2 TS808 (oof, what a bore!) not sounding the same

[arma61]

Hi m8s

boring you with another ''issue'' with a TS808, I'm building a second one (yep, only a 2nd one!  ) and, though all the parts are almost the same of the first one, they do not really sound the same, the ''distortion'' in the first one is ''stonger'' then in the 2nd one. Tonewise they're the same but I have to back the Drive of 1st at about 1:00 o'clock to let it sound as the 2nd.

Few info
- schematic is the same for both (so no mislabelled parts or what else) the second one has switch for diodes/LEDs, though it's not used in the 2nd one, LED not even soldered
- schematic is the one with buffer in and out (2n3904) I think it's the one from GGG
- PCB layouts are very little different, just moved few comps to let it fit the enclosure

change in component
- different TL072 used
- diode on the 2nd are reversed probably when redrwainng the schem with the switch I've reversed them
- 1st one has 2 x 1uF NP
- 2nd one has 1x uF NP and 2x470nF in parallel (they make a total of 998nF)


as far as you know is it possible that any of the above is making this difference in distortion, i'm at wotk at the moment so cannot post anything else.

Thx
Armando

[bancika]

even with the same components, tolerances in component values are wide enough to make two units sound differently. No two amps/pedals are exactly the same.

[Mike Burgundy]

I'd say the components make no discernible difference. There are always *slight* differences due to component tolerances (as Bancika just posted) but that's subtle with modern components.
Diodes are one in each direction (symmetrical clipping) right? So on #1 diode A goes "left to right" and B goes "right to left" and on #2 it's the other way around? Position on pcb doesn't matter for these - the electrons don't know the difference...
Unless there are very sensitive bits of circuit (input on a very high gain circuit, switched power supply) a good layout shouldn't be a problem. If it is, it manifests as a problem (squeal, oscillation, noise), not a gain difference afaik.
Barring any faults (solder joints, open diode) the likely culprit is the gain pot. Pots have a *very* large tolerance (20% on total resitance I think) - and the resitance curve (how much resitance changes per degree of turn) is usually a lot worse. It's quite possible both pots have fairly different resitances with the knobs at identical positions. If they sound the same with slightly different knob positions don't worry about it.

[arma61]

Thx m8s

Yes, about the diodes, on #1 their arrows go D1) to the right D2) to the left and on #2 they're the other way around. Isn't this related to inverting non-inverting input of the opamp (I don't really know what I'm talking about!)

About pots, #2 (the one sounding 'not good') with the drive pot maxed is far less ''distorted'' than #1 with pot maxxed. I'm going to check that pot tonight and report back


Thx

[bancika]

I'd say the components make no discernible difference. There are always *slight* differences due to component tolerances (as Bancika just posted) but that's subtle with modern components.

It's big enough to make noticeable difference in some cases. If capacitors are +-10%, it means that values may vary up to 20% between two capacitors of the same value. That's a lot. Resistors are mostly 1% or 5% which is tighter. I don't know about ICs, but JFETs are all over the place, so are tubes.

Cheers

[Mark Hammer]

Diodes can also vary.  It might be my meter, but my experience is that Si-type diodes can range from just under 500mv forward voltage to 630mv or so.  Germanium type vary too.

[Philippe]

Given these valid explanations...so much for the overhyped 'mojo factor(s)'.

Whether it's baking cookies, raising children or cultivating pot, the same paradigms seem to always apply...same ingredients/parents/seeds etc. --> varying flavors/offspring/plants.

[Mark Hammer]

And this is why I always caution people to not generalize too much when they have only one example of X and one example of Y to compare.  Under those circumstances, you cannot reliably tell if any differences you hear come from consistently occurring differences between the two pedal types (whether issues or models), or from mere individual variation.  They might be, be you can't be certain unless you have multiple examples of both X and Y.  Like we all learned in Intro Stats, the reliability of the estimate is a function of the sample size, and n=1 is a lousy sample.

[ayayay!]

I just modified another TS5 yesterday.  Y'know what amazes me is EVERY TS5 I get sounds the same.  I often hear more differences in different batches of TS9's (probably since they've had longer runs across maybe different factories or parts) but each time I modify a TS5 I a/b it with mine and it sounds identical.  YMMV. 

[solderman]

I would bet my money on the gain pot. When I measure my post's they can be all over the place more then 20% off. And in this circuit it will have a considerable effect on the gain.

[arma61]

Hi gys

I take that diodes orientation doesn't matter,given a deep closeup to both PCBs, looks like on #1 R6 is 2k7 and C3 is 104 ( a mod found somewhere? who knows? cant remember! damn me.. I'm not a tidy person!!)

in #2 they are as per this schem



could they be the culprit? (so I folled you in this case saing that all parts was the same!, sorry  )

still need to check about pots, though as #2 is already in the enclosure I just need kinda of confirmation before start messing with it!

thx for help m8s

[Renegadrian]

http://www.laster.it/self-made-effetti/tube-screamer-modifiche-e-migliorie-parte-seconda.html

I know why you have more gain...you modded it keeley style! I lowered that res to 1k and it's great!!!

[ayayay!]

could they be the culprit?

Most definitely yes, as Renegadrian pointed out. 

[arma61]

thx!!

yep, it really looks like that mod, though I cannot remember having red it!!

I'm going to try that tomorrow evening, I'm too tired tonight!

and I think I need also to make some cleaning on my schematics on my PC's HD, and take duly note of any mod I'm doing after completing a pedal!!   

[Mike Burgundy]

Diodes can also vary.  It might be my meter, but my experience is that Si-type diodes can range from just under 500mv forward voltage to 630mv or so.  Germanium type vary too.

Wow, never thought about that one - I always kind of "trusted" in modern production technology for current semiconductors. Looking at some datasheets for 1N4148 and 914 now, they state Vf max 1V. No minimum, no typical value. Just max 1V. That suggests quite a large possible variation.  Who'da thunk?

[arma61]

ok did the mods, now they're really close enough, though on #2, at max gain, distortion sounds like the distortion you get for too much volume into a small speaker! (you know like the old one trans portable radio in '70s!). I'm going to swap ICs ( and may be measure hfe on trans.?) as a last chance.

btw how much Vf should I look for on the 2 diodes ? I'm quite sure I've bought many of them from many different suppliers, so the batches may differ from each other.


thx
Armando

[acromarty]

Different opamps may have an effect even if both are nominally TL072s.
If they are from different manufacturers then not all parameters will be identical.
Using opamps in clipping stages relies on their large signal behaviour which is often not well characterised since "normal" audio applications stay well away from clipping and distortion. Sometimes the same type of opamp from a different manufacturer can have quite different performance in this area.