BUF634A: Combining differential amplifier with BUF634

Your attached schematic is not an imbedded power boost, and, the OPA1622 is not a differential part. 

Not enough clarity here to go far, but, this is of course possible - I dealt with this in a few recent AudioXpress articles if you want to see a working approach, April 2021 is the concluding one with some preparatory ones (using the OPA634A, which is not the best approach) in earlier months. 

Thanks Michael Steffes for your reply and joining the thread.

I'll take a look at the article for sure.

I'm really a newbe in schematic and audio definitions, so let me explain it in more detail.

As an example here is a Figure 40, schematic from TI tidu672c document. So my goal is to combine this schematic with BUF634A (used inside the feedback loop of OPA1622) as a composite amplifier in order to provide enough power for my 16 Ohm headphones. That's why I'm asking if it's OK to combine differential (summing) amplifier based on OPA1622 given in Figure 40 with BUF634 in this way.

Regards,

Hi Johingir,

looks stable for the OPA1622:

jahongir_opa1622_opa634.TSC

jahongir_opa1622_1.TSC

Kai

And the BUF634 is stable too:

jahongir_opa1622_2.TSC

The additional phase shift at 6.4MHz due to the output impedance of OPA1622 is less than 1°.

Kai

Hey Johingir, 

This came up some months back with the OPA634A and I started an article series on AudioXpress. Since that is a subscription magazine I cannot just send you my original. Be careful with the word differential - often you mean stereo or dual channel, but there are also true differential devices and designs using FDA's or dual op amps, a little different thing. 

Those articles start in the Feb2021 edition using the BUF634A. An easy way to get into trouble with these designs is to neglect the package and layout prop delay inside the loop. Eventually, I end up with a very low distortion audio headphone driver solution using the duals - OPA1612 and the TPA6120A2 (which is just an audio labelled THS6012) in the March 2021 edition. 

More recently a local audiophile has built that one up and claims to experience his best audio ever. That may be headed for publication as well, but I have kind of lost touch on that.