Tubescreamer problems...Should I use Carbon Comp Resistors?

[BrianK]

Hi,

I built a Tonepad tubescreamer. It sounds great with the tone knob turned all the way down...but if I turn the tone knob up, I get this terrible tinny noisy sound. Aron suggested I trace the tone part of the circuit with the Audio Probe, which I am going to do this week. BUT my stompboxing buddy emailed me this excerpt from Analogman.com's Mike:

TQR: So regarding the TS808 mods that you do, players have a choice
between the 808 or the 'brown' mod.

The brown option is still a 100% 808 circuit. The only difference is that
I use carbon comp resistors for the brown version, which weren't used in
the originals, and they warm up the tone of the pedal more than the
standard 808.

TQR: So you won't have to back the tone control down so far to cut that
harsh high end.

Yeah, some guys have to run that tone control way down to get that trashy
high end out of the signal."  

Is this the answer??  I'm not sure... because  R.G. Keen says this:  


Carbon composition resistors have a rep for sweeter sound from their use in guitar amps. There is a grain of truth in that. Carbon comps have the largest voltage coefficient of resistance of any resistor - which, in English, means that as the voltage across them changes, so does the resistance, so they actually generate some distortion themselves. The distortion is pure second order, and hence sounds nice to guitarists.

The amount of resistance change per volt (and hence, the amount of distortion) is tiny. You need hundreds of volts of signal change before it gets audible. In tube-type amps, this can actually be audible under some conditions. Sometimes it's not even audible there, but folks who're looking for magic-mojo tone fixes love to sort through this stuff, like deciding their tone is better if they turn all their signal cords the same way or something.

On top of that, carbon comp resistors are not very uniform. They vary a lot from unit to unit in all kinds of ways, but also in the amount of the voltage coefficient of resistance. Some of them make a lot more of this distortion than others. That alone makes getting a magic-mojo resistor hard, even if the circuit lets it sound out.

In effects pedals with a typical 9V power supply, there just isn't enough signal voltage - or power supply voltage! - to make the real effect come through.

As to brown sound, tweed sound, and the other stuff, near as anyone can tell, that's purely an urban legend. It's true that the amps with the most brown sound, whatever people really mean when they say that, are usually very old ones. That means that they have the oldest, most value drifted, poorest consistency carbon comp resistors ever made in them.

Brown sound and/or other magic mojo in carbon comps, as related to low voltage effects, is purely advertising hype. There is no real reason, and no measurable effect to having them there, except for the excess noise they create. The placebo effect sometimes makes people do and say strange things, so it's sometimes happens that a person really believes that their effects sound better because there's a carbon comp resistor or two hidden inside their favorite pedal, but *that* chain of events is psychological, not electronic.

And that's the story.

R.G.


So...who's right?  Aron, AnalogMIKE or R.G. Keen?

I am going to test my circuit with the audio probe because it's a good idea, but is there anything at all to this carbon comp resistor thing???


Thanks,

Brian

[petemoore]

I 'think' I did in fact 'probably' notice a 'small' like 'teeny' ie say .02% difference when trying like blazes to hear a difference batween CC and Films...and I can say with absolute certainty, that I'm still not completely convinced that film is 'better' than CC.
 CC's generally have looser specs IIUC, so some of the percived minisclule difference could be because the actual value between Films and CC's in a given position were possibly different.
 Just socket some prime experiment Cap 'slots' and see if you can decide whether ANY difference can Actually be heard.
 I use films for everything above say .47uf...I don't think it matters much for teeny high end roloff caps or high end 'pass capacitors...when you start into midrange passing through a cap, a very slight [easily no noticed] difference may or may not be percieved...like I say, I 'think' I heard a defference and opt generally for Film caps unless quanitiy is unavailable.

[smoguzbenjamin]

Pete he's talking about resistors not caps You could try it, maybe it adds more mojority

[BrianK]

Hi Pete....

Thanks for reply, but I was referring more to resistors than capacitors!

This, I believe, is where the debate is.

Thanks!

Brian

[AL]

Mouser http://www.mouser.com/ now has 5% Xicon Carbon Comps

AL

[Alpha579]

Am I right in thinking pete was talking about res?  :?
CC=Carbon Comp
Film=Metal Film

I cant hear any difference between CC and metal films, but i go with metal films 4 consistency and reliability.

[smoguzbenjamin]

Nah pete was talking about uF and cap slots

[Peter Snowberg]

I have to disagree about the point where the differences become audible. R.G. says hundreds of volts, but I would argue that it's more like dozens of volts. In any case, IMHO it's still more than your signal gets exposed to in a pedal.

In a pedal, I don't like to use anything other than metal films for the signal path. These are MUCH lower noise than CCs and lower noise than carbon films, they have the best temperature coefficient, and they're very stable over time.

Some of the “magic” of old CCs in a tube amp is easily associated with value drift. I’ve found that in tube amps at least, the actual value is generally something like 15 to 30% higher than the bands indicate. The general effect of this is that your amp picks up a little gain. You can simulate this by simply using 120K resistors instead of 100K. In addition, you can get the same “brown” tone with less noise.

I would put using CCs in a pedal in the same league as the Emperor’s new clothes.

Take care,
-Peter

[R.G.]

So...who's right? Aron, AnalogMIKE or R.G. Keen?

I hate to say it this way because I know Mike, and he's a pretty decent guy, but let's just leave it at this - I don't make any money selling carbon comp resistors. Everyone has to make a living, and the urge to make products attractive to customers has to be almost irresistable.

I would be willing to wager a substantial sum on an objective listener NOT being able to hear any discernable difference other than hiss in a fairly constructed test at 9V pedal voltages. No "brown sound", no subtle cork-sniffing overtones of ginger and rutabaga, no vintageness in the tone.

There likely will be additional noise, but no magic mojo.

Lest anyone forget, carbon comps do NOT have inferior frequency response to film parts. On the contrary, carbon comp was useful in RF rigs because they did not have the series inductance of the spiral element that would interfere at frequencies over a few megahertz. So it doesn't make much sense that they would brown-down audio, does it?

Brian, but your problems are not related to carbon comp versus other kinds of resistors. Changing to carbon comp will not help, except accidentally if that fixes a solder joint or some other side effect. If I had to guess, you likely have a biasing problem or something similar. No resistor causes a tinny sound.

[Dai H.]

doesn't seem like there is much point to using carbon comps in a Tube Screamer, IME, but if you want to be 100% sure, go ahead and try it out. I also doubt that that will solve your problem though.

[Transmogrifox]

Yeah, I always put Vaseline on my solder joints to make the current slide through more smoothly  :twisted: .  Another good TS mod is to have a jeweler replace all of the circuit board traces with high purity silver and to ultrasonically clean the IC :wink: .

It is also a good idea to air-tight and water tight the enclosure and fill it with oil for cooling the electronic parts so that power dissipation doesn't change your sound as you're playing.

[george]

I'd check the values of the caps in the tone control, and maybe the value of your tone pot.

I have a TS-9 and I need the tone control almost all the way clockwise, even on an amp set fairly bright, because it's just too muddy otherwise ...

[Chris Goodson]

I'm gonna go with RG on that one.  It seems to me that the value of the resistors is where the main difference could be.
:idea: Transmogrifox has a good point about ultrasonically cleaning the IC's, I've heard that's an important key to coping SRV's sound.

[petemoore]

Before I have the TS untrasonically cleaned, should I drain the cooling oil first?
 I heard Cascade is good for cleaning pots because of it's sheeting action.

[hawkeye2u]

No No NO You have it all wrong!!
Before You do anything You have to make sure that the resistors are polarized the right way around! ie You must make sure that all the colour coding is the same way around of all the resistors, starting from left towards the right, the tolerance colour (gold) have to be to the farthest right, THEN you can drain the oil , then ultrasonically clean the TC, reapply the amperegrease & voltage oils, in that order
Otherwise its a timewaster altogether
Don't forget to twist all the wires going to the pots & switches the same was aswell as that adds tonality