[Jason Stoddard]

He means ultrasonic noise (above human hearing) around the unit, not something that would affect playback, unless you were using a tube amp and the tubes picked up the oscillation in the air.

Nope, I mean RF radiated noise. Even if the switching frequency is, say, only 500kHz, you're talking a 500kHz square wave at up to 100-200V P-P depending on the power output of the Class D amp. 500kHz square waves at those amplitudes are going to have significant harmonics out into the tens of megahertz--which gives you the potential to take out AM radio reception, interfere with FM radio, cause problems with old-style RF interfaces--and, more importantly, be picked up by other electronics, rectified and folded back as noise or distortion. 
 
This kinda stuff is the kinda stuff the FCC does NOT like. Any device with a clock greater than 9kHz must be FCC Class B (consumer) compliant. Doing it with 3.3V P-P signals is sometimes problematic. Doing it with signals 30X that amplitude, especially when connected to unshielded (speaker) cables, doesn't thrill me.
 
If you take a look at the radiated noise of a Class D amp or a switching power supply on an RF spectrum analyzer, and then look at the ground noise of the same devices on a highly resolving instrument (today's digital scopes aren't all that great for this--I'm talking something like a Tektronix 7000-series mainframe oscilloscope with a 7A22 differential plugin, which gets down to 10nV/division) you would never want to deal with them, unless it's for an application where you're forced to use them, with space and power limitations, like portable devices.
 
Linear is our future.

 

[Xcalibur255]

He means ultrasonic noise (above human hearing) around the unit, not something that would affect playback, unless you were using a tube amp and the tubes picked up the oscillation in the air.

The older Tripath designs were particularly bad about RF noise.  They will totally disrupt radio reception in the room they are in.

 

[john57]

Man, I love those old Tektronix 7000 models. I have to keep radiated  RF noise to a minimum in my room otherwise my vacuum tube equipment would really pickup on it. Other than ground loops, radiated RF noise can cause all kinds of side effects in the audio frequency range of stereo and video equipment. With all the wireless devices we are using these days, including computer components, it is a good idea to plan out the room to minimized RF interference. I try to use as much wired devices before looking into wireless devices as possible, alone with other things. 

 

[Maxvla]

@Jason

That is sort of what I meant. His question seemed to ask if the noise was on the signal going to the headphones where it would presumably be audible (ie static/distortion). I stated, perhaps too simply, that the noise was from the unit itself, at rates above human hearing. I'm aware there are problems with interference with other gear, especially radios and tubes, but really, who listens to the radio when you are at your rig?

 

[Silent One]

  Man, I love those old Tektronix 7000 models. I have to keep radiated  RF noise to a minimum in my room otherwise my vacuum tube equipment would really pickup on it. Other than ground loops, radiated RF noise can cause all kinds of side effects in the audio frequency range of stereo and video equipment. With all the wireless devices we are using these days, including computer components, it is a good idea to plan out the room to minimized RF interference. I try to use as much wired devices before looking into wireless devices as possible, alone with other things. 

Prior to my first tube amp head-fi setup, I enjoyed slinging wireless devices around the home. I eventually moved the router out on the porch like a cat and went Ethernet. Made a difference... 

 

[65535]

  Nope, I mean RF radiated noise. 

 
You can imagine the shock when a professor of mine and a customer of the company I work for reported that our 400kHz position sensing amplifier was putting out noise in the 600-900MHz range with a 6V p-p on top of the -10/+10VDC output.

 

[peterzzz]

So the 'problem' with PWM (in any form, be it class D or DSD or delta-sigma bit reduction) is that its response depends on the internal state (of the integrators). So while it might measure fine for static wave-forms, its response to less predictable input can be much different.
 
ESS (of ES9018 fame) claim to have 'solved' this problem. See http://www.youtube.com/watch?v=1CkyrDIGzOE for a somewhat accessible explanation.
 
I've always wanted to do the math, but aside of a day-job and family, I do have to admit to probably having forgotten enough math for it to be an easy exercise.

 

[Jason Stoddard]

Hey all,
 
With all the work getting ready for Newport, I totally ran out of time to write this week's chapter. We'll be back on the chapter-a-week schedule next week...
 
Jason

 

[Ableza]

  Hey all,
 
With all the work getting ready for Newport, I totally ran out of time to write this week's chapter. We'll be back on the chapter-a-week schedule next week...
 
Jason

 
So that makes the title of this chapter, "Trade Shows always consume more of your time than you expect." 

 

[Rudiger]

 

[Jason Stoddard]

   
So that makes the title of this chapter, "Trade Shows always consume more of your time than you expect." 

 
Yes. They suck mightily. They are a huge distraction. And ten thousand things go wrong that you never expect. And ten thousand people ask to borrow stuff. And and and...sometimes I wonder why we bother, it's not like we're looking for distributors or dealers. 

 

[madwolfa]

  Yes. They suck mightily. They are a huge distraction. And ten thousand things go wrong that you never expect. And ten thousand people ask to borrow stuff. And and and...sometimes I wonder why we bother, it's not like we're looking for distributors or dealers. 

 
I wonder if this thread alone makes you more buyers than few trade shows...

 

[Ableza]

   
Yes. They suck mightily. They are a huge distraction. And ten thousand things go wrong that you never expect. And ten thousand people ask to borrow stuff. And and and...sometimes I wonder why we bother, it's not like we're looking for distributors or dealers. 

You could hire a marketing company to take care of all that stuff for you... oh, wait...

 

[Joriarty]

   
I wonder if this thread alone makes you more buyers than few trade shows...

 
I was considering a few other brands of amp and DAC for a new setup -- including Schiit, of course. Then I found this thread and had to buy some of this Schiit for myself. I've always just plugged my headphones into my computer, but now that I have a lot more disposable income I've finally dipped my toes in the water with a Magni and Modi that are on a FedEx plane right now
 
I say dipping my toes in the water, because if I enjoy the Magni and Modi as much as I hope I will, I may use them as an office set-up and buy myself a bigger stack of Schiit for home.
 
One customer, at least

 

[madwolfa]

  One customer, at least

 
I bit the bullet for a full Schiit stack after reading this one too. And I'm planning to buy even more Schiit in future.