The AM Forum

Metal film resistors are advertised as "quiet".  Really?  That you'd notice?

I've been using them because they are cheap, precise and stable but I'm just finishing a 1946 Meissner 9-1065 home recorder -- makes 78's and 33's and the carbon comps sure look right in there.  Incidentally, what a cool little beast that is even if it seems to have been wired by a monkey.

On better electronics like the HRO-60 that I can't wait to get to, carbon comps seem appropriate in that pristine, not wired by monkeys beauty.

 

Carbon comps can become noisy but it would have to be extreme to be heard with an antenna connected. Its different in a stand alone audio amp.

Many, many NOS carbons have drifted high but Allen-Bradleys are as new at least in my experience. I dont know how reliable the current imports are.

Carl

I've seen wire-wound power resistors act as pick-up coils as most of them are somewhat inductive.

Makes hum & crap where you would not expect it.

73DG

Yes, resistors can create noise and it is above and beyond the KTBR value we all use and know. The noise, referenced as EXCESS noise can be found I believe if you do a search on that term... EXCESS noise in resistors. Carbon R's vs. metal film and the use of of metal film in low noise audio circuits as Carl referenced is preferred.

73' Alan

Yep. Look up EXCESS NOISE is your search engine.

Yes, as do crawfish   ;D

Additional Info:

http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise

http://prola.aps.org/abstract/PR/v32/i1/p97_1

See section 10 of -  http://www.ti.com/lit/an/slod006b/slod006b.pdf

http://www.rle.mit.edu/avbs/publications/journal_papers/journal_16.pdf

Noise Calculator - http://www.sengpielaudio.com/calculator-noise.htm

http://en.wikipedia.org/wiki/Noise_(physics)

A very good description of resistor noise and the various types of resistors can be found here

http://www.eetimes.com/design/automotive-design/4009614/Strategies-for-minimizing-resistor-generated-noise (http://www.eetimes.com/design/automotive-design/4009614/Strategies-for-minimizing-resistor-generated-noise)

Pat

Thanks Pat. Good read.

Thanks, guys. Metal film for audio stages seem like a prudent choice.

Resistors being resistors chant very quietly: "hell no we won't glow".

That Vishay article is excellent back slapping; so what are the competitors up to?

I doubt if our low level modulator stages can benefit from such extremes but Im tempted to open up one of the Vikings and do a before/after test.

Note he didn't give any noise figure for the Vishay miracle resistor.  ;)

Maybe in a low level mic preamp. Most of the data that I have read indicated that the current has to be very low for even the Johnson noise or shot noise to be a significant factor in a conductor. That is not the case in a semiconductor.

Granted the thermal noise inherent to certain types of resistors may be higher than that of others, but doesn't the internal noise of the active devices in the circuit, whether tubes or transistors, swamp out any noise generated by passive elements such as resistors, assuming no arcs or other catastrophic break-down faults in the resistors?

and its gregorian
http://homepage.oninet.pt/862mch/rsetg.htm#prog

It all adds up.

Which seems to be what many folks miss - the cumulative effect of multiple degraded or otherwise-faulty components/stages, if only from aging. Not always noticeable until after the refit is done.

Fortunately, most AM signals don't require the skills of working moonbounce to hear. It's pulling in the weak stations from across the pond etc where it can truly help out.

Still, it's all for naught if you don't employ an oxygen-free power cord and custom, wooden knobs.

MTC...
Shot noise is inherent to Carbon Comp resistors. My understanding is the micro 'explosions" of oxygen under load. I had read somewhere that the British had come up with the idea of "Cracked Carbon" resistors to minimize this potential. In the (guitar) amplifiers I build, I use a simple rule of thumb. Metal film non-inductive resistors in the power supply & screens, and 1 watt carbon composition types everywhere else. I personally cannot tell the audible difference between the two as to sound coloration. I will leave that to the cork sniffer's. The many audio forum threads are rife with much hyperbole on this subject. I also tend to go with the rule that if a circuit calls for a 1/2 watt resistor, I go with a 1 watt where applicable except for screen resistors. Because they act as a fuse, best to keep them in the ballpark so to speak. Just sayin.
 Anytime a screen resistor installed is a carbon type, I promptly replace it with a metal film type. If and when the tube goes nuke, the metal film type will emit a soft white smoke as opposed to a cloud of black carbon that deposits all over the damn place, leaving behind lot's of little mini resistors in places where you can't see. Believe it. Been there done that.
Also, the use of Vishay resistors is a good one as I have had 100% success using their grade of components, never had a problem. The cheap garbage being pawned off onto the world by China is to be avoided, and there is a big presence of "Fake" Allen Bradley carbon resistors flooding the market. Buyer beware. Buy only known stocks of quality components, otherwise this rule ALWAYS applies: Garbage in, Garbage out.
Enough said.

Your buying into the Kool aid more than me.

I have sold over 500 Guitar amp kits in that past 20 years and I use those "garbage" Xicon 1/2 watt resistors - and as far as I can remember I have never had a "bad" one - I use them because C Composition resistors are demanded by the buyers. I don't think there is any difference in those and a Metal film 1% - not in simple tube circuits.

If they work why in the hell would you spend $1.50 for an Allen Bradley resistor?

Chinese Garbage is very relative - Lots of good quality parts come from China - It depends on the specs that they are manufactured to.

For personal stuff I use metal film or metal composition resistor or Metal Oxide  in the larger sizes.

Like I said, MTC.
I don't buy Koolaid. I have had numerous problems with cheap components of no specific brand and to be on point with your post. Xicon isn't one of them. I also do not spend a 1.50 on an AB resistor because I already own 1000's of them, but then again it's always a matter of choice isn't it? As a cautionary measure, I choose not to use a certain off brand component to minimize potential failure. Guess what? Not a single failure in the amps that I have built for my clients. Also to your point, providing an economic and workable product for your clients is a good thing. Many a happy kit builder I'm sure. The point I was making is about carbon composition resistors making noise and my experience with what I have already stated.
Your assumption about me is without merit and beyond the scope of this thread.

Sorry if I may have offended you  - I didn't mean it that way - but I just don't buy in to the NOS resistor NOS capacitor (used Black Beauties) stuff that the many guitar amp guru's sell. I have never heard a resistor have any sound coloration.

I have heard too much BS from the Gurus and the so called experts. I am one of Gerald Weber's hated "engineers' that just don't understand  how old stuff works - as if the laws of physic have changed since 1950. According to Guru Gerald - We just don't understand the physics of tube electronics - this from a guy who suggested that a good speaker simulator was the old voice coil removed from a speaker - Because it was actually from a speaker???

When I build custom amps - and I have built some - I don't use the Xicon CC - I do use new  IRC  C Comps in the signal path and  USA Name brand metal oxides and metal films. When I build them for my son - I use metal film throughout. I doubt that the meatl films have any effect on noise - but I still use them.

Pat

http://www.geofex.com/article_folders/carbon_comp/carboncomp.htm

If you have both why not have a little fun and try them both and see what you hear?

Looks like a call for "oxygen-free" carbon resistors.  ;D ;D


I understand some metallic film resistors are packaged to look just like carbon composition ones.  About the only way to tell the difference is to grind through the body of a sample to see what's inside.  I hadn't heard of counterfeit resistors; I reckon the Chinese (http://www.thisamericanlife.org/radio-archives/episode/454/mr-daisey-and-the-apple-factory) have branched out from Rolex Watches. Most of mine are pull-outs from salvaged equipment or n.o.s., so I'm probably OK.  But I always check the resistance; many of them have drifted in value over the years.

Sometimes if I can't find a specific value of resistor, but run across a drifted-value one that reads the sought-after resistance on the ohmmeter, I'll use it on the theory that over time as the resistance has re-adjusted itself, it has actually become more stable and will hold to its shifted value. I wonder if anyone has actually ever checked that out?

Don't know how it affects radios, but I was rebuilding an old RCA BC-3 audio console, and by swapping out the carbon comps for metal film I was able to reduce the noise some 6db. 

Scott Todd

I remember when the TS-930 was the latest toy on the block and the term "Phase Noise" was added to ham vocabulary.
A USN ham bored to death in a repair depot on Guam decided to experiment and replaced every 1/8W Jap resistor with mil-spec metal film in the synthesizer and reported a 10dB improvement. Then he heard other noise which turned out to be the score of 3 terminal regulators which he replaced with discrete components.

Audiophools think they can hear a bug fart but its just another brain cell dying off.

Since Im not into EME or extreme audio crap I'll stick to plain old common sense until someone proves using real engineering procedures that the old CC's in my BA's are causing me to miss something. At least Im not worrying about whiskers in SMD gear that will kill all the SDR's in a few years :D

I remember as a teenager at my first communications job there was a piece of test equipment to check component noise. I think it was a Heathkit. It worked by applying a B+ voltage to the component (resistor or otherwise) and had a high gain audio amp coupled to let you hear the noise. You could find a resistor that measured within tolerance but would be noisy.

Interesting story about the TS-930.

I'm with Carl - I'll not worry about it unless I have someone that is willing to pay for the extra cost for resistor sound enhancement - For that matter if they want to pay for Black Beauties - I'll use those too but no warranty is offered or implied.

The case of the guitar amp is radically different than something like a phono preamp or a mic preamp for example. In the latter noise is a factor, in the former, not much of a factor.

If you should take a nice classic tube amplifier like say a McIntosh MC-30 or MC-60 and replace all the carbon comp resistors with MF or MO resistors I am pretty confident you will hear a change in the character of the sound, assuming you have high quality gear and source feeding it, and suitably high quality speakers. Of course one's hearing can't be shot either.

There's no doubt that you would hear the change of coupling caps on that amp from old paper caps to new polypropylene. But that's not resistors, or resistor noise.

One can test resistors and see residual distortion, it's been done. The signal path is additive, keep that in mind.

But for ham radio it is clearly not a factor, except perhaps for things like K1MH mentioned...

                            _-_-bear