TC is important in high end audio. 5% is almost half a dB, not good enough gain accuracy in stereo or multichannel applications. And yes, resistor noise matter very much.
To get 5% change in the resistor value, a 50ppm resistor would need to change in temperature by ~1000C degrees.
To get a 5% difference in resistance value as a result of a difference in temperature between two similar resistors in opposite channels would require a difference in temperature of 1000C degrees.
If you tighten your acceptable change/difference to 0.5% then one must still look for temperature differences of 100C degrees between the resistors.
I don't see the issue you are calling a problem for any audio, hi end or otherwise.
To get a 5% difference in resistance value as a result of a difference in temperature between two similar resistors in opposite channels would require a difference in temperature of 1000C degrees.
If you tighten your acceptable change/difference to 0.5% then one must still look for temperature differences of 100C degrees between the resistors.
I don't see the issue you are calling a problem for any audio, hi end or otherwise.
Because the original claim was 'sensitive to TC or less than 5% change'. I myself took the 'or' part to refer to tolerance. Seeing as a tolerance of 5% can be positive or negative, L and R gain could have a difference of 1dB.
Incidentally a TC of 50ppm is fairly typical for a metal film resistor. Thick film are normally considerably worse. A figure of 300ppm comes to mind and very low values (below 1ohm) are much higher than this.
Incidentally a TC of 50ppm is fairly typical for a metal film resistor. Thick film are normally considerably worse. A figure of 300ppm comes to mind and very low values (below 1ohm) are much higher than this.
I don't know why no one has pointed it out yet, but as a rule of thumb the terminology for through hole resistors is different than the terminology for SMT resistors. "Thin film" SMT resistors are essentially the same thing as "metal film" through hole resistors. What is called "thick film" in SMT is referred to as "carbon film" or sometimes "metal oxide" in through-hole.
One key difference is that the common 1% resistors in SMT are thick film whereas the common 1% resistor in through-hole is metal film. Thus, in SMT I find I must buy 'better' 0.1% resistors in order to get thin film whereas I could get that as 1% tolerance in through-hole.
100ppm is the most common TC for 1% resistors
One key difference is that the common 1% resistors in SMT are thick film whereas the common 1% resistor in through-hole is metal film. Thus, in SMT I find I must buy 'better' 0.1% resistors in order to get thin film whereas I could get that as 1% tolerance in through-hole.
100ppm is the most common TC for 1% resistors
Listening to different types of resistors clearly indicates that metal oxide and metal film resistors sound miles
better than carbon resistors.
I didn't understand why because of the classic text book equation for thermal noise caused by resistors
THERMAL NOISE
V thermal = SRQT (4 * k * T * B *R)
where k = Boltzmann's constant
T is in kelvin
B is the bandwidth
R is resistance in ohms
However, resistors also have Contact Noise and Shot Noise
CONTACT NOISE
V contact = (K * I) / ( f * physical size)
where K is a constant based on the type of material a resistor is made from
This equation says - a 2 W resistor will create less noise than a 1/4 Watt - all else being equal.
Turns out the predominant noise in a carbon, metal oxide or metal film resistor is the contact noise.
This also, says wire wound resistors do not have contact noise.
However, its been my experience that most commercial grade wire wound resistors sound like hell.
Mills wire wound resistors sound pretty good - I haven't heard the double wound Mundorf's
SHOT NOISE
V shot = K * I
where K is another constant.
Looking at these equations - its pretty clear high resistor values at the front of the amp are critical,
because their noise gets amplified all the way through a preamp or amp.
This also explains why people buy those DACT volume controls - with rotator switches selecting metal film resistors,
instead of a carbon volume control.
I don't spend the farm on high end resistors - some of the high end Vishay's get pretty pricy - yikes !
The 1 watt Holco's sound pretty good at $0.26 each.
I've ordered PRP's but haven't heard them yet.
Here are 2 good reads on the subject
Resistor Types--Does It Matter?
http://www.eetimes.com/design/automo...enerated-noise
better than carbon resistors.
I didn't understand why because of the classic text book equation for thermal noise caused by resistors
THERMAL NOISE
V thermal = SRQT (4 * k * T * B *R)
where k = Boltzmann's constant
T is in kelvin
B is the bandwidth
R is resistance in ohms
However, resistors also have Contact Noise and Shot Noise
CONTACT NOISE
V contact = (K * I) / ( f * physical size)
where K is a constant based on the type of material a resistor is made from
This equation says - a 2 W resistor will create less noise than a 1/4 Watt - all else being equal.
Turns out the predominant noise in a carbon, metal oxide or metal film resistor is the contact noise.
This also, says wire wound resistors do not have contact noise.
However, its been my experience that most commercial grade wire wound resistors sound like hell.
Mills wire wound resistors sound pretty good - I haven't heard the double wound Mundorf's
SHOT NOISE
V shot = K * I
where K is another constant.
Looking at these equations - its pretty clear high resistor values at the front of the amp are critical,
because their noise gets amplified all the way through a preamp or amp.
This also explains why people buy those DACT volume controls - with rotator switches selecting metal film resistors,
instead of a carbon volume control.
I don't spend the farm on high end resistors - some of the high end Vishay's get pretty pricy - yikes !
The 1 watt Holco's sound pretty good at $0.26 each.
I've ordered PRP's but haven't heard them yet.
Here are 2 good reads on the subject
Resistor Types--Does It Matter?
http://www.eetimes.com/design/automo...enerated-noise
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Uunderhill,
Interesting, I haven't previously seen any indication for resistor shot noise.
I've typically seen shot noise expressed as a current proportional to the square root of the dc current.
Hope this helps
-Antonio
This article was also suggested by MickeyMoose - the URL works now
Strategies for minimizing resistor-generated noise
Thanks,
The first article says resistor "Shot noise is dependent upon current, ... "
But maybe he was saying in a casual way - he didn't say linearly dependent
.
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