Yet another buzz/static question

[cobs]

I built my crack with speedball last year and have not had a chance to use it much. I have it hooked up to a Schiit Modi with the PYST RCA Cables. I have tried other RCA cables and FIIO E10 and multiple pairs of headphones.

- Crack amp with no source connected is dead silent until about 3 o-clock on the volume knob and there is a slight buzz. I believe this is normal.
- RCA cables connected to unpowered MODI has slight buzz and you can't really hear it until about 12 o-clock and gets louder the higher you go
- If I touch the RCA cables I get a constant buzzing.
- When I plug in the Modi I get this weird static that changes as move the mouse around. This happens on different computers with the MODI and FIIO.
- If I ground out the center pin on the RCA jack it is silent. If I insert a wire into the jack and touch it I get the buzzing but if I ground the wire while touching it turns silent. 
- Modi is silent when connected to my Magni.

The noise isn't very loud but is very distracting during quiet times. Any ideas on what to check/change would be much appreciated!

 

[Alonzo]

Sounds like you have usb noise, and a ground problem.  Try a Wyrd to clean up that noise created by the mouse movement and isolate the computer and FIIO more.

 

[Deluk]

Not actually your mouse but the computer reacting to the cursor movement. Been there. My problem due to ground loops. With plugs for everything involved with the PC, Monitor, printer/scanner, external HD's, desk lamp etc it's easy to run out of available sockets. My Hi-Fi on a different wall socket and although I'm not recommending this, lifting the earth on my Luxman amp cured all of my noise and hum, so a ground loop via the audio cable from PC to amp.
I can make my newly finished Crack hum but it's running now from the Asus sound card in my PC and I can't get it to make even the slightest noise when on full volume. Having no noise at all seems rather odd, makes you think you might be losing something at the top end. S/N ratio of the Asus is well over 100db so far above the Crack specs (actually can't find those anywhere on the Bottlehead site. Are they there?) I have the PC output volume on 50% to allow the Crack volume control to work easily over it's full range but 9-10 o'clock is fine with my HD600's.
If you have a laptop or mp3 player try feeding the crack with that. I have a Kubic Rocca player and that has to be run flat out to get a reasonable sound out of the Crack but I have to run that out flat out too due to the low input signal. That makes for hum! Laptop is OK as you can adjust the volume on that the same way as on the PC. No earth problems with that of course when running on the battery.

 

[cobs]

That Wyrd USB decrapifier looks interesting but hard to justify the $100 to hopefully fix the issue. Considering my Modi is silent with my magni. I tried another desktop and have the same issues. Lowering the volume in windows makes the noise worse because I have to turn the crack up more.  For some reason when I hooked my Modi to my laptop running on battery the audio quality is terrible (no highs or lows just mids) but it still has background noise and changes when I use the touch pad. I cannot find my 3.5mm to RCA cable right now so I cannot test another source to the crack.  I will report back when I find/get another adapter cable to try other sources.

Edit: Just hooked up my crack to my Onkyo receiver and everything works great no buzzing or static. So the problem seems to be with the Modi but will have to wait and see how it works with other sources with 3.5mm>RCA.