MF-Drive

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

I traced this one a few months ago and never got around to putting the schematic up here. The only thing that bothers me is how the 9v supply is hooked up to the cathode of the bypass LED. I still have the box but the owner is not willing to desolder the caps to find the values. Any way to measure them in circuit to get a rough idea of what the are? In my experience NP0/C0G caps are usually lighter in color....like a grey and the X7R caps are a darker brown so that's how I marked them on the schematic. I plan on breadboarding this to see if I can get it to work with 2n3904 and 2n3906 instead of the super small packages they use on here. Also I can't seem to find any info on one of the transistors/jfets on the board. Q13 with a marking of LS1IF. Anyone have any idea what it could be?
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POT BOARD FRONT CROPPED.jpg
JACK BOARD 1.jpg
Schematic_MINIMOOGER - MF DRIVE REDRAW B&W_2021-04-02.pdf
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Lani
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Post by Lani »

Here are some more pics of the backside and a couple with the traces highlighted.
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POT BOARD FRONT CROPPED TRACES 1.jpg
JACK BOARD TRACES 1.jpg
POT BOARD BACK FLIPPED.jpg
JACK BOARD BACK FLIPPED.jpg

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bow_and_error
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Post by bow_and_error »

Did you ever get a chance to breadboard this? I'd also like to give it a shot, so let me you what values you ended up with for the unknown components.

I've got the Kassutronics Transistor Ladder Filter on a breadboard and I LOVE the sound, but the circuit required a lot of hacking to adapt the Eurorack power circuitry & signal level for guitar, and it's defo too big for a vero layout. I made mine with 2N3904 transistors, but I had to hand match each pair, which was quite time consuming. I also had better results after matching all the capacitors between each transistor pair in the ladder.

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Lani
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Post by Lani »

Sorry I never got around to breadbording this. I did make my own layout though which again I haven't built but if you want I can post the files up later so someone with more time on their hands can figure out the missing cap values. It's a bummer the customer wouldn't let me take the caps off to measure them. If I ever get another one, hopefully it will be different.

Lani

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Post by bow_and_error »

Go ahead & post the layout and I'll give it a shot. Maybe I can use the schematics from the Moog MF-101 MoogerFooger Lowpass Filter thread to guide cap selection.

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Lani
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Post by Lani »

Okay, I'll post it when I get home later tonight, I tried to use all TH parts on the layout and fit it in a 1590BB with onboard controls but I had to use a few SMD parts here and there. The BF862 I believe only come in a SOT-23 package but I could be wrong. Still haven't figured out what Q13 is (marking LS1IF) but I read somewhere that its a jfet, just unsure what kind.

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Lani
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Post by Lani »

Here you go. Again, I have not verified this layout nor the schematic so build at your own risk.
A couple of notes on the layout, 1) you can use TH diodes or the original SMD diodes in the power section. 2) its a tight layout so if you plan on etching this instead of ordering I recommend using the photo resists method rather than the toner transfer method, although with enough practice you can do it!! 3) I didn't have room for the protection diodes on the input and output so I left them off. You might be able to piggyback them to R10 and R11 and find VCC and GND somewhere (GND plane is on the top layer, VCC plane is on the bottom layer) but this shouldn't effect the sound as they are there to protect the active components (Q2 & U1).

If someone ends up getting to this before I do let us know how you make out, thanks and good luck!!!

EDIT: I forgot to mention that the inductors on the top side can be omitted by just jumping the pads on the top layer. Not sure how much they contribute to the sound but at only 20uH they can't be doing much.
3D PCB RENDER - MF DRIVE - BOTTOM COMPONENTS.png
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MINIMOOGER - MF DRIVE - V1.00 - 6.22 - ETCH FILES SCHEMATIC & 3D RENDERS.pdf
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bugg
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Post by bugg »

I have one here, I'll pull all the caps and measure them.

You've already done most of the hard work.


Were there any other questions that needed to be revisited?

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Lani
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Post by Lani »

Sweet, thanks Bugg. :worship:

Yes, there is a N-FET (all the info I could find on it) Q13 up on the top of the pot board. I never figured out what the part number actually is. Maybe I misread the SMD code LS1IF. If you could get some measurements of the parameters that would help narrow it down a bit or at least find something similar.
That and the LED circuit has always bugged me too (no pun intended). Maybe they had a batch of backwards marked LED's? Who knows. Other than that the caps would be a huge help. I'm going to go print the schematic and take a guess at the values and see how close I can get once you get around to measuring them. No need to de-solder the big film SMD caps on the matched pairs. They will melt easily so beware if you do. They where the only ones I could measure in circuit. Thanks again Bugg and great job on your site by the way. :thumbsup
Last edited by Lani on 11 Jul 2022, 10:20, edited 1 time in total.

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bugg
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Post by bugg »

I'm familiar with SMD film caps, learned about those the hard way years ago. :lol:

I can measure them all, it's not a problem. Since you can't safely remove the film caps you have to isolate them from the circuit by removing all surrounding components, then you can make an accurate measurement while they're still attached to the PCB. Takes a little extra time but it's worth it to get a reliable measurement. SMD tweezers make this a breeze.

It may take me a couple days, I have a ton of stuff on the bench, but I'll get it done.

I'll see if I can identify that transistor and will double check the LED as well.


I appreciate you tracing it, I've been meaning to do it for a couple years but just never got around to it.

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Post by bugg »

I'll pull Q13 later and throw it on the DCA75, but I think we might be looking at a BC847B. (1F marking)

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Lani
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Post by Lani »

Bugg, were you able to identify Q13 and the caps? Would love to get a working clone of this.... I suppose I can throw this board onto my PCB order this weekend to fool around with cap values.

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Post by towmotornoises »

Bumping to see if anyone has any more information on the caps and Q13... I have five of the PCBs from JLCPCB and some other bits and bobs on hand!

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Post by bow_and_error »

Based on the surrounding circuitry, Q13 looks like an N-channel JFET set up as a common-source amplifier. It has a 10k trimpot for biasing the drain, so in theory you could get away with using a any common JFET (J201/2N5457/etc.)

If they're using a BF862 for the input buffer JFET, I would think it would be easiest to use the same thing for Q13. That would probably make sense with the low value of the R61 source resistor.

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Post by Visualdistortion »

Any advencement? I would love to buy this one.
I wanna make it
I wanna make it wit chu
(again and again and again)

French... sorry ;)

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Post by albinalbinj »

Would be very interested in this schematic if the capacitor values could be measured, my friend lost his MF Drive a couple of years ago and I would like to build him a clone for his 30th birthday.

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