MXR - Custom Audio Electronics - Boost/Overdrive MC-402  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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TheKoala
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Post by TheKoala »

Hello everybody, here is a traced down version of the Rev E of that pedal, which has through-hole components. U1 is OP275 and U2 is LF442CN. Hope that will help someone one day. R30 is not shown and not mounted on the PCB.
Attachments
IMG_20200713_101527.jpg
IMG_20200713_101534.jpg
MXR Boost OD.pdf
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alexradium
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Post by alexradium »

Isn't r3 value 470k?

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sematyk
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Post by sematyk »

R3 is 470K,
R24 need be replaced by 470K also

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sematyk
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Post by sematyk »

boost== mc-401
overdrive==Black Cat OD-1

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sematyk
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Post by sematyk »

"The Black Cat OD-1 (a.k.a. Freddie Fuzz) is an original design Fred created based on the unique properties of the OP275, a dual operational amplifier chip made by Analog Devices. The OP275 is a high-quality op-amp that gives a distinctive linear output waveform. The Black Cat OD-1 can go from clean, to slightly crunchy, to all-out saturated distortion. It is unique in that it is extremely sensitive to the guitar; it responds to the player's pick attack, and like a good Fuzz Face, it cleans up well when you roll back the volume on the guitar. The Black Cat OD-1 has been used by Scott Henderson, Steve Lukather, Beck, Lyle Workman, Kyle Cook (Matchbox Twenty), and many others."

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bmxguitarsbmx
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Post by bmxguitarsbmx »

The op-275 data sheet is a very interesting read. It talks about distortion due to level dependent input capacitance (in my experience this is bad). And , while this is an extremely low distortion device, notice that distortion jumps drastically up at voltage supply levels less than +/-18V. No data, that I could find showed distortion for 9v single supply or +/-4.5v. Some interesting things may be happening that might be worth experimenting with. I think the Black Cat Od-1 sounds good enough that something interesting may be there.

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Matlevo12
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Post by Matlevo12 »

Victor Nery wrote: 12 Apr 2018, 00:54 Sorry, I don't know how to upload the images here. Here's the link for download: https://www.4shared.com/photo/ch79All5ei/402.html# I removed the fets that connect to the input and output. Problem remains the same as described. Here are the voltages. My power supply has an output of 7.98V.

1 - 2,76V
2 - 2.80V
3 - 2,53V
4 - 0V
5 - 2,53V
6 - 2,64V
7 - 2,90V
8 - 5,37V (that's the same as measured after R1).

Thanks.
Hi everyone.
I got one of these to repair. Easy fix, but I was kind of surprised about how the "overdrive" sounded.
I have a 9.4V power supply and am getting 7.6V on pin 8 of U2 (and 3.8V on pin 3... you get the idea).
I can't seem to understand why the voltages are so low.
I checked R1, R17 and R18 and they really are 470Ω, 100k and 100k... why is this happening ?
alexradium wrote: 12 Apr 2018, 06:07 The overdrive in reality is a fuzz, made with opamp with a starving supply to imitate a dying battery.
Values look appropriate for the circuit, you could swap the opamp with a good one to see if it changes.
I'm trying to find out if these low voltages would cause the "distortion/fuzz" sound this circuit has.
Since the OP275 works with 4.5V minimum, that shouldn't be the case, or am I missing something ?
Victor Nery wrote: 12 Apr 2018, 11:13 I've already tried other opamps (TL072 and NE5532). I shorted R1 (470r in series with power supply) and got the same problem. I've also made sure to disconnect all the FETs (removed them) from the signal so they're not the cause. The signal with no power supply connected is strong as it should till it gets to the opamp. The thing is when I connect the power supply, the signal gets blatty at the first input (even when I tried a jumper instead of R1). Thanks.
I thought about jumpering R1 since it brings the voltages to "normal", but if the circuit is a Black Cat OD-1 (apart from some cap values, probably because of the added tone stack), shouln't it sound similar ? From the demos of the Black Cat I've heard it 's pretty much the same, isn't it ?

Thanks a lot to anyone who can help a bit !

Have a good day y'all !

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phantombox
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Post by phantombox »

Hi guys.
I have exactly this board but with different components on it. On mine, U1 is also an OP275, but U2 is a TLC2262CP. Also, some resistors have different values. And the schematic diagram MXR Boost OD.pdf either is for a different pedal or has mistakes in it.

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karul
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Post by karul »

phantombox wrote: 16 Mar 2023, 14:32 Hi guys.
I have exactly this board but with different components on it. On mine, U1 is also an OP275, but U2 is a TLC2262CP. Also, some resistors have different values. And the schematic diagram MXR Boost OD.pdf either is for a different pedal or has mistakes in it.
Are talking about @TheKoala's schematic viewtopic.php?p=281301#p281301? He stated that it's traced from Rev E. What version is yours? What are the differences? Did you traced yours? It's not a bad thing if you post some photos from your pedal.

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phantombox
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Post by phantombox »

Here are some inside pics of mine. Well, its from a friend. The boost section does not work, so he gave it to me to see if I can fix it.
The ribbon cable to the boost switch was messed up, so I replaced it.
And yes, it is the Rev. E layout but with different components.
Attachments
MRX MC-402 Ver.E solder side-min.jpg
MRX MC-402 Ver.E component side-min.jpg

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