Odd in n out dc voltags on mx eq

[airbug]

Good morning from germany

Okay. Got it. I misunderstood you. Perfectly clear now. Thanks.

Mabe one more

If i start with 100 nf poly cap and go higher if needed. What might be maximum maximum value of cap and can there be a negative effect if it is too big. Like 4uf7 lets say..? The mxr eq allows for a broad band of 30 hz till 16 khz. Doubt I hear It so deep n high. But it sure needs uncut base frequency...

Thank you.

[PRR]

> it is a 10 band mxr eq equalizer

Exact model number, please, and link to schematic if you can.

MXR made those EQs for decades, several variants, not all with "18V" power.

Capacitor value is not why you have DC on the jacks.

By the way, when your meter sees DC on jacks, put about a 10K resistor (or a guitar) across the jack and re-check it. Many circuits "thump" DC at turn-on. But with a non-leaky cap and some load, this DC should bleed down before you can start to play. (Yes, a crackle in the guitar is a good sign of something bad.)

[airbug]

thank you prr
it is a maybe 5 or 10 years old mxr m108 10 band ( not the blue box) i could not find any schematic on it ( just for the blue box)
it has by manual 470kohm input impedance and 5kohm output imp.
there is a bunch of numbers printed on the pcb kind of serial number. would that be helpfull?

i will check with guitar plugged in.

thanks for that hint

[airbug]

So
I tried.
When a strat is plugged the 9v at input drop to about 100mV constantly.

Still too much I guess?

[PRR]

Leaky input cap. Replace it.

[airbug]

Thank you.
That's the diagnosis I hoped for

Sadly I dont know which one it is without a scheme.
There is a c2 or c3 from in jack
Or did you mean input cap comming from dc power input?

Being Smd makes it harder too. But that is doable

[ubersam]

Sadly I dont know which one it is without a scheme.
There is a c2 or c3 from in jack

I'm guessing that one is small pF value cap shunted to ground, and one is a nF value cap in series with the input jack's tip. Which one is in series with the input jack's tip? That would be the input cap.

Or did you mean input cap comming from dc power input?

That would be the power filter cap. That's not it.

[airbug]

alright. i ll start hunting for it. let you know.

due to being smd changing it involves a little risk of burning thing up. easily i smoke a block. happend sometimes, sometimes i was Lucky.

so as i see it three options:

a:
change cap, hope thats it, no dc anymore, no random faint crackle and faint blubbering (sounds like burning leaves silently) but still mxr popping when there is a bypass on-off switching. little risk.

b: install accepable Buffers before and after (cornish before, for example boss tu3 after) , live with 100mv dc blocked by the buffers. no popping hopefully. but still that blubbering . no risk.

c: do both

do you guys think that these conclusions make sense?

[Ashura]

alright. i ll start hunting for it. let you know.

due to being smd changing it involves a little risk of burning thing up. easily i smoke a block. happend sometimes, sometimes i was Lucky.

so as i see it three options:

a:
change cap, hope thats it, no dc anymore, no random faint crackle and faint blubbering (sounds like burning leaves silently) but still mxr popping when there is a bypass on-off switching. little risk.

b: install accepable Buffers before and after (cornish before, for example boss tu3 after) , live with 100mv dc blocked by the buffers. no popping hopefully. but still that blubbering . no risk.

c: do both

do you guys think that these conclusions make sense?

Hello airbug. Looking for schematic information and photos of the M108S PCB ( https://www.jimdunlop.com/product/m108s-7-10137-09564-9.do ), I found this one your post.
I'm not sure I can help you, because I'm starting to design (redesign ...) pedals. I have not even mounted one... but when you say "sounds like burning leaves silently" you mean a sound like leaf rustling? I think I've read something like this about 10 band MXR pedal.

As for what you said before:

by the way: how can i attach pics? at the attachments section there is nothing that allows attaching an Attachment

I believe it is now possible to post photos directly from your computer. Use the "Add image to post" option below the box where you type the text to be posted.

Is your pedal a black color model?
Do you have any schematic or photo of the PCB MXR M108S I am looking for?

[Rob Strand]

it is a maybe 5 or 10 years old mxr m108 10 band ( not the blue box) i could not find any schematic on it ( just for the blue box)

The schematic for the blue 10-band is on-line. I suspect it is reasonably close to the unit you have.