This is unacceptable behavior from an expensive amp! The seller should take it back and give you a refund. You need a new transformer! That's the only cure! My 40 year old GAS Son is still in use and remains dead silent (and sounding just fine!).
What is an acceptable level of transformer hum on a Krell S300i?
Greetings from a newbie. Just a quick intro:
Not rich, but I've been into hi-fi since college (Dual CS506 era). 20 years ago, I had progressed to Michell Gyrodec/Rega, Roksan Caspian CD/bi-amp, Sonus Faber Concertos.
The speakers never sounded as good as when the dealer had demo'd them hooked up to a Krell KAV 400i. But this was not a pressing issue as everything went into storage while I went travelling/working overseas.
Fast forward to present day. My brother has just got into vinyl (having discovered a killer high end McIntosh set up while staying at an Air B'n'B), so I unboxed my kit and set it up to show him what he should be listening to.
We both felt the sound was disappointing and my thoughts returned to that Krell demonstation 20 years earlier. My focus then wandered to eBay and I found myself winning the bidding on a S300i amp.
It is in excellent condition but it hums, even when in standby and without speakers or sources connected. I have tried different locations around the house, different houses, cheap mains cleaners and 3 into 2 mains plugs to eliminate the earth. Nothing makes any difference. When I press the mains switch on the back, the amp starts with a 'cough' which settles down to a constant hum after 2 seconds. I think it is higher than 50/60hz. Possibly closer to 200 hz. It does not vary at all after that. I convinced that this is the transformer because it also occurs in standby without any connections.
If the amp is on the floor and I stand next to it, I can hear the hum. At 15 feet away, I can't really hear it, but with it in the rack and in my seating position, my ear is only 5-6 ft away and it is clearly audible when the room is quiet. It is annoying when reading in silence to the point that I need to disconnect the power.
My question to you... is this an acceptable level of hum? I would have expected that unless I put my ear next to the casing, I would not be able to hear anything. I have hunted the forums and web but can't find an answer for this specific issue. I use Transparent cables but these aren't relevant because it hums without any cables connected.
Your comments/thoughts will be greatly appreciated. I have already raised this issue with the seller who claims that it did not hum when he sold it. If the hum was really loud, there would obviously be a problem with amp. It is at a level that I can't be sure about without anything to compare it to.
Kind regards.
Not rich, but I've been into hi-fi since college (Dual CS506 era). 20 years ago, I had progressed to Michell Gyrodec/Rega, Roksan Caspian CD/bi-amp, Sonus Faber Concertos.
The speakers never sounded as good as when the dealer had demo'd them hooked up to a Krell KAV 400i. But this was not a pressing issue as everything went into storage while I went travelling/working overseas.
Fast forward to present day. My brother has just got into vinyl (having discovered a killer high end McIntosh set up while staying at an Air B'n'B), so I unboxed my kit and set it up to show him what he should be listening to.
We both felt the sound was disappointing and my thoughts returned to that Krell demonstation 20 years earlier. My focus then wandered to eBay and I found myself winning the bidding on a S300i amp.
It is in excellent condition but it hums, even when in standby and without speakers or sources connected. I have tried different locations around the house, different houses, cheap mains cleaners and 3 into 2 mains plugs to eliminate the earth. Nothing makes any difference. When I press the mains switch on the back, the amp starts with a 'cough' which settles down to a constant hum after 2 seconds. I think it is higher than 50/60hz. Possibly closer to 200 hz. It does not vary at all after that. I convinced that this is the transformer because it also occurs in standby without any connections.
If the amp is on the floor and I stand next to it, I can hear the hum. At 15 feet away, I can't really hear it, but with it in the rack and in my seating position, my ear is only 5-6 ft away and it is clearly audible when the room is quiet. It is annoying when reading in silence to the point that I need to disconnect the power.
My question to you... is this an acceptable level of hum? I would have expected that unless I put my ear next to the casing, I would not be able to hear anything. I have hunted the forums and web but can't find an answer for this specific issue. I use Transparent cables but these aren't relevant because it hums without any cables connected.
Your comments/thoughts will be greatly appreciated. I have already raised this issue with the seller who claims that it did not hum when he sold it. If the hum was really loud, there would obviously be a problem with amp. It is at a level that I can't be sure about without anything to compare it to.
Kind regards.
23 responses Add your response
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In today's age with all the choices we have and the fact that eBay nearly always stand behind the buyer I would be demanding a return. If seller will not work with you just open an eBay case, they will be left with little choice. Both of the Krell amps I have owned for absolutely silent and I am pernickity about that sort of thing. Something is not right with it and unless it was sold under "for parts or repair" back it should go.I would not even,open it up as may give seller a possible out. Good luck |
Are you using RCA inputs or XLR inputs into your Krell? If using RCA , then “shorting pins” may be required on the XLR inputs. I had this happen to me on an old KAV250a amp. I was getting a terrible hum until jumpers were installed. I remember emailing Krell about this and not only did they explain this to me but they sent the jumpers gratus . |
You could well be correct on the xlr shorting pins, in fact if I remember right Krell suggests to not even use single ended if the shorting pins are not in,place. This was true on,older amps, not sure if the newer stuff is up to the same requirements. And I am afraid I must respectfully disagree on eBay. Only way you would really lose money is if you were not in the right or did not read the description correctly. After 19 years of eBay and multi 1000 feedback I might just know a thing or two there....... |
So this is definitely mechanical hum. It is unlikely to be a ground loop, but it could be DC on the line, but testing this in a different home eliminates that. Have you pressed your hand on the case? Is it something you can damp, or is it all sounding from the transformer? Having the rectifier and caps checked out is not a bad idea, but I am afraid you may have a bad transformer, with only one, very expensive fix. :( Erik |
I still say don't even mess with it, demand a return from the eBay seller. Not sure how much you paid or what the description was but it is obviously far from functioning correctly. Does not matter if his ad even states no returns, eBay will make them take it back if you state it is not as described. Good luck |
Thanks for all your constructive input, guys :-) I did contact Krell and quickly received a helpful, if not conclusive, reply. I was hoping for a categorical, ’under normal conditions, our amps are virtually silent’ but it did fall a little short of that. ’It appears to be residual transformer hum and happens more frequently than one might think and shows up more in 50Hz environments. Usually residual hum is heard only when in close proximity to the units. 5 ft away is unusual... Other than replacing the transformer, which does not always fix this problem, I am sorry to say that there is not a fix for this phenomenon.’ He also said that you don’t need to short the balanced inputs on Krell’s integrated amps when not used. I did press firmly with my hand on the unit which also has no effect. |
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Hmmm--I'll bet its a Toroidal Tranny too!--- Naim ones are the worst I've come across-- for the $$'s you'd think they'd get that right! I'd say its Frequency related-- I have the PurePower Regenerator and there is an external adjustable pot behind the front grill that you turn with a small screwdriver to up/lower the Frequency-- It cured mine ---there are other examples I'm told on the market. Good Luck T212 |
What is an acceptable level of transformer hum on a Krell S300i?It could be that the bias is too high taxing the transformer more, so it will hum louder. From memory the 300i I had for repair ran just warm after an hour of being on with no music, and the bias was set correct. If your is running hot after an hour or two no music, get the bias checked it could have drifted and now maybe too high. Cheers George |
OP Not quite sure why you decided lajollaplanars was the response you were looking for when quite a number here have already told you it should be dead quiet and is faulty and you should return it. A number of responces indicated past ownership of Krell amps unless you were waiting for that ONE person who had the exact same model? If you had bought from a garage sale or similar and had no recourse to return yes I can understand trying to fix it but with ebay returns it should be gone and you on the hunt for something better.... and quitter. Personally it would have been back at the ebay sellers door long ago by now..... |
Give the Blue Circle Audio RPD-15 DC Offset Blocker a try. It really cures transformer growl. https://www.bluecircle.com/page152a.html |