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Old 7th July 2004, 04:32 PM   #1
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Default PCM1794 output stage

Hey...

On my continued dac quest (and having realised the pin spacing on a PCM4104 ) the PCM1794 presented itself. As i'm after balanced outs would this circuit be okay? It uses the same i/v stage (using NE5534s) as on the application datasheet and a OPA1632 for a fully-differential output (that part from 1404 datasheet)...

PDF

Do I need to do anything else - i'm really wingin my way thru all this...

Cheers.
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Old 7th July 2004, 06:08 PM   #2
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Why do you have 100k resistors on the outputs???

I recommend you read through this thread Best opamp for I/V conversion? (DAC) before deciding on the 5534's.

The OPA1632 is a very good idea though.
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Old 7th July 2004, 08:29 PM   #3
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Why just not use the TI spec sheet for the PCM1794? or are you just wanting balanced out from one chip and not two, used in mono?
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Old 7th July 2004, 08:49 PM   #4
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Quote:
Why do you have 100k resistors on the outputs???
I put them there following the circuit in the PCM4104 datasheet (also using opa1632).

Quote:
I recommend you read through this thread http://www.diyaudio.com/forums/show...&threadid=34324 before deciding on the 5534's.
Interesting - could Jockos' discrete i/v stage be used in this instance then? this is where things get confusing for me .

Quote:
or are you just wanting balanced out from one chip and not two, used in mono?
Not quite getting that...I want 2 balanced outs (left n right chans) following the ti sheet for balanced mode means mono'ing the dac so I lose channel...

So, goin on schem as is - will it work?

Regards

Thanks
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Old 7th July 2004, 09:22 PM   #5
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I mean are you wanting to use only one dac chip and not two. So you want to use a stereo output from a single chip but get balanced.

Actually using these chips is a piece of cake, there is no reason why not to use two PCM1794's in mono mode. Obviously you need more opamps and chips etc so it will cost more, so if that is an issue then it makes sense to use one PCM1794. But appart from cost. I built my first DAC (still quite new in the digi threads) to see if I could get it to work.

If I make another one I think Ill use AD's upsampler and two PCM1794s on the output. Obviously this will give me balanced which I wont actually use but it cant hurt to have a chip on each channel.
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Old 7th July 2004, 09:27 PM   #6
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Quote:
I mean are you wanting to use only one dac chip and not two. So you want to use a stereo output from a single chip but get balanced.
Indeed.

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I built my first DAC (still quite new in the digi threads) to see if I could get it to work.
Yes, it looks very nice
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Old 7th July 2004, 10:32 PM   #7
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Quote:
Originally posted by meta

I put them there following the circuit in the PCM4104 datasheet (also using opa1632).
D'oh! Of course! I didn't think of this but there should indeed be resistors there, but it would work much better with 100R instead of 100k

I think you should remove the 22pF cap. It is only there in the datasheet because of the voltage output of the PCM1804, not functional when you use I/V converters.

Other than that it should work great! Build it and keep us updated!

And yes you will get balanced stereo out of one PCM1794 with this circuit.
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Old 7th July 2004, 11:27 PM   #8
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Quote:
Originally posted by meta
Yes, it looks very nice
Cheers

Quote:
Originally posted by ojg


D'oh! Of course! I didn't think of this but there should indeed be resistors there, but it would work much better with 100R instead of 100k

I think you should remove the 22pF cap. It is only there in the datasheet because of the voltage output of the PCM1804, not functional when you use I/V converters.

Other than that it should work great! Build it and keep us updated!

And yes you will get balanced stereo out of one PCM1794 with this circuit.
Yes 100R and not 100k, the data sheets for both the PCM1794 and 98 specify the 22pf cap, I have used the cap in my 98 DAC and it sounds really good so it certainly doesnt mess up the sound in anyway.
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Old 8th July 2004, 12:49 AM   #9
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Quote:
Originally posted by 5th element
Yes 100R and not 100k, the data sheets for both the PCM1794 and 98 specify the 22pf cap, I have used the cap in my 98 DAC and it sounds really good so it certainly doesnt mess up the sound in anyway.
Now I see that there are more than on 22pf cap here. REmove the one between the outputs of the 5534 and keep the ones between pins 5 and 8.
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Old 8th July 2004, 08:56 AM   #10
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Hi!

Some idea to utilize mono balanced mode of those DACs (PCM1798 and PCM1794 are similar) with balanced I/V converters.

This thread

Basically 1 DAC = 1 channel

BR,
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