Harold and Susan Vordos wrote:
Chuckle! Yeah, I could do that, but if you've priced Mc amplifiers (I'll
settle for nothing less), you'll understand how cheap large wire looks to
me.
While I would never argue the quality of Mc amps, I would think you want
low distortion more than you want high power.
The likelihood of me using anywhere near even 200 watts in the shop is
relatively remote.
If we are talking Sear's watts, I agree but if we are talking real
watts, that's probably serious over kill.
Back in the early 60's, I designed and built a stereo amp. It was based
on the use of op-amps (6 per channel including the power stage) and, as
no IC's could meet my performance requirements, I designed my own.
At the time I was teaching circuit design at U of Alberta and had
inherited the sound lab for lab space. The previous occupant had
retired. I kindly agreed to store the AR2AX speakers at home.
(Regretably, I returned them when I left.) Note that AR (acoustic
suspension) speakers, while producing superb sound quality, were
notoriously inefficient.
My amp was designed to clip (regulated supplies) at a little over 10
volts out. Into 8 ohms, this is 1.25 amps or 12.5 watts peak per
channel. This level was chosen because I wished to operate the power
transistors below or, at least not much above, the current where their
beta peaks. At the time the price of complementary Silicon power
transistors rose rapidly above this level. This philosophy produced
unusually low open loop distortion so very large loop gains were not
required.
Briefly, some specs:
Bandwidth: 1.59Hz (10r/s) to 100KHz +1, -3db (open loop bandwidth of
op-amps to exceed this). Actually, all was dc coupled except for a high
pass filter at the input. You'd be astonished how much thermal
potential you can get out of a phono cartridge.
Noise and hum level with tone controls set flat and gain set so a
typical classical recording was peaking just below clipping: 120 db
below full output.
Distortion at 10 volts peak output into 8 ohms: 0.05% THD. (It was
quite a project just to measure this at the time.)
Using a B&K sound level meter and a Tek scope, we determined that
Ravel's Bolero would give us 100+ db spl in our living room before
clipping. (This with the AR2's.) Since 120 db is accepted as the
threshold of pain (for non-atendies of rock concerts), this seems
adequate. A few years later I designed a 50w peak per channel version
for a friend's band. All that accomplished was to blow the snot out of
"150 watt" speakers designed for bass guitars.
I can fill a large (*very large*) room with a few watts.
It's very easy for me to overwhelm the loudest of noises with what I have
now, but I'd like the additional power in reserve for heavy passages at
moderate volume. Think 1812 Overture, Carmina Burana, or Toccata & Fugue
in D Minor.
Add to those, the Ride of the Valkaries and certain selections from
Ancient Airs and Dances. BTW, look at waveform from a violin some time
and you'll see something designed to scare low power amps. :-) One of
my tests was to get one of my grad students to play his violin live into
a pair of B&K condenser mikes driving my amp.
Thanks for the great input. Right now I'm still thinking 10 ga, but
certainly nothing smaller. From the figures provided, it looks like things
get right out of control with smaller than 12 gage wire.
I still think you should go for line level to the shop and an amp there.
One thing you haven't considered is the variation in speaker impedance
with frequency and the damping factor of speaker, enclosure and room.
That's why serious designers want there amps to have very low dynamic
output impedance. Ideally you would like your speakers looking back
into a dead short. The two amps I mentioned in this thread had output
impeadances of the order of a few milliohms. From Evcerwal's post
6ga = 0.05 ohms. This is a full order of magnitude above what I would
like.
Ted
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