2. speakers
  3. 1247418696

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
fplanner2000
616 posts
 
I would try another preamp, if you can get your hands on 1. Maybe borrow one from a friend. Sounds like there are several issues with the preamp that are being amplified in your circuit. Your comment that you have been tormented by speaker hum "in the past" may indicate the presence of yet another issue.

Another thought might be to connect the amp/preamp using balanced ICs if currently using single-ended, or vice versa. That cured a speaker hum issue I had in the past (which is documented somewhere on this site). Good luck.
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?
Post removed 
millicurie999
57 posts
 
As Swampwalker mentioned, amp and preamp in two different outlets can cause serious hum. Since you tried another preamp and it still gives you hum (albeit less), maybe it is indeed the ground loop introduced by different components in different power lines.

Can you borrow a power conditioner/surge protector and plug everything into one shared line?
More to discover