2. amps-preamps
  3. 190772-193755

Subwoofer Hum When Connected to Integrated Amp

Observed issue: 2 different active subwoofers have sustained hum when plugged in to integrated amp's preout RCA. One sub has the hum independent of where the subs gain knob is set, while the other sub has the hum in relation to the gain knob and it stops when the gain is set to 0. 

Troubleshooting: Different outlets on different circuits, surge protectors, RCA cable swaps with shielded and unshielded and length varieties. Cheater plugs on both the subwoofers and amps. Using 2 different preamps (solid state and tube) does not introduce the hum, along with using speaker wire input to subs from the amp. 

Noticed the hum exists after powering off and unplugging the power cord from the amp, but leaving the RCA connected to the sub. The hum pitch varies when I touch the front of the amp faceplate or the sides. 

Equipment: Creek Evo50a integrated. One subwoofer uses a Yung SD300 amp, and the other is a Pioneer of unknown amp brand. 

The Ask: What other troubleshooting steps or direction is recommended? My thoughts are isolated to the integrated amp, especially when the power was off and the varied hum pitch happened when I touched the case. Appreciate any input!

technophreak
technophreak OP
3 posts
 

Further troubleshooting using multimeter. Found that hum is almost eliminated when one probe is on case ground point and the other touches the exposed RCA of the preamp out. What kind of symptom would this lead toward?

paradisecom
308 posts
 

Usually the outside, ring portion of the RCA connectors are grounded.  You should show 0 Ohms when placing 1 probe on the chassis ground and those RCA's.  

You should also show 0 Ohms when testing between the Creek amp and the RCA connector on the subwoofer amp(s).  Essentially, they should all be using the same ground.  You should have 0 Ohms from the power outlet ground, the Creek chassis, the Creek RCA's, the subwoofer RCA inputs, etc.  It should be 0 everywhere.  

technophreak OP
3 posts
 

I am getting consistent non-zero value on the input RCAs and XLR of the Creek. And a zero value on the single preamp RCA out. 

technophreak OP
3 posts
 

Found the issue. The RCA module soldered to the PCB is damaged. There are 3 solder points and one of them, I assume the ground, is no longer connected to the board inside the module. This will require a replacement of the RCA module as a long term solution, or making a ground connection on one of the RCA jacks with a wire. I'm looking to have the long term solution done by someone more advanced at soldering. 

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