I'm ordering parts for a small amplifier project and it's getting expensive in resistors alone, because they often come in a minimum pack of 20, which adds up quickly when I only need one or 2. I've been limiting myself to metal film resistors and ruling out carbon film resistors (up to 5% tolerance).
What resistors do you consider to be acceptable in your projects?
What resistors do you consider to be acceptable in your projects?
I use mostly PRP resistor, they are metal film 1% in 1/2 & 1 watt. For 2 watt I go TKD. 12 watt is Mills. Those are the cheapest of the best quality you will find. There are much more expensive available but it gets stupid at some point. You can get them all any quantity too.
PRP are very well made, but expensive in small quantities.
hugz, who are you buying from? Mouser and Digikey will happily sell you 2 resistors at a time.
Metal film from any reputable manufacturer (Vishay, TE Connectivity, Panasonic) will be perfectly suitable. My go-to is the Dale (now Vishay) RN series, specifically RN55. For power resistors 1-3W I use Vishay PR metal film or TE Connectivity ROX metal oxide. Higher power I use Vishay / Sfernice RWM wirewound. Quality of all of these has been absolutely impeccable.
Tolerance very much depends on application - different parts of a circuit will tolerate different variations in resistance. There is no meaningful cost difference between 1% and 5% parts, so going all 1% is an easy choice. If I do require 0.1% or tighter for a specific application I usually buy 10 or 20 1% resistors and match them with a meter - any half-decent multimeter will be consistent enough for very tight matching 🙂. Plus I have a bunch of spares for the parts bin.
hugz, who are you buying from? Mouser and Digikey will happily sell you 2 resistors at a time.
Metal film from any reputable manufacturer (Vishay, TE Connectivity, Panasonic) will be perfectly suitable. My go-to is the Dale (now Vishay) RN series, specifically RN55. For power resistors 1-3W I use Vishay PR metal film or TE Connectivity ROX metal oxide. Higher power I use Vishay / Sfernice RWM wirewound. Quality of all of these has been absolutely impeccable.
Tolerance very much depends on application - different parts of a circuit will tolerate different variations in resistance. There is no meaningful cost difference between 1% and 5% parts, so going all 1% is an easy choice. If I do require 0.1% or tighter for a specific application I usually buy 10 or 20 1% resistors and match them with a meter - any half-decent multimeter will be consistent enough for very tight matching 🙂. Plus I have a bunch of spares for the parts bin.
Metal film, 1% for a small signal path (sometimes I use 0.1% for feedback circuits). And any other type and tolerance can be considered for a high-power or high current path.
In low power parts of amplifiers: run of the mill 1 %, 50 ppm/K, 0.5 W or 0.6 W metal film for critical places: feedback networks, filters, biasing of low-noise stages, 5 %, 0.25 W carbon film elsewhere.
I am quite off on that matter as i like aesthetics 😅 So usually prp is my main go to resistor for most values up to 1W. Above i go with NS vishays. I do love to go black and brown when using silmics, so dales are used then. All of those ypu can order in smaller quantities than 20 though.
In practice is there any difference between carbon film and metal film resistors aside from tolerance?
All of our favourite vintage gear (presumably) used carbon film
All of our favourite vintage gear (presumably) used carbon film
Metal film is slightly quieter (i.e. carbon film resistors have slightly more excess noise).
This won't matter at all except maybe at the input stages of high-gain audio amplifiers, where signal levels are very low.
Ironically, most of those sorts of signals (tape playback heads, moving-magnet record-player cartridges) have disappeared long ago, except for microphone inputs on mixers, and input stages of high-gain guitar amplifiers.
-Gnobuddy
Metal film are also more stable and change less with time and temperature. Most old equipment used carbon comp resistors which are noisier and tend to drift over time and absorb moisture which degrades them in sonics and value. There are places where some like carbon comp due to its low inductance but everywhere else it is not used. A lot of that vintage sound was the carbon comp resistors addition to the sound, noise and distortion. lots of people thought it was the tubes that made the hiss, it was the resistors!
Just want to clarify that the OP was talking about carbon film resistors, not carbon composition.
Carbon film resistors are perfectly good for 99% of uses.
As for carbon composition resistors, as far as I'm concerned, there is only one place they belong: in the electronics recycling bin.
In the weird and wonderful world of "boutique" tube guitar amplifiers, there are some unfortunate people who pay extra money to get the worst resistors available, namely carbon composition types. All I can do is tip my (virtual) hat silently in their direction, and say "I wish you hadn't wasted your money."
-Gnobuddy
I tend to over spec - party on reuseability grounds partly down to beginnerisms 🙂
1% normal, 350/500V and 1W as a starting point and then calculate based on the design use.
Metal (thin foil) but wirewound for the larger power.
Guilty of going vishay for signal but yaego for power and others, typically starting at the cheapest known brand that matches the voltage/power requirements but remain low noise.
Fan of CMF in the right place but not much reason for a bleed resistor.
1% normal, 350/500V and 1W as a starting point and then calculate based on the design use.
Metal (thin foil) but wirewound for the larger power.
Guilty of going vishay for signal but yaego for power and others, typically starting at the cheapest known brand that matches the voltage/power requirements but remain low noise.
Fan of CMF in the right place but not much reason for a bleed resistor.
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You can get multi packs of 5% resistors, and then channel match the values with a DMM. When I lived in LA with access to a lot of surplus stores, I would take my DMM in and pick only matched components from the bins. You can get decent parts on eBay or resold here. Go for oddball values, slightly off from the value you need. They are in less demand. Many of the nice milspec metal film are in odd values. 5% off of the schematic value will likely not affect the operation of the circuit, but channel matching the values is important. Getting an expensive Vishay bulk metal foil or Caddock, etc. can really make a difference in critical positions, such as I/V in a DAC. You need to know your circuit.
That's what I use as well. Metal film for low power, metal oxide for power resistors if metal film is not available.
0.5% tolerance SMD resistors (also metal film). Not because 0.5% makes any difference compared to 1%, but simply because they're available and the same cost as 1%, so why not?
Or even one at a time. If you need more than 1-2 it often is lower total cost to buy ten, though. That's especially true for SMD resistors.
That's been my observation as well.
You'd need more than a half-decent multimeter. 4.5 digits minimum for 0.1%, assuming the meter can actually measure that precisely. Usually the precision of a DMM is ±some percentage, ±1 digit, so you might actually need a 5-digit meter to match to 0.1%. Unless you do something clever like a Wien bridge.
Very few circuits actually require this level of precision.
0.1% resistors that were carved from a solid block of unobtanium 20 years ago are now available for less than $1/each. They get down around 10-15 cents each if you buy them in SMD and buy enough of them. So I personally don't see a point of hand-matching the resistors.
Tom