Carbon Comp vs Carbon Film

[ajeffcote]

Hello everyone.While I'm not totally new to this forum,it has been a long time since I have hung around.Hurricane Ike did a number on my house,and we are still displaced,in an apartment with little room.We moved out in sucha hurry that I can't even find my soldering iron.
So,I have not been able to tinker with the amp I built earlier this year.It is an Allen Accomplice,in which I used all the supplied components,no substitutions.Resistors in the signal path are carbon film.
The amp sounds pretty good,very good in some ways.But when playing clean,the tone is a little on the cold side,kinda brittle.
I have tried different new manufacture tubes.Currently in the amp are Tung-Sol 6L6GC STR's,a Sovtec 5AR4,and a combination of Tung-Sol and JJ 12AX7's.Just ordered some NOS(Brimar 6V6GT's,JAN Phillips 5AR4,Mullard 12AT7's for the verb and PI,and an RCA 5751 Blackplate for V1.
Also am running an Eminence Red,White and Blues speaker
I hope that these new tubes will improve the tone to my taste,but I can't help but think that carbon comp would sound smoother than the carbon film.
What do you think?

[Bruce / Mission Amps]

....
I hope that these new tubes will improve the tone to my taste,but I can't help but think that carbon comp would sound smoother than the carbon film.
What do you think?

Very sorry to hear about your loss...
As far as the question above... no. Snake oil stuff. You have some other minor tuning-tweaking issue.

[stokes]

I think the NOS tubes should make a big difference,especially the 5751.To me,most current production tubes are less than ideal,and I have found most JJ preamp tubes to be on the harsh,cold side.I would wait till you get the new tubes before you start changing components,they should make a big improvement.

[ajeffcote]

Ordered the tubes from KCA on Monday,and received them yesterday.Now that is prompt service!
The amp does sound better now.Not only warmer,but with more articulation in the mids and a sweeter top end.Plus,the larger bottle on the recto and the black Brimars just look cool.

[Robert M. Martinelli]

+1 vote on Bruce's and stokes' reply.

I would only like to elaborate a little....

The two main issues I can think of when I choose which resistors to use are their tolerance and their inherent noise - the other issues, ( e.g. inductive behavior in wire-wound resistors ) are "snake oil" issues ( Thanks Bruce ) at the frequencies of our interest ( audio ), and the chances to hear an audible difference are practically nil.

As to the tolerance, while it is true on tube amps tolerances of 10 or 20% are pretty normal, I like to get my RC network to work where I want them to, so I like to use precision resistors ( and caps, when I'm lucky enough to find 'em ).
I know there are other variables to be taken into account but nonetheless this way the chances to have a circuit working closer to the design values are greater.

As to the noise issue, noise across a resistor is mainly thermal noise, expressed by the equation : Nf=Sqrroot(4KTR), where K is the Boltzmann constant, T is the resistor's absolute temperature in degrees K and R is ( quite obviously ) the resistor's value.

The Boltzmann constant cannot be changed ( unless you've the power to re-define physical laws in this part of the universe ), the resistor's value will have to be the designed one, so, to lower resistors' noise, we can only lower the resistors' working temperature by over-sizing them ( e.g. using half watters where a 1/8 watter would be fine and 1 W resistors in place of 1/2 W ones ).

All in all, I think it to be far more important to get the "right" tubes for the kind of sound you're after....as I already said in another post, sometimes we DON'T want fidelity.

Maybe the best advice I can give is not to over-analyze it and simply trust your ears....

Hope this helps

Best regards

Bob

[stokes]

"....as I already said in another post, sometimes we DON'T want fidelity."
Absolutely,fidelity is for the HI-Fi guys who want pristine,undistorted audio reproduction.Even at the cleanest settings,we still want a certain amount of "oomph" for want of a better term.Like our power tubes always sound better with a little imbalance in a push-pull output,where for Hi-Fi puposes you want an absolute match as well as a balanced PI.We dont necessarily want linearity.An absolutely clean amp sound is desireable to some jazz players,but they get a certain amount of warmth from the big box guitars they use,if you use the same amp with a high output pickup in a solid body,you are gonna get a very harsh,brittle tone.

[tubeswell]

If you go to R.G.'s site, he has a hypothesis about where carbon comps are most likely to make a difference - i.e. "positions in the amp that have both high DC voltage and wide signal swings".

http://www.geofex.com/

I built a 5E3 clone thingy with CCs throughout - it sounds good (but was that as much (or more) to do with the other bits and pieces and the way I built it? Hmmm...)

[ajeffcote]

Thanks for all the advice.I like the way it sounds now,with the NOS tubes,so much that I have lost interest in changing anything about the amp.But when I build my next,I am going try both CC and CF.Maybe record the amp both ways and A/B the results.Sounds like fun and a worthy contribution,although it will still be an opinion.
Very interesting thoughts on where the CC would do the most good,and the sweetening of the note is exactly what I am looking for.
If all goes well,we will be back in our house around the 1st of February,and I can set up shop again.I am very ready to start another build.

[Bruce / Mission Amps]

Thanks for all the advice.I like the way it sounds now,with the NOS tubes,so much that I have lost interest in changing anything about the amp.But when I build my next,I am going try both CC and CF.Maybe record the amp both ways and A/B the results.Sounds like fun and a worthy contribution,although it will still be an opinion.
Very interesting thoughts on where the CC would do the most good,and the sweetening of the note is exactly what I am looking for.
If all goes well,we will be back in our house around the 1st of February,and I can set up shop again.I am very ready to start another build.

I think that is an excellent idea and then you can be the judge as to whether or not you think there is any real merit in CC vs CF resistors.
I for one do not think there is much, if any at all, mojo in this but I read frequently on the web where a builder is very pleased with changing out all the resistors.. one way or the other! ha ha.
I do have to relate a quick story though... I built a couple identical 40 watt Crusader reverb amps a few years ago and had a number of players try them out.
They were as identical as I could get them by measuring everything and making sure all the resistor and capacitor components of both amps were as close to the the same as possible. Not hard with decent test equipment.
One amp used all, 5% 1/2w carbon comp resistors (pre measured by me to be sure they were correct, and this actually took a little time) and the other amp used all 5% 1/2w carbon film, which were very accurate and needed no fiddling/tweaking... result, none of my many customers could tell the difference between the two as long as they had the same speaker connected.
But, with all those variables being as equal as possible, I did find that power tube idle current and swapping the first preamp tube with any other random tube made more of a difference in the subtle tonal differences of both amps then any other thing except the speaker choice.
And sometimes the cheap generic preamp tubes sounded as good as my +$50 NOS tubes!
Here's the other rub and what was really annoying to me, my brother Lew (who is the real pro guitar player in our musical family) loved both of the amps but would pick the damn carbon comp resistor amp out every time... no matter what tubes or speaker, even though he didn't know why nor could he quantify it! Sheesh!!
So with that, all I can only say is you must try it yourself but don't be disappointed if you don't hear any difference or if you actually like the carbon film amp better.
But more importantly, do not narrow your focus to just the CC vs CF argument as the real tonal differences will be found more in the items I described above.... and the power tube idle current effects the B+ to the rest if the amp so keep that in mind too when final tweaking is done.

[tubeswell]

soldering CCs

Just a wee tip - I found out the waster's way that CCs don't take much heat with a soldering iron to permanently drift them off their rated resistance. So keep your tip clean and tin the eyelets/turrets first etc so you don't spend too much time heating up the leads

[camnicklaus]

how about metal film vs CC or CF?
I've heard that they are quieter, but as to their "tone"???
I built a weber 5e7 with the components that came with it (metal film resistors) and it was pretty quiet even though my wiring and grounding was very novice. As I've been trying mods out I've been swapping in CC's and I could swear it has gotten a bit smoother sounding, course it could be any given mod as well...

[ajeffcote]

Just a wee tip - I found out the waster's way that CCs don't take much heat with a soldering iron to permanently drift them off their rated resistance. So keep your tip clean and tin the eyelets/turrets first etc so you don't spend too much time heating up the leads

I was afraid of that,with all components actually.I use an alligator clip as a heat sink for extra insurance.
I have a little experience with CC resistors.I gutted my Deluxe Reverb Re-Issue and rebuilt it using a turret board,new transformers,new speaker and premium components including CC resistors.I must say that it sounds almost too good for me to have done it,considering my inexperience.So much better than it's original form.And that is with cheap tubes in it.
Whether or not the CC's made it better I don't know,because I changed everything at once.But it is a killer now!

[ajeffcote]

how about metal film vs CC or CF?
I've heard that they are quieter, but as to their "tone"???
I built a weber 5e7 with the components that came with it (metal film resistors) and it was pretty quiet even though my wiring and grounding was very novice. As I've been trying mods out I've been swapping in CC's and I could swear it has gotten a bit smoother sounding, course it could be any given mod as well...

Although I can't compare the noise level of my CC vs. CF or MF in my DRRI,it is a very quiet amp,very little hiss.I did research lead dress recommendations before I jumped into it.
And it is very smooth sounding.