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Old 27th December 2005, 04:09 PM   #521
ergo is offline ergo  Estonia
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Davey,

Thnx for hint. I will try in near days with Audiotester software.

I had a problem with it and my soundcard under XP in 24/96 mode but in W2K it seems to work - so now I can make THD vs. freq measurements also hopefully

I plan to compare the "no analog stage" - passive only filtered output to my single opamp implementation.

To me it seems that even though the DAC is very capable to drive quite hard loads there is still limitations in there.

One of them seems to be when the signal is near full range (0dB), then the internal opamp is driven near rail to rail and the THD increases and also the sound is worse.

If you look at the performance with -3 or -5dB from full range it looks much better....


Ergo
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Old 27th December 2005, 04:12 PM   #522
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Wow, this thread was a bit sleepy and it seems I have reanimated it for a while

Have fun !

Thierry
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Old 27th December 2005, 04:13 PM   #523
ergo is offline ergo  Estonia
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mbroyles,

I think the transistor muting is there only to kill the switch on/off transient. This is the only condition when the DCX gives a transient with the analog stage taken out of the unit.

Ergo
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Old 27th December 2005, 05:31 PM   #524
ergo is offline ergo  Estonia
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This is how the PCB will look like for my single opamp mod.

Middle part is power supply regulators that attach to opamp PCB like _|_ this looking from side.

The PCB is designed to fit in space between the DAC board and back connectors.
Attached Images
File Type: png pcb.png (15.9 KB, 923 views)
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Old 27th December 2005, 06:01 PM   #525
AndrewT is offline AndrewT  Scotland
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Hi Kuei,
re post510;-
Thmartin's modified output is single ended (unbalanced).
The fig2.4 circuit provides both unbalanced output and balanced source impedances from a single ended source. It even blocks DC which according to Davey is also needed.
In my view, this is not the opposite to what is required.
It seems to give dual output options from the passive filter in lieu of the DCX multi opamp stage.
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Old 27th December 2005, 07:06 PM   #526
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by AndrewT
Thmartin's modified output is single ended (unbalanced).
The fig2.4 circuit provides both unbalanced output and balanced source impedances from a single ended source. It even blocks DC which according to Davey is also needed.
In my view, this is not the opposite to what is required.
It seems to give dual output options from the passive filter in lieu of the DCX multi opamp stage.
Actually the DAC has a BALANCED output. Why ON EARTH do you want to use it unbalanced and THEN to make a pretend balanced output from that, if you have a REAL balanced source?

What is needed is a series resistor/inductor (to taste) , shunt capacitor to ground and coupling capacitor PER PHASE connectiong to the XLR pin 2 & 3 with pin 1 to ground and DC leakage resistors from pin 2 & 3 to ground.

An unbalanced output is then connected between pin 1 (ring) and 2 (tip) if required. The circuit you suggest is entierly INAPROPRIATE when a balanced source exists!

Sayonara
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Old 28th December 2005, 11:12 AM   #527
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ehhhmm, sorry to ask but has anybody tried the circuit op page 19 of the AKM-pdf? Lets say with silver-mica caps and opa2134
This may be a stupid question but it is a bit difficult to see what you guys did do and/or simulated with what results. Or maybe I missed/not understood something
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Old 28th December 2005, 01:56 PM   #528
Ryssen is offline Ryssen  Sweden
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Question:How is the signal divaided (Sorry my English) from the dac´s
2 outputs to the six outputs?Is it trough the DSP or?
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Old 28th December 2005, 02:21 PM   #529
Davey is offline Davey  United States
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Ryssen,

There are actually 3 DAC's inside the DCX. DAC-1 handles Outputs 1 & 2, DAC-2 handles Outputs 3 & 4, etc.

Each DAC has two differential outputs and thus the six total available outputs. DSP allows the versatility in routing.

Cheers,

Davey.
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Old 30th December 2005, 04:33 PM   #530
Henckel is offline Henckel  Denmark
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Default Passive lowpass makes distortion

The low pass filter suggested by Thierry with the 33 Ohm and 100nF capacitor makes the output distort

Thierry´s measurement:
http://www.diyaudio.com/forums/showt...929#post799929

and mine:

Left channel is with the filter above. Right channel is without any filter ( just a DC blocking capacitor)


Click the image to open in full size.

And the big version here:
http://home19.inet.tele.dk/henckel/pic/IMD-big.png
Measurement conditions:
Digital in DCX - analog out of DCX and directly into Teratec DMX 24/96 soundcard - showing RMAA´s intermodulation distortion
Samplerate: 44,1 Khz/ 24 bit

This clearly shows that the Op amp in the DAC´s are overloaded. Calculating gives a Z value at approx 70 ohms at 30 KHz.

So what i suggets that we scale this passive low pass filter to values of 330 Ohm and 10 nF.

Any views on this ?
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