dac I/V convertion with very low distortion

[smms73]

This is the bipolar input version, some resistors value may yet be changed (R13,14,20,21). Final version only when pcb is finished.

edit:Q10,13,12,3 are bc550c , bc560c

[Joachim Gerhard]

I like the servo. This is really cool.

[bkdog]

I think the whole thing is really cool! I'm looking forward to trying this one day and listening to the difference between the BJT and JFET input devices. Keep it coming Sérgio!

[smms73]

Joachim tanks for your kind words and the incentive that you always give me, it means much to me , as i also admire your work in SONICS , i realy like the design of your speakers specialy the SONICS Anima, its a very beautiful speaker.

bkdog, it is almost done .

[RCruz]

Originally Posted by smms73

The servo that i test is this one, i use a 1Meg in R4 as staccatiss suggested but there is no difference, but i will leave it like that. the next image are the I/V converter noise floor with servo, the second image is without servo, the third is emu1212m alone. The last one is the power supply noise alone.

Sérgio, I am learning about servos.... would you explain how this one works ?

Does it have a low pass filter in the first stage ?

[Joachim Gerhard]

Thanks Sergio. i left Sonics some time ago. My new designs are now made by Canalis in Berkeley, California. There is also a new Anima in Bamboo.Canalis

[smms73]

I didn´t know that you leave sonics i have to check Canalis.

RCruz, Yes it has a low pass filter.
This is a convencional inverting integrator followed by a inverter to give the polarity that we need. If you look at post #553 , there are two servos , they both do the same thing but the first with the dual opamp will only use one capacitor, so we save the costs of the capacitor and the pcb space (that also have costs), so the choice of this type of servo is just a economic one.
The difference in this implementation is that normaly you see DC servos connected to input of the amplifiers and the noise of the servo opamp will be injected in the main amplifier, so you need to use a audio grade opamp for low noise like opa627 , but in this case the servo is not in the audio path (as Ken Newton has explain in post#561) so you just need to use a opamp with low input offset , the noise is not important (like for exemple max4238 less than 1€ and much beter in dc precision than audio opamps).
This is more economical (opa627 cost more than 20€) and better sonically as the servo is not in the audio path.

edit: Bob Cordell in his book "Designing Audio Power Amplifiers" has a chapter about servos , i recomend you people to buy this book.

[MiiB]

Ricardo... this servo implementation is exactly the same as the one I used in the Paradise, so at one point it should be familiar to you, here Sergio is really smart as he uses the Diodes of the transistor to create CCS's, that also has the capability to mirror in the cervo current in and add and subtract in on the drive current and thus push the output to 0. this is simpler and smarter....clever

In the paradise we had some debate on the use of a servo, but there and here the influence on the audio path is non existent.

[RCruz]

Thank you Sérgio and Miib.

Now I see the similarities with the Paradise.... I was wondering because in that case I did not see the final inverter.

[MiiB]

In the Paradise We only use one pole and one opamp.