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Test & Measurement interface for Soundcard
Test & Measurement interface for Soundcard
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Old 31st December 2009, 05:06 AM   #141
grufti is offline grufti  United States
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I re-checked mine with similar results. Winter in CA ... how about bad conditions for ESD. I have OPA2134s to spare when I get back home and INA134 on order. Oh, well!
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Old 31st December 2009, 06:59 AM   #142
DualTriode is online now DualTriode  United States
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A nice tool that I carry at work is an infrared thermometer. I have not calibrated my feigner tips yet. I checked the temperatures under the hood.
The measured temperatures follow:

1 Weller solder pencil 462 F
2 Tabletop 72 F
3 U1 86F
4 U2 77F
5 U3 104F
6 U4 102F
7 U5 82F
8 U6 82F
9 U7 95F
DT
Just For Fun!
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Old 31st December 2009, 04:45 PM   #143
kevinkr is offline kevinkr  United States
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Test & Measurement interface for Soundcard
Ordered all of the parts this morning for the interface.. Inevitably some parts were out of stock. The converter was out of stock at Mouser, but in stock at Digikey..

I'm going to use OPA2604 on the input because that is what I have on hand for the time being. I may have an OPA2134AP lurking around somewhere and may give those a shot regardless. Input noise is a couple of rtHz lower in the 2134 than the 2604 - in practice I suspect the input protection network resistors would be a significant noise source in most cases. (I haven't calculated their noise contribution, but I expect their noise contribution to make using a significantly quieter op-amp a non starter which is actually good since I have not found any except for bipolars like 5532/LM4562 which have significant input currents.) The tradeoff I think is worthwhile to be able to withstand a couple of hundred volts rms accidentally applied to the input. (My old design would not survive such a major overload.)

Pete, I have a couple of thoughts/questions:

I am building mine without the meter option as I don't really need it. (I may add it later) I have determined with my current choices of op-amp and INA/DRV amps that the total quiescent current is about 25mA - right at the minimum acceptable value for the switcher, so I am thinking of adding a couple of resistors to load the supply and bring the current up to 30mA or so..

I was wondering whether the dc offset null is actually needed if the meter is not installed? I assume the 10 ohm resistance in the offset null circuit significantly reduces cmrr in the INA134. I have ordered the parts for the offset null in case I do need it.

I will match the input stage resistors to maximize cmrr.

Now all I need is a monitor..
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Last edited by kevinkr; 31st December 2009 at 04:48 PM.
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Old 1st January 2010, 01:23 AM   #144
TheGimp is offline TheGimp  United States
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As a precaution, I rigorously cleaned the assembled pwb to get rid of rosin in case it was causing a high Z leakage path.

That made no difference as well, so I'll wait for new parts.
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Old 1st January 2010, 02:44 AM   #145
kmaier is offline kmaier  United States
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Default Almost done

I have mine almost completed.... just waiting on the 0.1uF caps. The original p/n was out of stock and I forgot to look up a substitute, doh! They're scheduled to arrive on Monday and should be completed shortly after they arrive.

I'm planning to use mine with a Digigram VX Pocket card and balanced cables to/from the interface. if all works well, I'll probably build a second for stereo use. Overall, very well done project, I'll post some feedback once I start get some use time in.

I did the full build, buying all of the parts. Between Pete, Mouser and Digikey the costs were around $270 USD.

Regards, KM
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Old 1st January 2010, 05:40 PM   #146
kevinkr is offline kevinkr  United States
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Test & Measurement interface for Soundcard
Quote:
Originally Posted by kmaier View Post
I have mine almost completed.... just waiting on the 0.1uF caps. The original p/n was out of stock and I forgot to look up a substitute, doh! They're scheduled to arrive on Monday and should be completed shortly after they arrive.

I'm planning to use mine with a Digigram VX Pocket card and balanced cables to/from the interface. if all works well, I'll probably build a second for stereo use. Overall, very well done project, I'll post some feedback once I start get some use time in.

I did the full build, buying all of the parts. Between Pete, Mouser and Digikey the costs were around $270 USD.

Regards, KM
I managed to chop about $130 off of that by not implementing the meter, and through careful shopping/raiding my parts bins.

Haven't got off so lucky elsewhere though as I had to build/repair a PC, purchase a keyboard/mouse (directron.com) and a nice used Dell 15" monitor on eBay and an M-Audio Audiophile 24192 which was fortunately on sale and heavily discounted at Amazon last week, Still a good deal. I will probably configure the other available channel for TS measurements a little further down the road.
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Old 3rd January 2010, 12:01 AM   #147
pmillett is offline pmillett  United States
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Quote:
Originally Posted by kevinkr View Post
I have determined with my current choices of op-amp and INA/DRV amps that the total quiescent current is about 25mA - right at the minimum acceptable value for the switcher, so I am thinking of adding a couple of resistors to load the supply and bring the current up to 30mA or so..

I was wondering whether the dc offset null is actually needed if the meter is not installed?
I bet the DC/DC converter will be fine... the voltage might creep up a little but I suspect not enough to worry about.

Definitely don't need the offset null without a meter. Actually you'd probably be just fine without it even with the meter...

Pete
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Old 3rd January 2010, 12:08 PM   #148
revintage is offline revintage
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Hey Peter,
When did you send my PCB. Still havenīt seen it.
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Old 3rd January 2010, 01:12 PM   #149
pmillett is offline pmillett  United States
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Quote:
Originally Posted by revintage View Post
Hey Peter,
When did you send my PCB. Still havenīt seen it.
Lars -

December 9th or 10th, via first class mail (not priority mail). They say that can take three weeks... maybe more with holidays.

Pete
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Old 3rd January 2010, 08:51 PM   #150
revintage is offline revintage
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OK Peter
Fingers crossed. Have never lost anything coming from the States before so I am not that worried.
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