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Old 18th April 2013, 01:40 PM   #1111
Waly is offline Waly  United Kingdom
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Quote:
Originally Posted by Edmond Stuart View Post
depending on which channel and which L22. Yes, I have two them, bought on ebay at roughly the same price as a new ASUS blah blah blah XTe thingy. Really 'snobbish', isn't it. ?
Wow, you are a true EBay business man! Second hand L22's are running at about twice that money today, and are barely available. People who will have the chance to get a L22 for 100 squid are indeed a good market segment for your software product.

And BTW, MC33078 is a horrible opamp, get rid of it ASAP.
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Old 18th April 2013, 05:08 PM   #1112
BV is offline BV  Slovakia
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Quote:
Any idea which IC in particular is responsible for it?
Hi Edmond,
I think it's the INA137 or the MC33078 in the first place.
I think booth, INA137 (input amp before A/D) and OP275 (output balanced driver), here is no MC33078..Output and input analoge circuits perform best at levels near 1V RMS.
And my name is Ladislav.
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Old 18th April 2013, 06:05 PM   #1113
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Default upgrading L22

Hi Ladislav,

So I think it is best to replace the chips step by step and check the performance after each step. As for the MC33078 (i.e the one just in front of the ADC), most of the time it is simply labeled '33078'. Or do you have another IC sitting there? Actually, I was a little amazed to find this mediocre chip on a L22. But, as I don't have reverse-engineered the card yet, I'm not sure if this chip sits in the signal path anyhow.
In the meantime I received a bunch of samples from ADI and TI. After getting (or making) a suitable desoldering tip*, I'll let you know about the results.

Cheers,
Edmond.

*Probably I'm making it myself, as buying one is too 'snobbish'.
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Old 20th April 2013, 06:07 PM   #1114
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Quote:
Originally Posted by Edmond Stuart View Post
...
*Probably I'm making it myself, as buying one is too 'snobbish'.
And so I did, made from a piece of 4/6mm copper oil tube and fitted on a 50 years soldering iron* (see 1st pic). Before modifying a L22, I will first practice on an old sound card (from Creative Labs of course, what else are they good for?)

The picture was taken with my new camera, of course also a 'snobbish' one: same performance as a Leica M9 (though 1/7 of the price). So which one is it? Have a look at the 2nd pic. The connoisseurs among us will (and should) recognize it immediately.

Cheers,
E.

*This one is 20W and probably it is too hot for desoldering SO8 chips, so I will use a variac to lower the temperature.
Attached Images
File Type: jpg SO8-C.jpg (884.3 KB, 325 views)
File Type: jpg handle-C.jpg (57.8 KB, 288 views)
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Old 22nd April 2013, 08:16 PM   #1115
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Default Modding a Lynx L22

Hi Ladislav,

I started with the ADC section. First, I replaced the MC33078 and INA137 by a LM4562 respectively AD8274. At 1kHz or 19kHz and 20dB or 3dB below FS, it had no significant effect on THD and noise. Only individual harmonics differ a few dB.
Next, I replaced the OPA2227's by LME49720's. At -20dB still no significant improvement. At -3dB and 1kHz dito. At 19kHz however, THD was 11dB lower. At least something has improved.

BTW1, you said "[t]here is no MC33078", so what else is sitting there? (I mean just in front of the ADC)
BTW2, the SO8 desoldering tip works fine and no variac needed, just pull out the mains plug when the tip is hot enough.

Cheers,
E.
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Last edited by Edmond Stuart; 22nd April 2013 at 08:35 PM.
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Old 3rd May 2013, 10:16 PM   #1116
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Here is the result from my onboard Realtek audio, going through a feedforward EC buffer of my design. It's better than the Xonar DX. Interestingly, this comes from an Asus M5A99FX Pro R2.0 motherboard. Same manufacturer of the Asus.

5th harmonic I think is a software error cause by Audacity or the drivers.

Baudline is the software I'm using. It is incredible.
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Old 3rd May 2013, 10:57 PM   #1117
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Hi keane,

Very interesting results. So the THD @ 1kHz is about -85dB. BUT.. is this figure dominated by the distortion of the ADC/DAC or by the EC buffer? Where can we find the schematic of your EC buffer?
Why do you think the 5th harmonic is an artifact?
One more question: What was the sampling rate and measurements bandwidth?

Cheers,
E.
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Old 3rd May 2013, 11:12 PM   #1118
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Sampling rate is 192KHz. Attached is a picture of the pure loopback test with a 5 inch cable.

5th harmonic was a lot worse when Audacity was at 96KHz. I switched it to 192KHz and it lowered significantly. The 6h harmonic wanders up and down regularly, which would seem to indicate sample conversion artifacts.

The Xonar was almost usable with the 5 inch cable but when I hooked it up to the few meters of cable to my bench, 2nd harmonic got significantly worse. However the left channel had H3 at -75db, which seemed to be a defect for that channel at both line in and output.

I'm afraid I don't want to show my EC buffer yet, especially since it should be capable of much less distortion, especially with the possibility of a complete function null. My previous post was a bit ill-conceived, sorry.
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Old 4th May 2013, 12:12 AM   #1119
PHEONIX is offline PHEONIX  Australia
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Default Distortion measurements

Hi keane,

I personally think that you should be interested in higher frequencies than 1KHz to exercise your EC buffer go why not 6Khz , 10Khz or for that matter 20Khz. Linearity at the low frequencies is not hard to achieve in my opinion and at the higher frequencies other things are revealed about the design.

Regards
Arthur
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Old 4th May 2013, 12:18 AM   #1120
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Quote:
Originally Posted by PHEONIX View Post
Linearity at the low frequencies is not hard to achieve
It is when you don't have feedback. This design uses 4 BC5xxC. I have tested it at 10KHz, but that is in between tweaking the whole test setup. I will do more tests eventually.
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