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Old 1st July 2013, 11:33 AM   #171
skidave is offline skidave  United States
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Yeah, I know the feeling about 'real work' getting in the way. Most of the time, life is in the way of my hobby!

Thanks for the updated information. I don't have a QA400 yet, but I would like to purchase one (currently using ARTA and a crappy USB interface). As nice as the Pete Millet interface is, I don't quite need that much. I would like to have a simple interface for high voltage device (power amps) and it looks like you have just about finished that.

I'll be more than happy to purchase a board from you if this moves forward. I'm not such a fan of surface mount builds, but if that is what has to happen for size, I understand.

Thanks for keeping this on your radar.

Dave
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Old 8th July 2013, 09:15 AM   #172
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I have a related question to the assembled intelligence here:

My lab PC causes a lot of hf garbage on my equipment ground. Even with the scope probe connected to its ground clip, and nowhere else, do I have a lot of 50-Hz synchronised switching noise, presumable from the PC switching power supply (it's gone when I switch off the PC).

Does anybody have a sure-fire way to get rid of it, short of building a complete linear power supply for the PC (it has crossed my mind...)?
Are there such things as (effective) mains filters for this purpose?

jan
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Old 8th July 2013, 10:13 AM   #173
FdW is offline FdW  Netherlands
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I wish (same problem here)
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Old 8th July 2013, 07:17 PM   #174
richiem is offline richiem  United States
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Run a laptop with battery power. It will certainly help. But I like the idea of a PC with linear power supply, too.
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Old 8th July 2013, 08:07 PM   #175
benb is offline benb  United States
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I just asked at the end of this thread on another forum. If there's a "quieter" PC SMPS, or even a linear one, recording would be the biggest market for it, and these people would be the most likely to know about it:

Website for optimizing computer performance for Audio - Page 4 - Gearslutz.com

It might be helpful to modify the power supply, put 0.1uF high-voltage ceramic caps across each diode in the primary bridge, add a big ferrite on every wire just before it exits the box, that sort of thing.

But nowadays with everything running on USB, a battery-powered laptop is probably The Solution.
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Old 8th July 2013, 08:31 PM   #176
1audio is online now 1audio  United States
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A linear supply for a desktop PC would be a losing proposition. There is a grey area between laptops and desktops with ITX board that can run on less power. You will still have switching supplies on the motherboard and linear regulators for those probably won't work if you could build them.

If you keep the total power under 100W or less (not hard if you don't need gamer graphics or dual I7's etc.) this Habey HB-LR1007-60W Accessories - Newegg.com plus a 12V linear will get you close. The other option is a big isolation transformer. Even if the PC is isolated you still have a monitor to deal with. . .
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Old 9th July 2013, 12:23 AM   #177
DDB is offline DDB  United States
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Quote:
My lab PC causes a lot of hf garbage on my equipment ground. Even with the scope probe connected to its ground clip, and nowhere else, do I have a lot of 50-Hz synchronised switching noise, presumable from the PC switching power supply (it's gone when I switch off the PC).
Does the hash reduce or go away if you remove the probe from the input and short the input to ground with the input switch?

Also you might try removing the probe long ground lead and short the probe tip to the grounding ferrule on the probe with a very short wire wrap or probe grounding accessory to see if your long ground lead is picking up most of it.
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Old 9th July 2013, 12:24 AM   #178
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I have no problems at all on my new HP laptop, battery or not.
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Old 9th July 2013, 03:36 AM   #179
RNMarsh is online now RNMarsh  United States
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Quote:
Originally Posted by jan.didden View Post
I have a related question to the assembled intelligence here:

My lab PC causes a lot of hf garbage on my equipment ground. Even with the scope probe connected to its ground clip, and nowhere else, do I have a lot of 50-Hz synchronised switching noise, presumable from the PC switching power supply (it's gone when I switch off the PC).

Does anybody have a sure-fire way to get rid of it, short of building a complete linear power supply for the PC (it has crossed my mind...)?
Are there such things as (effective) mains filters for this purpose?

jan
yes. Use a high quality (ground) isolation transformer on the PC. Such, those made by Topaz. Check their spec's on the www for the Ultra-Isolation series . Or one of their conditioners with isolation. These are Not made like regular isolation transformers.... these have extream (Ultra) rejection characteristics.



-RNM



Ultra-Isolation XFMR.JPG

[About $150 USD on EBay.]

Last edited by RNMarsh; 9th July 2013 at 03:51 AM. Reason: Ultra-Isolation Transformer -
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Old 9th July 2013, 02:55 PM   #180
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Quote:
Originally Posted by jan.didden View Post
I have a related question to the assembled intelligence here:

My lab PC causes a lot of hf garbage on my equipment ground. Even with the scope probe connected to its ground clip, and nowhere else, do I have a lot of 50-Hz synchronised switching noise, presumable from the PC switching power supply (it's gone when I switch off the PC).

Does anybody have a sure-fire way to get rid of it, short of building a complete linear power supply for the PC (it has crossed my mind...)?
Are there such things as (effective) mains filters for this purpose?

jan
Hi Jan,

In this context, one thing I've observed is that my Agilent 8 Gs/s DSO is actually internally PC-based. It actually has a fairly standard-looking motherboard in it, and I'm sure the main power supply is a variant of a PC switcher. The scope is vintage 2000 and the OS is a custom version of Windows 98 (yes, a disadvantage). Anyway, with all that bandwidth and sensitivity, it does not show a noise problem.

As someone else mentioned, even if you go to a linear supply to replace the ATX switcher, you still have a handful of Point-of-Load switching supplies on the motherboard to get all of the different voltages modern ICs require (sometimes down to 0.9V and at currents in the 10's of amperes). These POL switchers are non-isolated and operate at fairly high switching rates in at least the mid hundreds of kHz. So they are likely to be less problematic and certainly will not create any 60Hz-related noise bursts.

Cheers,
Bob
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