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Old 20th September 2012, 06:53 PM   #1
smms73 is offline smms73  Portugal
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Default UNIO a minimalist I/V converter

This is my minimalist I\V converter that i call UNIO.
It was designed based on the opinions i get from the other two thread that i start.
The almost universal opinion is that simple is better.

I have already build a prototype and i am very impress by the very good performance that this simple circuit produce.

This is intend to be use with a pcm1794a. but it can be redesign to work with others DAC.

the output voltage is 1Vrms in balanced mode or 0.5 Vrms non balanced.
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File Type: jpg UNIO_v1.jpg (57.1 KB, 328 views)
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Old 20th September 2012, 07:02 PM   #2
smms73 is offline smms73  Portugal
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This is some distortion measurements of the prototype.

the first image is from the emu1212m alone ( the distortion is a little bit higher than normal because the low impedance load 565 ohm).

the second image is the output distortion with 0.7 Vrms
the third image is with 1Vrms.

This test was done with full balanced input and output.
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File Type: png emu1212m.PNG (70.5 KB, 315 views)
File Type: png unio 100 9dbf.PNG (68.7 KB, 283 views)
File Type: png unio 100 6dbf.PNG (69.1 KB, 267 views)
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Old 20th September 2012, 07:07 PM   #3
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On what level is the DC offset at the input ?
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Old 20th September 2012, 07:10 PM   #4
smms73 is offline smms73  Portugal
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The prototype was built with 5% resistors and polyester output capacitors.
And the power supply was not very good.

For better performance use 0.1% resistors in R1, R2, R5, R9, R17, R18.
C0G ceramic capacitors for C3, C4, C5
Polipropilene capacitors for C1, C2
And is very important to match the transistors. And of course use a very low noise power supply.
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Old 20th September 2012, 07:15 PM   #5
smms73 is offline smms73  Portugal
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Hello Joachim.
with 6.2mA will be 34mV with a 5.6 ohm input resistor
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Old 20th September 2012, 07:16 PM   #6
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Very nice Sergio! Definately worth a look when I am doing my 1794a DAC

How did you take those ARTA measurements? I am curious to see a pic of your setup, because I am interested in doing my own measurements with ARTA too but I havent figured it out yet :/
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Old 20th September 2012, 07:27 PM   #7
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Thanks zxgravediggerxz .

I don´t know if i understand your question, can you be more specific. What is the difficulty you have ?
I use a emu1212m sound card.
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Old 20th September 2012, 07:31 PM   #8
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Forget to say that V3 is a blue led but you can also use a shunt voltage reference like tl431 , the output of the current source is 25mA.
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Old 20th September 2012, 07:40 PM   #9
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Can't Q1 and Q2 be in common base topology, i. e. the base and emitter swapped?
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Old 20th September 2012, 07:45 PM   #10
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Unfortunately no.
with a common base you will have zero common mode rejection ratio .
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