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Old 3rd March 2010, 05:42 PM   #91
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39 ohm according to the lampizator link you provided :-)
Talk about blinders. I must have read past that ten times to get to the differential output schematic.

Thanks

Bob
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Old 3rd March 2010, 06:07 PM   #92
glt is offline glt  United States
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Default Why Vout is degraded?

What is the theory behind voltage mode not being as good as current mode?

Is it because the DAC expects a lower impedance at the output? so driving current is "easier" on the DAC?

I also understand that if you add a balanced stage you will filter out a lot of the common mode noise.

That being said, if you are feeding directly to a balanced amplifier, a resistor I/V has some appeal due to its simplicity, linearity and low noise.
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Old 3rd March 2010, 07:10 PM   #93
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According to the datasheet, THD+Noise drops from -120dB for I-out to -108 for Vout.
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Old 4th March 2010, 07:29 PM   #94
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Quote:
Originally Posted by glt View Post
What is the theory behind voltage mode not being as good as current mode?

Is it because the DAC expects a lower impedance at the output? so driving current is "easier" on the DAC?

I also understand that if you add a balanced stage you will filter out a lot of the common mode noise.

That being said, if you are feeding directly to a balanced amplifier, a resistor I/V has some appeal due to its simplicity, linearity and low noise.
The reason is that the DAC likes to work into a constant voltage.

The only way to achieve that is for the DAC to drive an extremely low impedance. If the voltage the DAC "sees" modulates then it causes distortion. And, you would be surprised how even a seemingly small impedance like 10 ohms can have a pronounced negative effect and increase THD.

So in short you have to keep the voltage at the DAC output from modulating with the analog signal to get the best results.

Is -108db THD+N good enough? Well sure for many it will be, but I much prefer not to have that extra 10-12db of distortion present if I can help it.

Cheers!
Russ
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Last edited by Russ White; 4th March 2010 at 07:48 PM.
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Old 4th March 2010, 07:46 PM   #95
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When could we expect the "all questions clearing" manual ?
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Old 4th March 2010, 07:56 PM   #96
NicMac is offline NicMac  Italy
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When could we expect the "all questions clearing" manual ?
By good old TPA tradition probably just after the first kits arrive at destination
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Old 4th March 2010, 07:58 PM   #97
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It is probably obvious that manual writing is one of my least favorite things to do.

I actually just finished the BUF-II manual, but I am letting my editor(Brian) go over it before we make it public.

I am working on the IVY-III manual at the moment.

Cheers!
Russ
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Old 4th March 2010, 08:01 PM   #98
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In that case we won't disturb you any longer, sssshhhhh writing in progress !
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Old 5th March 2010, 05:31 PM   #99
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I plan on using a single Placid for the Buffalo II and a bipolar Placid for the IVY III. I know you sell 15VA and 30VA transformers, but I'm curious if we could use smaller transformers without compromising performance.
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Old 5th March 2010, 06:11 PM   #100
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I plan on using a single Placid for the Buffalo II and a bipolar Placid for the IVY III. I know you sell 15VA and 30VA transformers, but I'm curious if we could use smaller transformers without compromising performance.
Well, the 15VA is only 9V, so you would have low-ish rails. I do have some 25VA 15V transformers which are a little smaller, if that's what you are looking for.
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