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A previous poster stated that the Heathkit AR1500 and AR3a are a poor
combination. This is true if you listen at any level other than quiet.
Rolf, I have an AR-3a and an AR1500 and they seem to work together fairly
well. I don't know about "quiet" as that is a relative term.
My den is quite small and my normal listening level is less than 1 watt, but
occasionally I'll listen at levels higher.
A couple of years after introduction, the AR1500's output amplifiers
were updated and the AR1500A was born. The AR1500A has specific
circuits that limit clipping and other distortion when it is driving
low imperance speakers at high levels. It is possible to modify the
AR1500's output amplifiers to include this improvement; you'd have to
go to a Heathkit users groups to obtain that information.
Rolf, any chance you have the schematic for the power amp on the "a"
version. If I could see the "a", I could document the differences.
I would think you'd really have to to be driving the speakers hard to get
anywhere near clipping. My guess is the heavy current drain forces the rail
voltages way down, and this allows even modest signals to clip. Only real
solution is to "beef up" the power supply.
Driving AR3a's hard with an unmodified AR1500 produces a lot of
"clipped sine waves" that will blow the mid-range driver. If you don't
want to burnout the mid-range, but want to turn the volume up, add a 1
ohm resistor in series with each mid-range. This will change the
mid-range balance, but that's better than burning out the driver.
Well, Rolf, I've done just the opposite. I've taken all the pots out of the
AR-3a circuit and this significantly INCREASES the sensitivity of the
mid-range and tweeter. (Frankly, I'm a little surprised that the mid is
most susceptible to clipping damage. People on the AR forum worry far more
about the tweeters.)
In any event, "clipping" is no longer an issue for me. I'm now bi-amping my
AR-3a's. My AR1500 drives only the woofers. I have a nice little 30 watt
Kenwood powering the mid-range and tweeter. The Kenwood has rail voltages
of 40 volts!
With the pots out AND the fundamentals greatly reduced, it's hard to get
peak voltages of 3 volts going to the mid-range and tweeter. I mean, at 3
volts I can barely stand the volume.
Now, there is no question that at the same time that I have 3 volt peaks in
the Kenwood, the peak voltages in the AR1500 are much, much higher. I can't
see any clipping, but even if there were some, the mid and tweeter are
totally isolated from that amp.
The AR3a was sold in kit form as the Heathkit AS103a.
Let me know if you have any questions.
Rolf, if you have an AR1500 and a set of AR-3a's, I'd strongly recommend you
try a bi-amping experiment. Not only will you protect your mids and
tweeters, but there is a significant tightening of the bass that results.
Regards,
Jerry