biglee

Hi Chris, have put together a valve poweramp(for hi-fi) and when its got an input connected im getting a 60 hz noise not to far from mains hum now when i move the pre-amp away it stops which leads me to belive its some sort of emf interferance coming down the 2V o/p from the pre.
Whats your thoughts matey??

Lee

ECU Monitor Enthusiast

iTrader: (1)

It wont be a 60hz noise in this country...It will be 50hz !

The noise is most likely being radiated from the valve amplifier.

Is the pre amp in its own metal box and is the box earthed ?

biglee

hi simon long time no talky. yea preamp in a metal box now ive tried the pre on my other power amps.. no noise at all, tried earthing the2 together with piece of wire but it stays the same no change ive filterd the mains, i think its a component ocilating sumwhere, my spectrum anaylizer says its 61.5 hz thats how i guessed it wasnt mains ive got a monitor on the mains here and its not steady the voltage runs between 235 and249 the frequency ges between 49 and 55hz its pants, how am i expected to create quality audio with a supply thats so unstable lol im gona go thru it with my scope tomora track down the source,i think the whopping great transformer in the amp is makin sumthing buzz in the pre thatsgetting to the output of the pre

ECU Monitor Enthusiast

iTrader: (1)

Lee, I should have realised you would have proper kit to check things !

Yes, With my experience of valve amps, they can be a nightmare for noise emissions !

Especially if the valves are on show and not sheilded them selves with a box !

A scope may be your only way of sorting it, good luck !

biglee

its a substantial solid copper chasis. ive sheilded everythig very well indeed the amp is clean very clean for class A its only 40WPC rms but sounds great just not wen the pre is near it ive got a feeling the pre is picing up the noise. put cd directly into the amp and its perfect, yea gona pin point it tomora might be i have to screen the pre with some copper sheet etc, thats no biggy mind.

biglee

audio is a strange thing lol, vales are out just for heat soak to atmosphere, didnt want them in a box because of heat blah blah, my impeedance matching transformers is where the money is lol, oh and hows the laser thing getting on??