Shortwave Sportfishing wrote:
On Sat, 14 Jan 2006 19:04:30 -0800, -rick- wrote:

Eisboch wrote:

Saw an interesting study on amplifier distortion ratings recently. Typically
expressed as "THD" or Total Harmonic Distortion, it is generally considered
that the lower the number the better, resulting in amps with ratings of 1%
or less, often much less.

Turns out that in a series of blind tests with a control group for
comparison that were told what levels of distortion existed, the human ear
is very non-sensitive to relatively high levels of distortion. Furthermore,
the ear is frequency dependent in it's ability to detect distortion. I
forget the exact numbers, but it was something like above 8khz the ear was
most sensitive and both the blind group and the control group detected
distortion at about 3 percent. As the frequency lowered, both groups were
unable to detect higher levels of THD. At low frequencies (bass) it took
almost 100% THD for the groups to detect any distortion. Both group results
were almost identical also.

I also remember reading about Carver amps which were of a "magnetic amp"
design. Bob Carver, the designer of the original Carver amp claimed the
same thing as the tests described above. Carver amps typically have a much
higher THD rating than those of comparable competitors.

Oh, well. Useless information on a rainy day, 40 minutes from kickoff of
the Patriot's next victory on the way to the SB.

More useless info...

As I recall the Carver "magnetic" amp (the cube?) was a bit
of a misnomer. I think this design had a number of
switching power supplies that produced a range of output
voltages (+/-10V, +/-20V, +/-30V, etc. for example). The
audio output was switched to the power supply that was most
nearly equal to desired gain * input signal. A low power
linear amp would then correct the residual error and
switching glitches were reduced with a low pass filter. It
was quite efficient and needed minimal heat sink but did
have higher noise and distortion than most linear amps, not
that I could hear it.

Hearing sensitivity is intensity and frequency dependent as
shown by the Fletcher-Munson curves which may explain the
distortion results you noted.

http://www.webervst.com/fm.htm

The thing is I *want* the guitar amp to distort when pushed.
But I want "nice" distortion, like Eric Johnson's 600lb
violin sound. Hey, would that be a Srativarius?

http://www.ericjohnson.com/

Maybe some day I'll find time to experiment with a low power
tube amp and novel ways of crippling it. I have a recent
Fender Hot Rod Deluxe (40 watt tube) and it's ok clean but
way too loud to push the output stage and the preamp
distortion on the overdrive channels is just nasty.

with all the guitar players in this group, we all ought to get
together and find a drummer somewhere just to play through and have a
massive jam session.

In high school, I was in the orchestra and marching bands as a drummer.
I played Timpani in the orchestra. In my basement bar room, where I
practice and play guitar, I've got several percussion instruments
people can pick up and mess with anytime they want. I've heard some
pretty funky stuff there!! I've got a cheap djembe drum, tambourine, a
cheap bodhran. I'm looking for a used conga.