Dual Mono wiring for a Vout DAC

[cubano]

I just found a test that I made using the transformer for bypassing aop. I have the same value. The cause of the degradation is the transformer.

 

[RobLK]

Yep, I 2nd the idea of using a high quality op amp to make a converter. The last op amp circuit of figure 41 in the ak4490 pdf is also what was used on their evaluation board.

 

[cubano]

Cubano, for the ak4497 circuit figure 73 the two outputs that are connect to the top op amp must be in phase as it shows. If they are out of phase they will cancel out to zero where they are join at the 44 ohm resistors. The two outputs connected to the bottom op amp must also be in phase.
However, the two outputs connected to the top op amp must be 180 degrees out of phase with the two outputs connected to the bottom op amp.

I can use this config for unbalanced? (see below)

 

[themystical]

Should be fine! It's a basic op amp differential circuit. The capacitors are providing a bit of extra filtering. Change the value of the 520 Ohm resistor to get the gain you want.


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[themystical]

Did you do the RMAA test on the single ended output with the transformer in circuit? I would be very interested in your results.


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[cubano]

test transformer in stereo mode

 

[cubano]

I'm going to order the parts. Do you have any advice for components?

 

[themystical]

Thanks for the results. They are more or less what you would expect with around a 3dB improvement for mono mode.
In terms of components, if you wanted to reduce count you could use one dual opamp for both channels. ADA4898-2 or LME49720 are good dual opamps to use.
The choice with single opamps is unlimited. Personally I like the LME49990 of ADA4898-1.
The rest is the usual metal film resistors and polypropylene capacitors or COG/NPO if SMD.


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[RobLK]

Yes, your circuit does look fine. I think the ak4497 pdf says you should use 0.1% resistors for all lpf circuits. The lme49990 and ada4898 are excellent but the lme49990 is end of life now. I'm sure you could find some though.
The added op amp circuit will sum the inputs and multiply that sum by the gain to get the output. So if the the inputs are both 1 vpp then the output will be 2 x 0.903 = 1.806 vpp.

 

[RobLK]

The op amp circuit that you are adding on is a differential op amp circuit so it doesn’t sum the inputs as I said above, it takes the difference of the inputs. But since the inputs are 180 degrees out of phase you get a larger output. It’s like taking a positive number and subtracting a negative number.

 

[cubano]

The op amp circuit that you are adding on is a differential op amp circuit so it doesn’t sum the inputs as I said above, it takes the difference of the inputs. But since the inputs are 180 degrees out of phase you get a larger output. It’s like taking a positive number and subtracting a negative number.

Sorry, but i don't understand. can you explain me with a schema or Can you give me a schema for balanced and unbalanced lpf mono circuit, please?

 

[RobLK]

You have all that you need Cubano. The drawing that you made in post #43 will work fine.

 

[cubano]

ok