Same Pedal, Slight Differences

[dafortier]

I've been building pedals for a couple of years now but I've rarely ever built more than one of one kind of pedal.  I just built 5 aeon refractor pedals over the course of a couple of weeks.  I decided to A/B two of them next to the one I built for myself and I noticed a difference.  Mine is a bit brighter and a little more "open" sounding.  The other two are a little darker, and one seems to have ever so slightly less overdrive at the same knob position.

The differences are very subtle but noticeable to me.  I've compared IC voltages to mine and they're nearly identical.  The parts are the same in all of them.  Metal film resistors with 5% tolerance.  Caps have a 20% tolerance.

I've never built this many of the same pedal before so my question is, is this slight variation in tone to be expected? 

[Fender3D]

+-20% capacitance tolerance is +-20% away from desired (or expected) filters' crossover freq.
I'm too lazy to calculate the worst scenario, adding your 5% resistors' tolerance... but....

[antonis]

The parts are the same in all of them.  Metal film resistors with 5% tolerance.  Caps have a 20% tolerance.

Tolerance refers to + - , for a 100nF cap it can be 80nF to 120nF...
Same for resistors, of course so, calculate any kind first order passive filter of 100nF/10k with worst case values combination of 80nF/95k vs 120nF/105k... 

edit_1: Slower than Federico with same degree of laziness..

edit_2: Wellcome...!!!

[EBK]

Plus, I'd bet that the one that you were most excited to build sounds best to you.  I know that's always the case when I'm building.  (And the pedals that I think sound absolutely perfect are also the ones I won't let anyone else hear, so they can't tell me otherwise.  )

Welcome to the forum!

P.S.  Yes, I know you were talking about objective, not subjective, differences. I'm just having fun.

[dafortier]

Thanks for the welcomes!  And I understand how the tolerances work, but I think I'd be too lazy to calculate all of the high and low frequency cutoff possibilities.  Plus I'm not sure I'd be able to effectively use that information or how it should sound to my ears.

I measure each of my resistors with an ohm meter as I build but that's really just a quick way to confirm that I have the correct value.  I don't know how to measure the capacitors without a dedicated "capactior-measurer" so I'm just going off of the markings.  Who knows what the actual values are.  Do you guys use components with tighter tolerances?  Are you measuring each component and discarding the ones that are out of spec? Or do you just accept that there will be differences in each one?

I know about the subjective effects of the excitement-factor.  When you hit that first cord on the first pedal for the first time, and it works.  Its like magic! And it's no coincidence that the best sounding pedal is mine. .  I'm not letting anyone hear that one unless I'm using it!

[EBK]

If I'm ordering from Mouser (or equivalent), with hundreds of thousands of choices, I'll often set tighter specs to limit my choices to a reasonable number, but otherwise not.  Usually, I make sure I have the right type, value, voltage, and size, and stop there.  I don't typically bother measuring capacitors.  There are lots of non-ideal characteristics of capacitors that as affect how the cap behaves, so I just don't see a reason to bother, so long as the circuit sounds ok in the end.

[mimmotronics]

This is something that's always stumped me until recently. How can a large pedal company manufacture so many pedals and have them all sound the same when they're using components with tolerances on the order of 20%?

I've concluded that...well, they can't. Not one of those mass manufactured pedals can sound EXACTLY the same as another. It's all about what the designer wants to do; if tonal consistency is a priority then tighter tolerances are one of the factors that will get you there. If cost is a priority then you'll probably default to using wider tolerances.

[Ice-9]

As pointed out, component tolerances make a difference and this is accumulative throughout any circuit so  buying components that are of a tighter tolerance would be advised.

Resistors are available in +/-1% tolerance and I doubt you would see any real difference in price , its a no brainer, capacitors you will see a bit of a price difference but go with +/-5% as all this makes for a better consistency in sound.

This whole tolerance thing is part of why Pedals and amps from the 60's,70's of the same models usually never have 2 that sound exactly the same and also why some vintage stuff can cost half a fortune when someone has found a 'Good' one.

[Fender3D]

...I'm too lazy to calculate ....

...with same degree of laziness..

....so I'm just going off of the markings...

....so I just don't see a reason to bother...

What a bunch of lazy ass we are!!! 

[dafortier]

Agreed.. We are a lazy bunch! lol. I guess it depends on how anal you want to be about it.  If you can find lower tolerance componenets for the same price or only slightly higher priced, then that's prob the way to go if you're going for consistency.

However, just like the pedals and amps of old, I kind of like the idea that each one is a little different.  I mean, each guitar, amp, pedal chain and player is going to be different anyway.  Kind of adds to the voodoo of it all.

I suspected the accumulation of the tolerances would cause the subtle differences.  Just needed confirmation from other builders.  And some suggestions on what everyone else is doing.  Much appreciated!

[GGBB]

ever so slightly less overdrive at the same knob position

Potentiometers typically have very poor consistency - +/- 20%. The same knob position is meaningless.

[amz-fx]

Potentiometers typically have very poor consistency - +/- 20%. The same knob position is meaningless.

So true, and if you measure the total resistance of the pot using the outside lugs, you will find that it seldom comes close to the specified value.

I suggest that the OP take a look at the potentiometers as a place to start.

Best regards, Jack

[dafortier]

ever so slightly less overdrive at the same knob position

Potentiometers typically have very poor consistency - +/- 20%. The same knob position is meaningless.

I hear you. The knob position was more of an approximation than and exact position anyway.  I could have simply had the knob tightened at a slightly different degree than the other one. 

But I was unaware of the tolerances in the potentiometers as well. That makes total sense.

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[GGBB]

But I was unaware of the tolerances in the potentiometers as well. That makes total sense.

So back to your original post and following what Jack recommended, that extra brightness could simply be the variation in the tone pots. If you haven't already, compare the pedals by trying to dial in the same tone via the drive and tone knobs, rather than trying to match the pot positions. Try different settings as well. You might find the pedals are actually very close, but then again probably not identical.

I *think* most of us are using 1% resistors and 5% (sometimes 10%) caps, which makes for fairly subtle differences - maybe too small to hear. But the pots are always going to throw a wrench into the consistency works, so the component tolerances in some cases don't really matter if a pot is used in that section of the circuit. If you want a precise result, you either hand-select parts (or use very low tolerance components wherever possible), or you design for a little more range of adjustment than the ideal to account for component tolerance variations. The latter is likely the reason you don't see too many pedals being used with pots set at max or min (there are exceptions of course - often with max gain), and why well designed pedals always have all of the "useful" range of any control available on every unit, and then some. "Useful" is of course decided by the designer.

[antonis]

Additionaly, take in mind (or simply don't bother at all - if you classify yourself into forenamed lazy-ass group..) other component variances..
(e.g. transistor DC gain & transconductance, Op-amp open loop gain & gain-bandwidth product, e.t.c.)

In case of not carefully disgned active filters, the above deviations come to add to (actually, multiply with) passive components tolerances..

[Frank_NH]

This kind of variance is not restricted to pedal building.  You have this effect X10 in guitar building, with possible variations in wood composition, bracing, dimensional tolerances for body and neck joints, etc.  That's why players often go through a dozen of the same model guitar to find the one that has that something "special".

For pedals, though, I often use 5% resistors and 10% capacitors, knowing that by some random luck I may produce a pedal with that little something "special"!    

[dafortier]

Lots of great info here! Learning allot for sure!

So I did another A/B test tonight and tried to dial in the same tone on both no matter what the knob position. I had some interesting results.

I was able to dial in a completely transparent tone on both pedals with the gain at zero and setting the volume to unity. Then I slowly increased the gain on each. They both seem to have equal gain but pedal B is much more mid-range-y. Like a tubescreamer almost. My pedal (A) seems to add some overdrive while still maintaining the original tone. This is the desired effect.

Pedal B adds mids as soon as I turn up the gain. Im guessing there's a cap-resistor-filter thats off somewhere.

I did measure the pots and they were close. These values we're taken with the pots in-circuit.

Pedal A
Drive 1 99k
Drive 2 26k
Vol 10.4 k
Tone 10.k

Pedal B
Drive 1 105k
Drive 2 27k
Vol 10.7k
Tone 9.6k

Any ideas?


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[Quackzed]

there seem to be alot of suspects. on this schem c4 c6 c7 c8 c11 c12 , line em up , look long and hard into their eyes, and shoot the first one that blinks...  after that their resistor pals shouldn't be tough to crack! 
basically if the gain pot is adding alot more mids than it should, double check anything in that dual gain pots path? dirty flux paths to ground?
and after all that it's probably just component tolerance   

[duck_arse]

.... double check anything in that dual gain pots path ....

dual pot? if there is a dual pot involved, all bets are off. you'd need to also factor in the wafer pair mistrack/mismatch.

[dafortier]

Do you mean both wipers in the pot being out of sync with one another?  Hadn't considered that.  However, I compared the dual pots on both pedals and the values were the same on both.