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Old 7th February 2013, 03:03 PM   #671
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Maybe a bit cheeky, but I would like to buy a completed interface (or a an unbuilt kit including parts). I have tried to get the parts, but in my location this is nearly impossible....

Anyone has one spare or is not using his?
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Old 27th September 2013, 05:22 PM   #672
nickds1 is offline nickds1  England
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A couple of things...

I've seen people posting about using a 12mH choke in the Vcc supply to the NDTD converter.... I've not read the whole 67 pages and 670+ comments, but this should be 12uH (micro-Henrys) NOT milli-Henrys according to MuRata's data sheet at http://www.murata-ps.com/data/power/ncl/kdc_ndtd.pdf.

Secondly, is there a consolidated list of recommended mods anywhere as I've not had time to trawl through this thread in its entirety (see above )

Thanks
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Old 31st October 2013, 09:24 PM   #673
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Anyone ever used this interface QA400?
QA400 Audio Analyzer
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Old 4th November 2013, 11:30 PM   #674
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Quote:
Originally Posted by RodrigoRocha.RJ View Post
Anyone ever used this interface QA400?
QA400 Audio Analyzer

Here is a very good DiyAudio post to following: QuantAsylum QA400

I built Pete's Interface and I have used it with the QA400. I am still trying to understand all the gains and losses (that must be taken into account) between the DUT and the QA400 which are necessary for accurate final measurements observed on the QA400.

Here is a screen shot of the QA400 results from a Carver TFM-15 amplifier using Pete's interface. If you correctly map out all of the gains and then enter them into the QA400's software you get meaningful results.

Note: I am using an external generator instead of the QA400's internal generator.

The setup is HP339 Oscillator > DUT > Pete's Interface > QA400 > Laptop

Notice the figures report exactly 100 watts (verified with an external AC meter as measured on my dummy load). The reported distortion is also very close to my HP339 analyzer results. I was also able to determine exactly when clipping occurs by monitoring the spectrum for increasing harmonics. Clipping shows up on the spectrum well before you can observe clipping on the oscilloscope. Not perfect but also not bad for a inexpensive PC analyzer. A good tool for analysis paired with Pete's interface.


Click the image to open in full size.
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Old 19th December 2013, 12:42 AM   #675
kevinkr is offline kevinkr  United States
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If you are having hum problems with the sound card interface and you are not deliberately using the input as a differential amplifier try shorting out C2. The acquisition below was done at 100mVrms from an Amber 3501A with output in ground mode, and the input floating. Levels are calibrated.

Note DC on the ground will cause meter errors since it responds to DC.

My interface is fully shielded, I have installed clamp on ferrites on the audio cable and usb power cable, grounded the shaft of the range selector, and selected the best driver and receiver chips for lowest thd. I have also installed 0.1uF ceramic caps in selected locations. I have determined that the charger that came with my Samsung Galaxy S III smart phone is significantly quieter than the usb power even with the ferrites so I have ordered one of those.

The clamp on ferrites greatly reduced the common mode conducted noise from the PC. Previously the meter and indeed external meters indicated at least 7mV of noise which made setting low output levels impossible. (I'm designing a bunch of phono stages) The ferrites fixed this - now the meter indicates 00.0mV when no signal is input even on the 200mV range.

Based on the way the circuit is designed I recommend using floating mode only on the 200mV range with generator in ground mode, I still get much better results on all other ranges with the input grounded and the generator floating. Note that I can now get good results on higher ranges even with low amplitude input signals - that was not the case before.

Edit: I've added two graphs with the system acquiring 5mVrms input signals. And yes the Amber 3501 is extremely quiet - overall substantially better than the generator in my set up. (Note the consistent level of hum spectra relative to the noise floor at both 100mV and 5mV with the 3501A as the source.)

The sound card is an M-Audio 24192 running at 96k and 24 bits.
Attached Images
File Type: png 200mV range C2 Shorted.png (17.1 KB, 249 views)
File Type: png 200mV range C2 Shorted 5mV internal gen.png (17.3 KB, 244 views)
File Type: png 200mV range C2 Shorted 5mV 3501A.png (17.1 KB, 242 views)
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Old 23rd December 2013, 11:11 AM   #676
mogliaa is offline mogliaa  United Kingdom
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It seems like the Maudio Audiophile 192 is getting hard to find in the UK. Does anyone have any recommended SC for upgrading my test system to 192kHz/24bit?
Thanks
Ale
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Old 23rd December 2013, 11:32 AM   #677
HpW is offline HpW  Switzerland
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Originally Posted by mogliaa View Post
It seems like the Maudio Audiophile 192 is getting hard to find in the UK. Does anyone have any recommended SC for upgrading my test system to 192kHz/24bit?
Thanks
Ale
The future will be an USB 3 based ADC/DAC system....

or the ultimate would be a DIY project ADC/DAC, battery powered and feed the signal using a SPDIF I/O (feed using glas or fiber connection) to the digital sound card...

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Old 23rd December 2013, 11:45 AM   #678
AKN is offline AKN  Sweden
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Quote:
Originally Posted by kevinkr View Post
If you are having hum problems with the sound card interface and you are not deliberately using the input as a differential amplifier try shorting out C2. The acquisition below was done at 100mVrms from an Amber 3501A with output in ground mode, and the input floating. Levels are calibrated.

Note DC on the ground will cause meter errors since it responds to DC.

My interface is fully shielded, I have installed clamp on ferrites on the audio cable and usb power cable, grounded the shaft of the range selector, and selected the best driver and receiver chips for lowest thd. I have also installed 0.1uF ceramic caps in selected locations. I have determined that the charger that came with my Samsung Galaxy S III smart phone is significantly quieter than the usb power even with the ferrites so I have ordered one of those.

The clamp on ferrites greatly reduced the common mode conducted noise from the PC. Previously the meter and indeed external meters indicated at least 7mV of noise which made setting low output levels impossible. (I'm designing a bunch of phono stages) The ferrites fixed this - now the meter indicates 00.0mV when no signal is input even on the 200mV range.

Based on the way the circuit is designed I recommend using floating mode only on the 200mV range with generator in ground mode, I still get much better results on all other ranges with the input grounded and the generator floating. Note that I can now get good results on higher ranges even with low amplitude input signals - that was not the case before.

Edit: I've added two graphs with the system acquiring 5mVrms input signals. And yes the Amber 3501 is extremely quiet - overall substantially better than the generator in my set up. (Note the consistent level of hum spectra relative to the noise floor at both 100mV and 5mV with the 3501A as the source.)

The sound card is an M-Audio 24192 running at 96k and 24 bits.
Hi Kevin,

I also had to combat common mode noise.
In my case it was the Murata converter inside the interface that put out high frequency common mode noise and not the PC. I tried separate supply that had transformer with separate pre/sec bobbins - Noise walked right through. I also tried to altered decoupling - Still noise. Finally, removing the Murata converter - No CM noise.
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Old 24th March 2014, 02:11 AM   #679
Paulwv is offline Paulwv  Netherlands
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Quote:
Originally Posted by kevinkr View Post
My interface is fully shielded, I have installed clamp on ferrites on the audio cable and usb power cable, grounded the shaft of the range selector, and selected the best driver and receiver chips for lowest thd.

I have also installed 0.1uF ceramic caps in selected locations. I have determined that the charger that came with my Samsung Galaxy S III smart phone is significantly quieter than the usb power even with the ferrites so I have ordered one of those.

The clamp on ferrites greatly reduced the common mode conducted noise from the PC. Previously the meter and indeed external meters indicated at least 7mV of noise which made setting low output levels impossible. (I'm designing a bunch of phono stages) The ferrites fixed this - now the meter indicates 00.0mV when no signal is input even on the 200mV range.
Kevin, I also have a lot of hum and noise on my SCIF. I added the 0.1 caps to all elco's, added a 12 uH smt between 5V input and fuse, and shielded everything, grounded the housing of all the switches, still only got about 10dB improvement. (Now at 115-120 dB quite a bit left to do)

I ordered some ferrite clamps for the external cables, so that will hopefully help, but I'm interested in your selection of the driver and receiver chips you ended up using. I also cannot null the meter, I have also about 7mV of noise, and cannot null the meter reading.

Interesting, or coincedance? I'm puzzzled why there are so many noise floors published south of 130dB, and I started at 100
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Old 24th March 2014, 02:14 AM   #680
Paulwv is offline Paulwv  Netherlands
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Anders, did you end up using an off-board +/- 15V power supply? I also have excessive noise and high frequency pulses. My DC-DC is soldered in, so I would like to use that option as a last resort.

Tks
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