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Post by minglee on Apr 13, 2016 13:01:28 GMT -5
I am using an sa-250 amp plugged into a CMX-2 and hooked up to a pair of LS50s. I noticed upon turning the sa-250 on that there a slight hum comming from the chassis. ( need to have ear pretty close ) I cam also hear that tiny bit of hum through my ls50s when I put my ear close to the drivers,
Is there a problem with my amp?
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Post by smarties on Apr 13, 2016 14:00:09 GMT -5
Sounds like you have two issues
Transformer hum
Ground loop (hum)
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Post by minglee on Apr 13, 2016 21:21:01 GMT -5
there is no ground loop, I have tried ever outlet in the house and even brought it over to my friends house. It still has a slight hum whenever it is turned on. I can only assume its coming from the transformer
can any other sa-250s owners turn there amp on and put there ear next to it and see if they can hear some hum?
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Post by vcautokid on Apr 14, 2016 5:43:58 GMT -5
Have you disconnected the interconnects leading too to the SA-250? These too may cause ground loops too. Also proximity of AC power cables next too the signal interconnects could cause hum too. As for the hum coming from the amp, it may well be some resonance from the power transformer.
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Post by DavidR on Apr 14, 2016 12:58:08 GMT -5
I have (2) SA-250 amps. The first one was always quiet until a while ago it would have the slightest hum at the amp but still dead quiet thru the speakers. Then the hum went away, then it was back, then ........ I bought a CMX-2 and all is fine now. I believe my problem is the circuit I plug the amp into is shared in my son's bedroom where he has his gear AND he recharges his iPhone and a quick charger. These could be the issue. I measured .001VDC on my AC lines. The 2nd SA-250 is new and I have only plugged it in once. It goes into my HT/stereo system this weekend. It made no hum. However, I'm sure if I had put my ear down to the amp I would have heard something. How long have you had it? I talked to a friend who is an electrician an he says all transformers will make some noise when current is passing thru them. I also think vcautokid might be on to something with your interconnects. Check them with a multimeter for a ground problem. |
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Post by leonski on Apr 14, 2016 23:57:19 GMT -5
OTHER home issues can cause transformers to hum. Light dimmers are one source. Fish Tank pumps and heaters. Neighbors, espeically in apartments situations.
Turn everything in the house OFF and try again. If the hum is gone, at speaker or transformer, start turning stuff on again ONE piece at a time and monitor.
I love those LS50s. Heard 'em at THE Newport with Cary and later Parasound. NICE.
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Post by vcautokid on Apr 15, 2016 2:42:38 GMT -5
Some cable decoder boxes are also a great source of hum. Had a Motorola decoder that was poorly grounded where the coax came in. Grounded the the collar of the coax to AC ground, no more noise.
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Post by Jim on Apr 15, 2016 6:10:40 GMT -5
Some cable decoder boxes are also a great source of hum. Had a Motorola decoder that was poorly grounded where the coax came in. Grounded the the collar of the coax to AC ground, no more noise. Cable box was the source of hum for me. Was really aggravating! |
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Post by DavidR on Apr 15, 2016 7:26:07 GMT -5
Some cable decoder boxes are also a great source of hum. Had a Motorola decoder that was poorly grounded where the coax came in. Grounded the the collar of the coax to AC ground, no more noise. I had the opposite experience. A few years ago we switched from one cable provider to Verizon. The installer did not put an earth ground to the coax splitter (was located outdoors) and there's a ground screw provided. I put a ground wire to it and it made my HT system hum really bad. |
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Post by leonski on Apr 15, 2016 12:29:59 GMT -5
Yes, agreed. CABLE boxes, both wired and 'small dish' are the WORST offenders.
If you GROUND the splitter THAT ground can be at a different potential than the 'house' ground which is that copper rod driven in next to or near the box.
THAT will cause a hum.
In ALL my years with stereo / hifi / TV, I've mercifully been mostly Free of that phenom.
Finding the Root Cause is a process of elimination, usually started by pretty much stripping things down and isolating the hum-producer, than dealing with THAT.
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Post by minglee on Apr 19, 2016 18:52:51 GMT -5
i have it plugged into a cmx2. only thing plugged in is the power cable. unplugged everything else from the amp...
still has a mild hum
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Post by DavidR on Apr 19, 2016 19:18:15 GMT -5
i have it plugged into a cmx2. only thing plugged in is the power cable. unplugged everything else from the amp... still has a mild hum Mild hum is quite subjective. All transformers with current running thru them make some noise. Both of my SA-250 amps have a hum when your ear is placed right next to the amp. Barely audible and very normal. Some amps don't like to be turned on without a load hooked to them. 60 cycle noise current. |
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Post by leonski on Apr 23, 2016 22:53:19 GMT -5
Tube amps should NEVER be run without load. NEVER. I can't think of an exception, from SET to OTL.
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