Hi

Just got the 845 tube amp ,connect to a pair La scala which have updates the crossover . Not connect anny Cd player or anny else ,and I got Hum to the speakers .

The systerms I have before ,no probem ,no noise or hum ( Conrads Johnson MV 55 tube ,PV 10 A and a pair Cornway ) .

I do not know ,what cause for ? check the amp at the friend house ,have no problem  ....

Right know ,whenever I am turn the amp on ,then hear the hum on the speaker .

The amp ,Cd player ,DAC connect to the Monter power HTS 3500 MK II .

Pls help .Thanks

Lots of possibilities. 

First, does the hum go away when you connect the amp to a preamp or other source?  If so, then just don't ever turn on the amp without it being connected to something.

Second, does the amp's line cord have a grounded plug (one with three pins instead of two)?  Are you using a "cheater plug" to bypass the ground pin?  If you are, then DON'T.

Fourth, are there any lamp dimmers in the same AC circuit as the amp?  In fact, are there any dimmers in the entire house?  If so, remove them, dig a hole in your back yard at least 2' deep, throw them in the hole, cover with dirt, and jump up and down on it until they're packed-in so tightly that they can't escape.  Replace with real light switches.

If none of these work, then the problem may be in the amp.  Could be bad power supply capacitors, cold solder joints, or one of many other things.  But check the easy stuff first.

Greg

 The amp is intergate ,so not use preamp ,the power cable is good (kimber) ,have been test the ground on AC plug are fine ,and do not have anny dimmer light at home ,

The system set up at living room ,the same place I have system before .

The amp is new ,have been go to local tech ,check it out .No noise or hum at his shop .

I think some thing on the power line , not the amp or speakers .

I do lot reseach ,some one use the power insolate will help this problem ...

The 845 tube sound so good on La scala ,just the hum make sick 

 Can you provide more details about the specific 845 amp that you are using?  Was it built by someone for you, etc?

 That is the Dared 845 ,have been updates on cheap Chinese Cap ,and test at the shop couple day ,everything good ,no hum ,noise at all .

So just in house power line ?

Bonobo:

The amp is new ,have been go to local tech ,check it out .No noise or hum at his shop .

Was the amp tested with 104db efficient speakers at his shop..? 10db to 15db less efficient speakers could easily mask the amps inherient hum levels.

Unfortunately many amplifier manufactures don't design their amplifiers with the idea that they might be used with 100+db efficient loudspeakers and thus they don't worry about S/N levels of their amplifiers that are found to be satisfactory on less efficient loudspeakers.

Was the amplifier's output S/N measured by the tech and if so what was the voltage level measured especially pertaining to the mains frequency and it's 2nd and 3rd harmonics..?

mike tn

 Hi Mike

That good ideal ,I will check back my tech tomorow ..And ask him about that .Thank Mike 

And I still hunting the hum

 The schematic for the VP-845 shows a hum adjustment pot in the filament circuit even though the filaments are run on fairly well filtered DC.  Have you tried adjusting these to reduce the hum level?

introduce a 62 Hz hum.

jacksonbart:

introduce a 62 Hz hum.

 What kind of speaker is your friend using? It might simply be that if his speakers are less efficient (and possibly a higher ambient noise level at his location) would be enough to mask/not expose the 60Hz hum.

 I have some Wright 2A3 mono that are supposedly one of the more quiet flea powered SET amps. The guy I bought them from said he couldn't hear the hum on his Klipsch Forte. In my room with its very low noise floor and Klipschorns the hum is clearly audible. Just some food for thought 

 Thanks for all input.After couple day hunting and find out what cause the hum, the woofer I had replace ,make a hum .

The woofer are black widow 8ohm ,take it out and put the K 33 back ,and the hum gone .Right now I did not like the bass sound .The back window go lower and tight,and like them ,just make a hum when turn the amp on .

So what cause them make hum ? 

IT is very strange for the pair black widow ,nothing wrong .and..I put on my 78 Cornwall sound so good and no hum at all .

My La scala is 1978 with AA crossover (have been update new cap).Looking for better woofer and Tweter later as well .

Pls any recomment ,Thanks