tube screamer tone control not working

[Harry]

son of screamer
Built with this perf layout http://www.aronnelson.com/gallery/main.php/v/diyuser/son+of+screamer.gif
using a 20kw pot. Double checked values and continuity between connections around the tone control it looks good... but tone control does absolutely nothing The rest of the circuit works great! Any ideas?

[R.G.]

If the parts are good, and the entire circuit wired as it should be, Mother Nature ensures that it *will* work.

So one of those is not true.

[GibsonGM]

As said, physics...it has to work.  I'd suspect the pot or its wiring has some issue, or that something is shorted and acting like a bypass...

[Harry]

Lol, fair enough. I've consulted my old physics textbook didnt do me a bit of good .

I dont see any obvious shorts though some leads come awfully close to touching with this layout. Which btw the layout is not my own but looks ok to me. This is the first time Ive used someone's layout besides my own in a perf build. And NO I'm not trying to blame this on anyone nor am I accusing Mother Nature of playing tricks on me! I've just gone over it quite a bit and it has me puzzled. I'm ok with the fact that this is possibly (likely and preferably!) an error on my part and not a component failure or something.

The pot's resistance range moves throughout the sweep. It still looks wired correctly to me, the volume pot as well (functions correctly). The entire 2nd stage looks fine...

Where can i start? Is there a point i can audio probe? Would a picture help?

[R.G.]

Get out your ohmmeter, and print a schematic. Using the ohmmeter, verify that each part *at the leg of the part, not after the solder joint* has a near-zero-ohm connection to all the other part leads it's supposed to connect to. Do this from the part side, not the wiring side. Mark each part lead on the schematic in colored marker as you do the check. Make no "mental leaps" of "if this is connected, so is this one, of course". If all checks out, then the parts are at least connected up. This does not catch wrong-way parts or extraneous shorts. Include wires to/from pots, switches and jacks.

Then turn the board over. Look for places where things come close, but don't get soldered. Use the ohmmeter to verify that they're NOT near zero ohms.

It's worth noting that an open ground on the resistor/cap to the wiper of the tone pot would prevent it doing anything, as would an open or high resistance wiper.

[Harry]

Thank you for your time R.G.

I'm checking all connections now. Most components leads are under perf and far too cramped to probe topside so I'm checking those components' bottom-side lead before the solder joint.

I realize how this problem is screaming I've wired my pot wrong or the rc network isn't grounded. After the tenth time checking with meter rechecking values and examining solder joints, I can assure you the 20k pot is functioning as it should in regards to resistance, is wired correctly: lug 1-1k/220n/pin5, lug 2-220n->220r->gnd, lug 3-1k/pin6.

One thing occurred to me. Is the high frequency attenuation in this filter subtle or only effective in upper high range? The reason I ask is because I'm playing through a homemade amp and the amp is pretty dark. I've never had any problems with ineffective tone controls in other effects through it though.

[R.G.]

It's not that subtle.

[auwoodstock86]

As for what i know, everybody says that Tube Screamer tone control sucks (and that was documented at least by Jack Orman). The first half of the turn, it will do nothing in most rigs, then it will rise trebble just a little to, at the very last degrees of the turn, make a dramatical rise "which is hard to control".

I do recommend that you try a different (hopefully better) amp before going even further into troubleshooting. It happened to me with this very TubeScreamer circuit: i was testing it using my cherished Roland Micro Cube (in the "Black Panel" setting, which seemed to be clean enough) and it would just have TONS of hiss and all sort of buzzes, more or less with any of my pickups... and there goes poor me changing transistors and IC and rewiring the ground in all sorts of different arrangements to avoid loops, only to discover in a later moment of clarity that a modest Laney with a real clean channel was all i needed from the beggining...

[GibsonGM]

He may not like it after it's done, or find something better (*cough* Timmy *cough*), but this is how you learn, and a great one to learn on, as many other pedals are based on TS topology!  If you can't get a tone control to work, then you should focus on...how tone controls work, and how to troubleshoot to solve the problem.  Later, in more complicated builds, you'd be lost without the basic foundation....

A HUGE problem I'm seeing in the last couple years, and increasing log-style in the last few months, is that ppl are depending on Vero layouts.  Great if you get it to work, easy and all.   If you can't get it going, I really can't help you much, though!     You don't LEARN anything from them, so if one tries to help someone, you didn't learn much, and made US go thru a lot of work to figure out how you went wrong.  A schematic forces you to learn how things are connected, and to some degree, how they work.  Over time, you can't HELP learning what goes on - and they make troubleshooting 1,000x easier! Esp. for others, who may not have the pedal schema in their memory, and don't want to go digging for it.  I happen to have 'son of ts-9' saved, so here goes again:

The tone control WILL work if it's wired correctly.   You can audio probe either side of the pot (if it's the same setup I'm familiar with!) and hear a major difference at some control settings.    I suspect a solder bridge across something there, shorting the tone control's effect, or a bad part value, bad ground there.   *shrug*    Are you sure something else isn't to blame?   The WIPER is hooked to the cap?  All that stuff?

[Harry]

Ok found the problem.... yes, it's confirmed I'm a dingus. At least I can share the blame and save a little face. After checking the capacitor value a second time (haha yeah dont ask why it wasnt clear the first time) 202 is a .002uf cap! Shame on Mammoth for sending the wrong parts (i checked my order and i did order the right ones and they were bagged as 220nf too). Shame on me for not being thorough enough.

I agree with you Gibson about layouts. As i said this was the first time I used someone else's layout other than my own. In an effort to keep it compact and neat I ended up with two giant green radio shack tumors hanging off the board to remind me that I'll be using my own layouts from now on. Not because it was incorrect (its verified) but as you said it makes it that much harder to troubleshoot. Son of screamer is now saved in my memory and my eyes have glazed over.

Now that it's working "correctly", quite a big volume drop at minimum setting. I guess 6db+/- is a lot!? Other than the volume difference i like the tonal control on it. You saying the Timmy's tone control is an improvement? I have the clipping section alligator clipped to try out different configurations and Timmy's was already on my list to try.

[Harry]

Also, a big thank you to everyone for not allowing me to convince you i had it right 

[GibsonGM]

Ha ha, you're NOT a dingus, just made a human error. And we got you to go find it!   Have done the same.  Your tone control WAS working, just passing high freq's only dogs can hear to ground, LOL!   Well, around 4kHz at the 20K end of the pot, and 16kHz when you get near 5K.....all very high stuff going away.  I suspected this after you swore everything was connected right - it was the only other thing to check.

-3 db is half power....-6, half again.  So yes, you DO lose some volume there!  That is part of why so many ppl mod the thing.

I REALLY like the Timmy - not a huge leap from the TS, but there is a low end control off the clippers, AND a high rolloff on the output of the 1st stage.   I think the 2 controls are a  LOT more versatile...gives you a lot more control, 'tune-ability' wise.  Simple but very effective change to the circuit.    I use it to push my tube amp, not for distortion/OD (ok, I do add some dirt with it, but not a lot)....it makes an already good sound REALLY jump, IMO.   That little bit of control over your low end makes a huge difference, to me.   Once dialed in, I don't change it for other tones, it's not that kind of thing for me.  Build it!

Put an AMZ mosfet boost after the Timmy for leads, and there is your stage setup )    Maybe with a wah before both, though.

I have a 40W Fender amp with lots of headroom, so this setup is awesome.  

Edit:  YW, Harry, ha ha