Crack perfect on iPhone - extremely noisy on computer USB DAC

[fredrickj]

My old headphone tube amp sounded fine on my USB computer DAC (Digidesign by ProTools).  I finished my Crack today and was delighted to realize how fantastic it sounded on my iPhone.  Dead silent s/n.  So of course I wanted to hear it on a DAC.  (whats the point of listening on a analog iPhone output?).  When I plugged into my DAC I was shocked at how noisy it was.  At first I thought something went wrong between the time I unhooked everything and plugged into my computer DAC and let it warm up first for an hour.  So I plugged into my iPhone again, perfect!  I also have another tube amp by another manufacturer so I plugged my old tube amp into my DAC.  It was perfect too. 

Every device is silent by itself in combo with anything else.  So only the Crack in combo with the DAC/computer is a problem.  Must be a ground problem but I've no idea where to start.

thanks

[Doc B.]

Start by describing the noise. Is it buzzy 120Hz like a bad ground? Or is it a clicking or grumbling sound like digital interference?

You might want to try some different interconnects.

[sl-15]

what digidesign dac do you have? mbox? or something else? i have an mbox2 and also have an mbox1. they both had/have noise and are really picky about what cables you use. how are you connecting your dac to the crack?

[fredrickj]

the noise is not a single frequency like a hum would be.  It is all over the place.  Sounds more like interference. 

Important to note that the computer is the source of the noise as I hear the awful noise when I use my phones on the computers analog output,  but the noise is isolated when I use the USB Mbox Mini DAC on my other headphone amp but for some reason, is picked up thru the USB DAC on my Crack.  Weird..

Everything works fine on my laptop as well as my iphone so I may just end up using my laptop for my Crack.  Would be nice to figure it out though.   

Crack sounds awesome by the way....

[Doc B.]

Sounds like the 12AU7 is probably picking up airborne interference. Distance is probably at least a partial solution. And different cables might help.

[Paul Birkeland]

the noise is isolated when I use the USB Mbox Mini DAC on my other headphone amp but for some reason, is picked up thru the USB DAC on my Crack.  Weird..

I would be looking for a USB DAC that would accept power from an external source.  We have also found a tendency for coax interconnects to be quieter in this situation.

-PB

[JamieMcC]

Out of interest when you refer to your computer is it a pc or laptop? I have found laptops to be more prone to imparting noise into the signal. If a laptop when your using the usb dac, the connection with the dac could be helping by grounding the laptop more effectively. 

[kgoss]

If USB is your only option try a different port. If you have another one on a different bus it might be quieter. Or look for a DAC with a galvonicly isolated USB input which would prevent power (noise) from the computer to enter the DAC.

[fredrickj]

"If USB is your only option try a different port. If you have another one on a different bus it might be quieter. Or look for a DAC with a galvonicly isolated USB input which would prevent power (noise) from the computer to enter the DAC."

I've never seen this feature listed before but I will try to get some info about it.  Interesting idea. 

thanks for all of your inputs.  As the Crack works perfectly as advertised on the laptop I'm just going to use it with that

thanks to all

[kgoss]

One more zero cost thing to try if your source is a laptop would be to unplug it and run off battery. Can't hurt to try it.