eab@cblph.att.com (Eugene A Beer) (06/05/91)
Has anyone done the Musical Concepts upgrade on a Hafler Power amp (DH 500, 600, 280)? The upgrade consists of replacement driver boards. Is there a noticeable sonic improvement? I wired one channel up last night and when testing it with a current limiting light bulb in series with the amp, the board smoked. I DID follow the directions exactly, so maybe I had a defective board. Any comments would be welcome. Thanks Eugene Beer eab@cblph.att.com
filippo@quark.umd.edu (Filippo Neri) (06/06/91)
>Has anyone done the Musical Concepts upgrade on a Hafler Power amp >(DH 500, 600, 280)? The upgrade consists of replacement driver boards. >Is there a noticeable sonic improvement? >I wired one channel up last night and when testing it with a current limiting >light bulb in series with the amp, the board smoked. I DID follow the >directions exactly, so maybe I had a defective board. >Any comments would be welcome. Thanks > Eugene Beer eab@cblph.att.com I installed the PA-1 mod from Musical Concepts in an old Hafler DH 220. The instructions sent with the kit were wrong! Fortunately I was too busy to do the installation before I received a correction in the mail! So you may have followed the (original) directions to the letter and still smoked a perfectly functional board. I would contact Musical Concepts concerning this problem. With respect to the sonic improvements, in my rather minimal system, they are astounding. The old Hafler sounds like much more expensive units I have auditioned. The bass is much improved. I suspect that most of the improvement derives from the higher input impedance of the FET circuits that are used in the PA-1 boards. The expensive tube units I tried also have higher input impedance than bipolar transistor amps. All but the output transistors on the original Hafler amplifiers are bipolar. My system is as follows: SONY X77ES -> Power Amp (modded DH 220 ) -> Magnepan MSgs. No preamp ( I use the variable outputs on the SONY CD player ). This configuration, of course, requires a high input impedance amp. BTW do net people have suggestions for improving this system? What about using passive attenuators on the fixed outputs of the CD player? What about better speakers ( Like Martin-Logan CLS IIs ). Would they be wasted given the cheap and low power ( 100Wpc ) amps? In this case what amp would you suggest. Should I add a preamp, after all? What about silver cables, like Kimber KCAG? The CD player is the only unit that is not going to be replaced in the next two years, under any circumstance! Thank you, Filippo Neri filippo@ruflie.umd.edu NERI@LAMPF.BITNET