Choosig resistors thoughts anyone

[miltown]

Hey all . Going to start building an amp. I was wondering thoughts on choosing the type of resistors. Carbon comp, Metal film , carbon film ,composite?
Thanks.

Paul

[mozwell]

carbon can get noisy (it has happened to me, i had to replace 1W carbon resistors with metal film, as i got nopise from the first gain stage anode resistor), so i would just use metal film everywhere. Anode resistors should be 1W types (for the voltage rating). larger wattages ceramic power resistors.
Otherwise standard 1/2W metal film for everything else.
i assume this is a valve amp.

Others here with far more experience than me may have other suggestions.

[catalin gramada]

Everything works. Important are parameters like power, voltage rating etc. more than type. Acording to different schematics could be some 'nevralgic points' which request some types due to noise reduction or thermal derive for instance. Build with what you have and optimise just if is necessary

[miltown]

Starting to purchase parts so I'm deciding do I go to online electronic stores (not naming names don't want to advertise ) or do I go to a "tube amp" web site for the pricey stuff.

[Enzo]

I buy resistors from Mouser. Nothing against Digikey or others, I just usually shop at Mouser.

I use amp stores like tubesandmore.com for amp specific stuff the big parts houses don;t sell. Like 500v e-caps, tubes and tube sockets, a lot of the pots we use, chokes and transformers. There are other similar stores online.

[pdf64]

When considering what voltage a component is subject to / power dissipated, factor in all conditions, not just idle.
So the initial power up (eg all caps are effective shorts until they charge up), small signal, large signal and overdriven.
So a HT dropper that only has 20Vdc across it at idle may momentarily have several hundred V at power up, and continuously a hundred V when overdriven.
Some ceramic block resistors may only be rated for 100 or 200V and may eventually fail after a few switch on cycles

[R.G.]

Choosing resistor types has been pushed to the forefront of amateur electronics by the pressure to advertise and sell. There are real differences in the performance of different resistor types, but these get obscured in marketing and advertising. Here are some real things to consider.

Cost; resistors have become quite cheap, to the point that their cost can usually be ignored in the overall cost of a build. The exception to this is if you listen to the advertising schpiels that tell you that you can get a truly golden sound by using their gold-plated resistors. Resistors in the Golden Age of amplifiers were nearly always carbon comp, not because it sounded especially good, but because it was cheapest. Only special situations where carbon comp just couldn't live through the application got anything but carbon. We have the luxury today of having machines that will make metal film, metal foil, wirewound, ceramic, metal oxide, and other types that are very nearly as cheap as carbon comp.

Resistance range; not all types of resistors are made in a wide enough range of values. It's hard to find a megohm wire wound, as an example.

Resistance accuracy and drift; it used to be that it was difficult and expensive to get accurate resistors. A lot of the Golden Age amps were built with resistors no more precise than 10% - or even 20%! - when they were new. The technology to make them accurately and identically didn't exist, and it was too expensive to have a human sort them out. The cheapest and most widely used resistors were carbon comp, which are made by making up a vat of carbon granules and what amounts to special purpose glue, then filling up phenolic tubes of the mixture and letting it set up. This isn't a great choice for accuracy. It also drifts a lot, as the glue inside gets heated repeatedly and drifts. The metal resistors - wirewound, film, foil, etc. - have minimal drift with time.

Noise; all resistors generate thermal noise. It's the way the universe works. Resistors that are not carbon comp have pretty predictable thermal noise, depending on the resistance and temperature. Carbon comps have excess noise, greater than the noise that the resistance and thermal noise would predict. Sometimes MUCH greater.

Distortion; Resistors have distortion on their own. It comes in the form of what the data sheets call "voltage coefficient of resistance". This means that the resistance is not fixed, but changes with the voltage across the resistor. This is negligibly small for all resistance types except carbon comp. This is in fact the origin of the myth that "carbon comp resistors sound better". Carbon comp resistors can generate 1-2% of primarily even-order distortion. This can sound quite pleasing to the human ear, and is not generally noticeable as distortion. However, this subtle sweetening is only noticeable when the signal across the resistor varies by more than 70V or so, and doesn't really get going until the signal across the resistor is in the 100V plus region. That means that carbon comp in an amp doesn't generate "better TOOOONE!!" as the advertising says, except in the last stages driving the output tube grids. Other places, especially the input tube, they generate no good distortion and only excess noise.

Voltage rating; Resistance materials and construction can withstand varying amounts of voltage. This is based not only on the power generated in the resistor with higher voltages across it (i.e. P= V²/R) but just the electrical field working on the material. Get resistors that have ratings at least as high as you can reasonably expect the resistor to have across it.

Power and pulse power rating: the pros do this by computing the power generated in each resistor, then doubling that, and buying resistors at that 2x rating, to allow for temporary power peaks and to keep the resistor's surface temperature down. Most resistors reach their power rating when the temperature of their surface hits 100-200C. Not a good idea in a design unless you just have to do it and have special cooling. Carbon comp and MOX resistors have higher pulse power ratings than other types. If you have to worry about pulse power rating, you have a lot more reading to do than you find on diy amp forums.

My solution? Compute the power expended in each resistor, use metal film for input stages for low noise, and metal film wherever power lets me, use carbon film in later stages, and MOX where more power is needed.

[miltown]

Thanks for the wealth of info here . Am I going off topic if I ask about caps. Like getting Orange drops as opposed to those standard film caps and ceramic disks.

[R.G.]

Let me redirect this to a higher level topic. The internet is teeming with things designed to get you to pay extra for things, simply because you don't (yet) know what's good and what's not, or ever what "good" is. The smaller world of DIY amps shares this problem.

The real answer is to go learn what's good. But much of the world has been conditioned to look on the internet, the literal source of much of the mis- and dis-information to try to learn. The internet is a very untrustworthy place to learn much other than separately verifiable facts. It's a tough slog to learn much on the net without getting hoodwinked. So you have to look at least twice as hard, and separate a lot of chaff from what little wheat you find. As a humorous aside, my wife sometimes educates me about the difference in girl-speak and boy-speak. The two genders use the same words, but they do NOT always mean the same thing. She pointed out to me a bit of girl-speak wisdom: if you want to marry a prince, you're going to have to kiss a lot of frogs. Be prepared to do the same on internet wisdom.

It is generally true of components that "they don't make them like they used to". It's also true that they may not be able to make them that bad any more. Modern components are remarkably advanced. So don't just believe that the old ones are the only good ones. It's generally not true. It may be true about some side effect or secondary characteristic of parts. I got all wordy a while back and typed in why you can't trust an "Orange Drop" or any other part/brand to be just like they used to make them. I'll go look it up if need be, but the fact is that machines that make parts wear out and get replaced, the people that make the machines quit or retire, and even the raw materials change over time, so the "Orange Drop" or whatever of today isn't like the old ones. It may be better in many ways, but it won't be the same in all ways. It ...CAN'T... be.

So your job gets harder. You have to actually go learn what makes a capacitor, a resistor, an inductor, a transformer, wire, wire insulation, solder, speaker cones, etc. be good and not trust the internet fables. It's really >>HARD<< to do this, much harder than asking what's good on a forum. This forum is vastly better than most of them, but even here the real, hard truth has to be sifted out.

So harness up, and go LEARN.

[R.G.]

Dang. Just after looking for this, and posting the above abbreviated version of "you can't go home again", I stumbled on it. Here's the "genetic drift" theory of components.
==========
Let's play "Genetic Drift".

What's in an "Orange Drop" [or insert your favorite whatever here]? The folks who manufacture these go buy huge quantities of insulation materials, rolls of metalized film (or rolls of film and rolls of foil for that kind) from the cheapest supplier of such stuff they can find in today's market that also meets their quality needs. They buy lead wires, impregnating materials, and external epoxy dip, and then go run this stuff through their machines to make new [whatevers].

Are the results the same as a [whatever] that was made 20, 30, 40, 50 years ago?

No. First, the automated manufacturing machines are continuously updated as they wear out and/or are changed to produce more parts faster. The machines that are current are continuously tweaked to get the most good parts out of the incoming materials and labor time spent. So the [whatevers] are made on a continuously stepwise changing manufacturing line.

Are the materials the same?

No. You can't buy [whatever] today like you could decades ago. In most cases, you can't get materials that crude and/or wildly variable. In many cases you can't buy materials with the same environmental contaminants as decades ago. In fact, many of the suppliers from long ago are out of business, or they have been bought out by other companies and nothing but the brand name remains. This is much more common than anyone not involved in manufacturing realizes.

Are the factories the same? No. Clearly most of the workers have long since retired, as have the managers, and entire work force of the company. Factories weighed down by high-price work forces have been replaced by factories in low-cost labor places, or just newer, more modern factories.

It's important to realize that economic laws are as immutable as things like the law of gravity. If you can't stay out of bankruptcy making the [whatever] you used to make, you either go out of business or furiously find a way to cut costs and stay level with the competition.

Even in a relatively static manufacturing world, machines wear out, people retire, new laws make it illegal to use materials more dangerous than an ill-timed fart, all the little adjustments that we have to make.

The bottom line is that YOU CAN'T DEPEND ON A [WHATEVER] TO HAVE THAT MAGIC SOMETHING LIKE THE LAST ONE YOU HAD UNLESS THEY BOTH CAME FROM THE SAME MANUFACTURING RUN.

You have a much better chance of a huge manufacturer having some consistency across runs, but even huge manufacturers can and will change their processes with no notice to their huge customers, and they don't know you exist.

It is far, far worse with smaller manufacturers, especially little guys who make up small runs of very esoteric whatsits. It is possible they MIGHT be hand-building whatevers; in that case, they're either priced so high that they can afford to live on whatever gold-dust-covered clients believed their advertising. And their products are highly, high variable in quality, as everything done by hand is. By-hand is almost never repeatable. Did the winding-machine operator have the burrito grande for lunch? OK, we're getting bigger caps this afternoon.

Even worse is the small time guys who buy/contract for parts from the big makers, but re-label them as Platinum Eco-Caps, hand rolled on the soft thighs of Icelandic virgins. This might be OK, but (1) they're certain to charge you extra for their expensive advertising and business trips to Iceland, and (2) when their big-guy maker changes his process, well, you get more genetic drift.

Two last points. First: you can rely on the big guy makers of parts living up to the specs on their parts datasheets. No more, no less. If it's not on the datasheet, you'd be misguided to rely on it, because in most cases they don't even look for things not on the datasheet.

Second: you really, really can never go home again. Home changes out from under you. If you doubt this, go do a little research on who owns that trademark you are relying on.

[Mike Sulzer]

"This can sound quite pleasing to the human ear, and is not generally noticeable as distortion. However, this subtle sweetening is only noticeable when the signal across the resistor varies by more than 70V or so, and doesn't really get going until the signal across the resistor is in the 100V plus region. That means that carbon comp in an amp doesn't generate "better TOOOONE!!" as the advertising says, except in the last stages driving the output tube grids. Other places, especially the input tube, they generate no good distortion and only excess noise." --RG

Early stages in a guitar amp can have large voltage swing. In particular this includes the input stage. Some pickups have enough output to drive the input stage into clipping, or nearly so. One or more intermediate stages might have high level also, especially when distortion is purposely generated in the preamp section.

But I think the triode distortion dominates even in these cases, and so I doubt that using carbon comp resistors has a significant beneficial impact on the sound. But it is something to try if you have a lot of time on your hands!

[J M Fahey]

[COLOR=#333333]But I think the triode distortion dominates even in these cases, and so I doubt that using carbon comp resistors has a significant beneficial impact on the sound.

Same here.
The very high voltages needed to make the resistor somewhat non-linear, say 0.5% or 1% distortion (if that high) , pale compared to triode , say, 5% or 6% at same levels and straight clipping just a little higher.

Plus triode saturation is way more complex: besides overall basic curve non linearity (square Law), on the high peaks it plain clips, flat top, because it slams against a wall: it canīt go higher than voltage rail; while the negative peaks are rounded, reaching saturation is not "a wall", simply tube gets weaker, itīs harder to pull electrons from cathode with such low plate volotages.

That makes triode distortion way more flavourful than relatively mild CC resistor one.

Not saying they contribute *nothing*, just that itīs not too much.

[Mick Bailey]

Guitarist magazine ran a blind shootout to see which of their player-journalists could discern a Fender Deville from a Tone King Falcon, Redplate Blackverb, 3 Monkeys Grease Monkey, Splawn Nitro, and a Morgan AC20 Deluxe. In the blind test the Fender came out top of the list for 3 out of the 4 reviewers. Interestingly none of the reviewers could identify all of the amps correctly.

Fender does not use any 'mojo' parts. Just off-the-shelf industry-standard stuff. Mostly carbon film resistors, commercial-grade film caps, a few ceramics caps for low-pf, plus some flameproof and wirewound resistors where needed.

[miltown]

Thanks for all the input . Contrary to what RG you are thinking I'm not looking for a question answered in so much as hearing what people have to say on the subject and then scraping off the crud and making my opinion from there . I have a plan I'm just fleshing it out amongst the masses. It's what a forum is all about . I got good advice, I got long winded advice and stuff that just doesn't matter thrown in . I'm not an expert I'll leave that to you . I just appreciate others opinions on subjects. Thanks to all that are responding . Appreciate it . NOW I'LL GO LEARN. Shit where's my harness ?

[R.G.]

Good! Glad to hear you're going about this the right way, after all. That doesn't happen all that often in net forums, so I apologize for lumping you into that. It's hard to tell from just a post.