How important is the coupling cap?

[ivegotmono]

SCRs are French,
This from Angela.com. I don't know if they're Solens or not. I've never used them but I plan to try them soon.

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Angela Tin Foil Signal Capacitors For Tube Audio Gear

Made for us by SCR (Societie Des Condensatueurs Record) of France. These capacitors feature special high tension, non inductive windings, comprising two tin foil bands separated by two polypropylene films. The manufacturer claims that they are insensitive to humidity. The form of these tin 'armament' capacitors is cylindrical with axial tinned oxygen free copper leads. These caps are HEAVY in the hand! They scream, "QUALITY!" They bear some resemblance to the vintage signal caps found in premium '50s tube gear. The outer jacket is black with the ANGELA logo (see above) printed in white. The ends are neatly sealed in jet black epoxy. We think these caps offer a much neater appearance in your chassis than Orange Drops, Xicon, Panasonic, etc. Operating temperature range is -25 degrees C to +85 degrees C. Capacitance tolerance is 3% but typically measures less. Consider these fine sounding NEW Angela/SCR tin signal capacitors as a sonic upgrade over Orange Drops and other plastic caps found in tube hi-fi and guitar amps. To my ear, only paper in oil capacitors (especially the copper foil types...) offer richer sonics. Could it be that tin really is a better plate material for audio capacitors than the commonly used aluminum? You really should give these a spin in your next project.

SIZE = LENGTH X DIAMETER. LEADS = 1 &3/8 inches for .47 and above, 1 inch for .33 and below.
1. Angela/SCR Tin Signal Capacitor .022/630VDC, 7/8 inches x 1/4 inch. COOL TONE CAP FOR HUMBUCKERS. EACH $6.
2. Angela/SCR Tin Signal Capacitor .047/630VDC ,5/8 inches x 3/8 inches. NICE TONE CAP FOR FENDER TELES, STRATS, P-BASSES, ETC. EACH $6.
3. Angela/SCR Tin Signal Capacitor .1/630VDC, 1 inch x 3/8 inches. EACH $6.
4. Angela/SCR Tin Signal Capacitor .22/630VDC, 1 & 1/8 inch x 1/2 inch. EACH $6.
5. Angela/SCR Tin Signal Capacitor .27/630VDC, 1 & 1/8 inch x 1/2 inch. EACH $6.
6. Angela/SCR Tin Signal Capacitor .33/630VDC, 1 & 1/8 inch x 5/8 inch. EACH $6.
7. Angela/SCR Tin Signal Capacitor .47/630VDC,1.5 inches x 5/8 inches. EACH $8.
8. Angela/SCR Tin Signal Capacitor .68/630VDC, 1.5 inches x 3/4 inches. EACH $8.
9. Angela/SCR Tin Signal Capacitor .82/630VDC,1.5 inches x 3/4 inches. EACH $9.
10. Angela/SCR Tin Signal Capacitor 1uF/630VDC,1.5 inches x 7/8 inches. EACH $11,
11. Angela/SCR Tin Signal Capacitor 1.5uF/630VDC,1.5 inches x 1 inch. EACH $11.

 

[rdf]

Some broken links and not in English but the graphs are self-descriptive. Another interesting take on the subject:

http://www.ec.ss.titech.ac.jp/~hajime/uec/distortion/cap/

 

[amperex]

Coupling Caps - home entertainment amps

First be careful of opinions. If one does not have precise amplifier & stellar speakers, they can not hear much difference.

To our ears a huge difference can exist sonically in-between different coupling caps. A Sprague 716P has a $hit load of color in the sonics. I simply call it mid-range smearing. Just a nasty sounding coupling capacitor.

Better paper/oil designs, Russian Teflon, even AuriCap will kill a 716P sonically.

My 2 cents.

 

[Johan Potgieter]

When both channels in a stereo SE amp are powered from the same power supply, there can be coupling between the channels through the power supply. Put a load resistor on one channel and a speaker on the other channel. Drive the channel with the load to full power with a real music signal. Short the input of the channel with a speaker. Ideally there should be no sound from the speaker. Sound from the output transformer is normal. If you hear anything from the speaker, there is some coupling from one channel to the other.

Just to confirm to all that this a really good test. It is easy to perform on any amplifier, not just SE, and can be most revealing to DIYers. Also a look on the power supply line with a scope can be sobering, although very small signals found there do not necessarily mean that they will get into a particular channel in an objectionable way. But just the same.

Tubelab, yes. I have on occasion demolished new components, but always with a sense of sadness. I once had to take a loudspeaker (driver) apart to confirm that the voice coil construction was kosher. I blamed the dealers/makers, whose claims one can never be certain of!

We can most easily get Hitano electrolytics here in the RSA, of which I obtained some complete specs (also JJs). In the near future I will sacrifice one in the interest of science, and also do some impedance tests for the broadening of my horizons. If interesting I will post results.

Regards.

 

[rdf]

After examining a few of the experimental setups it bothers me all of them shunt the signal of interest to ground through the DUT. Wouldn't it be more revealing, and more representative of performance in a coupling capacity, to connect the low voltage end to 100kohm rather than ground? An alternative might be to the input of an I/V converter but I don't really know enough about them to see if it would work.

 

[Johan Potgieter]

Interesting, rdf.

If I understand you correctly I would agree with you. I recall that Bateman in his research devoted a whole installment to the testing device that he designed, and even provided p.c. boards for interested parties as the layout was critical. It became clear from that, that at the aberration levels he was measuring , down to <-110 dB, it was no simple operation by any means. The test setup must of course not add anything (or if it does it must be small and known).