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Metal Film vs. Bulk Foil resistors
Metal Film vs. Bulk Foil resistors
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Old 3rd November 2011, 06:25 AM   #1
audiogeekess is offline audiogeekess
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Default Metal Film vs. Bulk Foil resistors

Right now I have a voltage divider for each channel in my amp bypassing gain pots--fixed voltage divider of (0, 20k ohm). I am using a Metal Film 1% tolerance resistor right now for each channel--each measuring exactly 20.0k ohms on my multimeter.

Would I hear an audible improvement if I replaced those 25 cent metal film resistors with 20k ohm Vishay bulk foil resisters? They cost $20 for each resistor--so it would be a $40 "upgrade".
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Old 3rd November 2011, 02:48 PM   #2
carlmart is offline carlmart  Brazil
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Audible improvement will depend on how good your system (electronics & speakers) is in fine resolution.

There are also different types in Vishay BFs, and prices. Have a look at Percy's, that stocks them all and has good prices:

Michael Percy Audio Ordering Information
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Old 3rd November 2011, 05:12 PM   #3
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by audiogeekess View Post
Would I hear an audible improvement if I replaced those 25 cent metal film resistors with 20k ohm Vishay bulk foil resisters? They cost $20 for each resistor--so it would be a $40 "upgrade".
I very much doubt it. Metal films have good linearity and excess noise properties already. I think the only types of resistors with problematic linearity are carbon composition and thick film.
EDIT: Reading up, it seems carbon films aren't exactly the very definition of linearity either (though less bad than carbon comps), but I think they were used in lots of audio equipment in the past and few people ever complained. The voltage coefficient of metal films is only about 1% as high as with these.

Last edited by sgrossklass; 3rd November 2011 at 05:24 PM.
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Old 3rd November 2011, 06:42 PM   #4
simon7000 is offline simon7000  United States
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Spend your money on Linear Audio Vol. 1 where different resistors results are shown. With the change leftover you can buy some good resistors and a small bottle of wine.
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Old 3rd November 2011, 06:52 PM   #5
Mike Gergen is offline Mike Gergen  United States
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I've noticed more of an improvement by going to .1% from 1% then changing to bulk foil.

Susumu .1% 1206 SMT RG series from Digikey; 64 cents each.

Not a huge amount of money for a decent component.
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Old 15th November 2011, 09:37 PM   #6
audiogeekess is offline audiogeekess
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Mike, can I use the surface mount resisters like I do the 1% metal film resisters, and not on a printed circuit board?
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Old 15th November 2011, 10:10 PM   #7
Bone is offline Bone  United Kingdom
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The audible improvement will be in direct proportion to how much you pay for them.
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Old 15th November 2011, 10:29 PM   #8
john curl is offline john curl  United States
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NO, you are wrong, Bone. The best resistors will measure the 'best' as well for the most part. For example, $10 Vishay bulk metal does not sound better (to my ears and many others) as a Roderstein Resista ($0.10). The measurements show similar performance. So 100:1 difference in price is not that different. Trust me, I use both for serious designs.
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Old 25th August 2016, 02:30 PM   #9
PicoPete is offline PicoPete  United States
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Just came across this interesting post on Metal Film vs. Bulk Foil resistors from 2011 and thought I'd add my 2 cents:

Noise in electronic circuits is generally measured in nano-volts and is highly temperature and frequency dependent. For reference, one nano-volt is 0.000000001 volts, an extremely small value. In electronic circuits that use resistors and capacitors it is the resistors that contribute the substantial portion of noise and for the most part with audio circuits in the 20 - 20 khz, which is typically assigned to human hearing, you can completely ignore capacitors. In electronics the general formula for noise is E = 7.43 X SqrRoot(R X T X DeltaF) where E is in nano-volts, T is the temperature (in Kelvin), R is in K-Ohms, and DeltaF is in is the frequency bandwidth in K-htz.

In general, the formula says that noise increases as the resistance value goes up, the temperature goes up, or the frequency (or bandwidth) goes up or any combinations goes up. In reality all electronic components contribute noise to the system in which they used. And to be more specific, the noise that is attributed to different compositions of resistors is actually referred to as Johnson Noise, which is the random noise created in the material due to atoms moving even in the absence of an electrical signal.

Without getting into some rather complicated theory and associated math, I'll conclude by saying that when comparing certain types of resistors such as metal film, metal foil, carbon film, carbon composite, and wire-wound, for audio metal foil has been found to produce the least measurable noise contribution. However, whether one can hear the contribution of a reduction in noise as a result of using metal foil resistors is highly dependent on the specifics of the audio equipment being used and what, or who, is listening or measuring the noise levels. Since noise levels are highly affected by the voltages used in a circuit, it's questionable whether a person with average hearing will be able to discern noise levels at the nano-volt, or even micro-volt (which is an order of magnitude higher than nano-volt) levels.

In the early 60's the well regarded and famous Harmon Hardon Citation I Stereo pre-amp used carbon composition resistors in its circuitry and you could clearly hear the increase in "noise", usually a "hiss", when you turned up the treble levels beyond their flat settings. The Citation I used lots of feedback and was also known as the Feedback Pre-amp in its day. So circuit topology can contribute to noisy design as well. The Citation I used tubes rather than transistors and some of the plate voltages used were in excess of 400 volts, a level you do not see in today's transistorized and even more modern tube designs.

So to close this comment, I'd say that unless the audio gear has carbon composition (as in the Harmon Kardon Citation I pre-amp) which are the noisiest and/or is a tube design, then replacing the current resistors with more expensive resistors is unlikely to result in an audible improvement IMO. Also, keep in mind that resistor value accuracy has nothing to do with their inherent thermal and noise characteristics. For example, a 1000 ohms resistor rated at 5%, regardless of its composition, simply means that its value - and not its noise - can vary between 950 ohms and 1050 ohms and still be considered a 1000 ohm resistor. Similarly a 1000 ohm resistor rated at 1% simply means its value can be between 990 ohms and 1010 ohms and still be considered a 1000 ohm resistor.

So replacing 5% resistors with 1% resistors is not always going to result in a lower overall noise level - unless you know the circuit design requires more precise resistance values to achieve a more precise results. But that generally has nothing to do with noise levels. Now it is also true that 1% resistors are generally not carbon film and so were of a less noisy composition type, but that's just a byproduct of the tighter tolerance and not directly associated with it. In any case, interesting discussion.

Last edited by Variac; 26th August 2016 at 02:24 AM.
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Old 25th August 2016, 02:41 PM   #10
sgrossklass is offline sgrossklass  Germany
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I've still got a spare bag of line breaks here, let me know where to post 'em...
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