Pro Audio Design Forum

Hi,

I have been searching and try to learn about the supply bypassing, the most common method that I use is the B method, and I have seen some other circuit use the A and B method. Now I'm narrowing the IC to special purpose THAT IC rather than op amp especially model 1246, 1646, and 4301, is there any benefit for using method A? I suspect 1246 and 1646 will benefit since they deal with common mode and not for 4301?
Thank You.

The MS matrix board has the option for all three but I build them with the option "B" aka "common mode" method.

JR commented somewhere in this forum about his experiences with the differential decoupling method "C." As I recall, with the particular power supplies used there were issues with either oscillation or RF ingress.

Option "A" can be called "delta" since it resembles a delta connection to a three phase source.

From the perspective of the IC alone I suppose Vcc to Vee, "C" would be preferred - that's what you have when it is used with single supplies - but I don't think there's enough of a difference for it to matter. The C connection is (usually) from the supply to the IC's actual substrate.

It seems this has been well discussed here and elsewhere.

For a generic answer I prefer door number 2, but to be accurate you need to draw resistors and little inductors in series with each power supply lead so you can better visualize what we are trying to manage.

Something else I have surely mentioned before. Different opamps can have different PS sensitivities (+PSRR, and -PSRR), and where the load that the specific opamp circuit is driving gets grounded also matters since you should inspect the entire current path from PS via opamp to load and back to PS. While you may think the load current just goes to ground, but that is how it gets back to the PS to complete it's round trip.

Wayne will know better than I is there are any quirks or preferences for supply bypassing with those THAT chips. Of course look at the app notes for advice.

JR

Thanks John.

One thing that did occur to me was something unique to the THAT1646.
The 1646 has a sensitivity to series inductance in pin 3.
The best way to reduce sensitivity to that is to use method B or as John said "door number 2."

Thank You Wayne and John, I just checking this thread again and found that my last reply didn't posted, maybe I forget to hit the submit button.

mediatechnology wrote:The MS matrix board has the option for all three but I build them with the option "B" aka "common mode" method.

This is one of the reason I'm asking

JR. wrote:Something else I have surely mentioned before. Different opamps can have different PS sensitivities (+PSRR, and -PSRR), and where the load that the specific opamp circuit is driving gets grounded also matters since you should inspect the entire current path from PS via opamp to load and back to PS. While you may think the load current just goes to ground, but that is how it gets back to the PS to complete it's round trip.

JR, Is that mean if I can manage the ground layout isolated for power and signal and only meet in the PSU ground point it will better (oscillation and noise wise)? Is that some kind of star ground? And the application is for line level with various load around 5k-100k for each op amp.

Thank You.

Nescafe wrote:Thank You Wayne and John, I just checking this thread again and found that my last reply didn't posted, maybe I forget to hit the submit button.

JR. wrote:Something else I have surely mentioned before. Different opamps can have different PS sensitivities (+PSRR, and -PSRR), and where the load that the specific opamp circuit is driving gets grounded also matters since you should inspect the entire current path from PS via opamp to load and back to PS. While you may think the load current just goes to ground, but that is how it gets back to the PS to complete it's round trip.

JR, Is that mean if I can manage the ground layout isolated for power and signal and only meet in the PSU ground point it will better (oscillation and noise wise)? Is that some kind of star ground? And the application is for line level with various load around 5k-100k for each op amp.

Thank You.

I was offering general advice. I do not have any hands on experience with those devices. I defer to Wayne who has.

JR