Kenwood kr7600 distortion both channels

josumo1

Active Member
Was listening to my kr7600 recently when I began to hear a slight distortion from both channels. I put her on the bench and cleaned all the pots, and switches, waited 24 hrs. and hooked back up and the both channels were very distorted! New output transistors were installed last year and a bunch of caps have been changed. I really love this receiver, in fact I prefer it to my Marantz 2270 so I appreciate any suggestions that are offered. Thanks
 
Power supply voltages good. All lights work and the speaker relay clicks in after power up. Severe distortion when trying to play any of the input sources?
 
Connect the preamp out to a working amp and see if you get distortion. If so, problem is in the preamp. If not, problem is in the power amp.
 
The Kr7600 doesn’t have a pre out, main in connection. It has jumpers marked as adapter in,out? Not sure what they do?
 
Ok, hooked adapter out to a power amp. I got clear sound (no distortion). I guess at this point it’s safe to assume the distortion is coming from the amp section. Something curious that I hadn’t noticed before. When I turn off the power switch, the music will continue to play for about 5 to 10 seconds before it finally fades out! Don’t know if this can be related to the distortion issue? Any thoughts on what could cause distortion in both channels due to a problem with the amp section?
 
The adapter jacks are before the tone section so that doesn't rule much out.

I'd suspect a problem with the regulated voltages on the power supply "A" board (X00-1770-10). Check for +23VDC at pin 2 and for -23VDC at pin 5. Usually with these if either of those voltages is way off it won't come out of protection so it's a bit odd. But that's where I'd start.
 
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When I turn off the power switch, the music will continue to play for about 5 to 10 seconds before it finally fades out!
don't worry about this. all my big amps do this. the PS caps are discharging and it takes a while. I *always* turn down the preamp before power down so I never notice.
 
don't worry about this. all my big amps do this. the PS caps are discharging and it takes a while. I *always* turn down the preamp before power down so I never notice.

Rick - that's not normal on a KR-7600 (nor any other Kenny I'm familiar with that has a protection relay) The relay should open immediately when AC power is turned off.
 
Rick - that's not normal on a KR-7600 (nor any other Kenny I'm familiar with that has a protection relay) The relay should open immediately when AC power is turned off.

Thanks gort. My haflers don't have protection relays so they do fade out. My 9400 with a protection relay doesn't fade out. Thanks again for setting me straight.
 
Ok, I checked voltage at pin 2 and got -22.4vdc and +22.4vdc at pin 5. Voltages are close but polarity is opposite from your numbers? Does this tell us anything regarding the distortion issue?
 
It tells me that you probably had your meter leads reversed when you made the measurements but nothing about the distortion. 22.4V is close enough. Black lead (COM on your meter) to chassis, red lead to pin being measured.

New output transistors were installed last year and a bunch of caps have been changed.

I'd be curious to know which caps have been replaced, which output transistors were installed, and where the parts were purchased. The delay at power down seems like a big clue to me, just not sure what to make of it.

On power UP, do you have a 2-3 second delay before the relay clicks? On power DOWN, do you hear the relay click after the 5-10 second delay? Something's screwy.
 
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All the caps on the amp board, and the output transistors were purchased from Mouser. There is a 2-3 second delay on power up and 5-10 second delay on power down?????
 
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