I've owned both. They are two very different sounding amps. Make sure the GAS SOA is biased correctly; that is,it will run so hot that you cannot keep your hand on the top panel for more than 10 seconds. I've had technicians lower the bias to reduce heat and extend product life only to have me return the unit and demand it be reset to its original spec. Remember, this was the late 70's-early 80's - the Julian Hirsch and Len Feldman era.
In my experience the Hafler is cleaner, smoother, dark and slightly distant sounding. The SOA when biased properly will be a little more on the tube-ish side. Slightly plump bass, a nicely projecting midrange, and good but not ultra extension treble.
In my experience the Hafler is cleaner, smoother, dark and slightly distant sounding. The SOA when biased properly will be a little more on the tube-ish side. Slightly plump bass, a nicely projecting midrange, and good but not ultra extension treble.