I’m constantly A/Bing klones I’ve built with my Centaur, and sometimes each other. Usually, I can dial them in to sound identical, regardless of their specs. Sometime I can’t, and a day later I’ll come back and I can.
Lately I’ve been finding that when one unit sounds different from another, the cause is almost always the Output knob. Just the subtlest difference seems to sound not like one unit being louder than another, but fuller and ballsier than the other. If I have two units built to the same specs, and one seems to have more bass/lower mids, all I have to do is turn down that unit’s vol just the tiniest bit and they sound the same. Or increase the other unit just ever so carefully. The effect is the same- with the “louder” unit, I hear more of the frequency spectrum rather then just an increase in amplitude of the frequencies that are already present. This seems to happen at any volume range- I have this issue at room volume and when cranking it. I think this is a very large part of why we perceive unit-to-unit differences. Well, aside from hearing with our eyes. I’ve also tried it with old TS builds and it also accounts for the differences I used to hear.
The volume issue has been masking the impact of the Klon’s mid-sweetening resistor for me.
The most tonally significant difference between the first and last versions of the Centaur is a resistor labeled R15B that Bill added ” to give the circuit a very small amount of additional low-mid response”. We now know that this was added between the 2nd and 3rd revisions of the PCB.
I’ve know about this resistor for over 3 years now. Until a week ago, I didn’t think I could hear a difference whether it was in the circuit or not. I had even put it on an on/off/on switch that could swap it out with a pot to mess around with lowering the resistance. The effect is very subtle until you start getting lower.
Last week, I was messing around with a test unit that has this resistor on a plain old on/off switch. I noticed that with the resistor switched out of the circuit, the test unit was actually ballsier sounding than the real thing. That can’t be right. While barely perceptible, that resistor is supposed to add lower-mids. If anything, the real Klon (a v3) should be ballsier. The units’ volumes sounded identical, but the real thing was lacking on the lower end. So with the volume issue in mind, I switched the resistor back into the circuit. The test unit was still ballsier, just enough that I could identify which unit I was playing through while having a friend switch them in and out of the loop. Then I tweaked the volumes to where I couldn’t tell he was stepping on the looper anymore. The volumes still sounded identical, but they had equal fullness as well. Both pedals had the resistor in play and were indistinguishable.
From there, I switched the resistor out again on the test unit and compared. The difference was only apparent on the lower strings, at least in standard tuning, particularly when palm muting. There’s just a very small amount of extra meatiness there.
The problem was that the resistor adds so little that the minutest difference in volume can completely hide it. Without actually seeming louder, the “louder” unit will sound ballsier than a unit with or without that resistor. So in the past, when I was comparing a unit with R15B to one without it, I was compensating for the subtle loss in low-mids by tweaking the other unit’s volume and not realizing what I was doing. R15B’s toneshaping can be completely drowned out by just the lightest touch on the Output pot.