Carbon composition resistor on mic mod

[nisios]

I think this is my first post in this forum.
And it took a long time until i was able to sign in.
So.....cheers for everybody and many thanks for the tons of really usefull things you all write here.

I was looking for tubes and i saw that people making tube stuff...at least guitar stuff......are using carbon composition resistors. I dont remember where but i think i have read something stating that those resistors interact somewhat with frequency response or something....contrary to carbon film that only add noise or harshness or whatever to the sound.
Im about to do a royer mod to a mic i bought and im wondering if using those resistors is good or bad practice on this application.
I dont know what kind of resistors neumann guys used back in the old days....does anyone know?

 

[CJ]

I would shy away from carbon, might be too noisy for low level mic work.

 

[seavote]

i'll be doing this mod(sometime?) i already have 2,3 meg and 750 ohm carbon resistors. what would you guys,gals, do? didn't some high end older mics use carbon?

 

[mikka]

[quote author="seavote"] what would you guys,gals, do? [/quote]Solder them in, record ..... Replace them with metal film ......record and compare......... The more technical folks would probably sweep a signal through and see how that looked.... check the noise floor ...

 

[JohnRoberts]

[quote author="nisios"]I think this is my first post in this forum.
And it took a long time until i was able to sign in.
So.....cheers for everybody and many thanks for the tons of really usefull things you all write here.

I was looking for tubes and i saw that people making tube stuff...at least guitar stuff......are using carbon composition resistors. I dont remember where but i think i have read something stating that those resistors interact somewhat with frequency response or something....contrary to carbon film that only add noise or harshness or whatever to the sound.
Im about to do a royer mod to a mic i bought and im wondering if using those resistors is good or bad practice on this application.
I dont know what kind of resistors neumann guys used back in the old days....does anyone know?[/quote]

Resistors are generally more ideal components than typical capacitors or inductors. About the only thing that could affect frequency response for any other than wire-wound types will be lead inductance and this can be found in data sheets. A secondary consideration only of possible import for tube circuits is used with large DC voltage drop is excess noise (a voltage caused by granularity or nonuniform resistive matrix). In typical application with only audio voltage present the excess noise is so far below the audio to be imperceptible (by mere mortals like me).

In general metal film is superior for lower excess noise but there have been some examples of carbon comp with good characteristics (it can vary with manufacturer).

In general if you have the right resistor value I wouldn't expect any significant difference.

FWIW in tube guitar amps and most tube circuitry in general, things like crosstalk due to high impedance internal circuit nodes will cause more profound audio impact than resistor type.

JR

 

[seavote]

just sourced the 2 and 3 meg from digikey. i'll go with metal film. these resistors are not going to break me. why skimp.thx

 

[nisios]

Thank you all for your answers.
I think ill do the test.....
Im going to do 2 mic one for me and one for a friend of mine so i'll do one with metal and another with carbon composition.
Whenever i get to the point of testing it ill post some samples.

Well.....i´m not an electronics expert so this my just sound silly, but i hope the carbon composition will affect the tone of the mic and make it more vintage like.

As my goal is for the retro sound i bought a .1uF Orange Drop.

Is this a good capacitor anyway. Even if it doesnt affect the tone in any retro way is it good? Or are there a lot better capacitors for this job?

I bought it because these are widely used in guitar tube amps and i saw one being used in the diy factory web site on a royer moded mic....so.

As for the 1uF i bought a solen fast capacitor. Do you guys like these for the job in this mod?

 

[Gus]

nisios

Do you have access to the Book "The Art of Electronics" 2nd edition?

page 432 look for 1/f

pages 4 to 7


What people might be hearing is the voltage coefficient change R.G. has a nice wrte up

go to www.geofex.com and look for

Using the Carbon Comp Resistor for Magic Mojo

 

[seavote]

whoaa! thats some serious mojo(art of electronics 432). i'm sure i'll build 2 of these so trying both does sound like a good idea now. nice to think my lowly carbon resistors are one with the universe!

 

[nisios]

Hey Gus.
The art of electronic 2nd edition is this book? or is this the first edition? and does i t make any difference? Because im willing to buy it....just dont whant to buy the wrong one.

http://www.amazon.co.uk/Art-Electro...ef=si_1_3/203-5357264-2562358?ie=UTF8&s=books

 

[nisios]

Well for what i read on geofex:
The carbon composition resistors generate distortion on signals.
But those signals have to be swinging in large amounts at almost the limit of the resistor to have any audible effect. For instance a 100v dc with a 150 v ac wave imposed. Near the power limit of the resistor.
And worst....the new carbon composition resistors produce a lot less distortion than the ones made in the old days. Although i found a carbon composition resitor on farnell tha has the same Voltage coeficient or whatever they call it that the old ones.
Anyway, i dont think we will get any mojo other than white noise on a mic.....because we are talking about large dc voltage but a very very small ac voltage imposed. I didnt did the math but i think we are talking about ridiculously small ammounts of distortion and worst, in the royer mod the signal never really gets to pass in series with a resistor so i dont even now if this voltage coeficient thing applyes anyway.
But well....i think ill try it just for fun.

 

[thermionic]

I recently had a chat with an extremely experienced engineer and got a lecture on how carbon comps can generate gross 2nd harmonic distortion prior to failure due to them becoming "diodic"... IIRC, it's due to the lead junction. I have yet to find an explanation of this via the Internet, so I'm open-minded to any evidence.

I was also taught that it pays not to generalise when discussing noise properties of resistors, when I started a debate on carbon comps Vs Metal Film at Dan Lavry's group. Lavry explained that there was a lot of misinformation regarding thermal noise in resistors and that people often overlook current noise.

Lavry approves of this link: http://www.planetanalog.com/features/multimedia/showArticle.jhtml?articleID=177105460

Lavry explained that in many applications, there will be no discernable increase in noise from using carbons, and that it's foolish to generalise in terms of "carbons are noisier than metal film" unless you've studied the application in detail.

To be on the safe side, you could just use metal film exclusively, but I now appreciate that it's not correct to generalise about noise in resistors.

Lavry made me feel stupid, but at least I learnt something in the process!

(I don't think one should be embarrassed to admit being shown the error of their ways by Lavry, or PRR for that matter!)

Justin

 

[JohnRoberts]

[quote author="thermionic"]I recently had a chat with an extremely experienced engineer and got a lecture on how carbon comps can generate gross 2nd harmonic distortion prior to failure due to them becoming "diodic"... IIRC, it's due to the lead junction. I have yet to find an explanation of this via the Internet, so I'm open-minded to any evidence.

I was also taught that it pays not to generalise when discussing noise properties of resistors, when I started a debate on carbon comps Vs Metal Film at Dan Lavry's group. Lavry explained that there was a lot of misinformation regarding thermal noise in resistors and that people often overlook current noise.

Lavry approves of this link: http://www.planetanalog.com/features/multimedia/showArticle.jhtml?articleID=177105460

Lavry explained that in many applications, there will be no discernable increase in noise from using carbons, and that it's foolish to generalise in terms of "carbons are noisier than metal film" unless you've studied the application in detail.

To be on the safe side, you could just use metal film exclusively, but I now appreciate that it's not correct to generalise about noise in resistors.

Lavry made me feel stupid, but at least I learnt something in the process!

(I don't think one should be embarrassed to admit being shown the error of their ways by Lavry, or PRR for that matter!)

Justin[/quote]

What they are calling "current" noise, I learned as "excess" noise, but it is the same thing, a noise caused by the granularity of the resistive substrate in response to current flow. In general this was perhaps an issue in vacuum tube circuits where a high value bias resistor may have significant DC drop across it. In typical solid state circuits this excess noise is mainly present beneath audio signals and very low beneath these signals (from memory something like -90dB or more).

Another confusing tidbit, carbon composition was usually fingered as bad, but I recall a white paper written by a carbon comp manufacturer showing one of their series as superior to carbon films, so when in doubt find a data sheet and don't over generalize.

JR

 

[CJ]

I wonder if there is anything down at the library on this. I will have a gander tonight.

I can see there being a bunch of stuff on impurities,
propagation of electrons thru a carbon substrate, stuff like
this. You can get down to the atomic level on just about
anything. Including grill cheese sandwiches.

I see something interesting with Fenders, LF uses 1/2 watt carbons, which generate
mojo in the plate circuit due to

a) distortion
b) diode effect

Maybe thats why some amps sound better than others, the r
esistors have been cooked. I wonder if Weber undid all the
mojo by recommending 1 watters for pins 1 and 6. And if the amps
sounds good, therre might be a little resistor noise to put up with.