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Saturday 12 August 2017

More pedal power for my rig

One of the most recent pedals to be added to my arsenal is this clone of a 1970's op-amp Big Muff.

I completed this pedal some months ago, and I had started working on it a long time before that. But I stalled its assemblage at the point when I decided that I wanted to make a couple modifications to the build, and couldn't immediately do so.

I had soldered in the two IC chips / op amps, yet then decided I wanted to make one of them removable so that I could try different op amps in its spot. Different models of op amps produce different slightly tonal characteristics.

pictured - an op amp

For example, I think that the only difference between the original op-amp Big Muff and this recent modified clone of it:

... is that the original uses the RC4558 op amp chip, whereas the Eye See Pi modified clone of the original uses an BA4558 op amp chip, which I think gives it a bit darker of a sound, and slightly different distortion characteristic.

So, I decided to remove the relevant op-amp and to install an IC chip holder that I could install in its place and then swap different op-amps in and out of. And I destroyed the original op-amp in the process - which didn't surprise me, and also wasn't a big deal since I already had to order the IC chip holder and other op-amps I wanted to use, anyways. I just ordered another of the original op-amp along with those other things.

The other modification I wanted to add to the pedal is a mid frequency-scoop switch, like there was on the original op-amp Big Muff pedals, and also like there is for that Eye See Pi pedal. The Big Muff has a pretty large mid frequency-scoop by default, and the switch gives an added option to take most of that mid-scoop away. I think the switch should be included in the pedal kit by default, since it was part of the original production run (though not the later production run), and I've personally found the modified no-scoop setting to be the one that I'm using a lot more.

Installing the switch was pretty simple, and just required a precision drilling of a 1/4" hole to fit a toggle switch through, and a couple of wires and resistors to connect each side of the switch to the pedal's PCB. I also placed some electrical tape between the switch components and the PCB.

So, I had this pedal sitting in a semi-completed state on my desk for probably many months until I decided to initiate those modifications - and then I finished it up quickly.

dramatic re-enactment of the alleged desk (actually, just not cleaned up yet at the time of its photographic capture)

There was a problem with the pedal when I was first testing it out, being that the emitted sound would not stay entirely on while the pedal was engaged, but would flicker on and off. So, I opened up the pedal again, and looked for shorts, particularly where I'd installed the mid-scoop switch. But found nothing wrong there.

However, I noticed large amounts of flux residue around the potentiometer leads, which can cause a short, so cleaned it away using isopropyl alcohol-soaked Q-tip / cotton swap / cotton buds, and, thankfully, that solved the issue. Since then, the pedal has operated perfectly.

After testing out the 3 op-amps I ordered, RC4558, BA4558, and BC4558P, I've ended up keeping in the original RC4558. Of course, I can swap it out for one of the others at any time.

C~ Soundscapes

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