"Scott Dorsey"
"Phil Allison"
** Really ?? Not with domestic amps like Technics.
Such amps are never intended to drive 70 volt line ( step up)
transformers
are very likely to be damaged by so doing.
The issue is core saturation at low frequencies - hard to avoid
completely and deadly on anything but the most rugged amplifiers.
Wow. I had no idea Phil was still around! But yes, I have done it plenty
of times, even using some pretty shoddy amps based on STK modules (like
those Rane 1U power amps) and never had a problem.
** How dishonest.
Rane's 4ch 1RU amps are specifically designed to drive line transformers
with ELABORATE inbuilt filtering and limiting - an optional 1RU box with
4 toroidal line trannies goes with these amps.
http://www.rane.com/ma4.html
But I could see there
being an issue with undersized output transformers if you aren't filtering
the input of the amp.
** All transformers suffer from core saturation, larger ones just do it at
lower frequencies than smaller ones.
No matter how big the step-up transformer is - there are still all those
puny distributed ones at each speaker location, most of which saturate hard
at 70 to 80 Hz with nominal voltage input. The gross overload effect
thereby created is naturally reflected straight back to the poor suffering
amplifier.
What about a coupling capacitor or would that be a bad idea?
Bad idea if you put it after the amp, because the amp does not like
driving
capacitive loads.
** Nonsense.
SS amps used output coupling caps since they were first invented with no
such problem.
But put a filter before the amp so the amp never puts
low frequencies into the system, and you'll be fine.
** Such high pass filters really need to be built into the power amp to be
reliably effective - plus have a steep slope like 18 to 24 dB/ octave and
start rolling of at around 90 to 100 Hz.
External filters can still result in serious problems with switch on and off
thumps.
Rane seem to be well aware of all the issues.
http://www.rane.com/pdf/ma4dat.pdf
..... Phil