Krell KAV 300i Problem

Hi, everyone,

My beautiful Krell KAV300i has started to show some issue recently that I hope somebody here can address the problem. Well, I can explain the problem as follows;

1- Amp is on, nothing connected to the input jacks, when I get closer my hands or touch one of the input RCA jacks a very high, annoying hum starts,

2- Amp is on and I play and listen to something thru one of the single ended inputs without having a problem. But when I switch to an empty input channel annoying hum starts again.

This probably happens to be a grounding problem and just have occurred very recently. Something has failed inside the amp but what would it be? I have been using another system using the same AC outlet having no problem at all. I also tried this amp in another room but the problem was still there.

I’d like to have comments on this.
That doesn’t sound to me like something that is necessarily abnormal, even if for some reason it wasn’t happening previously. Susceptibility to that kind of effect is probably contributed to by the very high 210K input impedance of the integrated amp.

What would most likely eliminate the issue is to simply put shorting plugs on each of the unused RCA inputs. Googling "RCA shorting plugs" will probably turn up some inexpensive choices (as well as some unnecessarily expensive ones), or you could make your own by shorting out the internal contacts on some ordinary RCA plugs.

Or, if the problem is in fact being caused by some hardware issue that is developing in the amp, without having any knowledge of the specific design I’m guessing that it might be related to a line filter capacitor on the amp’s AC input that is becoming leaky.

Good luck. Regards,
-- Al

Malik, while it certainly can be a true problem, Al may be entirely correct about it not being abnormal. One thing though that could help differentiate between normal/abnormal and that you have not indicated... at what volume level does the hum occur? If the gain is substantial you certainly can hear a hum through unused (open and not connected to any load) RCA inputs if you switch the amp to that input. On the other hand, if the gain is all the way down this would not be normal. Just my .02
Thanks for your comment. Hum occurs in normal listening volume level. There might be substantial amount of hum in preamp but the weird thing is that I have not heard that much amount of hum before. Lastly I tried to drive the amp with my dac-headphone amp combo (ifi nano) it was enough to touch the dac for the hum suddenly appears and drove me crazy.
I agree it's broken and it needs to be fixed. The hum as you describe is not normal. I used to own the KAV 300i for several years and not once did it have any hum.  
Get a Vanguard and be done for life...saw Hifi Heaven is selling them for $3495!!  Unbeatable at almost any price.
I just found that 'preamp out' jacks of the amp shows short circuit when I check them with a multimeter. Is that normal? If not what would be wrong?  

(I actually took out preamp section before checking)
No, that doesn't sound normal, if you were measuring between the center pin and the ground sleeve of each of the two RCA connectors, or between the center pin of one connector and the center pin of the other connector.

On the other hand, if you were measuring between the ground sleeves of the two connectors it would be perfectly normal.

-- Al
Thanks Al, That would help. Now I know that one of the elements on the preamp circuit board is faulty and I should find and kill it if I can.