carbon comp vs. metal oxide???????

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by sovtekking, Jul 11, 2006.


  1. sovtekking

    sovtekking Supporting Member

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    whats the difference in using carbon comp and metal oxide resistors in the preamp section of an amp and why do most amps use the carbon comps? just wondering if there was a tonal difference or what the deal was. thanks guys
     
  2. Wakarusa

    Wakarusa Member

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    Most current production amps use carbon film and metal film, not carbon comp and metal oxide in the preamp signal path. The significant exceptions are where carbon comps are used to maintain a "vintage" appearance, or in plate loads where their poor stability is useful in tone shaping. Otherwise, the basic reasons for using different types are the usual suspects: tolerance/wattage/voltage ratings, stability, availability, noise performance, and cost.

    Now I'll sit back and drink my coffee while everyone else tells you that you need to use magical high dollar resistors for the elusive perfect tone. Available, of course, from the same vendors who sell capacitors at 10X common pricing ;)
     
  3. scottl

    scottl Member

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    I agree with RG for once..... Of course he is the same guy who says that you CAN'T hear the difference with coupling cap type changes and that ceramic discs make the best couplers.... Yeah... I am a delusional ass who "thinks" he hears major differences when a/bing caps.... He argues this one to the end btw.

     
  4. Wakarusa

    Wakarusa Member

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    One thing to keep in mind when reading that article is that he has focused on the distortion from the resistor's voltage coefficient -- leading to the suggestion to use the lowest wattage part to maximize the distortion. The down side to this is the effect of shot noise and the limitations of voltage ratings.

    Shot noise is a major source of hiss in an audio circuit. It's the noise generated by electrons banging into things and is a function of the cross-sectional area of the resistor. Smaller resistor = more noise. Turns out that lower dissipation rating (wattage) also = smaller resistor. The upshot is that to maximize the resistor distortion you're also maximizing the noise figure -- something CC resistors already have a problem with. (the interesting corrollary, by the way, is that tubes suffer badly from shot noise -- all those electrons smacking into the plate).

    A good rule of thumb for voltage ratings on resistors is the square root of the product of the dissipation rating and the resistance, usually with an upper limit of 250 for a 1/4W part, 350V for a 1/2W part, 500V for a 1W part, etc. So your run of the mill 1/4W 100Kohm plate resistor has a voltage rating of 158V. Endlessly entertaining when you look at modern PCB builds with all 1/4W or even 1/8W plate resistors in a 350V B+ line.
     
  5. Wakarusa

    Wakarusa Member

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    Gotta admit that I was once in that camp as well until someone turned me on to a proper test rig to measure frequency performance in caps. You can actually "see" the midrange smear in a ceramic. What I can't see is a performance difference between an Illinois (less than a buck each), a 715P Orange Drop (around a buck each) and a Sozo (more than a buck each). But we're talkin' resistors here.. not caps. Again.
    I will eventually learn to stay out of these threads :jo
     
  6. AL30

    AL30 Member

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    NO don't do that. That's good information. That's real, measurable info not opinions. Opinions are all over the board and can be debated (and are) for years. You can't really argue with numbers too much. Alright you can but it's more difficult.

    Aren't that Sprauges generally rated better in certain areas than the other caps? Or am I wrong on this? If they are rated higher wouldn't it be better to spend the extra pennies to get a little more "bullet-proofing"? I did just do a quick cap-job for a friends amp and the cheapo caps sounded just fine to my ears. MUCH better than the tired originals.

    Again with the caps. Sorry

    AL
     
  7. Wakarusa

    Wakarusa Member

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    I *think* the ODs are a better cap, but can't back it up with anything empirical. I stock both Vishay/Sprague and Illinois polyprops for builds. Which gets used depends on where it's gonna go (The OD are radial, the Illinois are axial) and my mood at the moment ;)
     
  8. TheAmpNerd

    TheAmpNerd Member

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    The sonic difference between metal oxide and the following
    resistors?

    MEtal oxide (ME) will sound sterile, flat, lifeless.

    Carbon Comps (CC) will sound warmer and fuller.

    Metal Films (MF) can sound overly bright and somewhat sterile.

    Carbon Films (CF) will also sound warmer and fuller.

    Tant Films...(TF) any one?

    TEflon Films...(TEF) any one?


    The latter two are expensive...$3 - $15 each

    vs

    MFs CFs $ .02 - $ 2 CCs

    Depens on what is "most amps". In days of olde, there weren't many
    choices in resistors and CCs were the most offordable for general
    electronic stuff.

    In modern amps on wave soldered circuit boards MFs are most common.
    In modern botique amps it looks like CF and CCs are most common.


    If you have any doubts try them and see.

    Here is some more good stuff from RAs Site:

    http://www.aikenamps.com/

    Tech Info
    Advanced
    Resistor Types


     
  9. scottl

    scottl Member

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    All Dumble amps used high quality milspec metal films on the plates. Hardly sterile sounding amps! The other types do not sound as good in this type of circuit. The milspec metal films add to the characteristic "chirp" in the DUmble od tone IMHO. Fwiw, RN65 Vishay/Dales sound much better to my ears than the cheap Xicon or Koa Speers.

     
  10. Blue Strat

    Blue Strat Member

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    Yes, but he's talking about hearing, you're talking about seeing something on a scope. If you can now hear it ONLY after seeing it on a scope........:D
     
  11. jbltwin1

    jbltwin1 Member

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    Are you guys telling me you can still hear? At our age and playing this stuff for 35yrs, I don't hear much of anything. Seriously, I'm in the "I don't hear squat of a difference" camp. I think if you change ANY circuit and put in resistors or capacitors that are even slightly different in value, that's more likely to change the mojo than anything. I could be all smoke and wet but if you take a handfull of carbon comps and actually measure them, you know you're going to get a lot of different values so if you go from metal oxide to carbon or the other way, I would compare the VALUE change first before I say this or that sounds different. That being said, I do use metal oxide's for plate resistors since they seem to handle the heat better.
     
  12. TheAmpNerd

    TheAmpNerd Member

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    I can only talk from experience.

    A customer brought in a vintage vibroverb amp, which cost him
    over $3500. He brought it to me because it sounded sterile,
    lacked tone, and had no touch sensitivity.

    When I opened it up and took a look inside, I knew why it sounded
    like ****. It had been recently serviced with all metal oxide resistors
    through out the signal and electrical path. It also had a hodge poge
    of vintage and somewhat newer electrolytics. All these had to go
    and replaced with something toneful, that would work and be
    reliable. I did what needed to be done and he is very happy
    with the result.

    Regarding the RN65s, I've also used these too. Regretfully in the
    first preamp stage and the output stage. These sound overly bright
    and brittle. During the winter you can actually hear the triboelectrical
    release (static electricity) when playing. It was annoying as hell.

    I returned a lot of 500 hi-end elecytrolytics under the false belief
    they were defective and arching was occuring during playing. It
    turned out to be the RN65 resistors, not the caps.

    Intermittants are had to track down. Only in the studio or
    living room something occur and not on stage or on the bench.
    Or just on stage and not on the bench. or where ever except
    when you want it to act up.

    Anyone who has experiemented with amps for any length of time
    will tell you similar stories of component problems, tubes, strange
    happenings, etc. You have to isolate and change one thing at a
    time....either sending components back, removing and replacing
    them, sucking it up and eating components that can't be returned.

    It is the nature of the beast.

    It doesn't take much to just do a simple R & R of components.
    Then again you'd be surprised at how sometimes it does.

    But when you want something to sound it's best, that sounds
    different from all the rest, then you have to do something different
    than what everyone else is doing to get there.

    Every amp is different. It is a hell of a lot simpler to
    make a production run then tweak 50 different brands of amps
    and make them all sound better.

    Don't mis interperate what I'm saying either. Production has its
    own unique challenges, with prototypes, suppliers, capital expenses,
    production runs and getting the process stable to where you have
    a fairly consistant batch of amps under one model.

    Any supplier feeding into your production can ruin your run and
    screw your reputation. Ask the guys who do the runs. Then just
    when you get things stable, your supplier runs out of cap A or
    resistor B. You've got thousands of dollars sitting in work in process,
    and have to substitute components. Your running out of your
    credit line and XYZ carrier just lost your shipment or they were
    all damged when acid seeped through the packaging.

    Or

    Something doesn't last like you thought it would and three years
    down the road your replacing power trannies in your production run.

    Or

    Your chassis builder goes out of business and you have to pay
    the start up costs all over again.

    There are endless scenarios and challenges.

    Pick a card,
    any card,
    Every one is a winner!
    Step right up and get it here.

    two will get you three
    five will get you ten.

    Step right up folks,
    every one is a winner.


    :D
     
  13. scottl

    scottl Member

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    I don't doubt you... I can only speak from experience that in the circuit I mentioned, RN65 resistors are best. They were original equipment as well in that particular amp. Fwiw, I have seen many photos of both degooped and ungooped models and they all had milspec metalfilms, most being RN65.......

    Agree on Metal Oxides btw. They are sterile to my ears.

    Scott

     
  14. TheAmpNerd

    TheAmpNerd Member

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    Ditto on that.

    Regarding Dumbles...yes the RN65 might indeed
    sound best in that circuit. Especially with the
    over driven nature and on the plates.

    Feel free to send some pics my way.
    Did Howard use the RN65 Dales or others?

    MFs "can" sound that way, not always.
    When used on the plates as many sites
    and some techs recommend to quiet the
    snap,crackle,pop of aged CCs on the plates.


    :AOK
     
  15. hasserl

    hasserl Member

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    I don't think it was RG who said there was no difference in caps, it was an article he posted on his Geofex site that was written by someone else. And in that article the guy mainly pointed out that it is rediculous to just claim you can hear a difference without doing some kind of controlled testing to support your claim. Anyone can claim anything, without some kind of controlled test how is anyone able to seperate factual data from false? I think that was the main point of the article, along with the request that if you think the guy is wrong, prove it. So go ahead, prove it.

     
  16. scottl

    scottl Member

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    Not sure about that.... I think I have seen RG post on Ampage the exact stuff I paraphrased.

    And I don't need to waste my time proving it... :Devil My ears got me to where I am at both playing and amp tweaking... I trust them! :BEER

    My apologies to the esteemed RG if I have him confused with someone else.... ;)

     
  17. hasserl

    hasserl Member

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    I understand Scott, I feel pretty much the same as you BTW. I've got way too much work on the bench and on the shop floor to take the time to set up a controlled test to prove something I think is true, just to satisfy someone else. Still, it would be cool if someone did it.
     
  18. Wakarusa

    Wakarusa Member

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    I like to understand what I hear (and what I think I hear). I know that some days when I'm playing I think my tone and vibe are spot on, other days I wonder what gave me the idea to pick the thing up in the first place. Same hands, same guitars, same amps, but what I hear is different.

    What I'm after is consistency -- something I know will sound a certain way because I understand why it sounds that way. I've got a queue at the bench as well, but, for me, particularly given the current environment of magically toneful components, it's worth my time to do the research, do the math, do the tests.

    What some folks may not realize is that there's a certain tyranny to all of this horsesh*t. Every time some P.T. Barnum comes out with some new toy my customers come to me with questions ranging from the curious ("what do you know about...") to the offensive ("you don't know sh*t about tone because you don't use...") to the litigious ("you ripped me off because you did/didn't use..."). And if they spend the extra scratch for the magical parts and the amp doesn't sound magical it's my fault, not P.T Barnum's for setting ridiculous expectations.

    But I digress... I'm tired of doing the Cassandra act. If you're convinced you hear it and you can convince others that they hear it too (between different brand resistors no less...) then we're in the realm of faith and you're right -- physics and measurement have no place in this conversation.
     
  19. VacuumVoodoo

    VacuumVoodoo Member

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    +1 :AOK

    We can measure what you can't hear ;)
     

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