Buzzing when I connect RCA inputs

[amerk84]

I finished my Crack amp, check the resistances and voltages and they all check out fine. When I turn on the Crack with headphones plugged in it operates quietly even with the volume turned all the way up. When I connect RCA input a loud buzzing starts. (I have already gone through and re-soldered all the joints)

I noticed some interested things:

1) if I touch the base plate with my finger the buzzing is significantly quieter

2) if I connect my phono RCA cables, which have dedicated ground wires, to the Crack input and I touch the RCA ground wire to the Crack base plate the buzzing also is greatly reduced

I noticed in some other forum posts that people suggested moving the Crack around to different parts of the room. That did not help. Another suggestion was that I try shielded RCA cables. The phone RCA cables are shielded.

Another possibly significant observation is that when I play music it comes through my headphones very quiet (using HD-650's).

What is going on here and how do I fix it?

[fullheadofnothing]

You mention phone and phono. Are you using these terms interchangeably, or are you testing separately with a phonograph and your phone (i.e. using a 1/8" -> RCA cable plugged into a cellular telephone)?

It sounds like you might have a ground loop. Plug everything into the same power strip and see if that fixes the problem.

Can you post pictures of your build?

[Paul Birkeland]

Is there anything plugged into the other end of these cables?

[amerk84]

@fullheadofnothing: That was a typo. I meant phono RCA cables.

@fullheadofnothing and @Caucasian Blackplate: These cables are connected to my turntable, which is powered by the same power strip that the Crack is powered by.

[Paul Birkeland]

Does your turntable have an RIAA preamp built into it?