MXR - Auto Q  [schematic]

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

Please let me know. Reversing is no option as I'm running toward a deadline. Will sign a NDA without a problem.
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fosnal1950
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Post by fosnal1950 »

mxrenvelopefilter_schematic.gif
Do you mean this one ?

Alf

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Dirk_Hendrik
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Post by Dirk_Hendrik »

Thanks.
But I'm referrin to the new one which has been bitching me for a full sunday and, though improving from completely dead to less dead (does bypass again, does do audio in affect mode again), to "does not do envelope effects yet". Although there's similarities to above schem the new one has a lot more junk under the hood.
Sorry. Plain out of planes.

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Post by n8b5150 »

A customer brought one to me that wouldn't pass signal, but Dunlop was no help and wouldn't give up a schematic. They had a $50 flat fee repair (this was about 2 years ago), so I had the customer send it to them. Not sure if this is an option for you.

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Post by Bernardduur »

Dirk_Hendrik wrote:Thanks.
But I'm referrin to the new one which has been bitching me for a full sunday and, though improving from completely dead to less dead (does bypass again, does do audio in affect mode again), to "does not do envelope effects yet". Although there's similarities to above schem the new one has a lot more junk under the hood.
Checked out my DisumBOMBulator scheme? It is similar to the old MXR with some add-ons and more 'junk'.

Maybe it helps
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Post by Dirk_Hendrik »

Thanks again.

I think I've got the bitch covered. Step 1 was no power. A burned 10 ohm resistor in the power line. Step 2 a dead 4049 (SMD naturally). Replaced and she could switch in and out again. Did filter but no quack, let alone wah. Replacing 2 Motorola TL074 like chips by LM324's made her quack again but rather distorted. I expect the replacements with real TL074's will do the trick.

No TL074's in tha house??? Plenty... but not in SMD... which I did for LM324's... :oops:
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Post by borislavgajic »

no doubt you are going to fix that....... :thumbsup


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pz
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Post by pz »

Does the new pedal still use PWM for the variable resistances?
I remember, while experimenting with PWM on my breadboard i used once LM324s and got ugly distortion (the chips were ok), which disappeared when i replaced them with 074's.
074 is a good chip :thumbsup

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Post by Dirk_Hendrik »

pz wrote:Does the new pedal still use PWM for the variable resistances?
I remember, while experimenting with PWM on my breadboard i used once LM324s and got ugly distortion (the chips were ok), which disappeared when i replaced them with 074's.
074 is a good chip :thumbsup

yep.

The 324 is made for a single supply. The TL's, like most opamps for a dusal supply. Hence the ugly distortion when using them in place in a circuit with a virtual ground, like almost any 9 volts effect.
Sorry. Plain out of planes.

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Post by Ice-9 »

Sorry to resurrect an old thread but I was wondering if anyone managed to find a schematic for this (M-120 Auto Q). I have one on the bench now for repair. It is in a poor state after someone tried to repair it with very bad soldering around all the IC's. I have got it switching but the output signal is very low. I'm just going to go through the signal path with an audio probe but a schematic would really speed things up if there is one.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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