Elekit TU-8550 humming

[Cutts911]

I'm seeking some guidance in troubleshooting a problem with my first ever tube pre-amp build.
I'm relatively new to electronics, and hence this post. I'm competent with the usually hobbyist projects, and after researching and reading a few key posts on this site about the Elekit TU-8550, I took the plunge and purchase a unit. I assembled the unit over a weekend, and then commenced testing.

All the voltage check points are within spec, though there is a very noticeable hum and occasional pop on the phono input that increase when the volume/gain increases.
On the advice of the supplier, I resoldered all my connections, though with no improvement. The other 4 inputs work perfectly.

I'd be interested to know if others in the audio community have experienced anything similar with this unit. I have read in the forums of people copper lining the chassis to reduce/eliminate external electrical interference. I don't believe this would solve my problem given the other 4 inputs are hum free.

Any guidance would be greatly appreciated.

In all, it's a great little build kit, with extremely informative instructions.

 

[CohibaJoe]

I'm seeking some guidance in troubleshooting a problem with my first ever tube pre-amp build.
I'm relatively new to electronics, and hence this post. I'm competent with the usually hobbyist projects, and after researching and reading a few key posts on this site about the Elekit TU-8550, I took the plunge and purchase a unit. I assembled the unit over a weekend, and then commenced testing.

All the voltage check points are within spec, though there is a very noticeable hum and occasional pop on the phono input that increase when the volume/gain increases.
On the advice of the supplier, I resoldered all my connections, though with no improvement. The other 4 inputs work perfectly.

I'd be interested to know if others in the audio community have experienced anything similar with this unit. I have read in the forums of people copper lining the chassis to reduce/eliminate external electrical interference. I don't believe this would solve my problem given the other 4 inputs are hum free.

Any guidance would be greatly appreciated.

In all, it's a great little build kit, with extremely informative instructions.

Have you contacted Victor (NA distributor for ELEKIT & Sunvalley) at diyaudio? Some internal pictures of the unit would be helpful. My build did have WiFi router interference that was too close which I lined the TU-8550 with copper sheets. Also, wonky RCA cable can cause Hum.

https://www.diyaudio.com/community/forums/elekit.134/

 

[dcgibby]

I use mine daily and it's dead quiet on all inputs. Definitely get in touch with Victor Kung. He stands behind his product. I've never heard of an 8550 with a hum problem.

 

[Cutts911]

Thank-you all.

I suspect there is some interference from other electrical devices. I did relocate the unit to another more isolated room in my house (away from other electrical equipment) and discovered the popping issue resolved itself. The hum is still present. I will take your advice CohibaJoe and both contact Victor, and also line my chassis with foil tape.

As requested, I've attached some pics of my unit.

And another observation: When probing within the amp with a wooden probe (chopstick), the hum changes significantly when hovering around the back of the 12AU7 tube on the Phono Eq Amp circuit. Note that I don't have to physically touch any components to manipulate the hum.

I appreciate your help to date.

 

[TriodeLuvr]

It's normal for a phono stage to hum if the inputs aren't terminated. You'll need to short the phono inputs to confirm whether there's a problem in the preamp itself. Defective tonearm wiring can cause this as well.

Jack