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Old 27th August 2009, 05:15 PM   #1
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Default DAC output voltage

Hi guys,

My dac is giving a output of 0.3v for a 0dB 1khz. Is it too low and what is the effect down stream, beside having to crank up the vol?

Thanks,

KK
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Old 27th August 2009, 05:33 PM   #2
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I assume you mean 0.3Vrms which would be 0.85V p-p. It all depends on your DAC supply rails so this might be reasonable for a 1.8V rail DAC. As long as the DAC is achieving the 96dB signal-to-noise that 16bit digital aspires to you should have no problem with adding clean gain.

I have seen 1Vrms as a more typical 0dBFS level. Care to share the DAC schematic and we could comment further.
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Old 27th August 2009, 05:50 PM   #3
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Hi Iain,

Yup, it is 0.3Vrms. As for the circuit, it is a TDA1541A to a I/V 34ohm resistor to step-up transformer. It has a output impedance of 4.5kohm. My intention is to put a unity non-inverting buffer after that.

Cheers,

KK
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Old 27th August 2009, 06:19 PM   #4
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Hmmm. Doesn't seem like it's stepping up much. Sounds like it may be mismatched somewhere. Do you have full specs on the transformer like primary inductance, turns ratio etcetc?
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Old 28th August 2009, 02:08 AM   #5
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From my measurement, the voltage after the I/V is 0.043Vrms. Hence, the transformer is a 16.9dB gain. I don't have much info on the transformer.

KK
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Old 28th August 2009, 02:49 AM   #6
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Oh yeah, it is an input trans for a tube amp.

Cheers.

KK
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Old 28th August 2009, 06:41 AM   #7
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43mVrms is about right for 4mA pk into 34ohm so that's encouraging.

Without a schematic and measurements it's hard to say how it works.
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Old 28th August 2009, 12:47 PM   #8
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The DAC is a simple I2S to the TDA1541A to the passive I/V. Nothing complex about it. The only thing that I thinking is to leave it alone with a low line out or change the value of the I/V or change to a higher step up trans.

Thanks Iain.

KK
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