Testing frequency response of caps

[tubesornothing]

FYL, you mentioned you did some testing with FFT and your sencore when doing your cap testing.  I have tried to do this with white noise input and measure frequency response with a 24bit scope and FFT.   I also tried doing it with XY curves on the scope.  However the results were inconclusive.

Basically all I want to do is to be able to have some objective measurements for different variety of caps so help explain - and most of all - help reproduce the sounds I hear.



thanks
ToN

[FYL]

A Sencore will only test capacitance, ESR and other basic - but critical - factors.

Steve Bench did some quite interesting tests a while ago using a scope in XY mode.

http://greygum.net/sbench/sbench102/caps.html

[tubesornothing]

Yeah, that's how I got onto the Lissajous patterns a while back.  I tried to reproduce his results, but I could not quite figure out how he did the test circuit setup.  I sent him an email, but no reply.  Any ideas?

I presume when you used FFT you were using it for testing frequency response.  What was your setup for this?  E.g. test circuit, input signal, etc.

[FYL]

I presume when you used FFT you were using it for testing frequency response.  What was your setup for this?  E.g. test circuit, input signal, etc.

Time, frequency, etc.

PC running Purebits Sample Champion Pro 24/192=> MLS or FFT signal => bench amp => load + DUT + attenuator => loopback.

You can do nearly the same using free software such as RMAA.
http://audio.rightmark.org/products/rmaa.shtml

[FYL]

Yeah, that's how I got onto the Lissajous patterns a while back.  I tried to reproduce his results, but I could not quite figure out how he did the test circuit setup.  I sent him an email, but no reply.  Any ideas?

X = pre DUT, Y = post DUT
Drive signal : 70 V @ 600 Hz, plus a low pass filter and a sensing R

Could be a simplified version of John Curl and Walt Jung's jig.
http://waltjung.org/PDFs/A_RealTime_Signal_Test_For_Capacitor_Quality.pdf

BTW, Dick Marsh and Walt Jung's original articles in Audio are still worth reading:
http://waltjung.org/PDFs/Picking_Capacitors_1.pdf
http://waltjung.org/PDFs/Picking_Capacitors_2.pdf

[tubesornothing]

Great thanks for the links - I'll dig into RMAA. 

Those articles help to improve my understanding.  I will digest and try some experiments.

[jcm-jmp]

good links!

what I got was the author is suggesting poly type caps everywhere the ac signal is present aand Film type caps with low DS and fast recovery times for ac ripple filteration on dc power rails. ceramics could be done away with and not used at all

very tech heavy read and for a EE probably very usefull, but on a tech level not so much. other than the common knowlege of poly type caps albiet more expensive, help replicate the ampified ac signal more accurately.
but
in old fenders some of glory of tone is the distortion created by the lesser desired cap types such as the ceramics in the tone tanks and PI.

so all though math proves the authors theory. the human ear will dispell this theroy to some degree. the human ear likes some of the distortions that are introduced by the use of tubes and lesser than optimum filteration.

just my .02 but none the less very good info presented in those links. realy more over for HIFI audio reproduction.

[tubesornothing]

I did not want to get into the "ears" versus theory debate on this thread.  I will leave that for the sozo caps thread.  I am interested in how "EE types" are measuring aspects of capacitor (and other components) performance.

[FYL]

what I got was the author is suggesting poly type caps everywhere the ac signal is present aand Film type caps with low DS and fast recovery times for ac ripple filteration on dc power rails. ceramics could be done away with and not used at all

Ceramics should be used in oscillators or as snubbers, film caps - most modern ones are OK - for coupling, high quality 'lytics or suitably rated film caps for decoupling and PS filtering.

but in old fenders some of glory of tone is the distortion created by the lesser desired cap types such as the ceramics in the tone tanks and PI.

Of course. My point here was that you should fully understand how each type of cap works and then use the right part for the job.

realy more over for HIFI audio reproduction.

Agreed. These articles were published in the now defunct "Audio", a hifi monthly.

[jcm-jmp]

I did not want to get into the "ears" versus theory debate on this thread

forgive me, this is not my entent. but when speaking about audio in the human listening experience, one has to consider that the human ear is not a perfect audio spectrum analizer.

the electrical fundamentals and characteristics of componants in coventional audio amplification can be analized and mathmaticaly explained and consistant results can be achieved.

My whole point is that it's not always mathmaticaly perfect circuitry that provides the best audio listening experiance for the human ear.

 

[Merlin]

I did not want to get into the "ears" versus theory debate on this thread.  I will leave that for the sozo caps thread.  I am interested in how "EE types" are measuring aspects of capacitor (and other components) performance.

There was a series of very detailed articles in Electronics World a few years back about caps, performance and sonics, which also provided details of a practical cap testing set up. It also pointed out some of the imperfections in Jung's articles linked above. I'll try and copy the EW articles at some point and let you have them. It ran for several months so it might take me a while to get them all together.

[tubesornothing]

I did not want to get into the "ears" versus theory debate on this thread
forgive me, this is not my entent. but when speaking about audio in the human listening experience, one has to consider that the human ear is not a perfect audio spectrum analizer.

Psycho-acoustic effects and subjectivity is exactly what I did not want to get into in this thread, I am only interested in objective measurement with test equipment.  I do human ears separately. 

There was a series of very detailed articles in Elektor a couple of years back about caps, performance and sonics, which also provided details of a practical cap testing set up. It also pointed out some of the imperfections in Jung's articles linked above. I'll try and copy the Elektor articles at some point and let you have them. It ran for several months so it might take me a while to get them all together.

Interesting!  That would be great.  I'll see if I can dig them up locally.  Do you know approx the year that these articles showed up?

[Merlin]

Interesting!  That would be great.  I'll see if I can dig them up locally.  Do you know approx the year that these articles showed up?

See 2002:
http://www.dself.dsl.pipex.com/ampins/library/ampartew.htm

[FYL]

There was a series of very detailed articles in Electronics World a few years back about caps, performance and sonics, which also provided details of a practical cap testing set up. It also pointed out some of the imperfections in Jung's articles linked above.

Jung et al. articles are 30 years old... Important, but far from exhaustive or representing today's state of the art.

BTW, the only article I remember in EW was "The Effects of Capacitors on Sound Quality", written by Paul Dodds, senior engineer at Clarity Cap (an ICW brand targeting gullible audiophiles), and published a couple of years ago.

It was mainly a re-written PR blurb, "Two Year ClarityCap Research Programme Finally Answers An Audio Capacitor’s Influence On Sound Quality" available online at http://www.icwltd.co.uk/claritycap/download/news2.pdf, itself hogwashed from an AES convention paper "Audio Capacitors. Myth or Reality?", AES 124 P7314, available online to AES e-library suscribers at http://www.aes.org/e-lib/browse.cfm?elib=14444

Dodds was filmed at AES 124 peddling his wares: http://www.sonicstate.com/news/2008/05/27/aes08-if-the-cap-fits-it-must-sound-better/
Just show the clip to a specialist and ask him/her about what Dodd's body language means. In layman's terms: would you buy a used car from this guy?

 

[FYL]

See 2002:

OK, the Cyril Bateman "Capacitor Sound?" series...

Availble online http://www.scribd.com/doc/2610442/Capacitor-Sound

I can summarize his findings in a sentence: tants distort badly; 'lytics are inductive at AF, they distort with a lot of H3 unless suitably biased.
 
His earlier article - published by EW in '98: http://techdoc.kvindesland.no/radio/passivecomp/20061223155312558.pdf

Another link worth considering: http://sound.westhost.com/articles/capacitors.htm