Test & Measurement interface for Soundcard

[buggsson]

The interface Pete did is slick, I like the concept. I just need to dig a bit deeper for software that I like and that works well with my HW.... would prefer to use my MacBook Pro, but oddly very little audio SW is Mac based... who knew.

Now it's been a while since this post was posted, so I might be a tad late, but I've seen similar posts as well. There is no problem using your MB Pro using the available tools for running windows on it. I've tried both apples product and now I'm using Paralells and that is really transparent. Maybe not everything will work, but so far, everything I've installed has worked, both audio SW and some CAD/CAM stuff as well.

My thoughts. I teach soldering, brazing and welding at my night job. Many of the metals we DIYers contact daily may be toxic. Even the screws and nuts (do not put them in your mouth) may be cadmium plated. Yes the solder contains lead. Even the copper pipe we drink out of is suspect. Blah Blah Blah.
Check out the links below to info about Heavy Metal Toxicity and a solder Material Safety Data Sheet.

Heavy Metal Toxicity: Online Reference for Health Concerns
http://www.bemidjistate.edu/offices/environmental_health_safety/msds/sldr_kstr.pdf

The first link did not work for me.

I would also like to add that it helps if you are knowledgeable about the substances and materials you are dealing with, as otherwise it can be quite harder to work with the stuff than necessary.

Take sucrose for example, laboratory grade sugar in my case. You are recommended to work with it in a fume hood according to the product sheet.

What do you think of undertaking this interface project for a complete electronics newbie? Is it doable?

Is there a better project for me? Measurement jig is what I'm after mainly.

 

[DualTriode]

Now it's been a while since this post was posted, so I might be a tad late, but I've seen similar posts as well. There is no problem using your MB Pro using the available tools for running windows on it. I've tried both apples product and now I'm using Paralells and that is really transparent. Maybe not everything will work, but so far, everything I've installed has worked, both audio SW and some CAD/CAM stuff as well.



The first link did not work for me.

I would also like to add that it helps if you are knowledgeable about the substances and materials you are dealing with, as otherwise it can be quite harder to work with the stuff than necessary.

Take sucrose for example, laboratory grade sugar in my case. You are recommended to work with it in a fume hood according to the product sheet.

What do you think of undertaking this interface project for a complete electronics newbie? Is it doable?

Is there a better project for me? Measurement jig is what I'm after mainly.

Hello,
Never too late. Jump on in. In terms of the dire warnings, remember don’t breathe the fumes, don’t pick your nose and always wash your hands. I do not work in a biosafety cabinet and I do make coffee with DI water. Actually RO water and my bones are not mush. Try this link.
KESTER SOLDER
Speaking of jumping in this project is the deep end of the pool. You will be able to do the assembly. However any trouble shooting will be difficult. Software setup is a hassle.
For the novice I would recommend taking a look at something like this site for real projects that are buildable and low voltage that will not kill you. Also good discussion, tutorials on soldering and beginning circuit testing.
Tangent Tutorials
Getting Started in Audio DIY
DT
All just for fun!

 

[AndrewL]

I did not install the meter circuitry, and the additional bypass caps those ICs used so I may try some additional rail capacitance and possibly ceramic bypass caps on some of the ICs. All components have been carefully checked against the BOM and are correct. (As I indicated parts of the unit seem to work under some conditions.)

Hi Kevin (or Pete),

Did you have a list of parts handy for just the audio interface? And any required changes to operate minus the volt meter? I'm fortunate enough to already own a good True RMS meter but am looking for an audio analyzer and having been outbid (again) on a spectrum analyzer on e-pay I'm starting to think Pete's excellent work is my best way forward.

thanks,

Andrew

 

[pmillett]

Did you have a list of parts handy for just the audio interface? And any required changes to operate minus the volt meter?

Sorry, nothing handy. Basically just leave out all the parts in this section of the schematic:

You can also omit U3 and C11, which provide regulated 5V for the meter.

Pete

 

[AndrewL]

Thanks, I seriously considering going the whole way now. I'm just trawling the thread and compiling up a resume of the most useful comments, questions and replies so that they are all in one place. I will post it when I'm done.

Andrew

 

[AndrewL]

Question

I took the BOM over to Digikey, they are out of stock of the
capacitors that are the DC blocking capacitors C2 and C3. Any
recommendations for a capacitor that will work well and fit?

Repy from Pete.

You could use a Panasonic part from Digi-Key, EF4105-ND. Or a CDE DME4W1K from Mouser.
Or you may find others... pretty much any 1uF 400V film cap that has a 22.5mm
lead spacing will work.

Question

Those parts are all easy. Its getting the 30-pin right angle connector that's driving me crazy.

Reply from Pete.

That connector should be available at Digi-Key. Note that it is a
"Value-Added" item - that means they do not have it in stock until you
order it. They get full-length strips from Samtec (100 or more pins
long) and cut them to the desired length after you order them.

Beacuse of that, they will always show up as "zero inventory" and
initially as "backordered". But unless they are out of the base
(full-length) material, they will still ship them to you (cut to size)
in one day.

Question.

Isn't the AD538 sensitive to temperature?

Reply from Pete.

(I assume you mean the AD536...)

Not particularly: +/-100 uV/degree C, and full-scale level out of the AD536 is 500mV. So the meter might move 2 or 3 counts going from the freezer to outside in the hot sun in Texas...

From Kevin "Ground the input selector."

Tonight I found out it is a really good idea to ground the shaft/body
of the rotary switch in order to eliminate pick up of 60Hz and its
harmonics. I noticed moving my hand closer to the metal knob on this
switch resulted in a >20dB increase in 60Hz spectra and the addition
of somewhat lower level harmonics at 120Hz, 180Hz, and 240Hz.. I
grounded the switch with a piece of 28ga wire between the lock washer
and the body of the switch and grounded it to the board ground. This
totally eliminated any pick up with no noticeable line frequency or
related spectra. (My case is totally shielded on the top and bottom,
but not sides, front or rear - and does not appear necessary to do
so.)

Question

I have a question about SW4, the Grayhill 2p 6t rotary switch. It >
comes with two small pins that insert into the switch body to limit >
the number of active poles. I want to only take this thing apart >
once to set the pins. This is where I start making assumptions. The >
switch will have 4 active positions. Oh yeah, I didn't really >
mention that, did I?

Reply from Pete.

Yes, the switch stops should be set for 4 positions. Position 1-4 are
used, so you can follow the instructions that came with the switch as
to how to put those little tiny pins in.

If I remember right, you make sure the flat on the shaft is opposite
the number "2" on the back. Then you insert pins just to the left of
number "1", and to the right of "4", as viewed from the shaft
end. Then you stick the shiny label thing on the front of the switch
body to hold the pins in.

I always make sure the pins are right by checking the switch rotation
before sticking the label on.

Be careful, those tiny pins are hard to hold on to, and they disappear
from the face of the earth if you drop them! I have sucessfully
substituted a short piece of piano wire or other steel wire...

Reply to Pete's reply on SW4

Facing the shaft end of the switch and with the flat of the shaft
opposite the 2:00 o-clock position I placed the pins in the holes at
12:00 and 4:00 o-clock. Things seem to work OK. If you want to take
a look at the Grayhill instructions look here

http://www.grayhill.com/web1/images/.../Rotary_71.pdf

More on SW4

If I set the knob with the set screw on the flat of the switch it
appears that the ranges are off

Reply from Pete.

With the switch in the 200mV position (CCW, position 1) the flat is
oriented opposite the "20V" label. You can see this in the switch
datasheet, page 4, here:
http://www.grayhill.com/web1/images/.../Rotary_71.pdf

Not exactly what one might expect...

Question.

I have at least one additional question: in which setting "Ground
vs. Float" do you calibrate the Zero Adjust?

Pete's reply

I don't recall it making much difference, but I guess "Ground" should be better...

From Pete, this web site has been corrected but this is added for
completeness and my notes.

I apologize profusely to all. These values were left in the schematic
from a time when I was running the RMS converter at a lower level. I
decided later to up the gain in the first stage to get more accuracy
in the RMS converter. The problem is, I forgot to go back and update
those two resistors that scale the output for the DPM in the schematic
and BOM!

R14 should be 15k, and R15 should be 27.4k (or any ratio that gets you
close, the pot can adjust it some).

You could also leave R14 at 10k and change R15 to something between
4-5k (4.7k would work). The control will be a little more touchy but
you should be able to calibrate it OK.

I have updated the files on the web site and it's uploading now. (It
might take a while because there are some PDF books transferring too.)

Again, very sorry to all for the confusion on my part!

From Kevin (sheilding)

You might want to try installing some aluminum foil inside the case to
create a faraday cage around the board (ground to one point on the
pcb) - this will prevent all electro-static coupling into high
impedance circuit nodes on the interface.

Most of the self noise in the front end is probably generated by the
49.9K resistors protecting the front end. You could try reducing their
values - you can also look for a quieter op-amp as well, ultimately
the ThatCorp INA is a few dB quieter than the BB, but this should be
the last thing you change. To do self noise measurements you need to
make sure that the inputs are shorted and you are not near any
external noise sources. The computer and the monitor (yes even LCDs)
spew broadband noise everywhere and if the interface is in proximity
that might cause a problem. In my old system I shielded all of the
cables to the sound card and found this was good for really reducing
spurious pick up from nearby noise sources. Balanced mode operation
should take care of a lot of the LF garbage, but CMRR degrades very
quickly above a few kHz in most designs unless great care is taken.

Question.

Does anybody know if That Corps 1512P08-U could be used as a
substitute for B&** DRV134PA, The B&B device seems to be in scarce
supply these days.

Reply from Pete.

No, the 1512 isn't really a driver, but the THAT 1646P08 should work
fine... in stock at Mouser

From Kevin.

Mouser has the ThatCorp equivalent in stock last week when I ordered
my parts. The ThatCorp 1646P08 has significantly better performance
than the currently unobtainable BB DRV134PA.

I would have gotten the ThatCorp INA in lieu of the BB INA as well,
but that part wasn't in stock at Mouser or Digikey.

Question.

Is it okay to sub a slightly higher or lower value or
RUSBF110? Perhaps RUSBF090 or RUSBF135?

Also, what is the largest dimensions that can fit for C2, C3? I
haven't received my boards yet.

Reply from Pete.

No worries on subbing a different PTC fuse. You could even leave it
out (replace it with a jumper), basically it is there as a safety
mechanism if you plug in the wrong voltage or polarity of DC adapter.

Same is true for the TVS. Any 1.5KE9.1xxxxx should be fine.

C2 and C3 are 22.5mm lead spacing, and the footprint is 26.8mm x 11.3mm.

Note.

It might be worthwhile to add four #4-40 x 0.25" sheet metal screws
for securing the board to the bottom of the case. Of course, with all
the panel mount components, perhaps it isn't a huge deal. Stuff like
this isn't easy to get at Mouser, but they sell them, as long as you
don't mind a few extras ( 5721-4-1/4-SS).

Note from Pete.

You do have low-ESR caps on the converter output, don't you? Generic electrolytics are useless here...

From Kevin

I measured similar or worse levels of ripple on the input and outputs
of the murata switcher..

I'm thinking perhaps a small common mode choke on the input..

See this thread for help.

http://www.diyaudio.com/forums/power-supplies/159705-when-you-need-15vdc-have-only-one-pole.html

grufti suggests

Shielding, grounding and part swapping has actually improved things.

I shielded the both the top and the bottom of the plastic enclosure,
grounded the switch, removed the "Zero Adjust" parts, converted to
THAT balanced receivers and drivers, and finally used a LME 49720 in
place of the OPA2134.

...

There is just a trace of some power supply harmonics left, and the
third harmonic of the input signal at close to -112dB.

From Pete.

Looks like the rotary switch I used here is out of stock
everywhere. If you need one, there are two other options:

71ADF30-01-2-AJN is the same switch with a 1/8" shaft (you'd need a
different knob and maybe some washers to mount it to the panel).

71BF30-01-2-05N is the same switch with fixed stops at 5 position. You
only need the first 4 and the switch will move an extra position
clockwise, but it should fit and work fine.

Both are in stock at Newark, and the 1/8" shaft part also at Allied.

 

[AndrewL]

I think I got must of the useful stuff, least I hope so. I always find it better if its all collected in one place.

Now, several dumb questions on my part.

For shielding, I know RFI is different to EMI but what's the best
compromise on this project? Both are required....I expect. Now, assuming I can't get any mu-metal, could I use copper tape for the top and bottom of the case?

For wiring the SC to the inputs, how do I wire the cable into the 1/4"
jacks? Its looks to me from the schematic that the 1/4" input jack use all
three, tip, ring and shield. Have I read it right? I assume the normal SC is single ended, mono mini-jack and the like, so just tip and shield is ground. So I just need to make up a cable that converts.

For the PCB screws, will M3 do instead of #4-40 x 0.25"?

I have an M-Audio Transit USB sound card, I assume this will be OK for testing and to get me going?

I'm sure there will be more, just need to convince myself to spend the money now....

thanks,

Andrew

 

[AndrewL]

For wiring the SC to the inputs, how do I wire the cable into the 1/4"
jacks? Its looks to me from the schematic that the 1/4" input jack use all
three, tip, ring and shield. Have I read it right? I assume the normal SC is single ended, mono mini-jack and the like, so just tip and shield is ground. So I just need to make up a cable that converts.

I think I found the answer to the cable wiring question.

The output (to the soundcard input) is delivered through a 1/4" phone jack, wired in the standard balanced configuration. The logic here was simply that it's what my soundcard uses (an M-Audio Audiophile 192). It is also inexpensive and readily available.

So I assume the SC has three connections too, if it doesn't then pseudo balanced is the way to go, with the shield just connected at the ATEST end.

 

[AndrewL]

I have 3 sets of parts on backorder, I can save the pain if I get these locally (Farnell), can anyone check if I've made a mistake translating them?

2 1uF 400V C-EU150-084X183 Cap, 1uF 400V film, 22.5mm LS Vishay BC BFC2 373 53105 = PANASONIC - ECQE4105JF - CAPACITOR, Metallised Plastic Film, 400V, 1UF

14 0.1uF C-EU050-030X075 Cap, 0.1uF 50V film, 5mm LS Kemet MMK5104J50J01TR18L16.5TR18 = PANASONIC - ECQV1H104JL - CAPACITOR, , Metallised Plastic Film 50V, 0.1UF

2 470uF 16V CPOL-EUE5-10.5 Cap, 470uF 16V electrolytic, 5mm LS 10mm dia Nichicon UPW1C471MPD = RUBYCON 16ML470M10X9

thanks

Andrew

 

[AndrewL]

Gents,

Is Rapid Electronics - Electrical & Power > Fuses & Circuit Breakers

An OK equivalent for the Resettable Polyfuse? It looks like it to me, typical in my swithering and researching Digikey have run out of them

 

[AndrewL]

The better half just bought me Pete's card as an early present, so it looks like I'm in business.

Andrew

 

[MarkFromNJ]

Murata DC-DC converter latches up on startup

HI,
I'm having a problem with the Murata converter and I am wondering if anyone else has seen this.

Problem: converter requires 1.4A from the 5V rail at power on (startup) or it latches up and pulls the supply down to ~0.9V (at 500ma current limit). If current limit is set >1.4A the converter starts and runs fine, and draws a normal ~ 180ma from the 5V rail with no op amps installed on the PCB.

PCB: No input short or output short; no continuity between 5V side and "isolated" side or between any + rail and any "ground"; no overload on +-15V rails.

Components tested: 470uf/16V input cap tests OK on LCR meter @ 448uf. No difference in latch-up behavior if polyfuse and/or TVS diode are in circuit or out of circuit.

I checked the Murata datasheet for any info on latch-up. There was none.

I thought this might be an artifact of the speed with which the Agilent goes into current limiting so I tried a switching wall wart rated 500ma. The wall wart was toasted. I also tried a transformer based 1A wall wart and that one worked, not a surprise since it can supply more than its rated output for a little while.

This is pretty clearly not going to work on 500ma of USB port power. Have any of you seen this behavior before? Is there any chance Digikey will take this beast back for replacement?


Thanks
Mark

 

[pmillett]

Problem: converter requires 1.4A from the 5V rail at power on (startup) or it latches up and pulls the supply down to ~0.9V (at 500ma current limit). If current limit is set >1.4A the converter starts and runs fine, and draws a normal ~ 180ma from the 5V rail with no op amps installed on the PCB.

This is pretty clearly not going to work on 500ma of USB port power. Have any of you seen this behavior before? Is there any chance Digikey will take this beast back for replacement?

This is pretty typical for switchmode converters - there is a startup surge to charge all the capacitors at the input and output(s). 1.4A at 5V is only 7 watts, not really all that big of a surge for a 3W converter.

I run mine from the USB power on a desktop computer and it works fine - but no doubt the computer has only a polyfuse or some similar crude overcurrent protection which is slow, so it can stand the start-up surge. I imagine something more sophisticated may very well shut down.

To run it from a switching wall wart, you'd probably need one rated for at least 1A, maybe 2A, to make it past the startup current.

Pete

 

[pmillett]

Gents,

Is Rapid Electronics - Electrical & Power > Fuses & Circuit Breakers

An OK equivalent for the Resettable Polyfuse? It looks like it to me, typical in my swithering and researching Digikey have run out of them

Looks like it would work fine. You could even replace it with a wire as long as you're careful to apply the right voltage and polarity supply

 

[MarkFromNJ]

This is pretty typical for switchmode converters - there is a startup surge to charge all the capacitors at the input and output(s). 1.4A at 5V is only 7 watts, not really all that big of a surge for a 3W converter.

I run mine from the USB power on a desktop computer and it works fine - but no doubt the computer has only a polyfuse or some similar crude overcurrent protection which is slow, so it can stand the start-up surge. I imagine something more sophisticated may very well shut down.

To run it from a switching wall wart, you'd probably need one rated for at least 1A, maybe 2A, to make it past the startup current.

Pete

I was thinking surge but usually a current limited input causes a SMPS to soft start, not latch up. In this case it looks like the controller is electrically latching up like some op amps do if you kill one rail but not the other; NE5532's are famous for this.

In a past life I designed switchers for use in undersea comm cables (or more precisely, the leak detectors therein), but the circuit soft started to prevent this kind of problem 'cause you can't pull a 5x surge through 25 miles of wire . I guess Murata doesn't think they need soft start. It doesn't matter here but it does pretty severely limit the applications for the part, moreso since the app sheet does not mention it.

Your explanation makes perfect sense since I did not see this behavior when I tested the unit out of circuit with a simple resistive load (no output caps).

If yours works on USB then it's good enough for me. I guess it's a case of using "too good" test equipment. Not the first time this has happened, or I suspect, the last.

Thanks very much for the quick response. Time to plug in the chips and calibrate!

Thanks,
Mark

 

[AndrewL]

Mark, can/could you put an NTC thermistor on the input to give you a soft start?

Andrew

 

[pmillett]

Mark, can/could you put an NTC thermistor on the input to give you a soft start?

Andrew

Probably will give the same result. The problem is that the converter presents a negative resistance at it's input - the lower the voltage, the more current it wants to draw. That's why you get the "latchup" from a current limited supply.

 

[AndrewL]

Possibly an update for the BOM?

Mouser seem to have changed part numbers or something as the caps used for C1, C4, C6, C9, C14, C15, C16, C17, C19, C20, C23, C24, C25, C26 seem to be out of stock. I rooted around for alternatives, these are in stock but they seem to be the same part.

MMK5104M50J01L16.5TR18

The old part number was.

MMK5104J50J01TR18L16.5TR18

Also, I found these caps, 667-ECW-F2W475JA on Mouser, I think I can replace C2 and C3 with these, they seem to be the same physical size but are 450v 4u7F, I'm not sure if there's any downside other then extra cost.

thanks,

Andrew

 

[MarkFromNJ]

Probably will give the same result. The problem is that the converter presents a negative resistance at it's input - the lower the voltage, the more current it wants to draw. That's why you get the "latchup" from a current limited supply.

Yes, but normally there is protection to turn off the power switches if the voltage gets too low; Murata does not include that feature. I suspect it comes down to a discrete transistor based (ie, old) design rather than a more modern design with soft start and current limiting built in.

This is only a concern to me because I want to use the sound card interface with a new high end laptop since that's all I have (Toshiba Qosmio 505). Laptops use USB chipsets with integrated power management, which includes a strict limit to current (500ma/5v) on each port. So while lots of you have used this successfully with desktops, which use little if any current limiting on USB, I would be interested if anyone has used this with a reaonably modern laptop, say post 2007. Given that in my testing the Murata "let the smoke out" of a 5v/500ma switching wall wart, I am afraid to try it.

Before I spend $$ on a TI soft start converter or messing with the input and output capacitors, any user history with respect to laptop use would be greatly appreciated. Thanks!

Mark

 

[MarkFromNJ]

Probably will give the same result. The problem is that the converter presents a negative resistance at it's input - the lower the voltage, the more current it wants to draw. That's why you get the "latchup" from a current limited supply.

Actually I think it would make it worse. The problem is not inrush current, it's that the Murata gets itself into a state from which it cannot recover if it is not given about 1.5 amps for a couple hundred milliseconds on startup, long enough to charge the 470uf input cap to 5v and the two 330uf output caps to 15v each.

Mark