How could I reduce the DAC output current? - diyAudio
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Old 12th October 2011, 10:03 AM   #1
Aiace is offline Aiace  Italy
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Default How could I reduce the DAC output current?

Hello,
I need to reduce the output current of a PCM1794 DAC. My purpose is kind of volume control at current level before to convert it into a voltage signal.
Do you have any idea ?

Thank you in advance
Aiace
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Old 12th October 2011, 01:48 PM   #2
qusp is offline qusp  Australia
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I dont think this is a good idea, its best to leave the current mode signal as short, direct and untouched as possible or you will lose resolution/dynamic range quickly, this is when signal routing is at its most important, as its very vulnerable, far more vulnerable than voltage signal. besides i'm not sure why you would want to do such a thing?

also adding any resistance inline with the current will just convert it to a voltage.
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Old 12th October 2011, 03:29 PM   #3
Aiace is offline Aiace  Italy
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Quote:
Originally Posted by qusp View Post
I dont think this is a good idea, its best to leave the current mode signal as short, direct and untouched as possible or you will lose resolution/dynamic range quickly, this is when signal routing is at its most important, as its very vulnerable, far more vulnerable than voltage signal. besides i'm not sure why you would want to do such a thing?

also adding any resistance inline with the current will just convert it to a voltage.
Your sentences are right both.
For the firsth, I could say that anytime you put something in your signal path you loose resolution/dynamic. So this might be weight with what I can gain with this insertion.
For the second: no comment. Infact this is the cause I decided to post my request. I have no idea how to reduce a current of a current generator keeping the equivalent circuit still a current generator.

Any Idea ?
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Old 12th October 2011, 07:18 PM   #4
oshifis is offline oshifis  Hungary
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You can shunt part of the current to ground.
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Old 12th October 2011, 08:02 PM   #5
jcx is online now jcx  United States
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its just a little hard to shunt a controlled fraction of the current when the DAC chip is designed/speced for use with a I/V converter with the lowest practical impedance that can be synthesized at a virtual gnd

translinear circuits can be analysized as converting I to a (log) V in transistor Vbe junction and back to current at the collector - so no joy there on strictly "keeping the equivalent circuit still a current generator"

since the DAC itself is already a current modulator of impressive resolution, linearity, low noise the simple engineering solution is to just get system gain structure after the I/V correct and then attenuate in the Digital domain - with 24 bit resolution you don't even need dgital dither - the noise of the analog I/V will be quite adequate

it can be hard to even match the PCM1794 preformance in subsquent anaolg stages - certainly when you start specifying a "required" design principle for a circuit rather than a result in terms of signal properties like noise, linearity

Last edited by jcx; 12th October 2011 at 08:04 PM.
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Old 12th October 2011, 08:03 PM   #6
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Why do you need to do volume control before the I/V stage?
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Old 12th October 2011, 08:19 PM   #7
Aiace is offline Aiace  Italy
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Quote:
Originally Posted by BionicSniper View Post
Why do you need to do volume control before the I/V stage?
I'm having an idea for a nice amplifier. But if I can't solve this issue my thinking is useless.
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Old 12th October 2011, 11:17 PM   #8
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Control the digital side. For example, some PC players will output variable digital signal - Foobar2000 for example.
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Old 13th October 2011, 05:56 AM   #9
Aiace is offline Aiace  Italy
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Originally Posted by SoNic_real_one View Post
Control the digital side. For example, some PC players will output variable digital signal - Foobar2000 for example.
Right, it will the latest solution. I prefear an analog solution instead a SW solution.
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Old 14th October 2011, 09:43 AM   #10
Koenjer is offline Koenjer  Netherlands
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Default pcm1792

Get the PCM1792 it has the same specs as the 1794 but has software controlled volume control.

Works likes a charm. Look at the Bdac from tentlabs.com
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