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Old 12th June 2012, 01:30 PM   #901
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OK.
I have missed out on quite a bit here.
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Old 12th June 2012, 04:44 PM   #902
heb1001 is offline heb1001  China
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Quote:
Originally Posted by regal View Post
...minimally higher input impedance which is a dubious theory at best at actually adding distortion to most DAC chips.
It's easy to measure distortion caused by I/V input impedance using a passive resistor I/V. You can google for people who have done so and published results. I've done some testing myself and have seen a big difference between a 50R resistor and a 2R reflected load from a tube amp output transformer used in reverse.
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Old 12th June 2012, 05:05 PM   #903
EUVL is offline EUVL  Europe
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In the 2SK369V SEN, the Zin is below 10R. I consider that low enough.

If you really believe in super low Zin, then opamp IV is your solution.
Or use (multiple) BJT with a high bias, something like 20mA.
You can see interesting discussions about BJT with Calvin at the start of the thread.


Patrick
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Old 12th June 2012, 05:42 PM   #904
bcarso is offline bcarso  United States
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Quote:
Originally Posted by EUVL View Post
In the 2SK369V SEN, the Zin is below 10R. I consider that low enough.

If you really believe in super low Zin, then opamp IV is your solution.
Or use (multiple) BJT with a high bias, something like 20mA.
You can see interesting discussions about BJT with Calvin at the start of the thread.


Patrick
Sub-10 ohm is pretty acceptably low, and low input Z is of course only part of the story anyway.

When I read the LA article and was led to this thread, which I've been following ever since, I started looking at some alternatives, that incorporated the SEN approach of floating supplies (which I like a lot) but applied feedback to the SEN input devices' gates from an all-JFET separate gain stage (no opamps per se, no feedback resistors). Other distractions have prevented this from getting beyond those simulations, but the sims looked very promising. Someday...
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Old 12th June 2012, 05:45 PM   #905
heb1001 is offline heb1001  China
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Quote:
Originally Posted by EUVL View Post
In the 2SK369V SEN, the Zin is below 10R. I consider that low enough.

If you really believe in super low Zin, then opamp IV is your solution.
Or use (multiple) BJT with a high bias, something like 20mA.
You can see interesting discussions about BJT with Calvin at the start of the thread.
Patrick
I went with 12 JFETs in parallel but the 3rd harmonic was a bit too high so I'm backing off with my 4th Sen instance to 6.

(After finally managing to match some JFETs to 0.1%, my 3rd Sen was a tragic fail due to some unset epoxy hardener under the heatsinks - it conducts).
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Old 13th June 2012, 11:22 AM   #906
regal is offline regal  United States
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Quote:
Originally Posted by heb1001 View Post
It's easy to measure distortion caused by I/V input impedance using a passive resistor I/V. You can google for people who have done so and published results. I've done some testing myself and have seen a big difference between a 50R resistor and a 2R reflected load from a tube amp output transformer used in reverse.
I said most DAC chips, and we are talking about much lower input impedance than 50 ohm with the SEN.
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Old 13th June 2012, 12:32 PM   #907
heb1001 is offline heb1001  China
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Quote:
Originally Posted by regal View Post
I said most DAC chips, and we are talking about much lower input impedance than 50 ohm with the SEN.
What you say is true. I think it's also true that SEN itself has very low distortion so for some DACs the effect of SEN's input impedance will be the limiting factor.
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Old 13th June 2012, 02:53 PM   #908
heb1001 is offline heb1001  China
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Default Improved balanced Sen?

RM1, as shown, looks like a fix for the gate capacitance issue and would allow you to parallel up more JFETs.

Simulation shows significantly reduced 3rd harmonic distortion.

I'll try it out shortly.
Attached Images
File Type: png Balanced Sen - linearize gate capacitance.png (53.0 KB, 463 views)
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Old 13th June 2012, 03:11 PM   #909
EUVL is offline EUVL  Europe
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Don't believe everything you see on Spice. That would be my only advice.
Otherwise feel fee to experiment.
We did our fair share, so we know what to expect.

And in the end, go and listen. Trust your ears.
Chasing distortion below -90dB is, for me at least, academic.


Patrick
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Old 14th June 2012, 12:35 PM   #910
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Hello Patrick. I have a question regarding Sen V18 components values (for es9018 dac).

Can I use for C1 and C2 values bigger or smaller then 220uf and with voltage rating of 10v or 20-25v? (for example can I use something like 470uf 16v or 330uf 10v) And what type is best for C1 and C2, can be used Aluminum Organic Polymer Capacitors for this purpose?

And about Civ. WHat formula should I use to calculate the Civ value. Can be used this calculator at the bottom of page with sign First order RC-filter? And what value should be Fc? I see in original Sen Fc is about 170kHz isn't this bad thing that can bring a lot of RF trash to music? Maybe 100kHz should be fine here?
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