MXR M87 Bass Compressor Demo

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

yep make sense george, i was sratching my head on this input topology, not making any sense , i was thinking about some sort of common base circuit, :D , silly me ,great link george , i will redraw and resume the work , thanks again
Those SMD parts drive you crazy when you can't ID the part. Too many possible options with only one magic combination that actually makes sense - it makes my head spin sometimes.

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Kingkorg
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Post by Kingkorg »

Has anyone completed the schematic? Or at least partially? I have a dead one that's making me nuts! Thanks in advance!

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Kingkorg
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Post by Kingkorg »

Found the issue, the ratio switch was dead. The usual symptoms, no compression when engaged, leds go crazy... i fixed the existing one. It took some teethpulling in order to remove it from the board, but i made it. One of the internal sliders that make contact got broken off the rotating wheel.

In case one needs to recalibrate the unit, it can be done the same way mnats 1176 or Gyraf 1176 are calibrated. You need external VU meter as the built in works in GR mode only. Audio interface or DAW software can be used for this.

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UncappedOptics
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Post by UncappedOptics »

Kingkorg wrote: 26 Nov 2021, 18:22 Found the issue, the ratio switch was dead. The usual symptoms, no compression when engaged, leds go crazy... i fixed the existing one. It took some teethpulling in order to remove it from the board, but i made it. One of the internal sliders that make contact got broken off the rotating wheel.

In case one needs to recalibrate the unit, it can be done the same way mnats 1176 or Gyraf 1176 are calibrated. You need external VU meter as the built in works in GR mode only. Audio interface or DAW software can be used for this.
Hey! I just snagged one of these pedals on ebay (broken). It seems to behave like yours does, it's slow to turn on and when it does there's no compression at all and the LEDs don't move, I tried beeping out the rotary switch and found none of the pins are connecting to each other.

Do you know the part code or pin configuration of the switch so that I can try a new one?

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Kingkorg
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Post by Kingkorg »

Sorry i don't. But the original part is terrible, the pins are weakly glued to the shaft. I opened it and glued the pins properly and put everything together.

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UncappedOptics
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Post by UncappedOptics »

That's no problem, I actually did the same thing.

Opened the switch up to find the contacts had snapped off the shaft and were only held in place by the grease.

A little superglue and it was as good as new, I suspect any knock or bump would be enough to break the original switch

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cluster
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Post by cluster »

https://www.flickr.com/photos/andresgal ... ed-public/
does anyone have the data sheet?

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plush
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Post by plush »

cluster wrote: 11 Apr 2022, 11:42 https://www.flickr.com/photos/andresgal ... ed-public/
does anyone have the data sheet?

LBJK
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I bet, it's a dc-dc converter, maybe lt3463

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guideb
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Post by guideb »

cluster wrote: 11 Apr 2022, 11:42 https://www.flickr.com/photos/andresgal ... ed-public/
does anyone have the data sheet?

LBJK
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Hi guys,

i have this pedal with same problem : leds light up as soon as i plug the 9v jack (no need to plug audio jack in it), and now sound when stomp is engaged but blue led shows up... led meter still stay lit then slowly go down one by one. Replaced the TLC2206 but no luck. I didn't know about the ratio switch and i will open it asap. An other thing make my curious is the previous answer from Cluster... sorry why are you talking about this ic ? The issue can be there ? Cheers

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