While I haven't built Pete Millet's Sound card measurement interface, I did pick up some of the MuRata DC-DC converters from DK which he used in his design. I pointed out on that thread that the NDTD2415C which I have (converts the 32V which I have in my Pioneer SX-838 to +/- 15VDC) benefits from a choke on the front end. While they have 12uH in the product data sheet, I picked up a little 12mH choke from a discarded switch mode power supply in the inductor junk box. Here's the before and after:
BEFORE
AFTER:
Load is 40mA on each side. The A-Wtd noise on the bottom is 2.6uV. Note that the scale on the top chart is 50mV vertical, the bottom 20mV.
BEFORE
An externally hosted image should be here but it was not working when we last tested it.
AFTER:
An externally hosted image should be here but it was not working when we last tested it.
Load is 40mA on each side. The A-Wtd noise on the bottom is 2.6uV. Note that the scale on the top chart is 50mV vertical, the bottom 20mV.
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Thanks for the info, very interesting. My first idea was to put filters on the outputs but this seems to work very well so I may not need to do this (I only have inductors with 3 Ohms resistance so would lose some voltage).
I still wonder whether it would bring any benefit to put some shielding around the PS components and/or move it to a separate board.
I still wonder whether it would bring any benefit to put some shielding around the PS components and/or move it to a separate board.
Just showing the implementation of the little Murata DC-DC converters -- with bipolar output. You can take 5VDC out of your USB jack and get relatively clean +/-15VDC for running opamps without bending yourself into a pretzel with a single supply configuration. A lot of Japanese receivers I've modded have a unipolar supply and use a bunch of electrolytics for coupling. This is easier.
12mH is not what Murata had recommended, and indeed it sucks a few mA more than the non-choke implemented supply...I was very surprised that the noise was as low as it was. Here's my implementation.
12mH is not what Murata had recommended, and indeed it sucks a few mA more than the non-choke implemented supply...I was very surprised that the noise was as low as it was. Here's my implementation.
An externally hosted image should be here but it was not working when we last tested it.
I've been using a similar DC-DC converter for the last couple of years and find them indispensable. They are compact, reasonably well regulated, and the small ripple on the output cleans up nice with a simple CLC filter.
Mine are BWR-15/330-D12A which take a 9-18VDC input. I bought quite a few of them off some telecom dude for about $10 each; they sell for almost $90 new.
Digi-Key - 811-1723-5-ND (Manufacturer - BWR-15/330-D12A-C)
I consider them my little black bars of gold.
Mine are BWR-15/330-D12A which take a 9-18VDC input. I bought quite a few of them off some telecom dude for about $10 each; they sell for almost $90 new.
Digi-Key - 811-1723-5-ND (Manufacturer - BWR-15/330-D12A-C)
I consider them my little black bars of gold.
With or without the 12mH choke that you included in your earlier measurement? I'm putting together Pete's design, and wondering if I should find a place to mount a small choke on the input.
I'm also putting together Pete's from end and that was my thought exactly, is a small choke the way to go and, if so, what part #?
thanks,
Andrew
Whoops that didn't type right! I'll try again....
I'm also putting together Pete's SC interface and was basically wondering the same thing? Do I add a choke and, if so, what one, can anyone recommend a part #?
thanks,
Andrew
Well, I've ordered a small 150µH choke (rated for 1.1A), and depending on how the board gets mounted in the chassis, I plan on adding it to the input of the unit...right before the 470µf 16V cap.
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