MXR - M-109 Six Band EQ

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Mr. G.
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Post by Mr. G. »

I tried searching first, but couldn't find any info on the pedal. So, here's my question... Has anybody ever added a volume pot to the M-109? I love the EQ, but sometimes wish I could use it without getting a volume/gain boost. Anybody care to shed some light on how to go about doing this? What type of pot would be best, and should it go before the circuit or after the circuit? Please tell me it can be done without touching those damn SMDs :|

I can provide pics if needed.

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Mr. G.
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Post by Mr. G. »

I think maybe this should have gone in the Workbench section instead of here. Sorry about that :oops:

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modman
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Post by modman »

I haven't seen a schematic for this one, so it was a good idea to post here first.
Don't worry about it. :wink:

If you're just trying to add a master volume, you don't need a schematic: signal out to wiper of 100k A pot, outer lugs to ground and output jack...
But I have the impression that's not what you're looking for. If you don't have any gain in the EQ circuit how are you going to boost certain frequencies? You will only be able to cut some freqs.

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Mr. G.
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Post by Mr. G. »

I mainly just want to use it as a tone shaping tool (with the option of using it as a boost if needed). As it is now, my dirt chain is as follows... Deaj's version of the Eternity ---> Crunch Box v2 ---> EQ ---> amp. Those 3 pedals are on one loop of a 3 loop TB pedal. So, it can get kind of tricky to have the clean volume the same as the dirty volume. That's the reason I want to add a volume pot to the EQ. I want to be able to shape the tone, and then set the level so that it matches the clean/non effected signal.

Could I connect the ground of the pot to the ground tab of the power jack (I don't use batteries)? Also, the in/out jacks are the barrel type, and are mounted onto the pcb. How would I go about disconnecting the output from the jack?

Here are some pics if they'll help...
>Top Side<
>Solder Side<

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Mr. G.
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Post by Mr. G. »

Well, I gave it a try, but I must have screwed up somewhere. After I got it all soldered up, and tried it out, there was almost no volume at all. Thinking back (I gave up on it for the night), I think I might have got the input and output of the pot backwards.

The output was connected to the two tip lugs of the jack, so I broke both of the jack's tip connections, and put insulation between them and the board, and connected the pot to the jack, as seen in the "top" picture. In the "solder side" picture, you can see where I connected the pot to the ground, and to the top output point . The green is the pcb trace, and the blue is the wire I added.
top2
solder side2

So, did I come anywhere close to doing it right, and maybe I just got the wires mixed up on the pot, or did I completely go about it the wrong way?

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Post by JiM »

Make sure the path from the output of the FX to the volume pot keeps connected to the board (the top green circle with blue wire in your picture should not be isolated from the board).
Everything else looks fine.
I only give negative feedback.

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Mr. G.
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Post by Mr. G. »

I switched the input and output wires of the pot around, and it worked fine. My only problem now is, getting it to work when it's all boxed back up :slap:

It never ends does it, :roll:

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Mr. G.
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Post by Mr. G. »

Got it working fine now, but I do have one issue I'd like to try to address, if possible. At the moment, the added volume pot effects the overall volume whether the pedal is engaged or not. I would like for it to only effect the volume if the pedal is turned on. If I have the volume rolled back some, and the pedal is turned off, I get a bit of treble loss. This is not acceptable to me, but isn't a problem at the moment, since I leave the volume all the way up, and use the pedal as a midrange volume boost. However, if I decide to use it as a tone shaper, I would like to be able to use it without having to compensate for the loss of highs.

Any ideas?

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