• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Kenwood KA-2500 "spirited" offset

bazzle592

bazzle592

New Member
Hello all!

I picked up a Kenwood KA-2500 at an auction a couple of months ago, and have been working to restore it. Unfortunately I've hit a bit of a roadblock.

20210215-212540.jpg


Upon initial testing I found that it had a light hum and a horrific +20VDC offset on both channels that gradually falls to a much healthier 40mv over the next 40 seconds or so. Gave my sacrificial speakers quite the jolt.

I have carpet bombed all of the electrolytics, and while this fixed the hum, the "spirited" startup continues.

20210215-212656.jpg


I've hooked it up to some actual speakers (after it calmed down) and it sounded excellent - very rich sound with plenty of deep, clean bass. However, I obviously can't put it into service with that surge. My limited troubleshooting knowledge with these things has left me stumped. Anyone with more experience have any ideas on what to check next?

Thanks!
 
Register to hide this ad
redk9258 said:
It is cap coupled and you cannot measure DC offset the way you are.
Click to expand...
Okay, I learned something! With a load there is no DC at the outputs, so it would appear that everything is functioning fine after all. False alarm. The inrush was just scaring me a bit - it gets quite a pop out of the speakers.

Would one of those soft starter boards help to curb some of that? Or is this just the nature of such an early solid state amp?
 
I think it's the nature of the beast. When the cap charges, you will get the pop. You could try turning the speakers off and power up with headphones plugged in. Do a search here on AK for "cap coupled turn on thump".
 
bazzle592 said:
Would one of those soft starter boards help to curb some of that?
Click to expand...
You could try turning the amp on with speakers turned OFF. Wait several seconds then turn speakers ON. Thump still there? If it's better, the the relay might work for you.
 
Coud put a speaker selector between amp and speakers...use it to keep them out of circuit until amp settled.
 
Just an observation as I have a 2500 on the bench now.

The power amp board is the same as in the ka2000 and a few receiver models of that time.

Replace the trimmers, the originals were terrible when new.

All the caps that go in the clamps, please get ones that fit the clamps, much safer than clamping foam around them, measure diameter of old and search mouser, speaker coupling caps go for Nichicons 2200uf snap ins, smaller filter cap Nichicon 1500uf snap in, main filter cap any 3300uf snap in, you will have to go up in value. Use ring terminals clamped and soldered to the cap legs for the ability to solder all the wires on. If you find the caps are still a little loose get some of that 3m double sided tape for mounting led screens wrap around the cap once, pry the clamp open as it will just stick to it before it's in place and tighten clamp when placed and hey presto that caps going nowhere.
 
You must log in or register to reply here.
Back
Top Bottom