Correct on the 4 ohm power, they are speced as though they double power
@ 2 ohm but in reality the 4 ohm power is just higher than speced and
the amp shows a typical increase of 50-60% from 4 ohm to 2 ohm.

I'm not sure how many versions of the original P450/650/850 there are,
but your assessment of them sounds pretty accurate. The ".2" version has
two versions, the first-gen was being produced in Phoenix and we then
debugged it before moving to turnkey production at the same factory that
had produced the PCB's all along. The ".2" models are pretty much
bulletproof and work flawlessly, provided you're willing to spend a
couple of hours getting acquainted with the front end features so the
installed product is configured optimally. It's easy to get in a hurry
and screw up the signal routing or make conflicting crossover settings.
I guess that's the penalty for having as much control and versatility as
these do - it does require a more competent installer to get the best
out of the installed product. Which isn't all bad...

JD

John Andreen wrote:

A/D/S did make some higher powered amplifiers prior to my working there. I
believe that they were 2 x 100, but I can't be certain. During my tenure,
the most powerful amplifiers were the ADS P450, P650 and the P850. They
actually made closer to 75 watts per channel. These amplfiers are really
PPI Powerclass outputs with the crossover sections being true ADS. The
input sections were my design. Not really, because I simply got my
inspiration from another design that I found on the web. I did change it
though to suit our requirements. I can also tell you that there are two
distinct versions of these units. Maybe three now, the third being DEI's
version. Without actually looking at the PCB's there is no real way of
telling if it is the earlier version ( pure A/D/S ) but has issues, mostly
turn on pop and the later versions ( A/D/S / PPI ) which are really
stellar performers. The digital displays of the PH30 and PQ40 are actually
quite worthless as it doesn't really display the frequency, but a frequency
found in a lookup table relative to the position of a potentiometer ganged
with the frequency pot. This is only an approxomation at best, and there
is inherent slop and backlash associated with potentiometers. I also had
to modify the software coding ( Many thanks to Campbell Kelly for his
help ) to stop the display from drifting or blinking.

I seem to recall 5 distinct amplifiers in the A/D/S line during my tenure.
the P450, the P650 and the P850 and the two models with the digital
displays. These other two units were the PQ40 and the PH30. These are the
units that make 4 x 100 (PQ40) and 6 x 75 (PH30). Really great amplifiers,
but never trust the frequency displays. BTW the LED displays were supposed
to be blue, but we had a butt load of RED LED displays leftover from an
older version. All the .2 versions of these 5 amplifiers have the true
balanced differential input section that I had a hand in. Makes for a much
quieter amplifier.

JA

Mark Zarella wrote:



I can also tell you that A/D/S pretty much made extremely good units


except


for a few choice "dogs". I can only currently think of only one. I can't
remember the model, but it had several DSP processors on board. Also had
5, yea 5 separate power supplies. Each one "yanking" the amplifiers


ground


all over creation. They also had a rather good Audio Engineer's ( Ed
Meitner ) pre-driver stage that was particularly good at rejecting Power
supply noise or any "common-mode" noise for that matter. It was partly
their saving grace. I think that your P840 shares this pre-driver
technology. If you can get your hands on a schematic of your P840, look
for the pre-driver stage. If you see some OPAMPS whose output pins are
tied to GND and has JFETS between the +/- 15 volt rails and the OPAMPS
input +/- supply pins, then you are indeed fortunate. This type of
driver
section is usually only used in audiophile grade home amplifiers. Ed
performed a miracle and got it to work for a car amplifier. Those amps
also typically us Burr-Brown Audio grade OPAMPS as well.


I've replaced op amps for people who asked me to before (sometimes along
with the discrete components so that I could modify xovers and the like,
but that's another story), and never found a noticeable difference
afterwards.
But admittedly, I never a/b'd them. I wouldn't expect a difference
though, since the distortion characteristics of modern op amps tend to be
top-notch (and in fact, superior to discrete components as I found out the
hard way in one design I was doing for another application).



In short, That amp of yours and it's next of kin the P850 are indeed
great
amps. Just stay away from Constant Bass. This function was implemented
incorrectly. If it were done right, it would be a blessing. But, it was
implemented wrong and kills your sound stage. Engage this feature and
listen to a "sound staging" test CD. You will indeed hear the loss of


your


soundstage.


I'd like to be able to find a higher power 2-channel relative to the P840
for my rear speakers. I currently have a 240 (?) that looks the same, but
I
was hoping to find something closer to 80x2. Did they make one?