[Jerry]

Peter Wieck wrote on 10/9/2006:
Jerry wrote:

To implement this, all I did was cut the lead on the pots going to the
drivers and the leads at the top of the pot. Twisted these together and
soldered. Put on a wire connector and sandwiched between mounds of
fiberglass (or whatever that itchy stuff is).

The yellow wires are still connected to the pots and from the pots on to
the
drivers. Everything else is exactly as it was. All the reactive
components
are intact.

OK, on the schematic (OEM), there is still 16 ohms in parallel with
each driver to ground, and 32 ohms across both drivers. If I read you
correctly, you have removed the green wire & the output wire from the
tweet-pot, joined them, and left them separated from the pot. The pot
is now out-of-circuit altogether.

Peter, that is exactly correct. Only one wire (yellow wire) is connected to
the pot and pot acts as a terminal strip. The other two terminals on the
pot are connected to NOTHING!

On the Mid side (again, if I read you correctly), you have removed the
choke wire and the wire to the mid from the pot, joined those and left
them separate from the pot. Now that pot is also out-of-circuit, as
well as delivering maximum brightness to the mid. So, not only is the
resistor gone across the drivers, but also across the pair. This will
increase the impedance of the speaker overall, and, of course, the
tweet and the mid.

Yes, it does increase the effective impedance of those individual drivers.

Let's assume the DC resistance of the drivers is around 3.2 ohms (by
themselves). So with the 16 ohms in parallel, the effective resistance
would be 2.67 ohms. Pot causes the impedance to be .53 ohms LOWER.

Notice, that with the pot across the drivers the impedance is lower in total
(some would argue 2.76 ohms is a 'tough' load for any amp), so the speakers
draw more current. The sound output (SPL), however, is also lower!

It will also send _ALL_ of the energy across the two
drivers, dissipating none of it across the two TWENTY-FIVE WATT, 16 ohm
fixed resistors (elements of the pots) as they are now out-of-circuit.
You are correct (more-or-less) in that it will not affect the frequency
performance of the crossover, but it will change its function.

Peter, you are correct again! With zero dissipation, the drivers become
more sensitive so we must reduce the energy (actually voltage) applied to
them. Reducing voltage is trivial as all I do is set the volume control
LOWER. Failing to do this results in way, way too much emphasis in the high
frequencies.

With lower voltage being applied, the headroom (difference between signal
voltage and rails) INCREASES. That is, it becomes far, far more difficult
to get into clipping on this amp. Then when we significantly reduce the
fundamental frequencies, it's just about impossible to reach clipping in
that amp. Impossible, of course, UNLESS we "fry" the drivers by over
driving.

Is this correct? On mine, I have soldered the output wire to the 'high
side', but I have left the fixed elements of the pots in place
electrically. This gains the 1dB - 3dB that the pot-in-place wastes,
and with replacement of the caps with 'tighter' caps, makes the speaker
a good deal clearer, at least to me. But there could be _A LOT_ of
power going into those beasts, I question the wisdom of pulling the
pots out of the circuit entirely.

Peter Wieck
Wyncote, PA

Peter, what you have done is equivalent to setting the pots to Max Increase.
This is the correct position for the pots (you also need just a slight
increase in the treble control), if you want a totally FLAT response. AR
did NOT recommend this setting back in 1968, because at that time all the
record companies were enhancing high frequencies to compensate for the poor
audio equipment in the general market.

Peter, you have accomplished something else, however, which is very good.
Specifically, you have totally by-passed the pot wiper!! That wiper because
of age and dissimilar metals corrodes and that corrosion reduces effective
energy sent to the drivers.

You cannot do what I did, Peter, without testing the resulting balance.
That is, with the pots out the drivers become so sensitive and that
sensitivity is over such a broad band, that you would have a very difficult
time bringing the sound back into balance. You could NOT do it with tone
controls. You'd have to have a minimum 7 band EQ and even then I have my
doubts.

Now, with a separate amp powering those drivers, it's trivial maintaining
the balance.

Peter, this is why I've been trying to get you to try your tube amps on the
mid/tweeter. There may be a problem with your tube amps, however.

If I'm not mistaken, your tube amps don't tie the shielding on the audio
inputs to chassis ground. If I am correct, you cannot use them with an ss
amp on the woofers without bring out adding a new terminal on the speakers.
In short, I think you are out of luck.

Regards,
Jerry