Low-distortion Audio-range Oscillator

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benb

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Joined 2010
Elvee said:
I have already experimented with the technique, but to remove crossover distortion:
https://www.diyaudio.com/community/threads/a-dive-into-the-past.252143/post-3839604
There are earlier, more detailed posts somewhere, but I cannot find them.
It should work for a transformer too, but the implementation is going to be tricky
Click to expand...
Oh, I missed that, but it was 10 years ago and I haven't read everything on the board since I signed up. I'll read through more carefully, and may want to start a new thread similar to that.

I'm thinking the reason this technique was never used outside of magnetic tape recording) is it's usually "too complicated" (too much extra circuitry) and not enough benefit, though it was clearly needed for magnetic tape.

Yet another thought, dithering noise for lower bit depth ADCs was common to reduce sampling distortion before delta-sigma took over everything. AC bias does a similar thing, and I'm wondering if such noise (probably filtered so that it's all ultrasonic) could be used in tape recording as well as other magnetic-related applications. This seems off-topic for an oscillator, but maybe not.
 
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1audio

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Another check of another 15K and a Yaego. The Dales are clearly defective. Both distortion and noise. The second 15K noise was 30 dB higher than the Vishay foil. The Yaego was about 10 dB higher than the Vishay, all measured at .1W. The noise problem suggest a real manufacturing problem, most likely termination but it could be flaws inthe laser trimming.
These instruments were created to weed out bad parts for high reliability applications, not for audio nuts BUT they are great for checking nonsense audio claims.
 
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mediatechnology

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1audio said:
Media Technology: I received the parts today
First quick check on a 15K resistor Distortion was high (off scale on the linear readout) and the excess noise index (Quan-tech 315C) was 20 dB higher than the Vishay foil. Really bad.
I will do a more detailed report later.
Click to expand...
Thanks for running the quick test. Will be interesting to see the rest particularly the ones that seem to measure clean.

Correction: The Holsworthy are the YR1B. I think all of my previous posts had the series part number reversed.
 
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mediatechnology

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1audio said:
Another check of another 15K and a Yaego. The Dales are clearly defective. Both distortion and noise. The second 15K noise was 30 dB higher than the Vishay foil.
Click to expand...
Wow.
1audio said:
The Yaego was about 10 dB higher than the Vishay, all measured at .1W.
Click to expand...
Not bad for the Yageo considering the "60 dB" difference in price. IIRC the Vishay S102 is at or near the noise floor?
 
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1audio

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I believe so. Unfortunately I have never found a manual for this version of the 315. Its quite different from the older version. However Noise index is a standard https://eepower.com/resistor-guide/resistor-fundamentals/resistor-noise/# and the S102 are at the low end on the chart. I think I have a 10K wirewound in my collection which will also have very low current noise. I'll also look for a carbon comp 10K.

Here is an interesting thought- carbon comp resistors could have noise modulation with the signal, particularly at low frequencies. Maybe thats a euphonic thing some people like?
 
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1audio

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Resistor noise index:
INDEX, the unit of measurement, as defined in the NBS report is “the ratio of the rms noise voltage, in
microvolts, to the applied dc voltage, in volts, expressed in decibels, when the associated pass band
for the noise is one frequency decade.” Or simply pV/V/Dec in dB.
 
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mediatechnology

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CG said:
Somewhat off topic, so please either indulge me or just ignore this...

Has anybody made similar measurements on SMT parts? Or, are they hopeless due to their low mass? Any recommendations?

Thanks!
Click to expand...

I have an older thread on SMT with measurements we did at THAT and test results from Dave Hill (RIP) of Crane Song.

https://proaudiodesignforum.com/forum/php/viewtopic.php?t=401

THAT's tests are on page 1; Dave's on page 2.
 
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CG

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Joined 2002
Thanks very much.

So, as a very broad generalization, SMT parts might be as good as through hole, depending on the usage and the resistor itself. But, if you don't want to spend a lot of time investigating resistors, it's harder to go wrong with through hole. Look at what you're going through right now.

For DIY guys like me, where volume manufacture isn't a consideration, through hole is probably best. Yeah, they take up more circuit board area which makes current loops larger, but it's probably a good trade off.
 
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PChi

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Joined 2012
There are some low distortion surface mount resistors available. I haven't tested them though.
Vishay PLTU series surface mount resistors claim a low voltage coefficient of +/- 0.1 ppm (typical). Mouser list only a few values and a few sizes so unless the design uses one of the values stocked they are of limited use and they are expensive.
Another is the Vishay Sfernice P series which list among features that the voltage coefficient < 0.01 ppm/V. Again Mouser stock only a few values.
I assume that there are other surface mount resistors out there that specify the voltage coefficient.
 
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JensH

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Does anyone here know of tests with the Vishay Precision Thin Film MELF (MMB 0207 and MMA0204) and the Precision Thin Film Chip Resistors (MCA 1206)? Or have the ability and time to do these tests?

0204 MELF resistors seem to be popular with many of the high performance DAC's from Topping etc. And Ivan seems to use 0207 MELF's in a lot of critical places in the Cosmos products. He seems to prefer the Viking resistors though.

For the SMM0207 series Vishay specifies the non-linearity:
1714328693864.png

It is generally quite difficult to find this specification in datasheets.

Panasonic mentions it in the datasheet for the ERA V type, where they state "excellent linearity". But no numbers!

The large MELF resistors are probably a good choice for critical applications, but how much difference is there really between these and the chip resistors?
AP use a lot of 1206 and some 2512 resistors, even in the APx555B, so the performance can't be terrible. I don't know which brand or other specifications though, like temperature coefficient etc.
 
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1audio

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Vishay doesn't even publish linearity info on the Bulk Metal resistors. https://foilresistors.com/docs/63140/var.pdf The numbers on the MELF resistors look like they are from an audio analyzer. Still respectable. The MELF seem to be traditional cylinder resistors with SMD compatible terminations. They have a lot more surface that SMD chip resistors which I'm sure will help with performance.
 
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mediatechnology

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tomchr said:
FWIW I've had no issues with the Susumu RG-series. There are other good types too.

I suspect the straight line from 100 Ω to 20 kΩ in Vishay's plot is the limit imposed by the test equipment and not the resistors.

Tom
Click to expand...
We used the Susumu 0805 RR1220 on the THAT mic preamp demo boards in some key locations and they measured almost as good as through hole. The 1 kHz preamp measurements were 0.0004% TH vs 0.0006% for the RR-series.

Dave Hill in his 2007 tests found the RCD BLU-0805-1002-BT25W 1/4W MF to measure 0.0008% and the Susumu 0805 RR1220P-103 also measured 0.0008%. He later followed up in 2011 to write "The RCD BLU and the Susumu parts have proven to work well since the original part of this was written."
 
tomchr

tomchr

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mediatechnology said:
We used the Susumu 0805 RR1220 on the THAT mic preamp demo boards in some key locations and they measured almost as good as through hole. The 1 kHz preamp measurements were 0.0004% TH vs 0.0006% for the RR-series.
Click to expand...
RR and RG are two different animals, though. RG is the better one. I've used many 0805 and 1206 sized RG-series in critical spots without issue, i.e., with THD well below -130 dBc. Not thereby said that they can't be bettered, but they do offer incredible value for the dollar.

Tom
 
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vicnic

Member
Joined 2004
Some 15k and 18k metal film and thin film resistor measurements.
Resistor under test was connected as OPA1656 opamp inverter feedback.
Measured via passive twin T.
Real scale at 3kHz.
1kHz 16V p-p (5,67V RMS) across measured resistor.
Three examples of each type.

15k reference resistor:
https://content20-foto.inbox.lv/albums/e/elterra/ResitorLinearityMeasurements/Reference15k.jpg

0805 1% Viking Tech ARG05FTC1502:
https://content33-foto.inbox.lv/alb...yMeasurements/1VikingTech0805ARG05FTC1502.jpg
https://content33-foto.inbox.lv/alb...yMeasurements/2VikingTech0805ARG05FTC1502.jpg
https://content33-foto.inbox.lv/alb...yMeasurements/3VikingTech0805ARG05FTC1502.jpg

0805 0,1% Viking Tech AR05BTCW1502:
https://content33-foto.inbox.lv/alb...yMeasurements/1VikingTech0805AR05BTCW1502.jpg
https://content33-foto.inbox.lv/alb...yMeasurements/2VikingTech0805AR05BTCW1502.jpg
https://content33-foto.inbox.lv/alb...yMeasurements/3VikingTech0805AR05BTCW1502.jpg

MELF 0204 1% Multicomp MCFRFTDV1502:
https://content33-foto.inbox.lv/alb...tyMeasurements/1Multicomp0204MCFRFTDV1502.jpg
https://content33-foto.inbox.lv/alb...tyMeasurements/2Multicomp0204MCFRFTDV1502.jpg
https://content33-foto.inbox.lv/alb...tyMeasurements/3Multicomp0204MCFRFTDV1502.jpg

Through hole 0,25W 1% Yageo MFR-25FTE52-15k
https://content33-foto.inbox.lv/alb...nts/1Yageo0-25WThroughHoleMFR-25FTE52-15k.jpg
https://content33-foto.inbox.lv/alb...nts/2Yageo0-25WThroughHoleMFR-25FTE52-15k.jpg
https://content33-foto.inbox.lv/alb...nts/3Yageo0-25WThroughHoleMFR-25FTE52-15k.jpg

18k reference resistor:
https://content20-foto.inbox.lv/albums/e/elterra/ResitorLinearityMeasurements/Reference18k.jpg

0805 0,5% Susumu RR1220P-183-D:
https://content20-foto.inbox.lv/albums/e/elterra/ResitorLinearityMeasurements/1Susumu0805.jpg
https://content20-foto.inbox.lv/albums/e/elterra/ResitorLinearityMeasurements/2Susumu0805.jpg
https://content20-foto.inbox.lv/albums/e/elterra/ResitorLinearityMeasurements/3Susumu0805.jpg
 
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