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Issue with Krell KSA-250

Hello-

It's been a minute since I've been on the forums here, but I'm glad they are still around!

I am the second owner of a Krell KSA-250 amplifier. For the past 10 years it hasn't given me any problems. Then today, when I turned it on, it emitted a rather loud buzzing sound. This wasn't coming from the speakers (like a ground loop hum), this was a very startling almost "mechanical" buzz sound. The buzz does not stop until I turn the unit off.

I'm not sure where to start. I called my local audio repair store, but they don't work on Krell. They suggested I contact Krell, which is my next step, but seeing as I'd have to freight this for it to be repaired, I'm hoping someone here might shed some light on what's happening. I've made a short 15-second video of the issue, but I don't think I can upload it here. I'm happy to provide it though.

Any thoughts you might have would be appreciated.

Thanks,

Blake

blakeh
jea48
4,425 posts
 

I know capacitors don’t buzz, but they can cause the transformer to buzz.

Yes, if they are putting a higher than normal load on the secondary winding(s) of the transformer. That in turn puts a higher load on the primary winding. (Louder than normal 60Hz hum/buzz.) Enough of an overload on the primary winding will cause the AC fuse to blow.

I believe they can also cause electronic components to buzz.

The fact the buzzing sound is not heard through the speakers is an indication the output L&R CH relay protection is working.

The sound frequency heard from inside the amp is well above 120Hz, imo.

120Hz test tone

I noticed in the video, the OP supplied, it took several tries pushing the off button to shut off the amp. Is that normal for the Krell amp? More relays?... Mechanical relays?...

Does the Krell KSA-250 amp have a soft start circuit? If yes, I noticed the buzzing started immediately after he pushed the power on button.

 

The Service Department

jea48
4,425 posts
 

It could be an electrical mechanical power relay(s) making the buzzing sound.

 Krell amp buzzing sound. http://www.stateofgrace.net/krell.mp4

Buzzing contactor    

Sound similar?

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invalid
1,186 posts
 

@jea48 there is a soft start circuit, and it’s a well known fact that the capacitors get hot because of where they are placed, right next to two 700ohm resistors.

Post removed 
jea48
4,425 posts
 

@invalid , Ya lots out there on the Net about problems with the Krell KSA-250 amp. Almost think the layout guy that designed the placement of components built in a self destruct feature.

You’ve probably already watched this video. (Krell KSA-250 recapping). The heat from those power resistors cause a lot of damage to everything that is near them. Including the soft start circuit board. Note the two relays. My gut tells me that is causing the buzzing sound.

Good chance, high probability, the electrolytic caps need replaced. Not sure I would spent a lot of money on the old amp.

 

DIY Audio, Krell KSA repair

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