For those who truly believe that carbon comp resistors improve the sound of your tube amp, here's your chance:
Electronic Goldmine - Giant Deluxe Box of Resistors
Note: I have bought parts from these people for years. I have no interest in the company other than as a valid parts supplier. I will be placing another order for their rotary encoders, but not for these resistors. I only use carbon comps for grid stoppers and I already have a few thousand!
Some, but not all, carbon comp resistors exhibit a slightly nonlinear resistance / voltage characteristic, and therefore can impart a unique distortion signature.....hence the belief that they are magical.
They are also non inductive and therefore good stoppers on G1 in a tube, and the gate in a mosfet. The use as a stopper does not impart any voltage drop across the resistor, therefore does not create measurable distortion.
Most film resistors use a spiral cut in the film to trim the resistance value, and therefore are slightly inductive. This is usually not an issue except with low value resistors on mosfets, and high Gm tubes with good RF characteristics.....In these cases a stopper can actually MAKE a part oscillate.
Electronic Goldmine - Giant Deluxe Box of Resistors
Note: I have bought parts from these people for years. I have no interest in the company other than as a valid parts supplier. I will be placing another order for their rotary encoders, but not for these resistors. I only use carbon comps for grid stoppers and I already have a few thousand!
Some, but not all, carbon comp resistors exhibit a slightly nonlinear resistance / voltage characteristic, and therefore can impart a unique distortion signature.....hence the belief that they are magical.
They are also non inductive and therefore good stoppers on G1 in a tube, and the gate in a mosfet. The use as a stopper does not impart any voltage drop across the resistor, therefore does not create measurable distortion.
Most film resistors use a spiral cut in the film to trim the resistance value, and therefore are slightly inductive. This is usually not an issue except with low value resistors on mosfets, and high Gm tubes with good RF characteristics.....In these cases a stopper can actually MAKE a part oscillate.
It didn't add any shipping to my purchase of 500 more encoders, so I popped for the $20 box of 1000 resistors.....Will they being me audio nirvana.....I doubt it, but there will be some experiments in a vacuum tube music synthesizer module I'm building.
I just got super excited but upon checkout they want $17 bucks in shipping bringing the total to $38. I use them for guitar amps and effects pedals so I think it's a good deal no?
I may still pull the trigger but I was hoping to pay <$10 shipping.
If they are old can't they soak up moisture?
I may still pull the trigger but I was hoping to pay <$10 shipping.
If they are old can't they soak up moisture?
Fahk it I just pulled the trigger, it's got to be worth at least $40.
I use them for grid stoppers and guitar amps and effects and I think I pay $.80ea. from Mouser.
Thanks George for the heads up on this great deal!!
I will re-post what I get when I get it.
I use them for grid stoppers and guitar amps and effects and I think I pay $.80ea. from Mouser.
Thanks George for the heads up on this great deal!!
I will re-post what I get when I get it.
I do see a problem with this offering. There's no mention of brands. Allen Bradley and Ohmite are the quality ones to have. Other makes like Stackpole, IRC or Clarostat are less desirable IMO. Of course I've only been using resistors for over fifty years so what do I know. And $17 is too much shipping.
Why you got poop on my parade 😉
I am one of those people that can't pass on a sale even if I don't need 300 pounds of peanuts.
I am one of those people that can't pass on a sale even if I don't need 300 pounds of peanuts.
It is often said that a grid stopper should not be inductive, hence people say that CC is best. However, some people deliberately use lossy inductors for stoppers (especially in RF circuits) so I am not convinced.
I use lossy ferrites and primarily metal film resistors (47R - 1K) as stoppers with mostly higher transconductance tube types (6S3P, D3A, 6J9P, 5842) and so far have not had a problem with oscillation in any of my recent designs.
What kind of ferrites do you use, and where exactly do you put it? I've found references both to the "big" VK200 and to very small ferrite rings (as found on SMPS). Merlin Blencowe suggests to put the ferrite ring on the cathode, but on some guitar amp I saw it on the grid.
Great discussion! I would like to know more on the grid stopper debate.
As for CC resistors having "mojo", I think they do bring something to the table. You won't believe how many times I get asked to use CC resistors for builds and restorations. Now I have some stock laying around for less than half the price I would normally pay.
George also plays guitar and builds guitar amps so I get the impression he finds them useful for adding some "mojo" too.
Thanks again George!
As for CC resistors having "mojo", I think they do bring something to the table. You won't believe how many times I get asked to use CC resistors for builds and restorations. Now I have some stock laying around for less than half the price I would normally pay.
George also plays guitar and builds guitar amps so I get the impression he finds them useful for adding some "mojo" too.
Thanks again George!
Yeah, that pi$$ed me off too. They usually offer a flat rate shipping deal in most of their sales. I have been buying their Alps rotary encoders off and on for over a year since I am using them in a modular synthesizer build. The price per encoder is around $1.50 when they are not on sale.
I will buy a bunch of them when I need to order something else and the encoders are $0.50 each or less. Just last month I bought 250 of them for $0.35 each and a bunch of other parts with the total shipping charge of $8. The lowest priced shipping has always been the USPS (delivery in 3 days). Cost per encoder delivered $0.38 each.
Today the encoders were $0.20 cents each, but the shipping on 500 of them was $17! Screw that. I kept changing the quantity and the shipping method until I wound up getting 300 encoders and the box of resistors for $14 shipping via UPS (very slow). Still the lowest cost per encoder yet ($0.25 delivered)
I tamed an unruly pair of 6J7G using salvaged small moulded on beads, on various terminals, some in series with carbon composition resistors (I wanted to keep the L lossy). I now use them on high GM devices, control grids, as an anode stopper when an OPT won't fit close by..
Shipping is $8 anyway so I payed $30 for over 1000 CC resistors, that's less than $.03ea compared to $.8 or more.
Still a good deal.
Still a good deal.
If I had to pick three values of CC resistor for grid stopper use, what values should I buy? And how do I decide which to use in a given situation?
ray
ray
It's my understanding that it's not the inductance but the capacitance and that carbon comps, having lower capacitance are still resistive at high frequencies. . . . but also that lead length and value are more important than cc vs. film and that the main area of superiority for carbon comps is in absorbing high voltage pulses.
There's also lots of references to baking carbon comps to remove moisture. When I first used them (when I thought they were the rule for stoppers) I had a few break when soldering them from moisture turning to steam and popping the body apart.
I don't seem to be having any trouble using metal film and/or ferrite beads for stoppers.
There's also lots of references to baking carbon comps to remove moisture. When I first used them (when I thought they were the rule for stoppers) I had a few break when soldering them from moisture turning to steam and popping the body apart.
I don't seem to be having any trouble using metal film and/or ferrite beads for stoppers.
I'm not so sure about the mojo. I routinely remove carbon comp's from old radios, and most HiFi electronics when REPAIRING them. I believe in using the correct replacement when RESTORING old guitar amps and vintage electronics when there is possible collector value, or owner preference.
Will I chase down vintage bumble bee "tone" caps? No, my old Fluke 407D power supply is full of them......it still works, so I ain't messing with it......I did take the four black plate RCA 6L6GC's out of my Knight Kit power supply and replace them with Chinese tubes. Will those RCA's wind up in a guitar amp? Probably.
There is a possible tonal implication in a guitar amp, especially in the plate circuit of a 12AX7. Most of my guitar amp builds use the generic metal or carbon film resistors I get from Mouser, with the exception of some stopper resistors. If a carbon comp resistor makes a difference in the tone, it will be a very small contribution. Can enough of them in the right places make a difference? Maybe, I have never really tested that theory myself.
I decided to buy the box of resistors so I could do some "resistor distortion" testing of my own. The kind of testing where I can MEASURE some difference. I will believe some of the stories that I have heard when I can see measurable results, done by myself or someone that I can trust.
I recently witnessed a rather convincing and repeatable demonstration that cable direction does matter.....I would have never believed it until I saw it. Granted the differences were at least an order of magnitude below audibility by even the most "golden" pair of ears, but the meter reading was definitely lower in one direction. The difference was more pronounced on cheap cables. Will it make a difference to me?....no it wont.
Early in the design cycle of the Tubelab SSE amp I discovered that the screen stopper resistor would fry when operated well within its power rating when the amp was severely overdriven with an EL34 output tube. The resistors were 1 watt 100 ohm carbon film resistors, two different brands. The amp was being driven by my ADA MP1 guitar preamp set on my "heavy metal racket" patch. A 1 watt carbon comp resistor would not blow no matter how hard I banged on it. The solution was to spec a 2 watt resistor in all SSE builds.
The "Q" of a resonant circuit is dependent on the circuit resistance. More resistance in a series resonant circuit, less in a parallel resonance, lower "Q", less likely for the circuit to oscillate. It was common to make a parasitic choke for the plate circuit in an RF transmitter by winding 8 to 12 turns of wire around (and in parallel with) the body of a low value (10 to 100 ohms) 1 or 2 watt carbon comp resistor. The resistance guarantees a "lossy inductor" which will have a very low "Q".
There was a common oscillator design years ago called the TPTG (tuned plate, tuned grid). Basically a resonant circuit was inserted into the plate path, and another circuit tuned to the same frequency inserted into the grid circuit of the same tube. The interelectrode capacitance in the tube provided the feedback path. This exactly what we are TRYING TO AVOID in a tube amp design. A low value inductive grid stopper can become a resonant circuit when combined with stray capacitance. Usually the resonant frequency is far beyond the operating range of most vacuum tubes. The high GM RF tubes that Kevin mentioned are exceptions!
I have seen the 5842 oscillate in a TSE amp. It was one out of about a dozen 5842's that I tried in the amp. There were four possible solutions, either one would be sufficient to kill the oscillations, but one was not possible in the existing design.
The 5842 has multiple grid pins, wiring them all in parallel with short fat traces leading directly to the stopper will lower the lead inductance, raising the resonant frequency out of the range of the tube. Too late to change the existing PC board.
The grid stopper was a 1K ohm metal film. A 4.7 K metal film was ok. So was a 1K carbon comp. So was a 1 K metal film with a small ferrite bead slipped over each lead. The ultimate oscillation killer was applied to that amp. I used a 6.2K ohm carbon comp resistor with a ferrite bead on each lead. Done, you can't make that amp oscillate even when trying.
However, connecting high Gm mosfets directly to the grid of a high Gm tube, or worse in between two of them, is still a recipe for a TV jammer sometimes, despite all the efforts I have thrown at it.
I got a big box full of ferrite beads at a surplus shop maybe 20 years ago. They are about 1/8 inch long, and 1/8 inch in diameter, with a hole just big enough to fit over a TO220 mosfet lead. I have no clue what kind of ferrite they are.
They create a lossy inductor out of a piece of wire that is passed through the hole. This is the principle behind the interference suppressors on SMPS cables and computer video cables. We used to use VK250's in solid state transmitter designs back in the late 70's. Don't see them much any more.
Other than the tube / mosfet hybrid creations I am working with, I have only needed to use a stopper resistor on the grid of a tube, or the gate of a mosfet. Some RF tubes like the 6146 and the 807 may benefit from the aforementioned lossy choke in its plate circuit. I have been known to loop the plate lead of a sweep tube through a bigger ferrite bead when working with a sloppily constructed breadboard just for good measure, but I'm not sure if it is really needed. For any tube capable of RF operation, you want the "common" element well grounded. This would be the cathode in most designs, the plate in a cathode follower (well bypassed to ground), and the grid in a grounded grid amp. Having any resonant circuit in the common element IS the recipe for an oscillator.
I restore lots of old Fender amps and what not and yes I usually use carbon film to replace noisy plate loads, 1 watters work best for me. If someone wants CC then they get CC. I made several 5E3's and 18 watt Marshalls and one time used all CC resistors, I swear it was the best sounding amp I made. I have a preamp I made (typical fender style) and I might gut it and use all CC types to test this out.
I am very interested in your measurements on distortion of CC vs carbon or metal film when you get around to it. Like you said on resistor might not do it but cascading high gain stages it could multiply the effect maybe?
I just read Small Signal Audio Design by Douglas Self and he had a good section on resistors that included distortion measurements of thick film vs. thin film resistor (showing substantially higher distortion in thick film) that I thought was very interesting.
He did state that carbon comps had a very high voltage coefficient, typically more than 300 ppm and he has a table that shows how much distortion that would create at a couple of signal levels, but there are no direct measurements of carbon comps graphed in the book.
He says that he covers resistor measurements in more depth in his active crossovers book but I don't have that book so can't confirm.
This seems to imply that some inductance may help a resistor to act as a good stopper. Hence no need to avoid inductance in the resistor.Tubelab_com said:
The carbon-composite resistor (CCR) is a very poor technology that not only offers no magickal mojo, but instead delivers distortion and noise.
All of the data needed to make an informed decision is available from manufacturers and learned tomes, and often by simple internet searches. I'm not going to footnote all of this because that's way too much work and I'd be here all night.
A CCR is made from a mixture of clay (non-conductive) and carbon black (conductive). The ratio determines the resistance; more carbon = less resistance, less carbon = more resistance. (This mix also tends to act like a jumble of diodes which causes peculiar properties. This is similar to the varistors made from copper oxides. That work, BTW, lead to Bardeen and Brattain inventing the transistor.)
The concoction is then bound together and covered by phenolic, which is not a very good seal, and degrades with time and heat. Those awful brown circuit boards that break and delaminate when desoldered? Yup, that's the stuff. Well, it's the old phenolic made using formaldehyde, as modern epoxy resin is also a phenolic resin and doesn't similarly degrade.
Physical Stability in the Presence of Moisture
The CCR, by virtue of its very construction, is not stable with moisture.
The reason for instability is that the clay is hygroscopic, and moisture affects the characteristics by swelling the structure and altering the grains. The phenolic used to seal the resistor is permeable and degrades over time. (Just as it does for ceramic capacitors, and barium titanate, BaTiO3, is hygroscopic as well. Look it up if you don't believe me.)
I've seen numbers that normal humidity changes can affect the value by 3% and high humidity can affect it by 10%. Most resistors not stored in a climate-controlled chamber are going to have value drift.
Measure these vintage magickal resistors and see what you get.
Measure the resistors in an actual amplifier that has been sitting around for fifty years and see the difference.
I've heard stories from radio restorers about routinely finding values varying from the banding by 15% to 50%, sometimes more.
Voltage-Dependent Characteristics
The value of a CCR fluctuates with applied voltage:
So, by its physical properties which cause a varying resistance with applied voltage, the only place CCR could possibly matter is as a plate load. Anyone who tells you anything else is (at best) mistaken or (at worst) self-deluded.
The Erie Resistor Company found differences of a few percent over several hundred volts. Others found 0.025% / volt for values below 1 MΩ and twice that, 0.05% / volt, for values above 1 MΩ. What that means, in practice, is at, say, 300 V the values below 1 MΩ would have about 7.5% drift and those above 1 MΩ would have about 15% drift.
That is substantial over the entire swing. Hence the comment about plate resistors with wide voltage swings. This effect won't show up at low voltages. So all those CCR solid-state guitar amplifiers running with 35 V (or lower) rails? Nope. No benefit from distortion.
Beyond the resistance fluctuations with voltage are physical problems with CCRs.
Heat-Dependent Characteristics and Vulnerability to Heat Damage
CCRs are damaged by high operating temperature or even by the soldering temperatures.
Ambient temperature of 70º C is sufficient to cause a temporary drop of up to 15% in value. Soldering temperatures may cause a permanent decline in resistance of 2 to 3% drop. By increasing the bonding between the carbon beads, high heat may permanently reduce inter-bead resistance . This is why resistors in high power applications—voltage droppers and dividers, and loads and current limiters—tend to easily go out of specification and may catastrophically fail from runaway.
Inductance
The inductance of a metal film resistor is trivial at audio frequencies. Enough said on that.
Dubilier, however, has presented data which showed it varies with wattage, and is:
So the inductance of the metal film, btw, is insignificant at audio frequencies, but does matter at high-frequency RF.
Wire-wound resistors are completely different, of course, as their inductance can and often does matter at audio frequencies.
For those of you who care, the high Equivalent Series Inductance (ESL) causes a wire-wound resistor to act as an inductor, resulting in cause large input-signal phase shifts, and may superimpose a ringing signal. A wire-wound can also act as an antenna, receiving noise broadcast elsewhere in the amplifier. They are problematic for anything but power supplies, and there need to be decoupled and their properties accounted for.
Noise and Harmonics
Don't get me started on Johnson noise and harmonic distortion from resistors. You can look that up, too.
These resistors are notoriously noisy with waterfall noise. Hafler experienced this with the Dynaco PAS and couldn't figure out where it came from. Neither could Hegeman. It turned out to be noisy resistors. See: hafler.com/pdf/interview-with-hafler.pdf
Conclusion
People like to talk about magical components because it makes them feel they have a special relationship with their equipment and possess secret lore and knowledge that others somehow lack. The adherents of the CCR repeat half-truths and outright nonsense they've read on the interwebs as if it were undisputed, verified, and well-accepted fact until it becomes dogma. But that doesn't make these beliefs true, it just makes them misinformed and incorrect.
Everything I've written can be verified by looking at datasheets, asking manufacturers, or reading the papers and books on the subject. Google is your friend on this.
That won't convince any of the CCR fans from taking issue with my analysis, of course, because it's better when inexplicable magic remains in the HiFi world, yours for a few dollars more. Particularly when the perceived value of a resistor is directly proportional to its cost.
The core of the issue is it doesn't matter what the purported "benefit" is as whatever effect is present is distortion. It must be distortion, i.e., an inaccuracy in sound reproduction. Deliberately putting distortion into an amplifier is fine (else we'd have no electric guitar sound) but call it what it is: distortion.
Now, some distortion, like second harmonic, makes an amplifier sound warmer and nicer. This explains why bypassed cathode bias can be perceived as "better" than unbypassed. (Yes, the feedback is eliminated but, again, the capacitor introduces all sorts of reactance, phase shifts, etc. and it causes distortion.) Again, not all distortion sounds bad.
The takeaway is that if you don't want magic and hearsay, metal film is a better technology for every single use in an audio amplifier. Not carbon film, that's bad, too. Metal film is usually made from nichrome or tin oxide.
If metal-film resistors existed at an affordable price when the amplifiers were being designed and built by the Olde Ones they would have been used instead of the CCR. But they weren't available, and so weren't used, and today we hear stories about properties that aren't borne out by physics, electrical engineering, or testing. But the truth—carbon-composite resistors add distortion—doesn't matter if someone needs to be able to show off how they were so smart and skillful that they put in magical resistors for the greatest sound ever.
All of the data needed to make an informed decision is available from manufacturers and learned tomes, and often by simple internet searches. I'm not going to footnote all of this because that's way too much work and I'd be here all night.
A CCR is made from a mixture of clay (non-conductive) and carbon black (conductive). The ratio determines the resistance; more carbon = less resistance, less carbon = more resistance. (This mix also tends to act like a jumble of diodes which causes peculiar properties. This is similar to the varistors made from copper oxides. That work, BTW, lead to Bardeen and Brattain inventing the transistor.)
The concoction is then bound together and covered by phenolic, which is not a very good seal, and degrades with time and heat. Those awful brown circuit boards that break and delaminate when desoldered? Yup, that's the stuff. Well, it's the old phenolic made using formaldehyde, as modern epoxy resin is also a phenolic resin and doesn't similarly degrade.
Physical Stability in the Presence of Moisture
The CCR, by virtue of its very construction, is not stable with moisture.
The reason for instability is that the clay is hygroscopic, and moisture affects the characteristics by swelling the structure and altering the grains. The phenolic used to seal the resistor is permeable and degrades over time. (Just as it does for ceramic capacitors, and barium titanate, BaTiO3, is hygroscopic as well. Look it up if you don't believe me.)
I've seen numbers that normal humidity changes can affect the value by 3% and high humidity can affect it by 10%. Most resistors not stored in a climate-controlled chamber are going to have value drift.
Measure these vintage magickal resistors and see what you get.
Measure the resistors in an actual amplifier that has been sitting around for fifty years and see the difference.
I've heard stories from radio restorers about routinely finding values varying from the banding by 15% to 50%, sometimes more.
Voltage-Dependent Characteristics
The value of a CCR fluctuates with applied voltage:
* If the voltage is relatively constant, which is the case for most resistors in an amplifier (dividers, bias, and the like), the resistor is just constantly out of specification, with the difference being a function of voltage and usually trivial for low (< 100 V) voltages.
* If the voltage is fluctuates between high and low values, the resistor offers non-linear behavior across the range. Aha! In the words of RG Keen, we have resistor distortion!
This is where the putative magic comes from.* If the voltage is fluctuates between high and low values, the resistor offers non-linear behavior across the range. Aha! In the words of RG Keen, we have resistor distortion!
So, by its physical properties which cause a varying resistance with applied voltage, the only place CCR could possibly matter is as a plate load. Anyone who tells you anything else is (at best) mistaken or (at worst) self-deluded.
The Erie Resistor Company found differences of a few percent over several hundred volts. Others found 0.025% / volt for values below 1 MΩ and twice that, 0.05% / volt, for values above 1 MΩ. What that means, in practice, is at, say, 300 V the values below 1 MΩ would have about 7.5% drift and those above 1 MΩ would have about 15% drift.
That is substantial over the entire swing. Hence the comment about plate resistors with wide voltage swings. This effect won't show up at low voltages. So all those CCR solid-state guitar amplifiers running with 35 V (or lower) rails? Nope. No benefit from distortion.
Beyond the resistance fluctuations with voltage are physical problems with CCRs.
Heat-Dependent Characteristics and Vulnerability to Heat Damage
CCRs are damaged by high operating temperature or even by the soldering temperatures.
Ambient temperature of 70º C is sufficient to cause a temporary drop of up to 15% in value. Soldering temperatures may cause a permanent decline in resistance of 2 to 3% drop. By increasing the bonding between the carbon beads, high heat may permanently reduce inter-bead resistance . This is why resistors in high power applications—voltage droppers and dividers, and loads and current limiters—tend to easily go out of specification and may catastrophically fail from runaway.
Inductance
The inductance of a metal film resistor is trivial at audio frequencies. Enough said on that.
Dubilier, however, has presented data which showed it varies with wattage, and is:
0.25W, 100 Ω = 0.0007 µH
0.25W, 1M Ω = 0.06 µH
1W, 100 Ω = 0.017 µH
1W, 1M Ω = 2.0 µH
Those values are MICRO (µ) henries, not milli (m) Henries. That's a factor of 1,000 smaller than a mH. (1,000 x 1,000 = 1,000,000)0.25W, 1M Ω = 0.06 µH
1W, 100 Ω = 0.017 µH
1W, 1M Ω = 2.0 µH
So the inductance of the metal film, btw, is insignificant at audio frequencies, but does matter at high-frequency RF.
Wire-wound resistors are completely different, of course, as their inductance can and often does matter at audio frequencies.
For those of you who care, the high Equivalent Series Inductance (ESL) causes a wire-wound resistor to act as an inductor, resulting in cause large input-signal phase shifts, and may superimpose a ringing signal. A wire-wound can also act as an antenna, receiving noise broadcast elsewhere in the amplifier. They are problematic for anything but power supplies, and there need to be decoupled and their properties accounted for.
Noise and Harmonics
Don't get me started on Johnson noise and harmonic distortion from resistors. You can look that up, too.
These resistors are notoriously noisy with waterfall noise. Hafler experienced this with the Dynaco PAS and couldn't figure out where it came from. Neither could Hegeman. It turned out to be noisy resistors. See: hafler.com/pdf/interview-with-hafler.pdf
Conclusion
People like to talk about magical components because it makes them feel they have a special relationship with their equipment and possess secret lore and knowledge that others somehow lack. The adherents of the CCR repeat half-truths and outright nonsense they've read on the interwebs as if it were undisputed, verified, and well-accepted fact until it becomes dogma. But that doesn't make these beliefs true, it just makes them misinformed and incorrect.
Everything I've written can be verified by looking at datasheets, asking manufacturers, or reading the papers and books on the subject. Google is your friend on this.
That won't convince any of the CCR fans from taking issue with my analysis, of course, because it's better when inexplicable magic remains in the HiFi world, yours for a few dollars more. Particularly when the perceived value of a resistor is directly proportional to its cost.
The core of the issue is it doesn't matter what the purported "benefit" is as whatever effect is present is distortion. It must be distortion, i.e., an inaccuracy in sound reproduction. Deliberately putting distortion into an amplifier is fine (else we'd have no electric guitar sound) but call it what it is: distortion.
Now, some distortion, like second harmonic, makes an amplifier sound warmer and nicer. This explains why bypassed cathode bias can be perceived as "better" than unbypassed. (Yes, the feedback is eliminated but, again, the capacitor introduces all sorts of reactance, phase shifts, etc. and it causes distortion.) Again, not all distortion sounds bad.
The takeaway is that if you don't want magic and hearsay, metal film is a better technology for every single use in an audio amplifier. Not carbon film, that's bad, too. Metal film is usually made from nichrome or tin oxide.
If metal-film resistors existed at an affordable price when the amplifiers were being designed and built by the Olde Ones they would have been used instead of the CCR. But they weren't available, and so weren't used, and today we hear stories about properties that aren't borne out by physics, electrical engineering, or testing. But the truth—carbon-composite resistors add distortion—doesn't matter if someone needs to be able to show off how they were so smart and skillful that they put in magical resistors for the greatest sound ever.
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