Danbridge (of Denmark) makes several passive component analyzers such as the CLT10, using a 10kHz sine wave and a 30 kHz bandpass voltmeter. I think the noise floor is something like -150 db, but can be pushed down to -170 db under certain conditions. It's been a while, but I found online application notes about testing both resistors and capacitors, and it's designed for both lab and production quality control.
danbridge
Needless to say, I can't afford it. Maybe I can cobble together a Wheatstone bridge and use it with my Tektronix AA-501 test set, which seems to have a distortion floor of around .001%.
danbridge
Needless to say, I can't afford it. Maybe I can cobble together a Wheatstone bridge and use it with my Tektronix AA-501 test set, which seems to have a distortion floor of around .001%.
Aren't you afraid that R3 and R4 contribute too much noise due to their high resistance?
These are very good points, especially about virtually eliminating the distortion of the generator as a factor. This is something that I have always liked about the operation of my Distortion Magnifier as well. Mitigating the contribution of the generator makes it possible to more easily get higher-voltage sources, like 40V rms, that would better reveal the resistor voltage distortions.
Not sure I would want to go the transformer route, but I'm guessing that a carefully-built differential amplifier could be made to do the job - perhaps a 3 op amp instrumentation amplifier built with LM4562 or the like.
I would still view the output of the bridge arrangement on a spectrum analyzer.
Thanks for the input.
Cheers,
Bob
My inclination is to make each branch an attenuator of about 10:1 or 11:1, so the input resistors would be 6800 ohms, for example. This allows larger voltages to be applied to the resistors without incurring large common-mode voltages. It also lightens the load on the source. Using a spectrum analyzer with a very small bandwidth helps with the noise. In one of my tests, I have the HP 3580A zoomed in to 3kHz with a 1Hz bandwidth. It is covering 100Hz per division and sweeping at 100 seconds per division.
Cheers,
Bob
This is a good point if it works well enough, and I encourage you or others to do a similar set of tests that way to confirm my findings. I just chose to do it this way. To each his own if it works. Improvements are always appreciated.
Instead of criticism of the methodology, I'm more interested in your constructive and insightful comments on the results.
Cheers,
Bob
Hi Waly,
PS, in my current setup, zoomed in on 3kHz with 1Hz bandwidth, the carbon film resistor with 4V across it is coming in at -133dB and my measurement floor is -140dB, all of which is noise in the 3kHz region.
Cheers,
Bob
If your instrument/sound card has residual distortions (for whatever reason) larger than the DUT, then don't use it for measurements, period.
Sound cards are not intended as measuring instruments, so complaints about -120dB distortion residuals should be directed to /dev/null. -140dB residual is (more or less) a lucky bonus, not a requirement for a sound card, even for an expensive one.
So resistor distortion, even for supposedly of the worst kind, is way, way overrated, not a big surprise. Don't forget to mention this to Mr. simon7000 and to all those paying obscene amounts for Vishay Bulk naked metal foil resistors, for the use in audio.
Anyway, thick film SMDs are likely, on average, not better than carbon film.
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So what I am taking away from this discussion so far is that the only place where I can see the voltage noise being really critical in audio would be for a RIAA type circuit for a turntable application and not much anywhere else is this an issue. I imagine that precision of resistor values is often much more critical than looking at them as noise sources to chase. It is just easier to use a high quality precision resistor than to have to sort through lower quality resistors for precision values, otherwise I don't see after reading all the discussions, and I know about the ones Waly is talking about over in the Blowtorch thread, why anyone would need to worry about the exact companies resistors that are being used. Audiophile thinking sure does cause people to worry about issues that don't seem to exist in reality it seems.
Thank you for your results Bob, not that I am going to go look for carbon comp resistors but I am not going to worry about having to use Vishay resistors, that is for sure.
Thank you for your results Bob, not that I am going to go look for carbon comp resistors but I am not going to worry about having to use Vishay resistors, that is for sure.
Anything wrong with improving a sound, because a crappy R's?
I don't think so. period.
Your assumptions are wrong, totally, and should be directed to /dev/null.
One more thing: Don't tell me what I should do or should not do with my sound cards.
Instead, write a letter to AP and tell them that they shouldn't use ADC's and DAC's that are intended for sound cards.
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Anything wrong with improving a sound, because a crappy R's?
I don't think so. period.
Your assumptions are wrong, totally, and should be directed to /dev/null.
One more thing: Don't tell me what I should do or should not do with my sound cards.
Instead, write a letter to AP and tell them that they shouldn't use ADC's and DAC's that are intended for sound cards.
You are picking up for a fight, I'm not biting. Do yourself (and myself, as well) a favor and add me to your ignore list where I was happily residing for at least one year.
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Excess noise in resistors was not discussed here, but you are, in general, correct. Carbon and thick film resistor are likely to have much more excess noise compared the metal or thin film resistor. I believe excess noise in poor resistors can be audible in a high gain RIAA MC preamp.
For audio purposes, voltage coefficient distortions, I would think it can be ignored in each and every modern resistor. If there's anything you must worry about, it is the thermal coefficient, in particular at LF.
None of these distortion mechanisms will ever have a proven audible impact.
Hi Kindhornman,
Bear in mind that we are talking about resistor voltage nonlinearity here, not noise. I think the best example of where this would be of concern would be when the resistor is used as the feedback resistor in a power amplifier, where it may see considerable signal voltage across it.
Cheers,
Bob
This is opposite to what B Hofer is saying and proving. He may be wrong but we are interested to know why because he is one of the most respected designer of ultra low distortion Equipment.
I prefer the reaction of another respected designer B. Cordell who immediatelly tries to measure instead of people writing as instant experts without even having the curiosity to read the paper of an authority .
Please read, explain why his arguments are wrong or make measurements and then come back, the rest is useless and full of vanity.
JPV