John Curl's Blowtorch preamplifier part II

[Steve Eddy]

Originally Posted by hitsware

Like a PC ?

They're everywhere these days.

se

[abraxalito]

Originally Posted by hitsware

Like a PC ?

Frank was asking about H field emissions - these would be right down the bottom of the list of worries for a PC.

[Steve Eddy]

Originally Posted by abraxalito

Frank was asking about H field emissions - these would be right down the bottom of the list of worries for a PC.

And hitswire was talking about the switchmode supply in a PC being a source of those emissions.

se

[abraxalito]

Oh, I saw a question mark - so it seemed he was asking if they were and I was replying that its far from the main issue with noise from PCs.

[RNMarsh]

Originally Posted by Steve Eddy

Not necessarily, no.

It depends on whether the interference is primarily E field or H field in nature. If it's primarily E field, then reflection loss is the most effective and high conductivity materials such as copper or silver are the most effective. If it's primarily H field, then absorption loss is the most effective and ferromagnetic materials or thick paramagnetic materials are the most effective.

se

I think you will find that in the typical home invironment it is as i said. E field dominate at >100Khz-1Mhzand above, while H fields are generally much below that range.

An issue for audiophiles -- the prolific SMPS can produce both field coupled and direct coupled noise. EMI/RFI government specs from equipment is typically directed to aircraft and emergancy, police et al frequencies and are tested to comply by agencies such as USA's UL. However, those tests and freqs are far above the audio range and thus audiophiles need a lot better performance than UL qualified equipment provides. And, they dont cover the direct-coupled issues into the ac power lines. Thx-RNM

[hitsware]

Originally Posted by Steve Eddy

And hitswire was talking about the switchmode supply in a PC being a source of those emissions.

se

Not only the power supply.
The logic circuitry itself.

[jneutron]

Originally Posted by Steve Eddy

Busy busy busy. You?

se

Very much so, home and woik.
Finishing up a bathroom reno, so my clock stuff is on hold. Doing the radiant heat next.

Originally Posted by Steve Eddy

Swtichmode power supplies come to mind.
se

Exactly. Moreso PC's though, Apple really paid close attention to EM radiation.

Originally Posted by RNMarsh

I think you will find that in the typical home invironment it is as i said. E field dominate at >100Khz-1Mhzand above, while H fields are generally much below that range.

Actually, in the HF range, it's E/M, propagating waves at 377 ohms that is a biggie. House wiring and line cords are long enough to couple to the air to launch the waves.

Ground loops will also help M fields launch.

E fields are generally the easiest to stop radiating. M fields are the hardest.

jn

[morinix]

Wait a minute! like an earlier post said! T&M gear like a tek scope; Not good enough shielding? Those don't cost 3K to fab.

[bcarso]

Originally Posted by jneutron

Exactly. Moreso PC's though, Apple really paid close attention to EM radiation.

jn

What was funny: Apple industrial designers had a strong influence on the JBL Soundsticks three-piece system, which featured transparent housings for everything and initially only a USB input. The Micronas USB DAC was promised to be low emissions according to Apple. Well, it wasn't, except in a standby mode, and a good deal of time had to be spent in the EMC lab to render the product compliant and still allow everyone to stare at the circuit boards. There was a fight over the ferrite doughnut in the input cable, much wringing of hands and wailing from ID over its inclusion.

The product was quite successful. Some mistakenly imagined that it was USB-powered since around that time a patent of mine issued for managing such (6178514). Another engineer supposed that the four drivers per satellite were driven in some sort of complex phase relationship (and warned us about Bose patents, which he was never able to produce ). But no, it used an a.c. adapter, and the drivers were acoustically in parallel while alternating in magnetic polarity to partially cancel adjacent monitor distortions.

At one point, since people were frustrated that they couldn't use analog sources, Plunkett changed the design to an analog-input version and added touch controls for volume to a redesigned satellite base.

[morinix]

And the case of the satellite speakers made great incense burner trays