Question about Output stages

Troubleshooting and Support
1

Hi,

I ‘m checking the schematics of the daisy patch for inspiration about my own project and one things that I don’t understand is the two op amps stages on the output :

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Why two ?
If I compare on simulate project ( like the mutable one ) they only use one amp stage for the audio output …
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I’m fairly new on electronic and I haven’t a deep knowledge of circuit.

Could someone explain me this choice of architecture and the advantages ?

Cheers

2

Short answer - each op-amp is an inverting amplifier - by using two of them you effectively get a non-inverting amp, so the phase of the output will be the same as the input.

I’m sure there are more details and other pros and cons, but that’s my quick and simple answer, maybe even correct!

4 Likes
3

Thx for the answer tunagenes !
It seems so obvious once I read your answer :clown_face:.

But now this the Mutable schematics that seems weird. They also use the same inverting op amp. Why do they not need to revert the output ?
Maybe they do that on the software side ?

4

Could be they do it in software, or it could be they just don’t care that the output is ‘inverted’ - it seems serious, but for many (most?) audio applications the absolute phase doesn’t matter. I think it becomes important when you are combining multiple signals.

5

The two circuits you posted above serve different purposes.

On the Daisy Patch, the “DAC Output” section of the schematic is for the unipolar control signal DAC channels. The output range is only unipolar positive. So a single-inverting channel as exists on the MI sch would result in a unipolar negative output. Alternatively a single-stage non-inverting amp could have been used on the Daisy Patch.

In the MI schematic, the single inverting stage can be used because the output is bipolar and the software can control the polarity.

That said, the Daisy Patch does use the double-inverting stages for audio as well, and while not necessary this just makes it so that the phase of the signal being read into, or being sent out of the Daisy is the same as what the user intends without having to know that it’s getting flipped in hardware.

1 Like
6

Thx both of you for your helpful insight !
I really appreciated and learned a lot !!!

Cheers