Background Hum - Worsens w/ volume + present without input.

[Grainger49]

If you short the inputs and it is silent this says that the Crack is silent.

 

[Paul Birkeland]

The only reason I did that test was recognize that the hum is intrinsic to the Crack itself. During testing with a source at half-volume (loud but my ears aren't bleeding) I am able to hear the same hum between tracks.

The next step would be to describe your cabling and your source, as the hum is coming from one or both.

 

[Kris]

FWIW I also use HD650 with my crack (no speedball yet).
With test that Doc recommended, you've just proven that your crack is dead silent also and the source of the hum is outside of your amp.

Kris

 

[Mike B]

This is absolutely noise free. 

With Senn 600's plugged in and nothing on the input jacks (no cables, no shorting plugs) just powered up and warmed up with volume control maxed out there is nothing coming out of the phones.  No hiss, no hum, nothing.

I did use shielded cable from the jacks to the pot and from the pot to the tube with shields drained to chassis by the added lug just in front of the pot.  Pot changed to Alps.

 

[JamieMcC]

I had  a similar problem to this as well it was cured in my case by twisting my inputting rca cables together.

 

[Acclaim]

This is absolutely noise free. 

With Senn 600's plugged in and nothing on the input jacks (no cables, no shorting plugs) just powered up and warmed up with volume control maxed out there is nothing coming out of the phones.  No hiss, no hum, nothing.

I did use shielded cable from the jacks to the pot and from the pot to the tube with shields drained to chassis by the added lug just in front of the pot.  Pot changed to Alps.

Mike, you are definitely correct in adding in the shielded cable.

I did some testing today and came to the conclusion that a shielded cable will fix my problem. While manipulating the braided cable, I found that the hum lessened the further away the braided cable was from the components. If I hovered my finger tips between the braided cable and terminals 17, 18 and 19 the hum dropped off even more dramatically.

 

[Mike B]

That's what I was thinking.  It was free too, I just used stuff that I had left over from Stereomour as I only wired 1 input.

If it is good for Stereomour, it will be good for Crack.  Yup, just add a lug to the chassis and drain one end only of the shields.

 

[Grainger49]

Mike,

Great advice.  I have a small spool of stranded shielded microphone wire from RS, Ca: 1972.  I have used it in a couple of builds and I have convinced myself it made a difference.

 

[Doc B]

If the input is shorted and it's silent it means the noise is coming in ahead of the input, i.e. from the cables or the source.