Unusual opamp+buffer arrangement in the Monarchy Audio 22B DAC

[Leolabs]

For the 22B, there is an extra section of opamp+buffer for the output, which is based on a single channel opamp plus a LT1010. Interestingly, the input for the buffer is taken from pin 5 of the opamp (as opposite to the normal pin 6). As pin 5 is normally a NULL/OFFSET pin for certain VFB based opamp, wondering what's the purpose of using that pin as an output instead.

Note that the opamp's original part numbers are rubbed off, leaving just a small white square on the top right(near pin 5),so I couldn't identify the actual part numbers.

 

[abraxalito]

Opamp might be AD744, on that pin5 is a compensation pin but brings out the input to the OPS buffer, allowing it to be bypassed.

 

[Georg Kovalcik]

Same with the NE5534, Pin 5 is the direct output of the internal VAS. This was sometimes used with a resistor to the output (see attached examples by Tektronix and Audio Precision) but could be used to drive a buffer as well.

 

[jan.didden]

It could be an AD844 where pin 5 is the current output.

Jan