Klon Centaur Question

[Ofek Deitch]

Hi everybody,

I'm looking at this scheme of a Klon Centaur (Below), and I know this is a dumb question, but - What is the dashed line going between the 2 Gain pots? is it a a dual taper pot?

schematic removed - Aron

Thanks guys  
Ofek

[mistahead]

Its the stream of pure dark matter mojo that makes the Klon so damned good as a transperant booster... seriously check out the telecaster forums - they know!

But yeah I think its a dual gang pot.

[Mustachio]

Its the stream of pure dark matter mojo that makes the Klon so damned good as a transperant booster... seriously check out the telecaster forums - they know!

But yeah I think its a dual gang pot.

Hahahaha! 

yup dual gang pot

[pinkjimiphoton]

it's a dual 100k pot, but you can use two 100k's if you want more versatility out of the circuit.
nice sounding pedals, i've built around 12 so far for friends.

mind you, use two chunks of shielded mic cable (2 conductors and shield) between the board and pots, and make sure the back of the pot casings is connected to ground well or it may
"squeal" some.

[Digital Larry]

I have to say, looking at the Klon schematic more closely, that it really does represent some out of the box thinking.  Not so much for running an op-amp into some diodes for clipping, but the frequency shaping networks which are sprinkled throughout.  I sense that the designer did a LOT of experimentation.

I also like the pot at the input of the op-amp that feeds the clippers.  Normally you'd see a non inverting op-amp with feedback (from output to (-) input) and shunt (from (-) input to ground used for complex frequency shaping and gain.  But by putting the other end of that gain pot at the (+) input, you can reduce that stage's gain to zero instead of one which is the normal minimum for a non inverting stage (it does it via brute force - shorting the (+) input to ground, but what the hey). 

[midwayfair]

Ofek: The term is "dual gang" -- that'll help you find the right part when you go looking.

That schematic has a few things different from the original Klon, mainly the lack of the charge pump. You may want to try rail-to-rail op amps if you're building that version as versions without the charge pump can clip U2A a little. They also sound (to me) a little dull in the treble.

[Mark Hammer]

The dual-ganged pot is accomplishing about 8 different things at once and is a big part of what makes the pedal.  Although one CAN use two single pots, it is the simultaneity of all those changes/adjustments that allow for the sound to be what it is.  Otherwise, it becomes a bit like serving you a spice rack and a bowl of unseasoned marinara sauce in the restaurant, saying "Here, you can season it the way you want".  Whether ANY dual-ganged pot accomplishes the objectives, or a specific brand of pot provided better tracking between pots, I couldn't tell you.  I know Bill Finnegan was VERY picky about parts.  During our brief collaboration, he had sent me a schematic to work with, and there were a bunch of component values on the schematic that were crossed out and replaced with 1% resistors.

And Jon is correct that the charge pump is an important element.

[Bill Mountain]

I had heard that the pots were special ordered.  So there may be a specific tolerance or taper needed for the best results.

[Mark Hammer]

Assuming the two sections are matched/identical, then taper shouldn't matter, other than with respect to dialability.  If they are different in some systematic way, however, then it would matter.

[midwayfair]

Assuming the two sections are matched/identical, then taper shouldn't matter, other than with respect to dialability.  If they are different in some systematic way, however, then it would matter.

At least a couple people report "better" overall sounding builds with closely matched tapers. Most likely it's the ratio of the flat-response dry signal to the mid-hump of the OD section.

It's not too hard to buy a pile of dual gang pots from Tayda and pick the "best" one. It only took me about 5 pots to find one within a couple K on each side of 100K.* The others can be used for speed pots in univibes and phase-shift LFO tremolos (with parallel resistors).

*Though since I mod a bunch of the tone shaping every time I build one of these, I doubt it mattered one iota. I'm not overly interested in copping the sound of the stock unit ... it's a fun circuit to mod.

[pinkjimiphoton]

The dual-ganged pot is accomplishing about 8 different things at once and is a big part of what makes the pedal.  Although one CAN use two single pots, it is the simultaneity of all those changes/adjustments that allow for the sound to be what it is.  Otherwise, it becomes a bit like serving you a spice rack and a bowl of unseasoned marinara sauce in the restaurant, saying "Here, you can season it the way you want".  Whether ANY dual-ganged pot accomplishes the objectives, or a specific brand of pot provided better tracking between pots, I couldn't tell you.  I know Bill Finnegan was VERY picky about parts.  During our brief collaboration, he had sent me a schematic to work with, and there were a bunch of component values on the schematic that were crossed out and replaced with 1% resistors.

And Jon is correct that the charge pump is an important element.

+1 . just said it could be done.

i haven't. i really like the centaur pedal a lot.

[Mark Hammer]

At least a couple people report "better" overall sounding builds with closely matched tapers. Most likely it's the ratio of the flat-response dry signal to the mid-hump of the OD section.

It's not too hard to buy a pile of dual gang pots from Tayda and pick the "best" one. It only took me about 5 pots to find one within a couple K on each side of 100K.* The others can be used for speed pots in univibes and phase-shift LFO tremolos (with parallel resistors).

*Though since I mod a bunch of the tone shaping every time I build one of these, I doubt it mattered one iota. I'm not overly interested in copping the sound of the stock unit ... it's a fun circuit to mod.

When audiophiles want a volume pot for a stereo preamp that offers perfect channel-to-channel matching, they use a stepped control, in which 1% resistors are used with a 22-position (or whatever) switch such that the amount of signal attenuation on the one channel is exactly the same as the other.  I suspect that digital pots have made all of that stuff superfluous...although never underestimate the tendency of audiophiles to cling tenaciously to older technology, regardless of cost or nuisance!

[Bill Mountain]

What's going on with that positive feeback.  It goes from R16 back to the input of the opamp.  When it comes to opamps what kind of effect does it have?

[slacker]

If you mean the path through R19, it's not positive feedback, the signal from the first stage goes through the R7/C16 filter which lets through frequencies below about 100Hz then through C19 into U2A. U2A is configured as an inverting mixer and pin 2 looks like ground for audio signals so there is no signal there to feedback the other way.

[Bill Mountain]

If you mean the path through R19, it's not positive feedback, the signal from the first stage goes through the R7/C16 filter which lets through frequencies below about 100Hz then through C19 into U2A. U2A is configured as an inverting mixer and pin 2 looks like ground for audio signals so there is no signal there to feedback the other way.

Your explanation makes complete sense.  I just wasn't looking at it that way.

Damn this schematic is confusing.

[DougH]

...And yet every demo I've heard/seen of this thing sounds like 'just another overdrive <yawn>' to me. I guess I'd have to be convinced in person that this thing is worth all the trouble to build. 

[Digital Larry]

I suspect that digital pots have made all of that stuff superfluous...

Don't think so, at least not in general...

Maxim for example:

http://www.maximintegrated.com/app-notes/index.mvp/id/1828

"While the digital pot steps are usually designed to give equal-value resistive increments, a by-product of the process variation is that the total end-to-end resistance varies widely from part to part, as much as ±30% in some types. This resistance variation must be considered when designing a circuit that requires close matching between two channels using separate digital pots."

[aron]

Doug, please try a real one. It does sound different through a Fender amp. Not saying it would be something you would like - but it does sound different.

[DougH]

Doug, please try a real one. It does sound different through a Fender amp. Not saying it would be something you would like - but it does sound different.

One of the issues I have is every friggin' "demo" of this thing I've heard has been someone using it as a simple overdrive, without driving the amp.

Yet, the Klon fans claim it excels as a booster, and has to be with the requisite "right" amp.

Okay, great. LETS SEE AN EXAMPLE, DAMMITT!!!!  

[Mark Hammer]

   If I had a nickel for every time.....

The Klon Centaur was never, I repeat, NEVER designed to have a sound of its own, but was intended to precondition the signal to push an amp at the edge of breakup into desirable/optimal breakup.  I had two in my possession at one point and I have to tell you that if you were going to dime them and feed them to a Fender Frontman 25 or any other solid-state amp set for clean, you would likely be sorely disappointed.  They were supposed to be supplemental front-ends for amps not pedals you feed into them.

When Bill Finnegan was making and selling them, contacting him would result in a very pleasant 30 minute conversation about your rig and your musical tendencies/objectives.  If Bill felt you were not likely to benefit from owning one, he would discourage you from purchasing one.  I have no idea just how many such conversations - of both the productive and unproductive nature - Bill would have in any given day, but it was one of the factors that limited his production output, and ended up driving the re-sale price as high as it became.  The "sales strategy" was that people would be satisfied with their purchase.  It was NOT to deliberately restrict output to make re-sale prices high.  Bill only saw money from the initial sale, and not a penny from the re-sale.  If he did, he would undoubtedly still be in business.  Decent honest guy who had no control over what places like TGP or HC would do.

Although he did not sink much money at all into advertising, on those rare occasions that one would see an ad in Vintage Guitar magazine (always on the B&W newsprint pages, never on the glossy colour ones, and rarely if ever larger than 1/16 of a page), the ads consisted of written testimonials.  The best, and to my mind most descriptive owner comment, was one where the owner said it sounded like his amp, only...bigger.  I guess if you want an example, listen to Warren Haynes.