Cerwin Vega D9 Hum question

Ran a few tests today. First threw in some test speakers and the hum is still there so that rules out the speakers. Used my DMM and the frequency is definitely 60hz. Tried swapping out the amp with HK citation I have and the hum disappears. Put the PL 400 back in the loop and the hum is back again. Now I can definitely hear it coming from both speakers and can confirm with the DMM. Tried swapping the L/R cables around and even the speaker cables and the hum persists regardless.

One thing I noticed is the transformer for the amp has the same hum when everything is turned on that isn't there with just the amp on. Put the DMM on the transformer bolt and I get 60hz. So it appears I have created some sort of ground loop hum if my research into the problem is correct.

Now the question is has this been there from the start and I have just started noticing it or is something slowly going wrong to make this more apparent. The hum is so noticeable I can't imagine this has been going on without me knowing.

I still don't know if the preamp has a common ground as I don't know exactly what I do to check that and didn't have the time tonight to look into it. Also I don't really know how to hook up the A/B part of the pre-amp outside of plugging the speaker into the back which didn't produce any hum or sound (I figure that was to be expected as the amp is now out of the loop). Also on the back of the preamp there are two connections for ground. Don't know if those could be used to possible eliminate this hum.

I appreciate everyone's help in all this
 
Try flipping the polarity of the preamp's power cord, hopefully it's two prong and you just have a 60Hz groundloop
 
Could be the plug. If it were me I would also clean up my case grounds. Take them off and clean good. I really don't know; but I stayed at a Holiday Inn last night. You might try some of that snake oil also. The snake oil I use trips and filters the AC plus regulates the power. Less than 200.00 and you have protection. Your snake oil may differ.
 
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Tried flipping cord already. Snake oil is out of stock here in San Antonio. Will try cleaning up grounds when I get home.
 
Don't you guys milk snakes down there? I'm just having fun. The Belkin is pretty good price. A few bought them in here. I'm just joking around in my own way with the snake oil. LOL
 
I think Texas would be number one exporter of all snake products (I wasn't taking anything serious just joining in on the fun). I looked into AC conditioner. Might have to get one.

The phase linear is stock except the capacitor upgrade. Pending full comp in near future.
 
mjstriker said:
I think Texas would be number one exporter of all snake products (I wasn't taking anything serious just joining in on the fun). I looked into AC conditioner. Might have to get one.

The phase linear is stock except the capacitor upgrade. Pending full comp in near future.
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Smart move...
 
MJ, I think I had your same issue. Per laatsch's post to me, I tightened them again but this time with a ratchet and wrench. I really tightened them and my hum is gone. I also put the caps on the rectifier but that was before I re-tightened them and it still had a slight hum. I think the transformer being slightly loose was causing the vibes from the trans to be picked up in the circuitry. All I know is mine is fixed now so give it a try.
 
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