Crack;Bottlehead OTL - Page 103

Curious how the Russian Military 6SN7 (ie 1578) works with the Crack?  Anybody know?  Since I have some NOS 1578's here that have less than 100hrs on them, I really need to find some way to use them! :)

There was a discussion on the BH boards a while back about how 6sn7's might not be an ideal match for the crack due to PS circuit.  My recollection is that the crack delivers ac to the tubes' heaters, whereas 6sn7's should ideally be getting dc - to say nothing of the possible noise introduced by the adapters.

At the time, this was enough to send me hunting 12bh7's instead - my favorite of which is a 1959 Tung Sol.  But I confess I am still curious to hear how a good 6sn7 sounds. 

I'm getting a lot of noise through my Crack when I attach a USB DAC to it. I hear the noise regardless of whether music is playing. Pretty sure it's the USB because when I unplug the cable from my computer it completely disappears. I don't get any noise from the USB DAC when I use my M-stage as an amp though.

When I use an E10 as an SPDIF interface and output coax to my DAC, it's dead quiet. When I input coax (SPDIF) from my Oppo 980H CD player it's dead quiet as well. However, when I use the E10 as the DAC and output it's analog line-out directly to the Crack, I hear the noise again.

Do I just have a noisy USB socket on my computer, or is it the cable, or is the DAC not filtering out the noise?

Or could it be that the braid on the wires from the RCA inputs to the pot in the Crack wasn't done well enough?

Any ideas on why I'm hearing so much noise?

Do you get the noise when plugging in an mp3 player? What about running the laptop from battery?

Is the noise like a low hum, or more like static/white noise?

My initial guesses would be noisy usb socket and/or power supply, or a ground loop.

It's like static/white noise that seems random but does have a slight pattern to it (if that makes any sense). It seems like it has a cyclic pattern where it gets louder and softer at intervals without me touching anything on the amp, DAC, or computer. I haven't tried an mp3 player or unplugging the laptop, will definitely try that when I get home later tonight.

Sounds like switching PSU noise polluting the ground. I had the same thing when trying to listen to my Crack on my old laptop.

So that's an issue with the power supply to the laptop? I guess this can be tested easily by unplugging my laptop, will do that later today.

Just curious, why does this noise not transfer when I use an SPDIF interface in the middle of the chain?

Also, if it is the switching power supply from the laptop, are there any ways to fix the noise? I don't really mind using the SPDIF interface, but I like keeping the chain as simple as possible and if I can avoid it, the better. Will certain DACs filter the noise better than others? How come the M-stage didn't pick up the noise?

The spdif is essentially isolated from dirty power noise.

It could be the Matrix has better power or input filtering, or is configured in a way that happens to reject that particular sort of noise. 

To "fix" the laptop... well, you could get a better power supply, or just run off battery (maybe a bigger battery, or external battery pack). You can also try a ground loop isolator. They're cheap... like $10 from radio shack. It looks like a regular RCA interconnect with a block in the middle (typically about the size/shape of a D cell battery). 

So I think the noise I was hearing is a combination of a couple things. I switched power supplies on my laptop to one with a 2 prong plug and it reduced the noise a lot. At first, I thought it completely eliminated the noise, but when I turned the pot up on the Crack past 12 I started hearing it again (albiet only slightly). Before I switched supplies I was able to hear the noise with the pot completely turned down to 6 (and it was much louder than the new supply past 12).

With the pot turned up to 12 using the new power supply, unplugging the power supply altogether slightly reduced the noise. The noise doesn't completely disappear unless I unplug the USB from my laptop. I'm thinking it's a combination of noise from the power supply (ground loop?) and a noisy USB port. I do most of my listening between 8-10 so it's not really an issue for me I guess. I only barely hear it at 12. I might still toy with the idea of the SPDIF interface though as it completely eliminates the noise.

Any ideas on what a powered USB hub would do?

Edit: this video gave me the idea to switch to a 2 prong plug power supply: http://www.youtube.com/watch?v=jSA2F1AwboU

The powered usb hub *might* help, but no guarantee. You're better off with the unearthed power supply or a signal isolator. 

Just curious, is he describing jitter or is it simply dirty power from the USB port?

I'm pretty sure it's dirty power from the USB port

There's no way any jitter would cause noise that bad. That'd be an utter failure of the device right there. 

Gotcha, thanks for the clarification.