MXR - Micro Chorus  [schematic]

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bluesbreaker62
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Post by bluesbreaker62 »

Hi all,

I've been enjoying this forum for too long without contributing anything.

I hope you like it:

Pics were re-uploaded here

If you need more pics, just ask

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Fermusicman
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Post by Fermusicman »

Thanks BB, good pics, :D We can to know the caps values?, :wink:

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lolbou
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Post by lolbou »

Thanks, nice and useful pics!

:shock: A double-sided PCB... Will need a second layer on the SVG file :wink: ....

Still the date interests me! And the wiring (color - device)...

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Post by Fender3D »

I reversed engineered it:

Image

or PDF http://www.wizardinside.it/foto/schemi/micro_c-sch.pdf

I assumed the values for RV1, R28, C1, C9, TR1 from MXR micro flanger's schematic values (I reversed engineered it as soon as I bought it some years ago... both are really similar :wink: )

I only hope bluesbreaker62 list the caps value too 'cause they're too much different from flanger (please do it :cry: )

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Post by Dirk_Hendrik »

Thanks!
Those 3 diodes give a serious :scratch:
Sorry. Plain out of planes.

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Post by Fender3D »

3 must be the perfect number :lol:
'cause the same 3 diodes were in micro flanger and in DOD effects too :hmmm:
they'll avoid the BBD bias setting

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Post by analogguru »

No mistakes on Rev 1.00 deserves the missing capacitor values, here you go:
C1: 50n
C2: 1n
C3: 1n
C4: 200p
C5: 300p
C6: 30p
C7: 10n
C8: 1n
C9: 50n
C10: 1n
C11: 1n
C12: 0,33µ
C13: 200p
C14: 20p
C15: 10n
C16: 20p
C17: 10µ
C18: 10µ
C19: 0,33µ
C20: 0,33µ

Please DON´T save the schematic as .jpg.

USE INSTEAD black/white .GIF or .PNG !

The schematic drawing will stay sharper and the file will be smaller.

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Post by Fender3D »

Thanks analogguru :D

Sorry for double post, but I really don't know how edit the previous :scratch:

Updated schematic with the caps values.
Added PNG http://www.wizardinside.it/foto/schemi/micro_c-sch.png
and GIF http://www.wizardinside.it/foto/schemi/micro_c-sch.gif,
but...
IrfanView blurred them too when converting from PDF :shock:

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Post by analogguru »

:hmmm: I didn´t know that you work directly into .pdf.

Anyhow here is the .pdf converted to .gif - first with ghostscript to .bmp and then with XnView (Freeware) to .gif - to show you what I mean.

resolution .jpg: 1123 x 793 (~ 100 dpi)
file size .jpg: 143.092

resolution .gif: 3508 x 2479 (300 dpi)
file size .gif: 95.015

the rest you can see below.

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Post by estragon »

Fender3D wrote:3 must be the perfect number :lol:
'cause the same 3 diodes were in micro flanger and in DOD effects too :hmmm:
they'll avoid the BBD bias setting
Take notice biasing is set in practice to VREF minus four (4) diode drops, as Q1 is an emitter follower whose output is one diode drop below its base. This arrangement varies with temperature. Wether it matched the variation required by the SAD512 or not, that's another story.

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Post by distortion_gfx1 »

Q: Can i convert this chorus into a flanger(Mxr micro Flanger)? though chorus and a flanger has some similarities..
tnx :lol:

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Post by mictester »

Dirk_Hendrik wrote:Thanks!
Those 3 diodes give a serious :scratch:
They're just there for the 3-diode drop they provide.
"Why is it humming?" "Because it doesn't know the words!"

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Post by distortion_gfx1 »

distortion_gfx1 wrote:Q: Can i convert this chorus into a flanger(Mxr micro Flanger)? though chorus and a flanger has some similarities..
tnx :lol:
anyone?

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Post by analogguru »

Why do you want to convert it ?
If you don´t like it as it is, sell the BBD-chip and you can buy two cheap flangers.

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Post by mistral »

SAD512D Replace or equivalent?
where i can buy it?
Regards

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Post by Dirk_Hendrik »

mistral wrote:SAD512D Replace or equivalent?
where i can buy it?
Both questions get the same answer, Nope.
SAD512D's are made of dried Pygmee foreskin leather which is even rarer than unobtanium.
Sorry. Plain out of planes.

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Post by mictester »

mistral wrote:SAD512D Replace or equivalent?
where i can buy it?
Regards
You might sometimes see them advertised at stupid prices on Ebay - DON'T bother buying them. You're very unlikely to get one that works, and any that you do get will be desoldered from broken equipment.

I remember this as being a sweet little chorus (correct me if I'm wrong, please), and I was thinking of reworking one to use something obtainable like an MN 3007. The delay with the 3007 will be too long, so the clock frequency will have to be increased to get similar results to the original. This could help with the aliasing problems....

OK. Updated Micro Chorus on the way!
"Why is it humming?" "Because it doesn't know the words!"

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Post by theehman »

mictester wrote:
mistral wrote:SAD512D Replace or equivalent?
where i can buy it?
Regards
You might sometimes see them advertised at stupid prices on Ebay - DON'T bother buying them. You're very unlikely to get one that works, and any that you do get will be desoldered from broken equipment.

I remember this as being a sweet little chorus (correct me if I'm wrong, please), and I was thinking of reworking one to use something obtainable like an MN 3007. The delay with the 3007 will be too long, so the clock frequency will have to be increased to get similar results to the original. This could help with the aliasing problems....

OK. Updated Micro Chorus on the way!
If you could come up with a way to replace the SAD512D in non-working pedals with an MN3007, you'd be revered as a veritable GOD!
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Electro-Harmonix info: http://electroharmonix.vintageusaguitars.com
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fx schematics and repairs

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Post by mictester »

theehman wrote:
If you could come up with a way to replace the SAD512D in non-working pedals with an MN3007, you'd be revered as a veritable GOD!
It won't be a pin-for-pin replacement, but there's no reason why you couldn't have a little "above" board with a 3007 and some biasing components. You'd also have to change the clock frequency because the 3007 is twice as long as the 512...

I'll do a rework of the Microchorus, and see where we get from there. I'll do a Vero layout as well.
"Why is it humming?" "Because it doesn't know the words!"

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Post by mictester »

Here we are:

A reworked MXR Micro Chorus using an MN3007 and a few component changes. I also added presets for the BBD bias and for the mix between straight and delayed signals, so you can maximise your chorus sound. It's breadboarded, and works well as shown. I'm going to play around with the values in the multivibrator to shorten the delay, and recalculate the values in the filters to get more top end through the delay path.
Microchorus3007.png
Veroboard and PCBs to follow soon.

Enjoy!
"Why is it humming?" "Because it doesn't know the words!"

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