Group Wisdom for carbon resistors

Mike Sweeney

Mike Sweeney

AK Subscriber
Subscriber
So the amp boards in the 2245 I'm working on have several carbon composite resistors and many carbon films. On my donor board just to see, I measured all of the composite carbon resistors and none are "out" of spec but a few are very close to being out of spec ( 5%)

What is the group consensus on replacing all carbon with carbon films since you are in the guts of the board anyways. I don't mind pulling them but I'm a bit torn since I'm not a "rip and replace" guy. Experience tells me that a resistor that has slightly drifted off spec rarely causes an issue. Its when they are turned into a carbon arc or have been abused by repeatedly overheating that they cause issues.

I don't buy into the use of boutique resistors like Sonic Craft for something like this. And I have had personal experience where putting everything exactly on spec caused me issues. The circuit had been designed to allow for slightly out of spec parts and for drift. Without it, the damn thing would never settle down.

opinions?
 
Carbon Composition can and do get noisy over time. My personal preference would be to replace them all, however my customers don't always have the budget for this extra work. My standard methodology is to replace any resistors that measure of of specification or show visible signs of heat stress and anything else I think/know is necessary to make the unit reliable. - Chris
 
Yea I'm not one to change design of a board. I won't even replace a NP electrolytic cap with a film though others swear by it. You need a shoehorn to get those films in. I feel these units sounded great when new so I stick to original design when I can.

I am in no way afraid to use higher quality parts. I use nichicon fine gold rather than elna in the audio path now because I like them better. I have looked at the takmen film resistors and thought the same thing you have but never went down that road. I would stick to carbon cause they are cheaper and it is original design. Not sure what film would do to the sound anyways.

My 2 cents.
 
One thing about carbon comps is they are very susceptible to moisture during storage. I've had some units where the CC resistors tested within tolerance. While other units of the same era were WAY out of tolerance.

I'll test a few to get a general idea of the condition of all the CC resistors. If they are OK I don't go looking for trouble. However if they are in the signal path and I'm feeling ambitious I'll replace them with CF or metal film. And sometimes it depends on the unit, age, general condition, to what level of restoration or upgrade I want to achieve, aka remove vintage sound.
 
Last edited:
Jonstigator said:
I would stick to carbon cause they are cheaper and it is original design. Not sure what film would do to the sound anyways. My 2 cents.
Click to expand...

Cost should should not be a consideration - A 100 ohm 1/2 watt 10% CC cost about 21 cents. The same resistor in CF is about 30 cents (single piece prices)

Originality and sound differences are valid choices that each person should make - Chris
 
Already in progress.. I've swapped out most of them tonight. And several were either right on the line of being out of spec or over the line. They seem to be on the money or off.. very little in between.
 
Mike Sweeney said:
several were either right on the line of being out of spec or over the line. They seem to be on the money or off.. very little in between.
Click to expand...
If you tested a few and there is that much of a variation then it could have been stored in a moist area. If in doubt then replace them with similar CF.

Damn auto correct!
 
Last edited:
my input.

many devices are voiced by their designers, some to the point of only boutique parts.
so, there are four stages in its life.
1. designer's test gear to sound/voice their designs - then they freeze the design
2. manufacturing then fresh out-of-the-box sound
3. 20-60 years later sound
4. re-cap and re-resistor.

I have recapped and re-resistored haflers. the sound changes, in my opinion
(I bi-amp and listen to orchestral symphonies) the sound stage gets wider
deeper, and I attribute a spooky black background to metal films. I've
done this on several DH101s. Hafler eventually went to all MFs for their
resistors in subsequent preamps. the few times I play rock, for visitors,
the telephone ringing in DSOTM startles.

I have looked at lots of Japanese gear and wondered about their continued
use of CC/CF over MFs. I came to the conclusion that folks who love their
Sansuis, Kenwoods, Pioneers, etc love the house sound and it is largely
a result of their voicing and use of components.

I'd keep everything as is, as long as it is safe (caps near rated rail voltages
being one culprit), and within spec, But with caveat of replacing 40YO ecaps.
 
Bob said:
I have looked at lots of Japanese gear and wondered about their continued
use of CC/CF over MFs. I came to the conclusion that folks who love their
Sansuis, Kenwoods, Pioneers, etc love the house sound and it is largely
a result of their voicing and use of components.
Click to expand...
I love my sound but I love longevity even better :) Old drifting CC resistors annoy me when I have to go back in a few years or months to readjust things. The point from Airtime is well taken about how the gear was stored or used. Most of what I get to work on has be .. "sub-optimally" stored :/ between the dirt, hair, water damage, they have not been well treated. I have two amp boards in front of me. One was original for the unit and it has drifting CC resistors all over the board. The replacement board is unknown origins but the resistors were in better shape. So I"m assuming it was better stored over the years. I think the opinion is to replace CC with CMF since none of us really know the history of these 40+ year old parts.
 
Mike Sweeney said:
I love my sound but I love longevity even better :) Old drifting CC resistors annoy me when I have to go back in a few years or months to readjust things. The point from Airtime is well taken about how the gear was stored or used. Most of what I get to work on has be .. "sub-optimally" stored :/ between the dirt, hair, water damage, they have not been well treated. I have two amp boards in front of me. One was original for the unit and it has drifting CC resistors all over the board. The replacement board is unknown origins but the resistors were in better shape. So I"m assuming it was better stored over the years. I think the opinion is to replace CC with CMF since none of us really know the history of these 40+ year old parts.
Click to expand...

I have given this a lot of thought. I almost did this a couple of years ago but worried about sound. These designs are based on a resistor's listed value taking into consideration of a 20% variance. Electronically Carbon films would be more stable with their 1% rating meaning adjustments would need less attention over time. I am not sure if my ear would be able to hear the difference. Furthermore since they are more stable, other components like transistors and caps should last longer (in theory anyways.)

Its not like the specs are getting changed.

I got a bent up 2220b I was gonna use for parts. I might do this to it then do a side by side demo. Hmm:idea:
 
avionic said:
CC ----> trash can:biggrin:
Click to expand...

Although, they have their use.

When I opened up an old Boeing 767 mode control panel to exchange a rotary encoder (I work at flight simulators) I thought about the carbon resistor debates at AK seeing them.
I took a shot of the SMPS or at least inverter components, assuming it was since there is a combination of TO-3 transistor, big diode, and toroid transformer hidden below the circuit card and the pictured parts on top.( I just searched the picture assy number on the internet and indeed it is called a power supply).
Being "Avionic" I presume you like the picturesP1010552.jpg P1010553.jpg ;)

So, here we have some components people hate in audio, being a SMPS or alike circuit, carbon composite resistors, and tantalum smoothing capacitors !

(as the panel enables autopilot/flight director and autothrottle as well, it is nice to know there are two of these supplies in the panel, pilots will have to fly totally manually if the panel fails)
 
Things noticed when you are thinking about them.. the tone amp in the 2245 has all CF resistors.. makes sense.. but the phono pre-amp is mostly CC resistors .. given that CC resistor can be a noisy bunch.. makes you wonder why the engineers would do this or maybe they were overruled and told to cut a cost. " you got your stupid pricy CFs in the tone board, now give it up and cut a corner in the pre-amp that nobody will notice with their dirty and scratched records"...Shame there are no records or interviews that I can find talking about this stuff.
 
I wouldn't think twice about ripping out any kind of carbon resistor and replacing it with a metal film. I built my F5 with Vishay metal films and Ohmite non-inductive wire wound resistors. Resistors are capacitive in proportion to their size and metal films are practically microscopic as well as highly reliable and very quiet. I'm not exactly crying in my beer because my amp isn't sufficiently colored by the components I built it out of. I'm planning to run through the Marantz I'm using and replacing all the resistors with metal films may be part of the plan.
 
You guys are killing me! I’ve never replaced a CC resistor that wasn’t bad and didn’t know I had a problem. Now I’m going to hear noise everywhere until I replace them. Ahhhhhhhhhhhh! :eek:
 
Like others said, CC resistors get noisy and are hydroscopic. There are two places where I wouldn't replace them with MF or even CF;
1. Power supply decoupling where a fault would cause a CC resistor to burn open, an MF resistor will just get red hot and burn through the board.
2. RF circuits and output snubbers where the inductance and self resonance of MF resistors will change the circuit performance.

Tom
 
Some more interesting notes.. I love these rabbit holes ;) I didn't know there were TWO types of noise generated..

Also, price point drove this in the 70s.. now it's reversed. They used CC because they were cheap and they could get away with it in the design for 95% of the time. I doubt in mass produced commercial gear, the audio aspects of CC vs CF were much debated. Not at the price point this gear sold at. The hand made high end gear is a different discussion.

1,000 1K 1/4 watt resistors
CC - .35 each
CF - .17 each.. if you buy 100,000 of them, it's .009 each :eek:


Noise generated by carbon composition resistor
The carbon composition resistor generates two types of noise: Johnson noise or thermal noise and current noise.

Johnson noise
The Johnson noise is the thermal noise generated by the charge carriers due to thermal agitation.

Current noise
The current noise is the noise caused by internal changes in the resistor when current is flowing through it.

Advantages and disadvantages of carbon composition resistor
Advantages of carbon composition resistor
  • The major advantage of carbon composition resistor is its ability to withstand at high energy pulses.
  • The cost of carbon composition resistor is low.
Disadvantages of carbon composition resistor
  • Poor stability: Poor stability is the major disadvantage of carbon composition resistor. Even within a short period, resistance of carbon composition resistor will change rapidly.
  • Generate high noise
  • Low accuracy
  • The most common problem occurred in the carbon composition resistor is water absorption. When the carbon composition resistor observes water, the resistance may increase or decrease
 
You must log in or register to reply here.

Similar threads

misterguitar
"Solid" resistors?
Replies
0
Views
197
misterguitar
misterguitar
dbxdx5
Deposited carbon resistors in Marantz gear
Replies
1
Views
153
Skywatcher
S
airtime
What's up with those cheap 1/4 watt resistors
Replies
6
Views
1K
airtime
airtime
RobinTW
Carbon Composite Resistors do drift over time - Kenwood KA-6000
Replies
17
Views
575
Binkman
Binkman
jstang
Finish Re-Resistoring the 500
Replies
17
Views
2K
jstang
jstang
Back
Top Bottom