Mosky XP Boost / Expression Pedal Modification

A forum devoted to mod, tips and suggestions for upgrading and rehousing your VERY CHEAP commercial stompbox to near boutique excellence.
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jimj3114
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Post by jimj3114 »

Hi All!

I bought a Mosky XP Booster pedal (one-knob clean boost) with the idea of hacking into the pot. and wiring a jack in it that I could plug an expression pedal into so I could run it as a volume-pedal / booster with a remote expression pedal.

I do like a linear expression pedal for my purposes more than an audio taper.

Does anyone know what value expression-pedal would be optimal, or even better how I could add an expression pedal that would make the range go 0-to-75%?

Thanks!!!

:) :) :)
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mauman
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Post by mauman »

Welcome to the forum!

Mosky say it's based on the Xotic EP booster, if so, thread and schematic: viewtopic.php?t=7881 The Boost pot is a 10kC that bypasses the Q1 source resistor (in series with a cap), so that would require a 10k pot in your expression pedal. Wire the pedal just like the Boost pot, with lugs 1 & 2 to ground, lug 3 tied back to the Q1 source bypass caps. You'll want a switch to select either the internal Boost pot or your external expression pedal, else they'll be in parallel and won't give you much range.

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jimj3114
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Post by jimj3114 »

Hi thanks so much for this!

10k is a relief, as there are a host of expression-pedals already with that value.

I think I'm just going to replace the pot with the jack and not have a pot on the stomp box.

One more question if you don't mind?

If I want to limit the range to 0-75%, could I just insert a resistor into the circuit to achieve this?

Thanks again!

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mauman
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Post by mauman »

If you're using a 10kB expression pedal, add a resistor in series, somewhere around 500 to 700 ohms. That will limit the 10kB to a 95% value at full rotation, which matches a 10kC Boost pot that's limited to 75% rotation. The fully counterclockwise direction will not be noticeably different, although the taper will be different.

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jimj3114
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Post by jimj3114 »

That's it!

Thanks so much for your help.

I am going to try that and just try to hit the sweet spot at clean-boost on full pedal-extension before saturation.

Thanks again so much for your kind help.

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jimj3114
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Post by jimj3114 »

Whoops!

I just had that "duh" moment.

I realize that the potentiometer on the booster pedal I ordered (Mosky XP Booster) will probably not be zero-volume to plus-boost sweep.

It will probably be a zero-boost to plus-boost sweep,

Now I am wondering if any combo of pots and resistors would give me a zero-volume to boost sweep?

Or should I rethink this and just find an active volume-control circuit and build it?

Thanks!

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mauman
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Post by mauman »

You'll need a traditional volume pot at the output to do that. Or you can set the boost at the sweet spot and put a volume pedal after this pedal.

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jimj3114
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Post by jimj3114 »

Hey thanks.

I've started looking at active preamp and/or active volume-pedal circuits.

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mauman
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Post by mauman »

Here's a good one.
Craig Anderton Active Volume Pedal.gif

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jimj3114
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Post by jimj3114 »

Oh hey thanks that is TERRIFIC!

I really appreciate that.

I'm trying to learn to build some stuff myself, and that is something I think I might be able to actually handle.

Thanks again!

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