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SPEAKER HUM

I have been playing with a new system. I was driving my speakers with a MingDa MC 34 AB tube amp (75 wt/ch ultralinear 40wt/ch triode) which is powered with 8 EL 34 tubes. It can be used as an integrated amp, and when I used it as such, it was DEAD quiet.
I decided to make a good thing better, and just got the matching MingDa MC 2A3X preamp to go with it. The speaker hum when both are powered up is awful...not that very low level stuff you sometimes get with an amp/preamp set up...but loud enough to hear during quiet passages of musical pieces.
I have been tormented in the past with trying to eliminate speaker hum...any help out there for this system??
Thanks so much
rsasso

Showing 8 responses by rsasso

rsasso OP
39 posts
 
To Fplanner2000

I have to share my ignorance. Don't you need XLR input/outputs to connect the preamp and amp with balanced IC's? These components have RCA connectors.
rsasso OP
39 posts
 
To Tvad,

I dont have any of these 6SN7's to rotate right now. The microphonic tube you mentioned as common; is that normal as well? The microphonic effect of tapping the tube doesnt mean the tube is damaged, correct?
rsasso OP
39 posts
 
To Millicurie

amp and preamp are plugged into separate outlets
rsasso OP
39 posts
 
To Millicurie

I substituted a small Tono preamp for the big Ming Da...result was LESS hum (and higher frequency)...but still some hum. I am not sure what that tells us.
rsasso OP
39 posts
 
To Millicurie

OK: I substituted the interconnects between amp and preamp with heavier shielded cables and that had no effect. The hum is NOT there if the amp only is turned on.

The hum is there when the preamp is on, even with no components connected to it, as soon as you turn on the amp.

If you TAP the preamp when the amp/preamp is humming...there is a ringing sound out of the speakers. If you even gently tap the ceramic bases of those 6SN7 tubes, there is a louder ringing through the speakers...now THAT can't be right.
Does that speak to defective tubes, or, more likely, a defective preamp????
rsasso OP
39 posts
 
To Newbee

Someone stole my cheater plug. I will get one at the hardware store and give that a try. Thanks
rsasso OP
39 posts
 
To Tvad,

Thanks again for your very knowledgable input on my setup. It is appreciated, and I will get some 6SN7's and try out your suggestions.
rsasso OP
39 posts
 
To Millicurie999

Since the amp is about 10ft away from the preamp,it would take an extension cord, but yes, I can get everyting (sources included) into the same surge protector.

Out of curiosity though, if that is the problem, would a cheater plug on the amp (plugged into its own outlet as it is now) diagnose the problem...would I expect the hum to disappear if the separate outlet situation is causing the hum?
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