living sounds wrote:
looks like this is exactly what I need as balancing/output driving stage for my discrete multichannel DAC!
I'd like to use NE5532 (got old Signetics ones that I consider the best sounding op amp out there), any reason why they wouldn't work here? What can you expect WRT to SNR and THD?
The LME49720 & LM4562 have nV input current so will have no offset with the 100k input resistor. The bipolar input of NE5532 will make dc offset on the output of the tradigrade as there are no output caps. You can reduce this by lowering the input impedance from 100k to 10k and change 1uF to 10uF Non Polar. Or if connecting to a opamp unbalanced output directly with no offset, link out 1uF cap so unbalanced output and input direct connect so NE5532 doesn't offset. But it will never be a good offset wise as the LME49720 & LM4562.
Also, I might need more gain from it, is there any reason not to simply change the feedback resistors to a slightly higher value to get more gain?
Easy to get more gain. link the 12dB pads and add resistor across last 10k in the resistor SIL. But if using NE5532 again dc offset will need to be addressed. Instead of solder link for 12dB pads fit a 100uF 10v Non Polar cap across the pads so gain at DC is unity to minimise dc offset.
The 1 uf decoupling caps are X7R ceramics I guess? What's the rationale behind using those instead of the usual combination of bigger electrolytics every 2-4 op amps (say 10uf) and 10 or 100 nf ceramics at the pins?
Audio path Cap is 1uF MKT polyester not ceramic. If lower input impedance is need then cap needs to be increased to 10uF etc so Non Polar electro will be best. The ceramic mono caps are power rail decoupling to keep the opamps stable. PCB has 8uF of these per +/-rail for super low impedance power.