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Old 1st September 2011, 02:31 PM   #41
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arround the three I/V (I/U) converter topologies about
http://www.passdiy.com/pdf/Z-IV.pdf
there are a wide range of posts, and I am not able to read them all.
I have heard only various op amps like OPA637, AD829 and OPA827 against a normal resistor with follow high input impedance line amp so as the D1-topology. From my view the D1 topology sounds at best, follow from the "only one resistor" topology about
Digi Scoop 1
I/U converter that used op amps like the above mentioned still sound "over analytic" and a bit harsh like a tart wine.
The topology with jFETs so as various other discrete op amp solutions I have never heard.

Where can I find a description about the perceived audible differences between this various topologies?

Is there a clearly audible advantage by an I/U topology with jFET's - as described here - compare to the D1 I/U converter topology with IRF610 MOSFET's ?
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Old 1st September 2011, 04:39 PM   #42
EUVL is offline EUVL  Europe
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Yes, but there is only one way to find out -- build both and do AB test.




Patrick
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Old 1st September 2011, 05:00 PM   #43
Calvin is offline Calvin  Germany
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Hi,

itd be interesting to compare JFET-versions to bipolar versions.
For parts of SEN-versions one could use the dual matched LSK389B (in my sims paralleling the transistors always resulted in higher THD-figures) or matched BF862 (if You can prevent them from oscillating). The BF862 would allow for a supply voltage as low as 9V for 2Vrms output signal.
What makes the bipolar versions interesting may be lower cost and easier to source parts, especially matched and complementary transistors, e.g the BC846/847 or BC847/857. They should require less supply current and lower supply voltage and allow for extreme compact building SMD circuits. THD-figures sim even better than the JFETs and they offer a decreased input impedance.
As a drawback, the bipolar versions of SEN-style need at least one additional voltage supply, referenced to gnd.
The ZEN-versions (or better CEN) need two supply voltages, referenced to gnd. But Youll probabely need additional supplies anyway to power a buffer stage at the output.

jauu
Calvin
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Last edited by Calvin; 1st September 2011 at 05:15 PM.
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Old 1st September 2011, 05:08 PM   #44
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Quote:
Originally Posted by EUVL View Post
Yes, but there is only one way to find out -- build both and do AB test. Patrick
Correct. But dependent on the impressions from the other guys I'm either very curious and carried out an A/B test or I say, it is not worthwhile to investigate this exactly. Therefore the question.
If I build both now and the last case occurs, I've wasted a lot of time.

Last edited by tiefbassuebertr; 1st September 2011 at 05:12 PM.
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Old 1st September 2011, 05:21 PM   #45
cviller is offline cviller  Denmark
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Quote:
Originally Posted by tiefbassuebertr View Post
If I build both now and the last case occurs, I've wasted a lot of time.
Well diy is a hobby... If you are afraid of losing time by not building the best, you'll have to wait forever. There is always something new and exciting.
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Old 1st September 2011, 06:02 PM   #46
EUVL is offline EUVL  Europe
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The bipolar version has much more distortion due to the base current, according to our simulation.
This has also been reported elsewhere in the forum (regarding the original Leach circuit).


Patrick
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Old 1st September 2011, 06:41 PM   #47
massimo is offline massimo  Italy
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A compact BF862 based SMD SEN I/V sounds nice... What do you think Patrick?
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Old 1st September 2011, 06:46 PM   #48
EUVL is offline EUVL  Europe
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This was also one of my first ideas.

But it is a lot easier to make the first prototype with TO92 devices, and there are quite a few to choose from (K170, K369, K117, .....).
SOT23 devices are limited to a few, even though you can also get LSK170 in SOT23.
Also thermal management is easier with TO92, as the size of the PCB is dictated by the caps.

Maybe I'll do a BF862 version later in the end, when I get time.
For now, I can only offer to help you try this out.


Patrick
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Old 1st September 2011, 09:03 PM   #49
Calvin is offline Calvin  Germany
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Hi,

I simmed the ZEN-style bipolar with:
+-2mA pp input current (as TIs PCM1795 and PCM1796)
BC847BS/BC857BS (spice models from Diodes) biased at 7.8mA
+12V supply
1k5 I/V-resistor + 220pF cap

Results:
V(out): 2.1Vrms
Total Harmonic Distortion (K2-K8): 0.000483% -106dB, clean spectrum
(even lower harmonics possible with increased supply voltage or differential output)
Noise (20Hz-20kHz): below 1V (depends very much on the current source that is needed to null out centre currents of PCM-DACs)
Zin(dc): 65Ohms
Zin(ac): 2.65Ohms (and very linear into the MHz-range)
current output DACs like the PCMs show increasing THD when Zin is increasing above app. 20Ohms due to protection diodes
Vin, resulting from Zin: +-5.5mVpp
Zout: 1k5 || 220pF
upper Bandwidth limit: ~470kHz
TF: -1386mV/mA

I think thatare remarkable values for such a simple and tiny circuit that may be build from SMD-parts and less than 20x25mm PCB-size.

jauu
Calvin
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Old 2nd September 2011, 04:15 AM   #50
EUVL is offline EUVL  Europe
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Congradulations.
Maybe also time for you to build one ??


Patrick

.

Last edited by EUVL; 2nd September 2011 at 04:23 AM.
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