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Old 6th March 2013, 03:23 AM   #21
davada is offline davada  Canada
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Quote:
Originally Posted by glt View Post
Hi David,
Thank you. Perhaps it is a good idea to just mod one channel in order to accommodate higher level sources in the other channel...
Yes and also the other channel is a balanced input. It takes an XLR.
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Old 6th March 2013, 03:27 AM   #22
davada is offline davada  Canada
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Quote:
Originally Posted by soundchaser001 View Post
Not a bad idea but if you want a reference channel for component measurement or corrected speaker measurements don't they have to be the same?
Yes this is true but the other channel still has a gain control and the gain scales can be matched. The noise floors will be different though.

With ARTA each channel can be calibrated separately.
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Old 6th March 2013, 03:41 AM   #23
davada is offline davada  Canada
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Default EMU 0204 right channel mod

I have arrived at R values to scale 0dB to the FS of the AK4385B.

The ADC FS is 2.9Vpp differential.

I give some details of performing the mod in another post.

Here are some schematics and results.

The first sch is the original. The second sch is the AKM recommended and the third sch is the mod.
The rest is self explanatory.

Cheers,
Attached Images
File Type: gif Emu orig sch.GIF (15.4 KB, 630 views)
File Type: gif AKM input.GIF (26.1 KB, 619 views)
File Type: gif Emu MOD sch.GIF (19.1 KB, 625 views)
File Type: gif 0db FS mod 44 1k.GIF (77.3 KB, 559 views)
File Type: gif 0db FS mod 44 1k ns.GIF (76.3 KB, 518 views)
File Type: gif 0db FS mod 48k.GIF (76.6 KB, 264 views)
File Type: gif 0dB mod 96k.GIF (82.0 KB, 254 views)
File Type: gif 0dB mod 96k ns.GIF (77.4 KB, 251 views)
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Old 6th March 2013, 03:44 AM   #24
davada is offline davada  Canada
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And two more.
Attached Images
File Type: gif 0dB mod 192k.GIF (82.0 KB, 252 views)
File Type: gif 0dB mod 192k ns.GIF (80.9 KB, 185 views)
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Old 6th March 2013, 04:36 AM   #25
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In your mod sch Rc is not equal to feedback resistor of the inverting opamp- inputs to adc will not be equal on each phase
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Old 6th March 2013, 04:40 AM   #26
davada is offline davada  Canada
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Quote:
Originally Posted by Capt Grogg View Post
In your mod sch Rc is not equal to feedback resistor of the inverting opamp- inputs to adc will not be equal on each phase
You can use an exact value if you like but the 3k worked just fine in mine and a lot better than what EMU had there.
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Old 6th March 2013, 04:49 AM   #27
davada is offline davada  Canada
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As an alternative you can input 1Vrms and bring the gain control up to clipping.
Reduce the input level to-10dB and calibrate ARTA with 316mV.

But the differential voltages to the input won't be balanced.

This mod is a bit cleaner though.

This is the alternative.
Attached Images
File Type: gif Altern.GIF (77.3 KB, 239 views)
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Last edited by davada; 6th March 2013 at 04:54 AM.
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Old 6th March 2013, 06:54 AM   #28
1audio is offline 1audio  United States
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I was confused at first but I believe what you are doing is making sure the differential inputs are equal at the DAC. this would give the largest dynamic rage on it. The lowest distortion is usually less than full input, typically -10 dB or so.

The AKD5394A uses almost the same input circuit and the docs are more complete (see below). Its not necessarily the best but it will give perfect balance at the chip.

For general purpose audio I find 1V is not enough. A preamp needs to be able to drive 3V or more to get full output from most power amps. The interface board project is intended to address this limit.

I have an EMU Tracker Pre, 0202, 0404 and Juli@. The Juli@ has a much different circuit so scaling is a different task, especially since it has different circuits for balanced and unbalanced inputs and JRC4580 opamps in a unique footprint. I'll open the other boxes up and post closeups of the circuits. I got the 0404 because it uses the AK5394A, but its not optimized for performance it seems. I am having a terrible time getting the EMU stuff to work in Win 7 64 bit. Its just funky. . .
Attached Images
File Type: jpg AKM Input circuit.JPG (71.8 KB, 479 views)
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Old 6th March 2013, 02:48 PM   #29
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
I was confused at first but I believe what you are doing is making sure the differential inputs are equal at the DAC. this would give the largest dynamic rage on it. The lowest distortion is usually less than full input, typically -10 dB or so.

The AKD5394A uses almost the same input circuit and the docs are more complete (see below). Its not necessarily the best but it will give perfect balance at the chip.

For general purpose audio I find 1V is not enough. A preamp needs to be able to drive 3V or more to get full output from most power amps. The interface board project is intended to address this limit.

I have an EMU Tracker Pre, 0202, 0404 and Juli@. The Juli@ has a much different circuit so scaling is a different task, especially since it has different circuits for balanced and unbalanced inputs and JRC4580 opamps in a unique footprint. I'll open the other boxes up and post closeups of the circuits. I got the 0404 because it uses the AK5394A, but its not optimized for performance it seems. I am having a terrible time getting the EMU stuff to work in Win 7 64 bit. Its just funky. . .
Hi Demian,

This same circuit is on Ak5385B data sheet. I didn't show it because I only addressed the right unbalanced channel.

The 1V is just our instrument maximum input level. What difference does it make if the input has to be attenuated to fit the range. It's a relative measure and quite proportional.
Having to attenuate gives a better SNR.

We do need what you have offered for a front end to handle the scaling for higher voltage inputs.

The magic is not in the mod it's the principle of scaling the entire ADC range for the measurement range and calibrating for that. It drives the relative noise floor down.
Then we can afford to add a front end system which will surely drive the noise floor up.

The maximum input level into the input amp on the 339a is 1Vrms that's full scale.
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Old 6th March 2013, 04:08 PM   #30
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Default Phase

Does this mod invert absolite phase for this channel? It looks like it would.
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