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Dick West 7th March 2005 12:36 AM

XL-280 Its Sound and My Fury
XL-280 Its Sound and My Fury

This amp sounds very good in the mids and highs but the low end quickly becomes ponderous, loose, too loud, and gives a sense of being out of control. Why? It sounds as if a bass boost circuit is engaged from about 150 hz on down. The mids and highs are great but the bass is bad, hence my fury!

I have used several different amps in my room with my nice 3-way PolyNatalia type speakers and all other amps sound OK. In other words, I sense no problem with speakers or their interaction with the 22'X 24' room. Speaker cables are from Kimber.

Recently I tried changing the feedback electrolytic in a DH-200 from 470 uF to 1000 uF and got the same effect. The bass became ponderous. This experience makes me wonder if I should try the reverse on this XL-280 and change its C8, a 1000 uF electrolytic, to 470 uF?

The XL-280 has circuit cards fed by a separate 75 VDC power supply. Could its two 470 uF power supply caps cause the bass problem if they are old? The bias is set at 270 mA and there is no DC offset.

FWIW today I removed one pair of MOSFETs from each channel and reset the bias and the amp now sounds better, the bass is less obvious and better controlled.

What to do? It is like it is two amps, depending on whether bass or mid/high notes are playing. Help is appreciated.

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