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Old 17th August 2009, 03:48 AM   #1
foo is offline foo  Tibet
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Default Any super current source?

Wanna feed the PCM1794 with constant current source to balance the middle current and lower the I/V loading.

Any suggested circuit for ultra precise and low noise current source up to 12.4ma?
yes 12.4 ma, cause my 1794 is paralleled.
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Old 17th August 2009, 04:19 AM   #2
jcx is offline jcx  United States
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if you're using a virtual gnd I/V the "best" current source is the highest value metal film or foil resistor biased with the quietest Vref you can afford
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Old 17th August 2009, 05:40 AM   #3
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You'll want to use the "High Performance" circuit option:

http://www.classicvalve.ca/tubepcb.html#CCS

Cheers!
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Old 17th August 2009, 06:58 AM   #4
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Quote:
Originally posted by Geek
You'll want to use the "High Performance" circuit option:

http://www.classicvalve.ca/tubepcb.html#CCS

Cheers!

Using high voltage parts? For a Dac?
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Old 17th August 2009, 07:19 AM   #5
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Heh, no, you don't have to

Come to think of it... I dunno if you'll have enough voltage to drive that circuit. Maybe Pinkmouse's CCS? It can run with much lower voltage.

Cheers!
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Old 17th August 2009, 11:12 AM   #6
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In 2007 AudioXpress had 2 articles by Walt Jung ( Audio Current
regulator test for high preformance) you might like to look at it. It is a real good read with lots of test results. Sorry you will have
to do your own google search for it.
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Old 17th August 2009, 02:24 PM   #7
jcx is offline jcx  United States
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if you're using the app circuit with a diff to single ended converter (or using balanced diff out) you don't even need really low noise Vref for the Ioffset cancelling Rs - use matching R from the same -Vref and the -Vref noise is common mode and mostly rejected by the diff output

easiest likey would be op amp inverting the +5V analog for the (common) -Vref and using well matched, low noise R to the +,- Iouts

separatly derived, active ccs circuits will give noiser outptut than the resistor scheme described above

the I bais isn't necessarily a "heavy load", a constant current source has an "infinite" small signal resistance - it also assures Class A bias of the example circuit's NE5534 op amps' outputs which is a good thing for their dynamic impedance and linearity

to improve over the app circuit I would put a fast pnp transistor or cfa op amp as a output buffer inside the I/V feedback loop to get even lower feedback Z (and add ccs Class A bias to the 1st op amp output), using the Ibias of the pcm1794 as a free ccs load for Class A bias of the I/V output buffer
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Old 17th August 2009, 03:35 PM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by woody
In 2007 AudioXpress had 2 articles by Walt Jung ( Audio Current
regulator test for high preformance) you might like to look at it. It is a real good read with lots of test results. Sorry you will have
to do your own google search for it.
go to Walt Jung's site.
__________________
regards Andrew T.
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