what have I done?

Almonds

Active Member
I have a kenwood ka-9100 and I was just cranking it with some JBL 4425s that i got recently and all of a sudden one channel started outputting a lot less power than the other side.

I can see on the meters that it's putting out less, and I can hear it. It still has sound, but it's much quieter than the other side, especially the bass it seems.

What might I have done?

I was playing it about as loud as it could go, I guess these speakers are not as efficient as what I was using before and I was trying to get it to levels that I've played at before, but I must have pushed it too far.

I'm just wondering what I should start checking?

Also, after that happened, I powered off and then back on to try to re-test, and I got a puff of static out of the weaker side for a couple seconds that faded away.
 
register and download the service manual at hifiengine.com. I would recommend that if you are confident - get a digital meter and calibrate the DC offset and bias for each channel.

My guess is that you have partially lost a small signal transistor. I recommend you separate out the pre and power sections of the amplifier to identify if the issue is in your pre or power section:

Plug a sound source with volume set to 0 in the "main in" RCA jacks at the back. set any relevant switch to "separate" - turn the volume on your source up a small amount very careful, ensure the kenwood's volume is also up a little bit - same problem?

Then - run some RCA cables from the "pre out" RCA jacks on the back - ensure that any relevant switch to "separate" - plug the other end of the cables into any input of another amplifier - run a signal thru an input on the Kenwood - same problem?
 
Don't power it up again until you have a dim bulb tester.

That had to have been effen' loud!

In the mean time, try your speakers on a known working amp to verify you didn't fry one.

If the speakers check ok on another amp, remove the amp covers and inspect the bad channel amp boards for burned resistors. If a transistor failed, the most likely to fail are Qe5,7,11 on the left channel and Qe 6,8,10 on the right.

Hope that you didn't toast the TA-100W
 
Don't power it up again until you have a dim bulb tester.

That had to have been effen' loud!

In the mean time, try your speakers on a known working amp to verify you didn't fry one.

If the speakers check ok on another amp, remove the amp covers and inspect the bad channel amp boards for burned resistors. If a transistor failed, the most likely to fail are Qe5,7,11 on the left channel and Qe 6,8,10 on the right.

Hope that you didn't toast the TA-100W

If I did fry the TA-100W, can I find a working KA-9100 and just swap?

The unit I have is my favorite amp- even more than my supreme 600. It’s also cosmetically very good and has 5 way bonding posts installed and I believe it has been recapped.
 

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Speakers check out ok.

I will test to see if the problem is in the pre or amp section later. Hurt my back earlier moving all the heavy stuff around and not in the mood to move more heavy stuff around and crawl on the floor behind the system.
 
Sure - you can swap in a replacement module, but I wouldn't without first verifying that the module there is bad. Buying another 9100 just for the module is an expensive way to go. Hopefully your module is fine, and the fact that it comes out of protection is a good sign.

The filter caps and the caps on the power supply board are original, which is fine.

Once you verify that you didn't cook a speaker there are also some power supply voltages to check

Build a dim bulb tester
 
Once you verify that you didn't cook a speaker ...

Once I couldn't get a Pioneer receiver out of protection. Turns out I did fry a speaker. Kind of pissed me off I missed this (and blew the woofer on a vintage speaker).

Don't overlook this and build a DBT and use a load on unknown gear.
 
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