5ayhx
    Would it be possible to apply these changes in this circuit?

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    1. hi, this little adapter you made and shared, is it usable every where for using 3207 instead of 3007? what about some adaptors which don't have caps? and an adaptor in the post?

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    2. hi
      greetings from austria!
      o hope i understand you right: i populate the board as shown in the layout above, and then i install your adapter board in case of the lm3207? is that correct?
      or do i have to replace some parts?

      thanks for your work !
      bluesanderl

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  10. I have not done this yet, but it seems to me that there is a mistake. In the case of MN3207 pin 7 and 8, the 47 K resistor should go on ground and not on power

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  11. I really expect that someone will solve the problem and everything will be clear with these microchips

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  12. This comment has been removed by the author.

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  13. My circuit, I had already worked with the changes I made before, but I went to test the "nupel53" change, because I found in the schematic "Thomeeque's EM3207" that 47k resistor (R39) connected on pins 7e8 and then ground instead of VCC. I did not notice big difference the effect continued to work, perhaps the oscillator has become a little more stable.
    What I have been testing are several voltages in Pin5, with 5V we have effect but with very little intensity, the best voltage I found was the 8v, we have effect turning the bias trimer half, which will give the Pin3 within 5.9V.
    I tested these changes with an adapter plate in effects that I had already done with the IC MN3007, like "Heladito-2 of Tonepad" and "Touchstone of Madbeanpedals" and with some adjustments in the Bias soon gave effect of chorus.

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  14. Has anybody got it working? I'm really missing a nice little chorus in my DIY collection...

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  15. I already have this circuit working for some time, I was waiting for 10uf and 330nf tantalum, to make one more pcb like the original one.
    The changes are not many, I send here, the layout and the pcb for those who want to do. The pcb was half a inch wider and no longer fit in a 1590B we have to use the 125B.
    The chorus effect is very good, but I would like to implement a switch or pot to change the Depth, does anyone know how?
    https://www.dropbox.com/s/c5orxvypzapubzp/MXR%20MICRO%20CHORUS%20MN3207.pdf?dl=0

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  16. Sorry, the link had an error, here is one that works!

    https://www.dropbox.com/s/3w16vrdui5ai8m8/MXR%20MICRO%20CHORUS%20MN3207.pdf?dl=0

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    1. Hello friend, Is it 100% verified and working?
        Thank you

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    2. I made this circuit with your pcb with 8v regulator but it has some problems. the chorus effect stops working.strum the guitar and after 3 or 4 seconds chorus works and after a stops again and comes the clean sound .it is not stable. by the way layout is so very small

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  17. I have a problem, the sound on the output is clean. I tried to swap resistors 7.5k and 100k. Nothing changed.

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  18. how should the 220k potentiometer be set ??

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  19. Did anyone add a depth pot already?

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  20. hi everybody
    i,d like to build this one, but the list of changes is huge!
    has anyone build this succesfully?
    and is it possible to update the layout above? ( or is this the final working version?)

    greetings from austria
    bluesanderl

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    1. I've been working on it, but like you alluded to, the change list has been a little confusing to wade through.

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    2. Brother any updates on this. ? I just made today its not working

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  21. thank you for your kind answer!
    so i,ll wait a little and do some other cool projects of your page!

    bluesanderl

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  22. Hello, i done this pcb with the MN 3007 ; it didn't work (only clean sound); after i see the additionnal little pcb to convert but i don't understand how to connect it to main pcb.

    Sorry for my english !

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  23. Looks like I'm having the same issue, only clean coming through using a 3207. Any word as to why? I see a bunch of suggestions but no progress on an actual layout fix

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    1. I just swapped the 7.5K and 100K by the 3207 and it works :)

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    2. Shoutout to Methode for figuring this out for me, with that little change this layout works with the 3207.

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    3. Sorry, I don't understand what the change is. What should I do with the resistors. I built this circuit a long time ago and I have it waiting for a solution. Thank you very much!!!

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    6. @rjflyinghokie change 7.5k and 100k to what? Can you make it clear?

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  24. el esquema no es el definitivo verdad?? lo pregunto antes de comenzar su construcción,.

    Podrían decirme que elemento es el cuadrado de 220k, no lo habia visto hasta ahora soy novato.

    Gracias!

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  25. I really love the original pedale. Is there a possibility to verify this build?

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  26. Boa noite. Essa modificação é para usar usar o MN3207 no lugar do MN3007?
    Comprei um lote de 05 unidades do 3007 na China, 04 vieram com defeito. Comprei outro lote com 10 unidades do MN3101, 06 vieram com defeito.
    Alguém pode me ajudar?
    Grato.

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    1. João esse layout é problemático, as pessoas que conseguiram faze-lo funcionar (ou apenas dizem isso, e acho que estão mentindo na verdade), simplesmente dizem que trocaram um resistor ou outro e na hora de explicar o que exatamente fizeram, pelo que trocaram, simplesmente somem, meu conselho? Monte o Ce-2, queria muito esse pedal, mas já fiz de tudo e não funciona

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  27. Hello, where can I find the board for the MN3207 / mn3007.

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  28. Padahal efek chorus ini sangat bagus, tetapi setelah saya mencoba merakit efek ini, ternyata tidak berhasil. Hanya suara jernih yang keluar dari efek ini. Memutar potensiometer juga tidak mengubah suara yang dihasilkan. Apakah ada yang berhasil mengubah rangkaian ini agar dapat berfungsi dengan baik ?
    Salam hangat dari indonesia

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  29. Swapped 100k and 7.5k from pin 4 of 3207 and worked. Really good sound. Thank you very much for sharing.

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    1. That was the only modification you made to make it work?

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    2. I don't understand what the change is. What should I do with the resistors ? Please help.

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    3. @ryohei jpn Is that the only change u made from this layout?

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  31. I swapped the two resistors and the chorus effects is working, but... get a ticking sound coming through too. Any idea how to fix?

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    1. Disregard... Was able to adjust the trim pot down until the ticking stopped. All is well with it

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    2. can you share the solution with a photo or video?

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    3. @ImpostorXXX - I've already given the pedal to a friend. This is a great sounding circuit, but... It does have it's issues. The ticking I mentioned earlier continues to come back, even after adjusting the bias on it. He has to continuously adjust the bias on it to get the ticking to stop. I'm thinking of making another, try to get a bias pot with a tall adjustment, mounting it on the solder side and bringing it up through the enclosure for easy adjustment. But, this is a lot of work and I just don't know if it's worth it.

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    4. You think the ticking sound is the pot's fault?

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    5. Analog pedals
      What resistor did u change with 7.5k and 100k?

      What did u keep in place of them?

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  32. Do someone know where I can find a working MXR Micro Chorus Schematics/PCB?

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  33. Built this one last year and its awesome chorus! Nice sounding and tnx for this layout anyways more power!Regards fr Philippines. Jun.

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    1. Can u share the solutiom with photo, video or schematic ?

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    2. Sir , below is what i did on my mxr mic chorus i hope this can help. Jun fr Philippines.

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  34. Mn 3207 bias voltage on pin 4 guys should be approx 8.36v.remove the 7.5k and 100k resistor and replace it with a 100k trimmer and thats it!with the 220k trimmer the bias voltage on tlo62 should be around 4.7v or just turn the trimm until you get a nice sound output. Dont frget to replace that two 100k resistor connecting the trimm with 560k on the positive side and 270k on the neg side.
    I hope this would help in any way to let the chorus roll. Regargs fr Philippines.Jun.

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  35. The above schem is verified with just a little adjustment..

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  36. So if you remove the 7k5 and 100k resistores where does the trimmer go?

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  37. Verified its working

    I did few things

    1. Swapped 7.5k and 100k with each other( both are connected to pin 4 of mn3207.
    2.removed 47k resistor which is situated in middle of 20k and mn3207.

    Thats its

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