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Old 25th January 2008, 01:41 PM   #31
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I never meant to convey that its not as good as the Opus.

It is easily as good as the Opus. I would just say they both sound excellent. I would not say either one is "better" than the other.

The COD is certainly better now than it was with passive I/V. With the TXD doing I/V instead of the resistor the COD is a completely different beast than it was.

Cheers!
Russ
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Old 25th January 2008, 09:03 PM   #32
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Hi Russ

How exactly do you configure the TXD as an I/V? I'm interested in trying this.

I'm also considering taking the output of the TXD (as I/V) and putting it through the Ballsie to get both differential and single ended outputs.
But, I feel like the signal's going through too many stages just to get to my bosoz and eventually the power amp.

Do you see any problems with this setup?

I'm thinking about this to save myself some of the effort of building an active I/V stage since I have the TXD boards. Passive I/V with resisitor is far from optimal as discussed in a few threads here and elsewhere (although so is using feedback but there's lots of debate about that).
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Old 25th January 2008, 09:46 PM   #33
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Quote:
Originally posted by HeadSh0T
Hi Russ

How exactly do you configure the TXD as an I/V? I'm interested in trying this.

Do you see any problems with this setup?

I will be building a fresh one tomorrow, so I will take some pics and describe the process. Its very easy.

You basically just use the THS chip (I have used THS4131,4141,and 4151), 2 feedback Rs (221-390R seems to work well for me). and 4 jumpers. Its cake.

I would not interject the BOSOZ, its redundant.

I would instead just give the I/V as much gain you you think you will need, and use something like a joshua tree between the I/V and the ballsie.

I am very happy with my setup, it is absolutely silent (no hiss or noise) and the sound is superb with both headphones and through the poweramp.

Cheers!
Russ
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Old 26th January 2008, 12:50 AM   #34
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Quote:
Originally posted by ezkcdude
I knew it was only a matter of time before you guys adopted PCM1794.
AD1955 sounds better.
And I always found it suspicious TI doesn't put linearity graphs in their audio DAC datasheets...
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Old 26th January 2008, 12:52 AM   #35
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Quote:
Originally posted by Russ White
Just for reference.

This is not a complete schematic, the buffers are missing etc. But it gives you a good idea of what I am going to do.

This is also not the current version (it is actually one of my first simulation attempts) , it is just representative...

Is this intended for I/V? If so, the input nodes should be low impedance--emitters, not bases.


Also, where's the clock? Is it on the back side of the PCB?
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Old 26th January 2008, 03:40 PM   #36
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Quote:
I would not interject the BOSOZ, its redundant.
That's what I was thinking but I use the Bosoz to allow for multiple inputs such as my cable tv receiver, Wii, and other analog sources and they all go to the power amp. So, my plan was to use the dac as just another input into the bosoz.

Maybe this will work if I set the TXD (the THS opamp) for unity gain, running as I/V and let the BOSOZ add the gain??
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Old 26th January 2008, 03:52 PM   #37
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Quote:
Originally posted by HeadSh0T
Maybe this will work if I set the TXD (the THS opamp) for unity gain, running as I/V and let the BOSOZ add the gain??
It will work more than fine. I am sure it would be superb.

I would just use a lower value Feedback R for the TXD, something like 221R.

Cheers!
Russ
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Old 26th January 2008, 04:52 PM   #38
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Default TXD for I/V

Here is a TXD configured for IV.

This one is using 390R resistors.

On the backsides are just THS4131,THS4141, or THS4151, any of those will work fine. In this case I happen to be trying THS4151.

Calculate the resistor for the swing (Vpp) you want by dividing Vpp by the peak to peak current swing of the DAC, in the case of the COD that is 7.8ma so I wanted roughly 3vpp so I chose 390R (.0078 * 390 = 3.042).

I hope this helps.

Cheers!
Russ
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Old 26th January 2008, 05:33 PM   #39
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So for nominal Red Book levels (2Vrms, 5.66V pk-pk) you want 5660/7.8 = 725Ohms, nearest E24 value is 750.
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Old 26th January 2008, 05:40 PM   #40
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well you have to remember the output is balanced.. so if you look at the swing from output to output it would be double redbook levels. 390R would get your closer...

Cheers!
Russ
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