Issue with Krell KSA-250

You may not be able to send it to Krell.  There is a thread where a customer sent his amp back for repair and 9 months later, he still hasn’t gotten it back.  The owner of Krell passed away and the company has been closed to grieve.  The person said no one was answering the phone. 

Thanks for the response. After I posted this message, I saw on Krell's FB page that they had essentially closed after the death. It looks like they are slowly opening up again, but I'm guessing there is a backlog, so it may not be the best choice to send it to them.

It's the power transformer. Can you still play music through the speakers? 

The problem is probably the transformer drawing a lot of current.  Are the heat sinks getting hot fast?

Though I wouldn't rule out the power transformer, it's more likely to be a bad capacitor.

Though I wouldn't rule out the power transformer, it's more likely to be a bad capacitor.

Caps don't buzz! Transformers do. That amp needs a new transformer.

Since the AC fuse didn't blow it is not drawing excess current.

My plinius did exactly the you are describing OP all I did check the power cord and it’s loose. Problem solve.

I upgraded  the power service  into my house to a 200 amp service.  Anyhow every system  in the house gained both sound quality  and a hum. I got rid of the old wore and went copper all the way. Had the electrician  come  again and had him check all his connections.  He tighten  the main ground. It was already  tight but he made it tighter and the hum was gone from every system in  the house. Above where the fellow says check the power cord that is free and only takes a few minutes  if it is not the problem it was free and o ly took a couple of minutes.  Sometimes  things are that easy and that cheap.

Heavy power cord can turn loose either one iec of the amp or from the wall socket.

Or if you add new gear next to your amp that can be the source too.My ViVa  integrated and my Ares denafirips DAC don’t get along. I get hum from my amp and speakers if I will connect the Ares to to viva.Solitions the two got divorce lol.

@jayctoy Jayctoy more good ideas eliminate  the cheap easy things first. Sometimes  it does get the problem  but many times you can find an improvement  non the less

I had one of those bad babies & had the same issue.  I wouldn't turn on again.  It needs some serious help.  If you can personally deliver in lieu of shipping that would be the best bet.  I had mine damaged on the return trip back from service and back it went with zero listening time  Sad story indeed.

Contact either George Meyer AV in Los Angeles or The Service Dept in Bridgeport, CT for repair.  Krell's itself service dept is in a giant holding pattern whilst the company gets sorted out after the owners passing.

Hey make sure the negative and ground are not reversed in the new wiring

Did that here had ground loop

Thanks so much for all the feedback!

I have taken the cover off to take a look inside, but I don't see anything immediately wrong or smell anything out of the ordinary.

I do have a large power cable, and I tried re-seating it both in the unit and in the wall. It didn't stop the issue.

I haven't added any equipment, but this is 100% something wrong inside the unit. I really wish I could post the video! That would make what I'm trying to describe much clearer.

I've found a place in Chicago that said they work on Krell equipment. It's about a 75 minute drive, so that will be preferable to sending it off via freight both from a cost and a potential damage standpoint.

I will not be turning it on again.

I don't know if the forum will allow me to post a link, but I'll try. Here is a video of the issue:

http://www.stateofgrace.net/krell.mp4

Thanks!

I don’t know if the forum will allow me to post a link, but I’ll try. Here is a video of the issue:

@blakeh

That’s not the power transformer making that sound, imo.

http://www.stateofgrace.net/krell.mp4

OP I did not know you are from Chicago, they are few repair shop here. Midwest , stereo rehab, etc.

Blakeh the sound I heard from the link, it needs repair. Don’t turn it on again.

@blakeh

I listened to the video several times. Hindsight is 20/20. Shame you didn’t leave the top cover off for the video demonstration. I would have placed one hand, with finger cupped like holding a softball, and lightly touched the top of the round can covering the power transformer. (I believe a Toroidal transformer.) If the sound is coming from the transformer you would feel the vibrations of the sound.

Example of a 60HZ hum/buzz sound from a power transformer.

60HZ

60Hz

That’s not the frequency sound in your video, imo.

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@jasonbourne71  I know capacitors don't buzz, but they can cause the transformer to buzz.

Is the amplifier a ksa 250 or 250s?

@jayctoy Do you know of any other reputable shops in the city/'burbs? I know Stereo Rehab is well regarded, but their turn-around times can sometimes run into the 3+ month range. I'd like to get my amp back a little quicker than that. Midwest Audio is closed as far as I know. Not sure where else to call. Any leads would be appreciated.

@invalid This is a KSA-250.

I am an original owner of a Krell KSA 250 , when my KSA-250 had a buzzing sound I drove from Massachusetts to Ct service department . They had to replace all the caps large and small . They actually said they never seen a KSA-250 with that many caps that needed replacement ! Being an original owner, willing to bring in the amp myself ,  and having an unusual number of capacitors gone bad , they gave me a break on the repair bill . Great service department , friendly service manager . 

Best of luck with your repair

@jdsmichaels  you had it serviced at Krell or The Service Department?

The owner of The Service Department used to be the service manager at Krell, though I think he is a little more expensive.

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

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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@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.

@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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What I would first start to look for:

Check for DC at the wall outlet. Check if the transformer cover can be moved by hand, if so then look at the bolts holding down the cover. Remove the cover and see if the rubber or elastomer bushing is still intact.

That is a 60hz buzz so it’s an AC issue, and it’s either the transformer or the soft start relay coil (those are the only two ac inductors I can think of). If it’s the transformer, then it’s probably the bridge rectifier has an open diode and only 60 hz is getting to the secondary instead of 120hz. If it’s the relay, then its probably a shorted rectifier diode, sending ac instead of dc to the coil and causing the contacts to chatter.

OP, very common issue with this series of amps. My buddy had the kinda rare KSA-250s and he had it repaired for the same issue like 3-4 times in a 10yr period. You could look at George Meyer but they may be backed up as well - https://www.georgemeyer-av.com/

Thanks for all the advice! I ended up taking it into Stereo Rehab in Chicago and the experience could not have been better! Casper obviously knows what he's talking about. Turns out it is a front relay. No problems with the caps or transformer. He took me through the whole unit, explained what was happening and gave me a reasonable estimate to fix it (cheaper than I thought it would be). Just an all around great experience. I should have it back in about four weeks.

Thanks,

Blake

@blakeh Good to see that You already have found the problem. I am late answering but I can give some info. I have several KSA 150 and KSA 250. What 9 times out of 10 goes wrong with them the is the sofstartcard that sits right behind the front cover. Someone mentioned the 700 Ohm resistors next to caps. That was almost right but it is not caps. Krell did a design flaw and placed two big 700 Ohm resistors on the softstartcard just besides the two Omron relays that have plastic covers. What happen is that the resistors get so hot that the plastic relaycovers melt and finally destroys the relays. You are lucky if it is the only problem Your amp has! It seems so because You have been wise enough not to start the amp again. If one forces the amp to start with faulty relays next (it is doable....)  what will happen is that the small trafo on the softstartcard will burn taking other components with it to. That is serious trouble! Those trafos are extremely hard ,if not impossible, to find. To avoid this problem in the future there is a modification I have made on all my KSA 150 and 250 amps (not S series) and it is to upgrade the two 700 Ohm resistors to Vishays with aluminium covers with small cooling fins and mount them on the back of the thick frontplate. You only have to drill two small holes gor each resistor and four small screws to attach them. DO NOT DRILL TO DEEP so You drill through the fronplate. The resistors are available at Mouser. They are quite expensive but is is small, well invested money in Your wonderful amp and You will never have the problem with overhetd softstartcard again! I have had no problems with my 7 modified KSA 150 and 250 since I made the mod. Tell Your tech to do it for You while the amp is disassembled. Good luck!

@dclone I for one thank you for your post. It helps to hear from someone that has hands on personal experience with the Krell KSA-250 Amp.

I do have a few questions about the soft start circuitry I hope you can answer.

It’s a shame with an amp this old the manufacturer/designer never released or authorized the release of the schematic wiring diagram of the KSA-250 amp. Especially because of the problems with the soft start circuit board. Release of at least the wiring diagram of the Soft Start Circuit Board.

Just a guess the two 700 ohm resistors that are mounted practically against the AC power relays are in series (or in parallel), with the hot side feed lead of the 4.5KVA power transformer. (In series with the contacts of one the power relays.) The circuit provides the soft start, therein reduces the voltage fed to the primary winding of the 4.5KVA power transformer and thereby reduces inrush current. Simple Ohms law.

So I imagine when the button on the front panel of the Amp is pushed one of the two relays contacts closes and completes the circuit to energize the primary winding of the 4.5KVA power transformer. The two 700 ohm resistors instantly heat up to over 400 degrees F. (maybe more). The coil of the relay is only energized for maybe a second or so, or maybe not de-energized at all. ??? The second power relay contact closes after the initial second or so startup and supplies full AC power, voltage, to the primary winding of the power transformer of the Amp. The full power relay circuit could just shunt across the two 700 ohm resistors. Basically diverting current from the two 700 ohm resistors to the full power circuit provided by the other relay. Sound about right so far?

So the damage that is done by the heat from the two 700 ohm resistors is momentary, cumulatively, over many years of turning the amp on. Correct?

Scratching my head though... All the above posting is based on the purpose/reason for the two 700 ohm resistors. Looking at the picture of the soft start circuit board the four white color rectangular power resistors on the other side of the two relays look more like what would be used in the soft start circuit. ???

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Soft start circuit board shown here:

https://www.youtube.com/watch?v=Ng3RlJb1SsU

A close look of the board here;

https://www.diyaudio.com/community/threads/krell-ksa-repair.402617/

Attachments

Click on first photo of the blocks of photos provided.

Note. Four white rectangular power resistors have been removed.

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Jim

@jea48 Hi! It looks that You have found exactly the right places to guide KSA 150, MDA 300, KSA 250 and MDA 500 owners in restoring those beautiful amps!

I started by watching Mike at Liquid Audio restoring a KSA 150 which was my first Krell poweramp and it of course blowed the softstartboard after two weeks. Sounded just like the OPs KSA 250 before dying. I am also very lucky to have a friend who is a highly skilled, but now retired, Krell tech. He was head of Krells service, repair and spareparts department in Europe and worked his way up from tech to head of the department. He for sure knows Krells!! He have taught me how to disassemle, reassemble, searching for faults, Krells design flaws better substitutes when changing parts etc, etc, etc. His nickname is "The Krell Doc" in Sweden. A very good friend who has access to all the schematics, of course. I do highly respect him for, not even to me, give copies of those. He is loyal and a man of honour.

I do agree 100% with You that Krell would benefit a lot and we owners even more if they made the schematics public and easy to acess. There is no "tradesecrets" to protect in those schematics. For what I know Krell actually give copies to repair techs which they think can do the work correct. Theu do not give them to private persons only to tech companies who are skilled enough.

One must be aware of, and this is very important, that Krell has so many revisions of both PCBs and values of cf components that they hardly even now for themselves what schematic is for which unit. They must have the unit in front of them to tell. I have seven KSA 150 and two KSA 250 (and a lot more Krell poweramps including the monoversions of KSA called MDA) One thing 150 and 250 (and the MDAs) have in common is the softstarboard and its problems. If I look at my seven KSA 150 I have four different versions of softstartboard and not one single board of all seven has the correct colourcoding printed on them!!! You need to take a lot of photos and as I do, document every single step with pen and paper. Also, just work on one amp at a time!!! The KSA serie are easy to work with (if You now how to do of course) because the way they are built in modules. really high quality parts and not a single unnecessary cable. Instead brass bars are used! Fantastic! 

Under the busboard the 4 big caps are situated. I have change mines (probably not necessary) to Kemets. One really important thing is to discharge the old caps before starting to work on the unit in any way. Even after 3-4 weeks the caps holds lethal amount of power inside them. I discharge them with a big ceramic resistor holding the resistor with leather gloves (heat hurts and give You nasty blisters I have learnt that the stupid way...)

So document, document and take photos. Do the softstartboard modification, change caps and effect resistors and, if You want to do it really well, transistors, (begins to be really hard to find Krell marked Motorolas and there are a lot of fakes on eBay etc.) I even have changed the Neutrik XLR contacts, rubber feets under megasized trafos (necessary because they get dry and loose) and speakerterminals etc. Not a fast job. I have sestored approx 12-13 Krell poweramps and 6-8 Krell preamps during a period of 9-10 years.

I will try to send three photos of one of my KSA 250 currently in use in my small homeoffice room. Hopefully You can see the Vishay-Dale 700 Ohm resistors mounted on front plate, the Kemet caps under busboard and the busboard how it is supposed to look when everything is OK and not overheats.

EDIT: I realise that I can not attach photos. I have to learn how to do it first. But my mod is nearly exactly done as at in one of Your links. That guy have even used exactly the same resistors, aluminium shielded Vishay-Dale military grade and seems to have used the same big Kemet "beercan" caps.

@jea48