Opa660 I/V

[gaetan8888]

860 is direct replacement for 660....

Boky

Is it the difference are that the OPA660 have an open loop output buffer and the OPA860 have a close loop output buffer ?

Btw, would I get a better result than using a THS4031 as a I/V amp ?

Thank

Bye

Gaetan

 

[jan.didden]

860 is direct replacement for 660....

Boky

Agreed. Better linearity also, apparently.

jd

 

[jan.didden]

Hello janneman

I've use wayback machine at the web.archive.org and I found the new link for the dc servo file ;

http://web.archive.org/web/20041027034615/home20.inet.tele.dk/kou/dcservo.html

You can directly download the file there;

http://web.archive.org/web/20041027034615/http://home20.inet.tele.dk/kou/files/servoamp.zip


Btw, would you know if I can use the OPA860 as a drop-in replacement to goes into the circuit in the post 46 ?

Bye

Gaetan

Thanks!

 

[Nazar_lv]

Btw, would I get a better result than using a THS4031 as a I/V amp ?

If 4031 in right schematic and PCB tracing - no, if in standart - yes

 

[gaetan8888]

If 4031 in right schematic and PCB tracing - no, if in standart - yes

Hello

Here is the THS4031 I/V amp and also the OPA860 I/V amp (replacing the OPA660 by the OPA860 if I use this one) schematics I would use;

Any comments or suggestions ?

Thank

Bye

Gaetan

 

[jan.didden]

Hello

Here is the THS4031 I/V amp and also the OPA860 I/V amp (replacing the OPA660 by the OPA860 if I use this one) schematics I would use;

Any comments or suggestions ?

Thank

Bye

Gaetan

If I would use the 860, I would not fiddle with the input offset compensation. I would run a servo into the base pin 3. Clean, stable, no need for adjustments that will drift.

Anyway, these two circuits are completely different concepts and cannot easily be compared. The 860 is best for the DAC and I would prefer that, but not having tried out either it is just my preference.

jd

 

[Extreme_Boky]

If 4031 in right schematic and PCB tracing - no, if in standart - yes

Hi Nazar,

I have checked your web-site.... nice analog power supply regulation for that DAC... and nice I to V for that Analog Device DAC... any info in English?

Boky

 

[Nazar_lv]

Here is the THS4031 I/V amp and also the OPA860 I/V amp (replacing the OPA660 by the OPA860 if I use this one) schematics I would use;

Any comments or suggestions ?

transformation current / voltage is happening here at the resistor (the resistance 50om is too much, DAC will produce distortion, moustly the quadratic through lack of compensation in the initial displacement -2mA 1541) Operation amplifier serves only noninverting amplifier with Ku2.
OPA660 here included in the usual way without negative feedback, sound not bad, but for my ears a bit too much distortion and "colored"

Hi Nazar,

I have checked your web-site.... nice analog power supply regulation for that DAC... and nice I to V for that Analog Device DAC... any info in English?

Boky

Hi Boky,
its not only power supply regulation, the analog part of the device (1794DAC) is organized on the principle of "double Mono", electrolytic capacitors are not used, instead are used negative feedback free electronic substitutes, with has a stable impedance ~0.2Om in the band to several tens of megahertz shunting NP0 0,1 microfarads Murata GRM31 in close to chips. This structure provides in a comparison with the best series audio electrolytic capacitors significantly better results as well as the simplicity, accessibility and small price.

That I/U stage based on 860(and 844+5534) have negative feedback only in audio band, therefore has only advantages of NF

I dont have English translation yet, only in Russian at the moment, if necessary i can do, i read in English very well (especially technical text), but the writing and speaking difficult to me, no practice. I Designing DAC/ADC in a long time, if you have any questions about that devices (DACs 1541, 1794, I/U, electronic training of electrolitic capacitors, amplifiers and others) i will answer, but here it is OFF, in another(new) topic on this forum

Best regards, Nazar

 

[Nazar_lv]

If I would use the 860, I would not fiddle with the input offset compensation. I would run a servo into the base pin 3. Clean, stable, no need for adjustments that will drift.

it will not work, current output of the most parallel(multibit) DAC should be under the potential of zero volts. For this potential on DACs current output the pin 3 opa860 should also be zero volts (it puts potential of pin2)

 

[gaetan8888]

transformation current / voltage is happening here at the resistor (the resistance 50om is too much, DAC will produce distortion, mostly the quadratic through lack of compensation in the initial displacement -2mA 1541) Operation amplifier serves only noninverting amplifier with Ku2.

Best regards, Nazar

Hello Nazar

Ok, I could reduce I/V resistor to 30 ohm.

Thank

Bye

Gaetan

 

[jan.didden]

it will not work, current output of the most parallel(multibit) DAC should be under the potential of zero volts. For this potential on DACs current output the pin 3 opa860 should also be zero volts (it puts potential of pin2)

I stand corrected, you are right. But I would still like to use a servo, only at another point. haven't looked at it yet, but should be doable. I hate adjustments that need to be adjusted and can drift

jd

 

[Nazar_lv]

Ok, I could reduce I/V resistor to 30 ohm.

1541 with I/U resistance >15ohm give "coloration". opamp amplifier has gain only 2, with 30ohm resistor i/u you would have only 0.24v p-p (0db) on out with DC 0.06v

I stand corrected, you are right. But I would still like to use a servo, only at another point. haven't looked at it yet, but should be doable. I hate adjustments that need to be adjusted and can drift

servo is simply another feedback loop, if the quality is above all that the servo should be used very carefully and attention. You have two options with the servo
1 shift by current on current input of i/u (860/861 power supply symmetry +-6v)
2 shift by voltage in the second stage after 860 (860/861 power supply asymmetry +9 -3v)