Hi Jon,
I have to agree with Ed 100%. Although I didn't know that the "bulk metal foil" types were close to metal film types, but it would make sense.
In test equipment in critical locations you will often find Dale RN55 or similar types or an equivalent. They aren't used for the temperature range they have.
Otherwise you're right about using most mil-spec'd parts as they often don't have any other positive attributes over temperature extremes and physical toughness. In this case, those Dale resistors absolutely do have other positive traits. Voltage and temperature coefficients being what we are looking for. They are also known to have very low noise.
-Chris
I have to agree with Ed 100%. Although I didn't know that the "bulk metal foil" types were close to metal film types, but it would make sense.
In test equipment in critical locations you will often find Dale RN55 or similar types or an equivalent. They aren't used for the temperature range they have.
Otherwise you're right about using most mil-spec'd parts as they often don't have any other positive attributes over temperature extremes and physical toughness. In this case, those Dale resistors absolutely do have other positive traits. Voltage and temperature coefficients being what we are looking for. They are also known to have very low noise.
-Chris
Hi diyralf,
No, not any MF will do. I have even found inductive metal film resistors. The quality of the part varies widely and for anything important, use good parts. No name metal film resistors are not the way to go! For certain applications, I will buy and use Dale close tolerance parts. That would include anything in a high gain circuit or anything that needs to hold a calibration. Try that with cheap metal film resistors.
-Chris
No, not any MF will do. I have even found inductive metal film resistors. The quality of the part varies widely and for anything important, use good parts. No name metal film resistors are not the way to go! For certain applications, I will buy and use Dale close tolerance parts. That would include anything in a high gain circuit or anything that needs to hold a calibration. Try that with cheap metal film resistors.
-Chris
You can try:
TI YR1 and YR2
Vishay MMA0204 and MBB0207
Holco H4 / H8
Dale / Vishay CMF and RN
Dale / Vishay PTF
Welwyn RC55Y
All have 15-100ppm temp
1% - 0.1%
Use the largest size which can fit and choose best precision and tempco in more critical locations.
For those cost conscious Vishay Beyschlag seems the best deal going for a 50ppm 1% resistor.
https://dcc.ligo.org/public/0002/T0900200/001/current_noise.pdf
http://conradhoffman.com/papers_lib/TI_Noise_Prec_Resistors.pdf
Im with Ed, I’m also usually partial to the Dale RN**E (E designation = 0.1% 25ppm)
Or the Dale / Vishay PTF series, which I think go all the way down to 5ppm? I believe 15ppm is standard in that series.
TI YR1 and YR2
Vishay MMA0204 and MBB0207
Holco H4 / H8
Dale / Vishay CMF and RN
Dale / Vishay PTF
Welwyn RC55Y
All have 15-100ppm temp
1% - 0.1%
Use the largest size which can fit and choose best precision and tempco in more critical locations.
For those cost conscious Vishay Beyschlag seems the best deal going for a 50ppm 1% resistor.
https://dcc.ligo.org/public/0002/T0900200/001/current_noise.pdf
http://conradhoffman.com/papers_lib/TI_Noise_Prec_Resistors.pdf
Im with Ed, I’m also usually partial to the Dale RN**E (E designation = 0.1% 25ppm)
Or the Dale / Vishay PTF series, which I think go all the way down to 5ppm? I believe 15ppm is standard in that series.
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Hi MikeFarad ...
I have been listening to CMF55, CMF60 (TMK non-lead RNxx types), RN55, RN60, RN65D, & RN65E (lowest temperature coefficient) and Charcroft CAR/S which are similar to the TX2575 (Z-foils).
IMHO the RN65E is the second best sounding in terms of resolution & nuance whereas the Charcroft CAR/S somehow is in a different league. Very revealing, nuanced and with a tonal detailing that I did not hear in the RN65E.
However, if I may add a personal comment: If you are to build a stepped attenuator the price of the TX2575/CAR/S is significantly higher than the RN65E. Would the rest of your system be up to this level of sound quality?
Just a thought - of course entirely up to you ;-)
Cheers,
Jesper
I have been listening to CMF55, CMF60 (TMK non-lead RNxx types), RN55, RN60, RN65D, & RN65E (lowest temperature coefficient) and Charcroft CAR/S which are similar to the TX2575 (Z-foils).
IMHO the RN65E is the second best sounding in terms of resolution & nuance whereas the Charcroft CAR/S somehow is in a different league. Very revealing, nuanced and with a tonal detailing that I did not hear in the RN65E.
However, if I may add a personal comment: If you are to build a stepped attenuator the price of the TX2575/CAR/S is significantly higher than the RN65E. Would the rest of your system be up to this level of sound quality?
Just a thought - of course entirely up to you ;-)
Cheers,
Jesper
Only you can decide whether is sensible to spend $20 a resistor for 40 resistors or so, when $2 resistors are roughly equivalent. Even Ligo seems to be avoiding the pricey use of foils. If you can reliably hear the difference between 5 and 15ppm you could make a living as an audio show sideshow attraction doing A/B/X testing. In a shunt position one can’t hurt.
Personally I think there are better things to be spending time and money on. For example, build a DCB1 to go with it. Please share with us your preamp design so we can give you more informed suggestions. Without context it’s shots in the dark.
Personally I think there are better things to be spending time and money on. For example, build a DCB1 to go with it. Please share with us your preamp design so we can give you more informed suggestions. Without context it’s shots in the dark.
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Sometimes the difference between resistors are how the military wants them labeled. The military standards are more conservative. A 1/4W has to be labeled as 1/8 watt resistor sometimes although it's exactly the same thing. Probably the mil spec measures at what power the resistor fails. and doubles it to make it more reliable .
Hi diyralf,
It's the external, ambient temperature change. As long as they all drift the same way and by the same amount percentile you should be good. In a voltage regulator, the drift is important. Think of the drift at 300 VDC or so.
I haven't checked, but the low drift parts might also be the lowest noise parts too.
-Chris
It's the external, ambient temperature change. As long as they all drift the same way and by the same amount percentile you should be good. In a voltage regulator, the drift is important. Think of the drift at 300 VDC or so.
I haven't checked, but the low drift parts might also be the lowest noise parts too.
-Chris
I am talking about self-heating by e.g. 20Hz. The temperature and resistance then oscillate causing distortion.
The OP wants the attenuator for a preamp - why are posts extolling the virtue of voltage coefficient, or even temperature coefficient ? Wouldn't tolerance and drift with age be the only tangible attributes from an accuracy and repeatability perspective, including that of the switch contacts as well as the channel matching?
Lower tempco seems to be directly linked to less drift. Lower tempco also seems to be more common amongst precision resistors. Drift over lifetime is usually a function of hours at rated power. https://vishayintertech.assetbank-s...5_Leaded Fixed Film Resistors_INTERACTIVE.pdf
See page 7, equation under Temperature Coefficient. Less tempco, less % of rated power, less ambient temperature = less drift. Also moisture plays a role. My hunch is that more heat will damage the resistor coating and allow moisture to enter and will compound problems, further deforming the coating from temperature cycling.
Lead handling, soldering technique and allowing sufficient airflow would also be quite relevant. Some resistors can vary up to 1% from the soldering process. Or for example the more of the lead is exposed the less it will dissipate heat from where the lead joins the resistor body, reducing damage / cracking to the coating. Sufficiently derating can minimize some of these other effects. All of these parameters are interrelated.
My guess is this is why surface mount resistors on the whole are less reliable than their through hole counterparts. But yes. Trobbins is correct. You want best channel matching, best precision, least drift. To accomplish this, choose .1% matched parts with low tempco, derate, solder and assemble carefully (solder once and minimize lead mangling- don’t bend resistors very close to the resistor body!).
This should result in an attenuator that will stay at least 1% channel matched and 1% desired accuracy over its full lifetime. Again the options I provided above will be suitable. Keeping these issues in mind imho is more valuable, more relevant and will provide a better long term cost effective result than simply purchasing the most expensive resistor you can locate.
Also it’s practice can be extended beyond attenuators to provide more stable builds across the gamut.
See page 7, equation under Temperature Coefficient. Less tempco, less % of rated power, less ambient temperature = less drift. Also moisture plays a role. My hunch is that more heat will damage the resistor coating and allow moisture to enter and will compound problems, further deforming the coating from temperature cycling.
Lead handling, soldering technique and allowing sufficient airflow would also be quite relevant. Some resistors can vary up to 1% from the soldering process. Or for example the more of the lead is exposed the less it will dissipate heat from where the lead joins the resistor body, reducing damage / cracking to the coating. Sufficiently derating can minimize some of these other effects. All of these parameters are interrelated.
My guess is this is why surface mount resistors on the whole are less reliable than their through hole counterparts. But yes. Trobbins is correct. You want best channel matching, best precision, least drift. To accomplish this, choose .1% matched parts with low tempco, derate, solder and assemble carefully (solder once and minimize lead mangling- don’t bend resistors very close to the resistor body!).
This should result in an attenuator that will stay at least 1% channel matched and 1% desired accuracy over its full lifetime. Again the options I provided above will be suitable. Keeping these issues in mind imho is more valuable, more relevant and will provide a better long term cost effective result than simply purchasing the most expensive resistor you can locate.
Also it’s practice can be extended beyond attenuators to provide more stable builds across the gamut.
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Hi spaceistheplace,
Yes, I agree. Using the Dale parts, or an equivalent, will probably result in an attenuator a lot closer than 1% and would remain that way longer than the equipment it's installed in would last. There are a lot more expensive resistors than the Dale products we are talking about.
-Chris
Yes, I agree. Using the Dale parts, or an equivalent, will probably result in an attenuator a lot closer than 1% and would remain that way longer than the equipment it's installed in would last. There are a lot more expensive resistors than the Dale products we are talking about.
-Chris