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Old 14th February 2013, 02:10 AM   #231
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Good idea, I'll email Thorsten but ... he may be tight-lipped!

Maybe a detailed model is too tall an order but surely I can improve on:

basic Tina TDA1541A.png

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Old 14th February 2013, 02:14 AM   #232
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sure, cahnge the Isource to a full scale p-p pulse with ns edge rate
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Old 14th February 2013, 03:17 AM   #233
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PCM1704 inside, this is all I have.

Cheers George
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Old 14th February 2013, 12:41 PM   #234
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Quote:
Originally Posted by AudioLapDance View Post
AD844/TDA1541A freq resp
Attachment 330117

-3dB @ 100k
63dB gain ?!? Hmmm, that's not right ...?!?

AD844/TDA1541A tina file
Attachment 330120

Anybody know how to model a current DAC in Tina (better yet TDA1541A and PCM1704!)?

Thanks,
Jeff
63dB is not far off. I think in the 50's is about normal.

I use Tina a lot. I use a current generator, set to 1Mohm internal impedance. I think use external current sources to simulate the DC offset.
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Old 14th February 2013, 02:13 PM   #235
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Quote:
Originally Posted by jcx View Post
sure, cahnge the Isource to a full scale p-p pulse with ns edge rate
Thanks, this sounds like it will provide some of the staircase current waveform. What the DAC puts out.

What I'm also looking for, is more info on how the 1541 1704 "looks": RLC, like dirkwright's suggestion to change the "internal impedance" to 1M instead of infinite.

Last edited by AudioLapDance; 14th February 2013 at 02:18 PM.
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Old 14th February 2013, 02:18 PM   #236
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Quote:
Originally Posted by dirkwright View Post
63dB is not far off. I think in the 50's is about normal...
How is Tina calculating this? Usually gain is Vo/Vi but we have Vo/Ii?

Quote:
Originally Posted by dirkwright View Post
...
. I think use external current sources to simulate the DC offset.
The first menu of the current generator has a "DC level [A]" which I set to 2m for the 2mA offset.

basic Tina TDA1541A.png
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Old 15th February 2013, 05:58 PM   #237
MiiB is offline MiiB  Denmark
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No need to run the AD844 with an output-cap..!!

It has a maximum of 50uV thermal drift and can be offset adjusted either by the DAC counter-current or by adjusting the offset by trimmer like in page 16 of the AD844 Datasheet. To maintain DC coupling there is the task of getting the thermal-drift of the DAC and the counter current stable.
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Old 15th February 2013, 08:56 PM   #238
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With my i/v 844 with or without inbuilt buffer in circuit, with Abraxalito's dc offset circuit between dac and 844 input I can get the dc offset stable to within +- .5mV on the output of the 844, so a dc coupling cap is definately not needed.
I hate caps in the signal path, I can always hear them no matter how good they are compared to direct coupled. One proviso you my get a small switch on or off thump, but I think this would happen anyway with a coupling cap as well.

Cheers George
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Old 16th February 2013, 05:57 PM   #239
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Quote:
Originally Posted by AudioLapDance View Post
How is Tina calculating this? Usually gain is Vo/Vi but we have Vo/Ii?

The first menu of the current generator has a "DC level [A]" which I set to 2m for the 2mA offset.

Attachment 330372
If you use a probe, you can see that there is a small voltage at the input to the opamp from the current generator. I assume that it is using that voltage to calculate gain.

Setting the DC current level in the generator is fine for single ended operation, but the PCM1794 I was trying to simulate has balanced outputs with DC current in the same direction on both of them. I don't know about the DAC you are trying to simulate.
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Old 20th February 2013, 10:26 PM   #240
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After listening now for a while, I get the best sound taking the signal from TZ of the AD844 2.7k & 560pf to ground, then to my opamp based LP filter (AD825 as 3rd order L/P) The inbuilt buffer when used of the 844 has a touch of 2 dimentional sterility to it, not as good as coming straight off the TZ.
Now here is something that had me scratching my head, what do you guys think of it, I removed the 560pf which I believe is a 1st order L/P at –3db 105khz , you would think that having no 1st order l/p filter except still for the 3rd order 825 opamp I would see just a little more noise on the output, but nothing worth mentioning. But the sound difference if anything should have been a little more emphasis maybe in the top end, but no the opposite happened, I got a more relaxed presentation of the top end, still just as detail but a little laid back than with the 560pf attached. The only thing I can think of that the output of the I/V stage is not dynamically stable under musical conditions with the 560pf capacitor loading, and maybe it is a little unstable and can ring/oscillate a little with any caps on it to ground and makes the topend sound a little peaked?

Cheers George
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Last edited by georgehifi; 20th February 2013 at 10:45 PM.
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