Would the THAT 1200P08-U be a slight improvement over the THAT 1240P08-U?
http://www.thatcorp.com/datashts/1200data.pdf
http://www.thatcorp.com/datashts/1240data.pdf
http://www.thatcorp.com/datashts/1200data.pdf
http://www.thatcorp.com/datashts/1240data.pdf
(bump)
Parts trickling in for mine; I cut and punched a piece of Ultraperm 80 that nests in the bottom of the enclosure and is laminated with plastic tape to help prevent short circuits. Having next to no information on the material, I can only report that a heavy pair of scissors cuts it cleanly and a paper punch out of my desk drawer did the holes neatly. I will similarly cut a sheet for the top cover. Whether it'll do a good job of magnetic shielding remains to be seen. Suppose I could try a double layer, but first I have to get the meter running...
Parts trickling in for mine; I cut and punched a piece of Ultraperm 80 that nests in the bottom of the enclosure and is laminated with plastic tape to help prevent short circuits. Having next to no information on the material, I can only report that a heavy pair of scissors cuts it cleanly and a paper punch out of my desk drawer did the holes neatly. I will similarly cut a sheet for the top cover. Whether it'll do a good job of magnetic shielding remains to be seen. Suppose I could try a double layer, but first I have to get the meter running...
I will post this separately -- I think it would make sense to put a choke on the input of the MuRata NDTD2415C -- the company shows this in the test setup. The frequency is ~370kHz -- not a problem for a soundcard set up per se but it may radiate into everything else, causing some issues with opamps.
Within the audio band, the output of the MuRata converter measures 30.03uV RMS "A-Wtd" and 21.45uV Avg, CCIR-2K with 40mA load on each side.
An externally hosted image should be here but it was not working when we last tested it.
Within the audio band, the output of the MuRata converter measures 30.03uV RMS "A-Wtd" and 21.45uV Avg, CCIR-2K with 40mA load on each side.
Yes, look at the supply voltage rating.. They will fail on +/-15V rails, +/-13V is about the maximum safe voltage. I used AD8620 in the front end and signal chain of an ATE instrument I designed about 4yrs ago and otherwise they are pretty suitable.
At a minimum some etch cuts would be required. I'm wondering whether the linearity of the diff amp would suffer due to the additional circuitry required to force balance..
Hi Jack,
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..
Last edited:
Thank you for catching that. I assumed when I should have looked.
While I'm going through the options: NatSemi LME49720 - supply voltage ... check, just about everything else ... check. Is input current a concern? Anything else that I am not considering?
I generally use fet inputs where I want high input impedance and/or some level of intrinsic rf immunity. Bi-polars with input bias current canceling circuitry may work quite well, (I think the LME49720 falls into that category) - offset currents if present may interact with the tempco of the input resistors and result in significant offset drift which might be a problem with the meter. Given that you probably have input sockets you can try anything you want. The best fet based op-amps are generally at least 10 - 20dB noisier than the best bi-polars, however given the low front end gain I expect the noise performance of the diff amp following them is going to play a huge role - probably the fet is going to be good enough. My first attempt at this 10yrs ago used 5532 and that worked quite well.
Scale values of all input resistors by a factor of x 10, and you will have to add a small shunt capacitor (trimmer) across the 909K resistor in order to compensate the high frequency response. (Look at what they do on scope probes, and how they do it for guidance.)
Use a good JFET op-amp on the input. (no bipolars!)
Do not scale the feedback or protection resistors!
Expect the noise floor to come up at least a few dB, and shield the case as I have described previously - add choke Jack discusses in his latest psu related post.
Use a good JFET op-amp on the input. (no bipolars!)
Do not scale the feedback or protection resistors!
Expect the noise floor to come up at least a few dB, and shield the case as I have described previously - add choke Jack discusses in his latest psu related post.
Kevin,
Thanks for taking the time to mentor me on this.
I have studied and have a basic understanding of frequency-compensated dividers but have a couple of clouds remaining in my mind. I was planning on using a X100 probe, since that is all I have that is rated for the voltage that I will be seeing. It will obviously have a trimmer cap in it.
I am building a driver stage that puts out (hopefully) about 200Vrms and would like to be able to measure its distortion.
To do this right would I need a trimmer from input to the attenuator setting that I will be using? I'm thinking I would set this trimmer to compensate for Cin of the op-amp and then set the compensation of the probe last. Does that sound right or am I off on my thinking?
I was going to use the OPA2134. Is there a better amp for this high Zin version?
As far as the choke goes, should I go common mode or do it like the test setup in the converter data sheet shows?
jackinnj has started a thread where he goes into more detail about his choke for the Murata DC/DC chip
1) grufti: I would like to see what you have concerning "When you need +/- 15VDC and have only one pole" ... (the link/file does not show up when clicked ?)
2) I am a firm believer in external DAC / ACD "soundcard" devices as opposed to PCI "soundcards", in part because of the reports from pmillett. "... You can now see 60Hz and harmonics of 60Hz show up. Interestingly these are present (at somewhat lower levels) even with the power disconnected, so they are being picked up from the environment. ...") ... External "soundcards" generally do have better noise floor specs because of (USB, FireWire) power filtering and isolation from the computer cases, switching supplies, unintentional ground loops, power cord connections to house power, etc., whether powered up or not. That computer case is "dirty", always has been, always will be = an antenna with high impedance shorts, stray capacitance and gnd loops. ... Anyone else?
3) Toward that end, I have several variants of external "soundcards" that may be borrowed for test and comparisons using Mr. pmillett's very interesting device. ... ( Echo Digital AudioFire2 FireWire Audio on the Go - IndustrialComponent.com and M-AUDIO - FireWire Solo - FireWire Mobile Audio Interface for Songwriter/Guitarists ) ... Sy? Pete? Kevin? TubeMack?
4) Aside: looks like my attempt to build the TI audio analyzer kit is for naught?
... Oh well ...
2) I am a firm believer in external DAC / ACD "soundcard" devices as opposed to PCI "soundcards", in part because of the reports from pmillett. "... You can now see 60Hz and harmonics of 60Hz show up. Interestingly these are present (at somewhat lower levels) even with the power disconnected, so they are being picked up from the environment. ...") ... External "soundcards" generally do have better noise floor specs because of (USB, FireWire) power filtering and isolation from the computer cases, switching supplies, unintentional ground loops, power cord connections to house power, etc., whether powered up or not. That computer case is "dirty", always has been, always will be = an antenna with high impedance shorts, stray capacitance and gnd loops. ... Anyone else?
3) Toward that end, I have several variants of external "soundcards" that may be borrowed for test and comparisons using Mr. pmillett's very interesting device. ... ( Echo Digital AudioFire2 FireWire Audio on the Go - IndustrialComponent.com and M-AUDIO - FireWire Solo - FireWire Mobile Audio Interface for Songwriter/Guitarists ) ... Sy? Pete? Kevin? TubeMack?
4) Aside: looks like my attempt to build the TI audio analyzer kit is for naught?
... Oh well ...
Last edited:
Of course you are right. The PCI audio interface is everywhere, justifiably = It is cheaper to manufacture and clears the desktop of extra cables, boxes, etc.
But, if you want to get the best specs (noise floor, power supply rejection, dynamic range, separation, "audiophile" quality, etc.) ... external devices seem to have a distinct advantage. You just can't sell 'em off the shelf in your basic computer store without extra effort. Take a look inside a professional recording studio if you want to see some interesting DAC/ADC gadgets = The computer is used for storage of the high resolution digital results and seldom used for playback except through an external higher quality DAC.
Apple Laptop to Echoaudio.com stereo DAC/ACD w/ silver & teflon wire, balanced in, unbalanced out to Bottlehead tube pre-amp ... and it sounds pretty good, too ... IMOP.
Last edited:
SY: " ... Pete's data show the internal PCI card is very quiet. ..."
As noted. Yes the M-Audio 192k PCI soundcard is about as good as it gets. Pete made reference to the fact that, when the computer was powered down, the residual noise increased (!) and seemed to come "from the equipment", meaning that "dirty" computer. (Check it out, if you want, try one of mine. You have my email, right?)
As noted. Yes the M-Audio 192k PCI soundcard is about as good as it gets. Pete made reference to the fact that, when the computer was powered down, the residual noise increased (!) and seemed to come "from the equipment", meaning that "dirty" computer. (Check it out, if you want, try one of mine. You have my email, right?)