On Wed, 5 Jan 2005 22:38:03 +0200, "Iain M Churches"
wrote:


"Jim Lesurf" wrote in message
...
In article , Iain M Churches
wrote:

"Don Pearce" wrote in message
...

First the capacitors. Go through many samples with a meter to make
sure they are as far as possible equal in value. Install them in a
switcher box so they can be changed without delay.

OK. The service technician at the studio has promised to select with a
bridge carefully matched samples from those we give him.

I would wish to know the details of the measurement. Frequencies used (if
sinewave), distortion levels, signal levels, measurement system
calibration, etc. Ideally, I'd wish to know values measured across the
audio band, and get a match to a tight level.

Just a moment. Not long ago, the general opinion seemed to be that we
would not be able to tell the difference when changing between two
caps of the same value and voltage working from different makers.
Now we are being asked to match them to a tight level :-))

Yes, to ensure that they are *exactly* the same value. If this proves
to be impossible, then you should run the tests twice, once with the
Jensen being the slightly larger value, and once with the Jensen being
the slightly smaller value.

If you are using a single-frequency cap bridge, you may need to consider
the effects of series ESR, etc. Given the points made elsewhere about
the dc you may also find it useful to measure with dc applied, and perhaps
even before/after use to see if this has had some effect!

The original claim was that a listening panel would be able to
differentiate between an industrial/commercial grade coupling
capacitor andJensen capacitor.

Afraid I am quasi-paranoid about such things as I've spent 20+ years
working on precision measurement systems for people like the NPL 8-

It shows:-) But I am sure it is a good thing, and that we can all sleep
more
safely in our beds:-)

I believe that Jim is just covering the bases, I myself would be happy
with a simple check of value at 100Hz and 10kHz.

I think I'd like to know things like the frequency and phase response with
each cap in circuit, again with a fair degree of precision.

Those are surely things that will have to be determined afterwards, to find
out why there is a difference in sound, if one can be established.

Agreed, there's little point in intensive investigation *before*
you've observed an audible difference.

We could use a random numbers generator to pick from three numbers, and
feed these to the desk automation.

Erm... how are you planning to do the switching?

As mentioned earlier, The source material and the console both run to time code
and so we can program the changes to TC. This way we will be able to repeat the
experiment with great accuracy. It has been suggested that we should use odd
bar counts (not many people will expect this) in multiples of fives, sevens and
elevens, and switch within the bar:-)

I'm not sure about this TC business, it seems to introduce an
additional stress, and has nothing to do with identifying the Jensen
per se.
--

Stewart Pinkerton | Music is Art - Audio is Engineering