Hafler Pro125

I have a couple of these Pro125 in my collection. Apparently, they were manufactured in 1988. That would make them 9 years after the DH-200. Power output is at 60W@ 8Ω. I can’t find any info on 4Ω but from my Lm60, it should be 80W.

There is very little information I can find on the internet about the Pro125 but I was told the Hafler SE120 is the same. I have yet to take a look inside the Pro125 so I don’t really know whether the outputs are 2SK134 and 2SJ49. What I do know is the SE120 uses the newer 2SK1058 and 2SJ162.

Hafler SE120 Power AmplifierFig 1 – Hafler SE120 Amplifier Schematic

It appears that after 9 yrs, Hafler decided to simplify the circuit of the Pro125/SE120 (Fig 1). It doesn’t mean that the Pro125 is inferior to the DH-200. They have abandoned the more complicated mirror image topology in favor of a tradition single ended VAS.

However, it is more than that. Starting at the input differential (Red line), they adopted a pair of current mirrors. This is what is known as an active load. It has a higher impedance compared to a single resistor. Because of that characteristic, the voltage gain is much higher.

In the VAS, they have also installed a cascode to extend the bandwidth. After the VAS, it is quite conventional. A pair of drivers drive the gates of the power mosfets.

Summary

For a 60W amplifier, the circuit is quite elaborate. It only goes to show Hafler’s dedication to sound quality. Owners will not be disappointed. This is an outstanding power amplfier.