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EQUIPMENT FORUMS >> SE84UFO25 >> Hum
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Message started by joralieu on 12/24/21 at 03:16:18

Title: Hum
Post by joralieu on 12/24/21 at 03:16:18

Have some 60hz hum with my 25th zen. How much is normal? I can hear it when I walk into the room with no music playing. My Bottlehead sex is dead silent when change to it.

Title: Re: Hum
Post by GroovySauce on 12/24/21 at 12:50:12

I had a UFO25TH on my 96db PAP quintets and it was silent.

Can you hear the amp humming? how loud? a faint hum, I wouldn’t worry about.

If you turn the volume all the way down on both channels does it still hum? Does it hum with no RCAs attached? (volume up and down) If it stops try a different set of RCAs. Try replacing all the tubes. Try a different outlet.

That is a starting point for troubleshooting.

Is it a new amp? If it's bearable let the amp run for a few hundred hours, sometimes the hum settles down with time. I would do some troubleshooting and schedule a call with Steve after trying a few things.

Title: Re: Hum
Post by duaneh on 12/24/21 at 14:18:29

My SE84UFO25 is behind my TV to keep it safer from my three year old grandson. When I contort myself around my speakers and the TV’s back to turn it off, bending close to it, I notice a very, very slight 60 cycle hum, nearly inaudible.

What comes out of my 99db Heresy III speakers with volume up is bliss; what comes out without a signal (and with the source turned on), even when I max the amp’s gain, is perfectly nothing, a black hole.

Though I don’t mean to imply that the slight hum is normal, I’m able to disregard it.

Title: Re: Hum
Post by Tubecan on 12/24/21 at 19:28:04

Joralieu,grab your right gain knob and twist from fulll on down too off,and if you hear staticky clicking it could be your input tube,repeat left gain and listen for scratchyness.

Just remembered I have a pair of amperex OC3 vr’s that sometime hum,once in awhile they’ll flicker and somedays will be ok.

Title: Re: Hum
Post by joralieu on 01/26/22 at 03:20:35

Hum is still there after 100hrs break in, only hear it when music is not playing. I still bothers me that my bottlehead is dead silent and the decware has hum.

Title: Re: Hum
Post by Beni on 01/26/22 at 14:03:57

Is there perhaps a ground loop through a radio or TV antenna cable in your system? If so, I would diagnostically remove all antenna cables or the connection to these devices.

Title: Re: Hum
Post by kulafu on 01/27/22 at 00:54:51

I have just over 300 hours on mine. I might have heard a slight hum in the beginning with no music an even tested with no speakers connected, no inputs ..... I have not noticed any lately but will have to listen more closely. Bottom line at least for my use case and my ears, I dont even notice if it is there.

Title: Re: Hum
Post by CAJames on 01/27/22 at 01:09:28

Quote:

Hum is still there after 100hrs break in, only hear it when music is not playing. I still bothers me that my bottlehead is dead silent and the decware has hum.

Did you check with nothing attached? Did you try moving it to a different room? Did you try different tubes?

It should be dead silent, but there are things in your house/room/system that will make it hum. You need to try to isolate those and eliminate them before looking at the amp itself.

Title: Re: Hum
Post by joralieu on 01/27/22 at 01:22:11

Yes checked it with nothing attached and a in a different room system. Still has more hum than my bottlehead. Its really not that loud I don't notice when music is playing. Just curious why it is there.

Title: Re: Hum
Post by Archie on 01/27/22 at 06:39:00

I had system hum for years that I finally tracked down to some ICs close to the power outlets. Simple fix by rerouting wires.

Title: Re: Hum
Post by joralieu on 01/08/23 at 03:18:52

Okay, I just discovered that if I touch one of the speaker outputs with my finger the hum goes mostly away and the VR tubes dim a little bit. What's up with that?

Title: Re: Hum
Post by JOMAN on 01/08/23 at 04:42:04

Quote:

I had system hum for years that I finally tracked down to some ICs close to the power outlets.

I just went through a similar experience. My understanding is that you can expect some transformer hum but it should not be audible unless your ear is very close to the speaker and at the driver level.

I just installed a Puritan PSM 156. That required that I adjust the power cable lengths. I also read the write up on the new DHC2 power cables. I have DHC1 cables that I terminated with Furutech plugs.

My intention was not only to adjust the power cable length to get rid of the excess so as to prevent any cables from touching each other but also to determine what lengths of shielded cables I would need.

I tightened all the plugs and made sure that the ground was well seated. Then as I went to turn off the UFO25 I contacted one of the VR tubes and the power cable to the amp and the amp momentarily shut down. WHAAA????

I was sure that I had the IEC well seated but checked it just in case only to discover that it was not seated all the way. Then I checked all the IECs only to find that the IEC on the Puritan was not fully seated. I was sure that it was.

After making sure that all cables were not touching each other and that all the plugs are fully seated I stood by the speaker, leaned over and heard nothing. To hear any hum at all I pretty much have to touch the grill with my ear. Before, to hear any hum I had to stand by the speaker lean over and be within a foot of the speaker, which I thought was normal.

So now I'm on a mission. Before I change any more components all the power cables are going to be changed to shielded cables and routed so none are in contact with any other cable.

Maybe some of this can be of help.

Title: Re: Hum
Post by joralieu on 01/08/23 at 04:59:45

Also the meter's drop from about 30 to 20 when I touch a speaker output terminal.