Kenwood pops when turned on

iamthejeff

Active Member
I replaced the relay in my Kenwood KR-6400 and everything was working fine for a few weeks. Then one day, there was nothing, and the relay didn't click on anymore.

I reflowed the solder joints and made sure there were no cold joints, and it works again now. But now after the relay kicks in, there's a little pop out of the speakers. I thought this was common with cap coupled designs (without a relay) but since this unit does in fact use a relay I am not sure what would be causing it. Is it a sign of a problem or is it okay? I don't remember there being a pop like this before.
 
Is there a delay (a couple of secs) when powering on before the relay closes? If so, then the relay & associated circuitry is doing the job properly, as least as far as power-on goes. If that's the case, then check the DC offset. There's no adjustment, so correction will mean replacement of the diff-pair transistors with new matched ones.
 
There is a couple second delay between powering on and the relay click, yes.

Left channel reads about 10mV and right channel reads about 42mV. Not too crazy but you think replacing some transistors should fix it?
 
Those readings aren't really high enough to warrant fooling with, unless you simply have nothing better to do. But, you might consider some new electro caps for the amp board and regulator.

You can also increase the value of Ce30 in the protect circuit to lengthen the turn-on delay and allow the amp to settle a bit more before the relay clicks on. Stock value is supposed to be 100µf 25V. Could try 180µf or even 220µf and see how that works.

I'd also take a good look at the regulated +/-14V and make sure that you don't have something like +15/-11 or some such. They should be fairly close to being equal value/opposite polarity (within 1/2 a volt).
 
Thanks. I think I'll leave it. I noticed the speaker pop thing happens more often if I previously turned the receiver off while it's in the middle of playing music. If I pause the music first, then turn the receiver off, it doesn't happen next time.

I'll experiment some more to see if this is the case or not.
 
Just want to bump this thread to say that I am getting the same issue with a KR-8006, even after a full recap of the power supply and everything. The relay clicks in fine, but there's sometimes a little pop from the speakers immediately after.

DC offset on the 8006 is 2mV and 16mV so nothing to worry about there. Like I said, it only happens sometimes and I can't really figure out how to reproduce it 100% of the time.

Is this fairly common or should I even worry about it? Is it a sign of any failing components?
 
Just want to bump this thread to say that I am getting the same issue with a KR-8006, even after a full recap of the power supply and everything. The relay clicks in fine, but there's sometimes a little pop from the speakers immediately after.

DC offset on the 8006 is 2mV and 16mV so nothing to worry about there. Like I said, it only happens sometimes and I can't really figure out how to reproduce it 100% of the time.

Is this fairly common or should I even worry about it? Is it a sign of any failing components?

You need to look at the output with an oscilloscope to see what is happening immediately when the relay clicks in. Most likely the amp hasn't quite settled down yet, so there is some DC offset when it turns on, causing the pop. Doesn't take much, especially with efficient speakers. You can lengthen the delay time on the turn on for the relay and that will fix it. Replace CK9 with a 220uF / 25V cap.
 
Thanks. I don't have a scope yet :p

I guess the cap replacement is just a bandaid solution anyway, but do you think it's worth worrying about?
 
Thanks. I don't have a scope yet :p

I guess the cap replacement is just a bandaid solution anyway, but do you think it's worth worrying about?

If it's a loud pop, it is worth fixing. Even a soft pop can mean that every time it turns on the speaker relay you burn the contacts a little. This is not a bandaid fix. After it has settled you are getting reasonable DC offset, so there is no point in replacing the diff pair. The best solution is to increase the wait time for the relay to come on.
 
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