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|1st April 2015, 01:26 PM||#1|
Join Date: Apr 2015
Two balanced line receivers (switched) at one balanced input
I'm trying to design (as a beginner's project) a preamplifier board with PGA2310 /Arduino to be used with Icepower 125ASX2 amplifiers. Input to the pre is always balanced and symmetrical.
As a specialty Arduino should be able to switch the 125ASX2 from BTL to SE mode, depending on the module being used for Stereo active loudspeakers or for Sorround-setup.
This demands the following setup:
- In SE mode two unbalanced signals are needed to drive the 125ASX2
- In BTL mode a symmetrical signal is needed
- Icepower output needs to be switched (here I'm planning to use a power relay)
I'm trying to use as less parts as possible for this. Further, I chose the THAT1200 as balanced line receiver for SE mode, as it has quite a good spec.
To come to my problem:
As my input is always symmetrical I could directly forward the symmetrical IN+ and IN- to the PGA2310 for BTL mode, however inputs should be buffered for the PGA so this would potentially require 2 additional OpAmps. Further, I might need additional input RFI and AC coupling filters. I came up with the attached circuit, which (for BTL mode) forwards IN+ and IN- to both THAT1200 with inverted polarity at the second THAT1200.
As I'm quite new to electronics and audio design I have some questions:
Is there some reason that this is a bad idea? Is it generally going to work?
When both THAT's are driven in parallel is the input filtering still working as expected?
Thanks a lot and I'm of course open to other/better suggestions to solve this problem!
|1st April 2015, 06:08 PM||#2|
Join Date: Nov 2004
Looks like it should work, with no major side effects except the expected (differential and CM input impedance halve in BTL mode, reducing CMRR a bit). The worst that could happen would be some click/pop noise upon switching.
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