resistor replacement?

[Roy Skinner]

Much is written about replacing caps, but seemingly little about resistors. They work together. As I understand it, the resistors are carbon comp, and absorb moisture from the air. So why aren't they replaced routinely like caps? Yes, this is in reference to my Marantz 2216.
Thanks in advance for the help.

 

[drspiff]

Yes, the carbon comp resistors would degrade if the resistive material was exposed to moisture. However, these resistors have a thin shell that encapsulates the carbon and excludes air.

The likelihood of resistors drifting is pretty low, so there is less bang for the buck redoing resistors. Caps have always been developmentally behind resistors. The technology to make good carbon comp. resistors probably reached maturity in the late 50s or early 60s. Tech for good, stable caps is still maturing.

All this reflects my limited experience with electronics starting in the late 50s. YMMV

 

[jaymanaa]

I change out 90 % at least of the CC I come across. They're noisy, they drift with temp, and just plain suck IMHO. Carbon or metal film is what I use now.

 

[Roy Skinner]

That explains why they are more stable than capacitors. Seems Jay would still recommend testing before assuming they are fine. I don't think we will be starting the resistor abyss.
Are the physically larger resistors in tube equipment less stable, not coated?

 

[Goldie99]

I'm new to the DIY side, but from what I've seen / read / and to a lesser extent heard, I suspect there are some gains to be had by selectively upgrading certain resistors, in combination with the other obvious cap upgrades, and I'd certainly welcome more expert opinions as well.

Some areas & thoughts I'd have would be:

# MM / MC input stage - possibly change to metal films & 1% for lower noise ?
# CC resistors used directly in the signal path - maybe more contentious, and likely to have more impact on sound of the amp - possibly upgrade to carbon films to retain vintage sound ? or more exotic varieties to alter sound characteristics ? Are there any generalities here ?
# hot running voltage dropping resistors in the for example the power supply etc. - change to newer higher wattage equivalents, likely to be a similar size but lower noise - ideally metal film, but being careful to observe any flameproof requirements ?
# voltage divider resistors in the power supply - move to 1% metal film (if not already) ?
# Finally , any fusibles, that tend to drift high - replace like for like (if you can find them - I'm still looking for a fusible 120R/0.5W - anyone ?), or replace with metal film - there seems to be 2 schools of thought here. In any case, be careful to observe flameproof requirements.

As with recapping, I don't think there's any general best or worst recommendations, but rather more specific options for the location & function of the resistor.

These are very much personal thoughts, based on what I've read in a great many forum threads, so hopefully some of the experts will either shoot 'em down, or expand further.....

 

[HypnoToad]

Some people remove metal film resistors in the signal path and put in carbon composition's, the thinking is they have a warmer sound. Each to his own.

 

[bare]

Carbon Comp resistors DO drift with time.
If in Tube gear (high voltages) the drift can be massive.
Lift a lead and meter Every resistor If only for peace of mind.

 

[gslikker]

I have many new old stock ones and many times those never used resistors did drift also.
Usually resistance seems higher.

 

[Vinylcafe]

Well, this is something I have been pondering for a while.
I've been rebuilding the phono section of a Sony TAE 8450.
First all the JFETs then the Bipolars and all the electrolytics.
Noise seemed to be reduced, but it could be wishful thinking.
I am about to replace 80 carbon comps with low noise industrial Vishay metal films.
These things are available in military grade.
This is for both the head amp and equalizer board.
Should be interesting ... I will report back.
I am expecting a further reduction in the noise floor.
We shall see!

 

[Goldie99]

I have tried replacing the usual carbon comp. resistors in a NAD 3020, with 1% metal films (similar to some of Leesonic's restorations), just to see whether it's worth it - and it does reduce the noise floor. I'm not sure I'd recommend it routinely on a 3020 though, it's probably more work than it's worth, unless you're regularly using say an MC cartridge input.

 

[JURB]

Only resistors in certain places in the circuit have any significant effect on the sound. The trick is to know which ones.

 

[Goldie99]

I'm sure that's true, but what are the 'tricks' to knowing which are key ? Anyone have any useful reference links ? or tips ?

Signal path seems obvious, but I assume there are others also - as an example, the ('85) Sony TA-F222ES I'm working on at the moment uses predominantly carbon comp. (except for power resistors / fusibles), including several resistors directly in the signal path and everything on the tone (control) board, but with selected 1% metal films in the MC cartridge input section, and around the NE5532 pre-amp IC's. I assume the (more expensive then ?) 1% metal films were used in those locations specifically for the audio performance.

 

[roger2]

Much is written about replacing caps, but seemingly little about resistors. They work together. As I understand it, the resistors are carbon comp, and absorb moisture from the air. So why aren't they replaced routinely like caps? Yes, this is in reference to my Marantz 2216.
Thanks in advance for the help.

The vintage gear that I have been inside of uses predominantly carbon film. I believe I read somewhere that carbon film superseded carbon comp for general use before 1970. Carbon film resistors do not drift in value like carbon comps are known to do. In fact, I have measured over 100 carbon films removed from my projects and found them to be surprisingly close to their nominal values. I believe that would explain why resistors are not routinely replaced like capacitors are.

I don't know about Marantz though. Are most of the resistors in your 2216 carbon composition? Have you measured any out of circuit? I have read discussions about upgrading resistors in Marantz gear where, like with most things audio, there were dissenting opinions. Some believe that the resistors Marantz used contribute to the "two martini sound" and were opposed to replacing with metal film. I have no opinion here, merely reporting something relevant to your OP.

 

[roger2]

I am wondering if there might be some confusion about carbon comp vs carbon film. Goldie99, I looked at the pics in leesonic's NAD 3020 threads and the before pics show mostly carbon film. Vinylcafe, are you sure those 80 resistors in your Sony TAE 8450 are carbon comp? Goldie99 are you sure that most of the resistors in your Sony TA-F222ES are carbon comp and not carbon film?

 

[roger2]

Only resistors in certain places in the circuit have any significant effect on the sound. The trick is to know which ones.

I'm sure that's true, but what are the 'tricks' to knowing which are key ? Anyone have any useful reference links ? or tips ?

Signal path seems obvious, but I assume there are others also .....

Here is something relevant said by Doug Self in a diyaudio thread (see post #28):

"...The main noise sources in a power amplifier are the input transistors, their emitter degeneration resistors, the current-mirror, and the NFB network... "


I have found a handful of other references to the NFB circuit as a key area and suggestions of upgrading components there.

 

[LWB]

Search AK

There are several other threads covering this topic. My experience changing out Carbon Comps with Metal Films was a revelation for me. I used cheap Xicons, I wonder if 'better' resistors would make for a noticeable difference.

 

[Roy Skinner]

Drspiff, I enjoyed your understatement about your years of experience.
Roger, I would not know a carbon comp from a carbon film if they came up and shook hands with me. My goal is to repair this while disturbing this as little as possible. My friend that first helped me with this started out by removing and testing all of the transistors, but the outputs. We found one of the output transistors had a burnt leg. It was severed. I do not recall which one it was. Gee just might be the problem. The presenting problem was no output from the right channel.
I decided to replace the caps because, well that seems to be what we do.
I just placed an order for the caps from Digi key today. I called and spoke with them, and they were great. That was so much easier than my attempt to order on line with my limited understanding. I ordered a mix of Panasonic FCs, and Nippon Chemi Chons.

 

[roger2]

Roy,

Yes, it would seem that you have found the main issue. Transistors do require 3 good legs to work as far as I know. Most would agree that replacing electrolytic caps (and tantalum, if there are any) would be a good thing to do. IMHO it might be wise to repair the receiver before replacing caps because, if there are complications in the repair, it will be helpful to not be 2nd guessing your new caps installation. Not disturbing other things anymore than necessary, as you mentioned, would probably be a good idea too.

As an FYI here is a pic showing the two common types of carbon resistors and an overview of 3 common types: carbon comp (CC), carbon film (CF), metal film (MF). CC are the noisiest and their resistance value can drift over time. CF are noisy, but less so than CC, and their resistance value doesn't drift like CC. MF are the least noisy of these 3 types, and also do not drift. MF are also more stable in other ways not mentioned here, and are available in tighter tolerances. Most (not all) MF look like the carbon film in the pic, except that their bodies are usually some shade of blue instead of brown.

Unless you have a good reason for changing resistors, i.e. any that may be related to the transistor failure, I would suggest leaving them alone for now as you have a lot on your plate already. Unless...

Does anyone know if there are any fusible resistors in Marantz 2216?

 

[Goldie99]

I am wondering if there might be some confusion about carbon comp vs carbon film. Goldie99, I looked at the pics in leesonic's NAD 3020 threads and the before pics show mostly carbon film. Vinylcafe, are you sure those 80 resistors in your Sony TAE 8450 are carbon comp? Goldie99 are you sure that most of the resistors in your Sony TA-F222ES are carbon comp and not carbon film?

Thanks for the correction Roger2 - don't know what I was thinking !? You are of course correct, the Sony is predominantly Carbon film.

 

[triode17]

Remember something else about Carbon Comps, they drift with voltage across them (aka voltage coefficient) and they drift with temperature (aka temperature coefficient). So even if they measure OK at room temp. using a battery operated Ohmmeter, they may not work well at temperature and with high voltage applied. The only place I still prefer them is for Control Grid or Screen Grid resistors because they have very low inductance. Otherwise, use Carbon Film or Metal Film. The "vintage" sound you want is not in the resistors.