From: jch@teak.Cray.COM (J.C. Hamlin)
Subject: Re: Autotek Amplifiers? (1 ohm stability stuff)
Organization: Cray Research, Inc.
Distribution: na
Date: 13 Apr 92 13:52:09 CDT

In article <1992Apr10.041531.7286@helios.physics.utoronto.ca>, biancol@bullet.ecf.toronto.edu (BIANCOLIN  FABIO S) writes...
>
>     I wouldn't say that though!  They don't handle 1ohm loads.

Actually, the Autotek 9100 (2x50), 9050 (2x22), 7100XX (2x50), and 
7050XX (2x22) all handle 1 ohm loads nicely.  However, they are very small 
for their power output, and therefore you will have some problems with 
overheating them if driven at 1 ohm loads without a substantial cooling system.

>     I bought a 7600...yes the 900 watt monster!)
>     Then i got tired of it and sold the 18's and bought 6 Kicker 15's
>     I used the 7600 to power all of these speakers...
>     (I was running the amp with 3qty 4ohm speakers on each channel...
>     calculated out to about 1.33 ohms per channel)
>     the amp just cut out....

The 7600 is only rated into 2 ohms per channel.  You "fried" it because the 
amplifier wasn't engineered to (and therefore cannot) drive a 1.33 ohm load.

>  MORAL?
>        don't buy an autotek (except the high current ones) unless you
>        plan on running it in its specified limits... if you overstep its
>        boundaries... it will fry itself!!!  My suggestion would be to get
>        a PPI amplifier (2200 or 2300) for a little more than this amp
>        costs and save you the headaches

These are most of the high voltage amplifiers (rated >150-200w into 4 ohms) 
on the market:
   Alpine 3544, Autotek 7600, Crunch 600, Earthquake PA-2300, 
   HiFonics Colossus, Kenwood KAC-1023, Kicker 500 si, Linear Power 5002 IQ,
   Monolithic PA-5000, Pioneer GM-H200, PPI 2300 AM, PPI 2200 AM, Pyramid 
   Super Pro 2300, U.S. Amps US-500A, Wavelength PWR400, Zapco Z300.

All of these amplifiers are 2 ohm stable, and none of them are 1 ohm stable.
One ohm stability with such high voltages as what these amplifiers are putting 
out requires huge amounts of current that the amplifier just isn't engineered 
to produce.  If you attempt to drive any of these at under 2 ohms, you will 
probably damage it.

If you examine audio amplifiers on the market, you'll find that most 1 ohm 
and 1/2 ohm stable amplifiers are lower power (rated 50 watts or less 
into 4 ohms).  And, the "monster" (high voltage) amps are only 2 ohm stable.

The trick (in 4 ohm rated power classed competition) to using 1 ohm and 1/2 
ohm stable amps is not the 4 ohm rated power.  You don't connect a single 
speaker to each terminal with these guys, you add extra speakers to it--and 
each one will get the same amount of power as the single driver connected to 
it (theoretically).  It is like getting a free amp.  Or, you bridge the 
amplifier whichs doubles the power, and then use a 4 ohm speaker dropping the 
impedance per channel to 2 ohms--thus quadroupling the power per driver.  
Depending on the amp, you should be able to connect multiple drivers bridged.

Here's one example (the one I am using thanks to a suggestion from Joshua 
Poulson).  I am running four 4 ohm C-10s bridged across the terminals of 
an Orion 225HCCA (2x25, 1/2 ohm stable).  This produces 100 watts per driver 
and a 2 ohm load on each channel per driver.  With four drivers, you get a 
load of 1/2 ohm on each channel and 400 watts of power total.  From a 
50 watt amplifier. :-)  I am considering using a Phoenix Gold MPS-2500 
(2x50, 1/2 ohm stable) to get 200 watts per driver, but I am unsure as of 
yet.

Moral?

Follow the amplifier manufacturer's specifications for the minimum load 
impedance and you'll prolong the life of the amplifier.

When searching for an amp to produce a lot of power into many speakers (one 
that is low impedance stable), don't expect a lot of power per driver unless 
you bridge it or use 2 ohm drivers.  Of course there are notable exceptions 
like the Orion 2100 HCCA (2x100, 1 ohm stable).

> >  Can they handle 2 ohm loads (mono and stereo?)?
>    Yes, but only 2ohms per channel maximum (not 1 ohm or less)

(see comment above about Autotek amplifiers that are 1 ohm stable)

J.C. Hamlin
jch@Cray.COM
Newsgroups: rec.audio.car