Harman Kardon HK775 mono

Ann4 · 27th February 2012, 01:53 PM

I bypassed the filter board on one of my hk mono blocks so that the signal goes from input straight to the pre-driver board with no ill effects so far. I was warned by an electrical engineer friend that the move was risky, but there have been no ill effects so far. The speaker driver is in the same position when the amp is powered on and off. And I inadvertantly powered the amp on and off with upstream components powered on. Nothing blew up. And the sound quality is significantly improved. Has anyone ever bypassed the filter board on these amps or have an opinion on whether I should go ahead with the other amp and make this modification permanent?

Ann

sgrossklass · 27th February 2012, 02:29 PM

Looking at the schematic, I am not sure where any significant improvements in sound would be coming from. Are you sure that the effect is real? If anything, you could have cleaned the subsonic and ultrasonic filter switches and possibly replaced the two series-connected 100µ/16 caps with a new 47-100µ bipolar with the same result.

Ann4 · 27th February 2012, 02:50 PM

OK. I should have explained that one of these amps started dying and that working the subsonic filter switch caused it to work intermittently. I attempted the bypass in the interest of straight-wire-and-gain. Years ago a high qualified tech bypassed all the switches except balance on the companion preamp with a dramatic improvement in clarity. Thanks. Ann

27th February 2012, 01:53 PM	#1
Ann4 diyAudio Member Join Date: Feb 2012	Harman Kardon HK775 mono I bypassed the filter board on one of my hk mono blocks so that the signal goes from input straight to the pre-driver board with no ill effects so far. I was warned by an electrical engineer friend that the move was risky, but there have been no ill effects so far. The speaker driver is in the same position when the amp is powered on and off. And I inadvertantly powered the amp on and off with upstream components powered on. Nothing blew up. And the sound quality is significantly improved. Has anyone ever bypassed the filter board on these amps or have an opinion on whether I should go ahead with the other amp and make this modification permanent? Ann

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27th February 2012, 02:29 PM	#2
sgrossklass diyAudio Member Join Date: Nov 2004 Location: Germany	Looking at the schematic, I am not sure where any significant improvements in sound would be coming from. Are you sure that the effect is real? If anything, you could have cleaned the subsonic and ultrasonic filter switches and possibly replaced the two series-connected 100µ/16 caps with a new 47-100µ bipolar with the same result.

27th February 2012, 02:50 PM	#3
Ann4 diyAudio Member Join Date: Feb 2012	OK. I should have explained that one of these amps started dying and that working the subsonic filter switch caused it to work intermittently. I attempted the bypass in the interest of straight-wire-and-gain. Years ago a high qualified tech bypassed all the switches except balance on the companion preamp with a dramatic improvement in clarity. Thanks. Ann