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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Two balanced line receivers (switched) at one balanced input
Two balanced line receivers (switched) at one balanced input
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Old 1st April 2015, 01:26 PM   #1
barcley is offline barcley  Germany
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Default Two balanced line receivers (switched) at one balanced input

Hi,

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!

Best,

Sebastian
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File Type: pdf THAT1200_Input_switched.pdf (34.4 KB, 47 views)
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Old 1st April 2015, 06:08 PM   #2
sgrossklass is offline sgrossklass  Germany
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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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Old 2nd April 2015, 09:36 AM   #3
barcley is offline barcley  Germany
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Thanks a lot, now I can proceed and design the rest of the circuit !
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Old 4th April 2015, 08:17 AM   #4
Nisbeth is offline Nisbeth  Denmark
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Two balanced line receivers (switched) at one balanced input
Remember that you should control the "BTL-sync" pin on the ASX as well (an arduino pin and a transistor should be enough for that).

/U.
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Old 7th April 2015, 11:47 AM   #5
barcley is offline barcley  Germany
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Yes, thank you . I was planning on controlling BTL (and also enable to avoid pop/click noises) by arduino.
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