Insight into the EHX Micro Synthesizer

S. Thompson · Post by **S. Thompson** » Tue Oct 26, 2010 1:53 pm

So, right now, the tracking on the thing can be quite crummy. I've heard the bass variant has substantially better tracking and is only different by four parts, so I'm considering doing that mod. A list I found lists the parts, but I'm also interested in trying to balance out the various voices more. Right now, the square wave is quite loud and the two octave voices are quite soft. Does anyone know offhand which parts will affect the volume of the octave voices?

- Steve

S. Thompson · Post by **S. Thompson** » Tue Oct 26, 2010 2:46 pm

Also, from looking at the schematic, is there anyway to tell what kind of capacitor C10 is? Looking for a 100uf one via google and they all seem to be electrolytic, but I wasn't sure if there was a way to tell if the current one is ceramic or what...

- Steve

ekwatts · Post by **ekwatts** » Tue Oct 26, 2010 2:46 pm

Yeah, having this problem too. I managed to get it properly "tuned in" to my middle pickup on the Nu Sonic, but it's still a bit flappy. Have you messed with the trimpot at the back?

ekwatts · Post by **ekwatts** » Tue Oct 26, 2010 2:47 pm

Oh yeah, I've also been using a compressor/sustainer before it to stop the dreadful cutoff that tends to happen.

S. Thompson · Post by **S. Thompson** » Tue Oct 26, 2010 3:07 pm

ekwatts wrote:Oh yeah, I've also been using a compressor/sustainer before it to stop the dreadful cutoff that tends to happen.

I know that I adjusted the trimpot to change this. It's much more natural now than when I first got the pedal (no sustain for anything at all virtually).

Michael Dunn from Shotgunn mods apparently has a mod to balance out the voicing properly. He won't, however, share his knowledge for free and I'm a cheap bastard.

- Steve

S. Thompson · Post by **S. Thompson** » Wed Oct 27, 2010 12:58 pm

Bump.

Anyone know a good way to determine the type of capacitor for one of the components without actually opening up the box?

Maybe it's a safe assumption that it's a ceramic, but the rating seems kind of uncommon on part sites I was checking out (0.1mf).

- Steve

timhulio · Post by **timhulio** » Wed Oct 27, 2010 1:07 pm

S. Thompson wrote:Bump.

Anyone know a good way to determine the type of capacitor for one of the components without actually opening up the box?

Maybe it's a safe assumption that it's a ceramic, but the rating seems kind of uncommon on part sites I was checking out (0.1mf).

- Steve

No. You're better off asking at Freestompboxes or DIY stompboxes.

0.1uF is 100nf is a perfectly common value of ceramic cap.

S. Thompson · Post by **S. Thompson** » Wed Oct 27, 2010 2:01 pm

If it's 0.1mf, wouldn't it be 100uf? Heh, I'm getting confused.

- Steve

timhulio · Post by **timhulio** » Wed Oct 27, 2010 2:14 pm

S. Thompson wrote:If it's 0.1mf, wouldn't it be 100uf? Heh, I'm getting confused.

- Steve

0.1μF is 0.1 microfarads, or 0.1mf if you really must.

0.1 μF = 100 nF

S. Thompson · Post by **S. Thompson** » Wed Oct 27, 2010 2:26 pm

timhulio wrote:
S. Thompson wrote:If it's 0.1mf, wouldn't it be 100uf? Heh, I'm getting confused.

- Steve
0.1μF is 0.1 microfarads, or 0.1mf if you really must.

0.1 μF = 100 nF

Thanks for the info! I'm still pretty new to all this stuff!

- Steve

Julian · Post by **Julian** » Mon Nov 01, 2010 4:19 pm

Here's the confusion: Some sites list capacitors as mF (m standing for micro) however the metric abbreviation for microfarads is μF

nf is nanofarads, pf is picofarads. Generally everything above 1 uf is electrolytic, and everything below is interchangeable, though people will tell you certain ones sound better. Just make sure whatever your using has a high enough voltage rating for the circuit. I think the old big box microsynths have +/- 15v supply, so getting something rated for 30-50v would be a good idea.

avj · Post by **avj** » Mon Nov 01, 2010 4:25 pm

ekwatts wrote:Yeah, having this problem too. I managed to get it properly "tuned in" to my middle pickup on the Nu Sonic, but it's still a bit flappy. Have you messed with the trimpot at the back?

Oh yeah, I've also been using a compressor/sustainer before it to stop the dreadful cutoff that tends to happen.

I've found that by using a compressor (as you already are) to tame the transients and level out the attack a bit, as well as rolling back the tone knob a bit really helps with the flappy fart-farts. I also set the trimpot so that unity is about the second hash mark down from the top on the Guitar fader rather than all the way up. This seemed to help a bit, with the nice effect of also allowing a bit of boost if needed.

S. Thompson · Post by **S. Thompson** » Mon Nov 01, 2010 6:08 pm

Hm, speaking of trimpots, there are two on the back of the board. The one is accessible through the hole on the back of the enclosure (old box anyway). The other trimpot isn't accessible without taking the enclosure apart.

What does the inaccessible one do? I know the one you CAN access controls volume, doesn't it?

- Steve

S. Thompson · Post by **S. Thompson** » Wed Nov 03, 2010 1:02 am

Any variation between models of this pedal or a chance that maybe EHX used oddly colored/marked components to confuse cloners?

The resistor at R69 that needs to be changed out to convert the pedal to the bass micro synthesizer appears to be a way different value than expected.

- Steve

S. Thompson · Post by **S. Thompson** » Wed Nov 03, 2010 1:24 pm

Here is a picture of the resistor in question for anyone who has messed with these before.

- Steve

avj · Post by **avj** » Wed Nov 03, 2010 2:07 pm

Terribly sorry I can't be of more help. I'm only familiar with the newer XO-style version; I believe the same goes for ekwatts.

S. Thompson · Post by **S. Thompson** » Wed Nov 03, 2010 2:52 pm

avj wrote:Terribly sorry I can't be of more help. I'm only familiar with the newer XO-style version; I believe the same goes for ekwatts.

The "smoothing filter" caps are also all different values than expected. Very strange and very frustrating...

- Steve

S. Thompson · Post by **S. Thompson** » Wed Nov 03, 2010 6:32 pm

Apparently, there is a lot of misinformation floating around on the internet about which components should be swapped to make the change from guitar to bass micro synth.

Over on freestompboxes.org, a guy said:

C6=2u2 (1u)
C7=1u (0.47u)
C8=0.1u (0.056u)
R62=12k (2k2)

For whatever reason, the component list listed earlier in the thread is wrong.

I think this clears things up for now. Sorry I keep bumping this thread, but I figured I might as well keep track of my progress to help others out in the future.

- Steve

avj · Post by **avj** » Wed Nov 03, 2010 7:18 pm

No problems on the bumping here, especially since it's to provide clear and proper information on a not-oft discussed topic.

I have been thinking of investigating these modifications for the XO MicroSynth as well, but given the SMD format in the XOs, who knows. I'm sure the layout is drastically different -- hopefully the component values aren't.

ekwatts · Post by **ekwatts** » Thu Nov 04, 2010 3:24 am

Aye, mine is the XO version with just the single trimpot on the inside, accessible only by opening it up.