"Don Pearce"
Jim Lesurf wrote:

http://www.st-andrews.ac.uk/~www_pa/...g/howlong.html

Doing the usual maths on your table of cables

A = 8.5

** Cable "A" would be a woven multi-strand cable like "Tocord" - it was
sold under other names too.

So as far as top end flatness goes, characteristic impedance is the best
predictor of performance. Despite high capacitance, which might be thought
of as predicting a sagging top end, the high cap cable (A) at 8.5 ohms
impedance is the only cable which is actually flat. And of course a
further implication of this is that this cable does not present a
capacitive load to the amp - it connects the speaker almost invisibly,
presenting the speaker impedance to the amp essentially unchanged.


** Jim got the results he did because of the *artificial* way he set up the
model.

1. The amplifier has no output impedance at any frequency.

2. The speaker load is an 8 ohm resistor.

In the real world, NEITHER of these is EVER the case.

Cable "A" ( which is an 8.5 ohm transmission line) WILL in fact present a
severely capacitive load to the drive amplifier when used with real
speakers, virtually all of which have a steadily rising impedance above
20kHz.

Also, if the cables are ever attached at the amplifier end but not at the
speaker end the load is a pure capacitance.

Some hi-fi amplifiers are highly allergic to capacitive loads in the ranger
of 5nF to 30nF and immediately break into supersonic oscillation - thence
overheat and self destruct.

Most NAIM models were famous for this and the power amps made by Phase
Linear.

Due to its penchant for amplifier destruction, dealers became reluctant to
stock it and Tocord was soon pulled off the market. Other 8 ohm
transmission line cables have exactly he same problem.



...... Phil