Author Topic: Built 2 Rustbuckets - 1 works great, 1 is a bit off  (Read 374 times)

Imuthant

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Built 2 Rustbuckets - 1 works great, 1 is a bit off
« on: February 16, 2019, 05:46:55 PM »
So I built two Rustbuckets at the same time, with the same parts. The second one was for my bandmate. First one sounded great right off the bat, really great circuit...and I just "biased" the second one and it's much louder.

On the Rustbucket 1 (sounds great) the gain trimpot is nearly maxed. On Rustbucket 2, even with the gain trimpot all the way down, its significantly louder than RB1. Even at low amp levels, RB2 either feeds back, or feels ready to feed back.

I've double checked components and orientation, and everything looks to be the same (i.e. the edge switch is off on both)

I recorded some audio on my phone real quick, where both pedals have the pots at the same settings. The iffy pedal, RB2 is played first. Then I swapped pedals and played the same notes on RB1. RB1 sustains longer and more smoothly, probably because the difference in gain is effecting the interaction of the sense/attack/decay controls.

Any ideas as to what might be causing these differences in the second build?

(I can't get the audio file to load...I need to look into how to attach audio...)

Govmnt_Lacky

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Re: Built 2 Rustbuckets - 1 works great, 1 is a bit off
« Reply #1 on: February 16, 2019, 06:24:56 PM »
So I built two Rustbuckets at the same time, with the same parts.

You mention you used the "same parts" but, I'm wondering if maybe a rogue resistor may have slipped into the wrong pile.

Double check all of your resistor and cap values and see if maybe a wrong value got onto RB2's board.

Imuthant

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Re: Built 2 Rustbuckets - 1 works great, 1 is a bit off
« Reply #2 on: February 16, 2019, 06:31:33 PM »
 Thanks! Iíll check all of those once I get back home.

DLW

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Re: Built 2 Rustbuckets - 1 works great, 1 is a bit off
« Reply #3 on: February 17, 2019, 07:32:28 AM »
Are you able to swap the ICs from the working Rustbucket into the one that doesn't? If it now works, that would isolate the problem to a faulty IC.

My Rustbucket was a dud on the first pass. Turned out to be a dead CA3080.

Stomptown

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Re: Built 2 Rustbuckets - 1 works great, 1 is a bit off
« Reply #4 on: February 17, 2019, 11:52:28 AM »
I would check your voltages.  I built one that worked but seemed a bit off a few years ago.  When I finally checked voltages on the ICs, it turned out voltages were way off on 4 ICs. I actually just finally pulled all 4 ICs yesterday and Iím waiting on a replacement order to see if I can get it working right...

Imuthant

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Re: Built 2 Rustbuckets - 1 works great, 1 is a bit off
« Reply #5 on: February 17, 2019, 07:52:35 PM »
After probing around and checking voltages to locate the problem, the issue ended up being embarrassingly simple...turns out RB2 was actually the pedal that was working properly, whereas RB1 wasn't biased correctly.

There was an accidental "sweet spot" (for me at least) exactly 1/4 turn ccw from the proper "bias" trimmer location. That resulted in much less voltage going to pin 3 of the mn3007 and much lower overall gain. The weird thing is, I initially preferred the improperly biased pedal, because after turning the gain trimpot all the way up, it was still usable gain-wise, and the output was smoother and less overdriven/dense.

Turns out that Attack Decays are supposed to sound like that, so I rebiased it and lowered the gain trimpot all the way. Sounds great, of course, I had just never heard one before. I can probably blame the feedback difficulties on my Harmony Rocket. Thanks for the help!