A New Take on the Classic Pass Labs D1 with an ESS Dac - Page 90 - diyAudio
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Old 15th February 2012, 03:15 AM   #891
opc is offline opc  Canada
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Exactly what he said ^

The chassis looks great, and again, kudos on putting in all the extra work to etch your own board! I'm looking forward to hearing your impressions.

I recently took a few more measurements of my NTD1 using a separate outboard ADC and patching it digitally into the AP. This allows more accurate measurements as the outboard ADC has much lower distortion than the internal one on the AP.

As I always suspected, distortion is significantly lower than originally measured.

Remember this post?

A New Take on the Classic Pass Labs D1 with an ESS Dac

Compare and contrast to the graphs attached below:

1. DPR @ -4dBFS - 2nd and 3rd harmonics are down 131dB and 127dB respectively
2. DPR @ -6dBFS - 2nd and 3rd harmonics are down 131dB and 133dB respectively
3. FFT of the output @ -6dBFS. Scale the whole thing up by 12dB if you want values in dBV. This puts the noise floor at between -138dB and -158dB!
4. THD vs. Freq @ -6dBFS. Values below 10Hz and above 7kHz are not valid due to high and low pass noise filters at 20Hz and 22kHz.

Hopefully that's some encouragement to get your project finished!

Cheers,
Owen
Attached Images
File Type: png Distortion Product Ratio -4dBFS 192k.png (47.0 KB, 461 views)
File Type: png Distortion Product Ratio -6dBFS 192kHz.png (47.7 KB, 443 views)
File Type: png FFT -6dBFS.png (102.2 KB, 444 views)
File Type: png THD Level v freq -6dBFS.png (75.6 KB, 421 views)
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Old 15th February 2012, 04:28 PM   #892
syklab is offline syklab  Hong Kong
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Hi OPC,
Any schedule for the whole thing to be availabvle for order?

Thanks
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Old 16th February 2012, 09:40 PM   #893
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Great distortion figures. But I'm not too nervous about perfect tech specs. My Aleph30 clone made years ago is still one of my preferred amp, and doesn't test so great. I have a CLIO analysis system and I'll certainly have a look at the specs, but I'll be happy if the dac sounds just great
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Old 17th February 2012, 01:33 AM   #894
qusp is offline qusp  Australia
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well get ready to be happy
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Old 17th February 2012, 04:12 AM   #895
igwt is offline igwt  United States
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Quote:
Originally Posted by qusp View Post
well get ready to be happy
Yes Dire Straits "Iron Hand" Playing right now Thru Owen's D1...scary good! Me Happy!

Thanks Again Owen.

igwt
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Old 17th February 2012, 06:34 AM   #896
qusp is offline qusp  Australia
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indeed, hard to describe the sound, but the best way i know how, is that it has all the scary deep resolution of a top flight opamp stage, without sounding like its trying too hard.
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Old 17th February 2012, 03:44 PM   #897
igwt is offline igwt  United States
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I added a shunt reg between the on-board regulator and buffalo ll.

With distortion levels so low from source to output tweaks are audible ,this one
seems to be a positive one to my ears.

My NTD1 Bll combo does not suffer from what I call "digitosis"...you know the junk that makes some of Madeleine Peyroux's recordings fatiguing and sends your tweeters into fits on a most digital systems. I think reviewers call it "glare" Well the glare is gone! Analog tone with digital detail.

igwt
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Old 18th February 2012, 08:12 PM   #898
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Hi. I may doing something wrong. The DAC VA/2 = 1.64V, and can be easily measured at the output of the Buffalo DAC output (nothing connected).

Then without connecting the DAC, I adjusted all four D1 FET gates to the same voltage of 1.64V, easily done.

I connected the DAC it is was very wrong. The DAC Vd and Va where drag lower than normal, VD was 4.52V instead of the normal 5V, the DAC stop to works, and the DAC outputs where stuck at -0.7V.

If I change to D1 FET Gate until the DAC sees 0V at its output, it is working again, at this point the FET Gate voltage is about 3.3V.

With the D1 pot I can vary the DAC output voltage (connected to the D1) from -0.7V to +0.7V only, not the expected 1.64V.

It is if like the protection zener are conducting at 0.7 and not 3V.

Remember, I'm using my own PCB. It can still be wrong. I already found and corrected a few mistakes.

Any idea? Anything to test?
Thanks...
SB
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Old 18th February 2012, 09:49 PM   #899
opc is offline opc  Canada
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This could be a few things:

1. The gate voltage is not what you should be measuring! You need to adjust the pots to measure 1.65VDC on the SOURCE of the mosfet (where the DAC outputs connect to) relative to GND.

2. The protection zener diodes were incorrect on the PCB. This error has been covered several times throughout the thread, but it's easy to miss. If you want to keep the protection zeners, you need to make a little tee-pee putting two zeneres back to back on the same pad. There are instructions in the thread somewhere with pictures.

Fix the above two things, and you should be good to go. Do not attach the DAC to the I/V stage until you've got the proper 1.65VDC at the source of each fet! If you have a high voltage there, you could damage the DAC.

Regards,
Owen
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Old 18th February 2012, 11:44 PM   #900
qusp is offline qusp  Australia
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thats my fault, I mispoke in my instructions as we had been just talking about gates, so i had gated head; but we corrected that straight away in the subsequent posts. maybe i should get the mods to correct my first post?

Last edited by qusp; 18th February 2012 at 11:49 PM.
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