EH MICRO SYNTH mod I've been pondering...

[pbailey1129]

Greetings all, this is my first diy forum post.

Although I like to tinker with pedals etc. every once in a while, I am more of a musician...So my electronics knowledge is quite limited..
Which brings me in here!

I've been using the EH microsynth off and on in the studio and on stage for a few years now, and I've thought for a while how it would be great to be able to control the Start Freq and Sweep Rate sliders with an expression pedal. Obviously this would involve drilling some holes for some new jacks, but would this be possible in the circuit without damaging other components? Looking at the schematic it looks like the sliders are 100k linear pots.

Any help - suggestions are much appreciated!

,Patrick
btw, that is the first smiley face I've ever used in a message board..been meaning to stick one of those in somewhere

[puretube]

Hi Patrick, & welcome to the forum!

can`t help directly,
but I think these precisely defined mods ought to be doable...

[moosapotamus]

Welcome, Patrick.

Try giving The Tone God's Rock N' Control article a read.
http://www.geocities.com/thetonegod/rockncontrol/rock.html
I haven't tried it, myself. But, I think it would work for what you want.

From the copies of the schemes I have, it looks like the Sweep Rate pot (slider) is setup as a variable resistor (one leg is not connected). So, the 2 pole version ought to work there.

The Start Freq pot (slider) appears to be setup as a divider (one leg to ground, one leg to V-, wiper to circuit). So, the 3 pole version ought to do that.

I guess you could find room for some wires and a place to drill for a couple of new jacks. But, the other bits might fit better in each of your expression pedals.

~ Charlie

[RaceDriver205]

The fact that the pots are 100k makes this perfect for an expression pedal. Smallbearelec.com sells an expression pedal shell and 100K wah pots.
That will give you what you want. You will just have to disconnect the slider pots and run a cable from the wah pot to the connection points.

[woolley]

Hi,
I made an expression pedal jack for the stop frequency. i wasn't as cool as i'd hoped, but not bad. Set the start high and use the stop as a foot controlled LPF with resonance. The rate knob set the 'reaction speed' of how fast i moved the rocker. slow rate takes a while to recognize your sweeps (smooth), fast rate is instant. It was on my DIY microsynth (big box, plenty of room).

i put in an INSULATED stereo jack and a dpdt toggle. toggle 2 of the wires to the pot (-Vs(3) and wiper(2)) to the pot itself or to the jack. circuit ground to the sleeve of the INSULATED stereo jack. i think i had -Vs on ring and wiper on tip. it was a while ago, can't really remember. i used an insert cable to my cheapo stereo volume pedal (2ins, 2outs). send (wiper) pluged into in1 and return (-Vs) into out1.

it was something like that. i can't ensure that all that is correct but i did short the power supply a few times before i used and INSULATED stereo jack

i guess the start pot could be moded in the same way. interesting idea, setting the point where it goes wooOOSH woooo000OOSH w0o w0o w0o woooOOSH or SHEEOow SHEEOow. could get some woooOOSH OOSH or SHEEOow ow ow. sorry about all that, i like the microsynth filter. good luck

[moosapotamus]

You will just have to disconnect the slider pots and run a cable from the wah pot to the connection points.

I kind of assumed that you would still want the sliders to work when not using the expression pedal(s). But, if disabling the sliders is OK, that would work, too.

~ Charlie