Reply-to: Association for Recorded Sound Discussion List <ARSCLIST@xxxxxxx>
At 06:20 PM 2008-10-20, Larry S Miller wrote:
The current discussion of power cables brought me back to my
days as an audio equipment salesman.
Hello, Larry,
I fully agree with you that making changes in the system can make
improvements. In the case of the audio cables making a difference,
and I agree with you that the synergistic effects are the general cause.
Another phrase for this is "using rubber gloves for leaky fountain
pens". I will credit one of my mentors, the late Hans Schmid, for this.
In my past days as director of engineering for McCurdy Radio in
Toronto, a maker of high-end broadcast audio consoles, we were asked
to make an eight-bus mixer for a client. The systems engineer placed
the card-mounted buffer amplifiers for the bus submaster faders in
the equipment pedestal, about 15 feet away. He also used relatively
high-impedance faders (I think balanced 5K or 10K ohms). The test
department discovered that the frequency response of the console
through the submaster chain varied depending on where the faders were
set. Well, this is no surprise, a 10K potentiometer will provide
about a 2.5K ohm source impedance when the voltage level is at half.
The cable capacitance was loading this down. We replaced the
miniature shielded twisted pair audio cable that we usually used
inside the console with heavy (like about 0.4" diameter) data
twinaxial cable with far lower capacitance per foot and the response
variations were then well within specification, and much smaller. The
ideal solution would have been a buffer amplifier directly at the
fader, but we did not make enough of this configuration to warrant
this additional module in our line.
This comes around to the Nakamichi Dragon cassette decks that have a
similar configuration, but unbalanced. I use short, reasonably
quality jumper cables between these and the IHF balancing units
(Aphex 124A) and then run the balanced cables to the patchbay. Only
those units within about six cable feet of the patchbay use the
balancing units in the patchbay. In addition, with this
high-impedance signal being unbalanced, longer runs are more prone to
hum pickup even from segregated AC Mains cables.
As to the hospital grade receptacle, this could be one of several
things including lower impedance on the current carrying conductors
and/or a lower impedance ground connection.
I continue to see comments disparaging my use of the phrase "properly
designed". I do think that we need to get after manufacturers to
properly design equipment so that these synergistic cable effects are
minimized. One major mistake that I think has been made over the
years -- and I see some correction in this regard -- is insisting on
unbalanced interconnections between audio components. Balanced,
low-impedance, voltage-matched (i.e. not power matched)
interconnections make a lot more sense than unbalanced ones.
Remember my statement at the beginning of this post about "rubber
gloves for leaky fountain pens". Sometimes you may wish to continue
to use the fountain pen for sentimental reasons or it has a nib that
works just right for you, but in a production environment, purchasing
decisions should avoid purchasing the leaky fountain pen in the first place.
Cheers,
Richard
Richard L. Hess email: richard@xxxxxxxxxxxxxxx
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.