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8 x AK4490 with current output
8 x AK4490 with current output
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Old 11th January 2018, 04:54 PM   #1
nemantree is offline nemantree
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Default 8 x AK4490 with current output

Gentelmen,


I'm building the DAC from Japanese kit. After several try and errors got nice 1Khz waves ~1.9Vrms (and squares) at the output. I did not listen yet to it, waiting for the ordered Amanero board. Now I'm thinking about I/V stage if it is essential here.
There are 4 AK4490 per channel, 2 per rail, ~140Khz LPF (like in datasheet) per DAC chip. Every output summed through 681 Om resistor. So it looks like this is +-30mA current source with 170 Om per rail impedance. Am I right?
What would you recommend as I/V converter for this? My choices at the moment:
- composite amp with LME49600,
- composite amp with discrete buffer,
- LL1684,
- just OPA1688 with 173R feedback,
- or nothing at all (the input impedance of my preAmp is ~10Kom).


Thanks in advance!
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Old 12th January 2018, 04:28 PM   #2
Dimdim is offline Dimdim  Greece
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8 x AK4490 with current output
The ak4490 is a voltage out part. It has a built in I/V stage.
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Old 12th January 2018, 04:58 PM   #3
nemantree is offline nemantree
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Yes, sure. But according to it's designer the output is the current source and he sells also I/V stage (composite + LME49600 / 180R fb).
I think this is similiar of the Esoteric design:
http://www.esoteric.jp/products/esot...g/photo_13.jpg
(; why I went for it
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Old 12th January 2018, 06:15 PM   #4
lemon is offline lemon  Greece
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Yeah,
We are free to name our designs as we want!
I/V, V/I e.t.c
But, the true is only one and this is: that the AK4490 is voltage output DAC chip.
'Οϊ Παναήα μου, τί εστί τούτος!
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Old 13th January 2018, 01:25 AM   #5
Dimdim is offline Dimdim  Greece
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8 x AK4490 with current output
I suppose you could treat a bunch of paralleled 4490s as a current source, but I seriously doubt that such a topology would offer any benefits compared to treating them as a voltage source with a much improved output impedance.

But then again, I'm no expert regarding the analog parts of these chips.
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Old 13th January 2018, 01:50 PM   #6
nemantree is offline nemantree
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This is the source, where the VGs are voltage generators 5.2Vpp ground referenced. I can name it current source (5.2/(681/4)=+-30mA) or voltage source, probably does not matter. The matter how to amplify it; why again the need for inverted opamp?
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Old 13th January 2018, 01:59 PM   #7
zenelectro is offline zenelectro  Australia
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Quote:
Originally Posted by Dimdim View Post
I suppose you could treat a bunch of paralleled 4490s as a current source, but I seriously doubt that such a topology would offer any benefits compared to treating them as a voltage source with a much improved output impedance.

But then again, I'm no expert regarding the analog parts of these chips.
I believe the OP stages inside chips are switched capacitor filters using Cmos opamps.... definitely not current OP

T
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Old 14th January 2018, 11:19 PM   #8
nemantree is offline nemantree
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I'm about to try OPA1688. According to modeling results it looks OK.
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Old 18th January 2018, 12:11 PM   #9
esl 63 is offline esl 63
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nemantree
add a bandwith limiting capacitor as well in the feedbackloop.
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Old 18th January 2018, 01:48 PM   #10
nemantree is offline nemantree
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Well, does 100p+100R limit bandwidth?
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