Single rail splitter for preamp for TPA3116 - diyAudio
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Old 21st August 2014, 06:24 AM   #1
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Default Single rail splitter for preamp for TPA3116

Hi there,

I'm looking to put together a simple integrated amplifier based on a high quality preamp and the new Sure TPA3116 Class D board.

The chassis will accept 24vdc input for the sure board, but I'd like to use this supply to power a preamplifier board too.

I suppose that means I'll need to split the rail from +24vdc into +12vdc/-12vdc for the preamp board.

Questions:

1. Is it wise to run the (rail splitter + preamp) and (amplifier) in parallel off the 24vdc supply?
2. What is the best way to split the rail? A TLE2426?

Thanks in advance!

Chris
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Old 21st August 2014, 12:00 PM   #2
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When using capacitor-coupling, you wont need a split-supply. The get the voltage down, use a step-down-converter followed by a linear regulator to get a better PSRR.

24V -> 15V (Step-Down) -> 12V (LDO)
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Old 21st August 2014, 12:50 PM   #3
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Quote:
Originally Posted by undefinedza View Post
1. Is it wise to run the (rail splitter + preamp) and (amplifier) in parallel off the 24vdc supply?
2. What is the best way to split the rail? A TLE2426?
Even with the TLE2426, the potential at the output is going to be half the rail voltage, so you will need a coupling capacitor. The TLE2426 will source or sink 20mA -- probably enough for one opamp, but barely two.

You can make a higher current functional equivalent of the TLE2426 with a pair of resistors and a buffer like the LME49600, or one of TI's higher current unity gain stable opamps.
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Old 21st August 2014, 01:00 PM   #4
xrk971 is offline xrk971  United States
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You can also use two voltage isolated DC-DC converter chips that will let you make a dual rail supply from a single. I have used these parts from Murata before, about $6 ea and size of a 7812 regulator. With dual rail transformer you will also need a 7812 and 7912 to regulate the supplies and their ancillary parts. These isolates also eliminate ground loops in your supply vintage when powering preamp and amp from same source.
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Old 21st August 2014, 01:20 PM   #5
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If using the Murata converters, make sure to use a small choke on the input, bypass the output both at the converter and opamps power pins with 0.1uF ceramics. The linear post regulators are not very effective at eliminating the switching noise above some 10s of kiloHertz.
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Old 21st August 2014, 10:12 PM   #6
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Thanks for the replies guys!

It looks like splitting the rail isn't going to be easy.

jackinnj: Do you know if I can get a small pre-assembled module like this? I don't have PCB fabrication facilities.

As an alternative: Are there any high quality preamp modules available that take a single supply up to 24vdc?
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Old 21st August 2014, 10:33 PM   #7
xrk971 is offline xrk971  United States
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Quote:
jackinnj: Do you know if I can get a small pre-assembled module like this? I don't have PCB fabrication facilities.
Preassembled Murata DC to DC modules was what I was telling you in the above post. They probably make dual rail DC DC converters so you only need to buy one.
Not hard at all.

I don't know how much current you need but this is good for 83mA. Bigger ones are available.

NMK2412SC | Bipolar / Dual Output Isolated | DC-DC Converters | Products | Murata Power Solutions
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Old 22nd August 2014, 07:36 PM   #8
Nisbeth is offline Nisbeth  Denmark
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I have experimented a little with some DC-DC converters, so this may be of interest to you: dc-dc | theslowdiyer

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Old 23rd August 2014, 05:27 PM   #9
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I have experimented a little with some DC-DC converters, so this may be of interest to you: dc-dc | theslowdiyer

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Thanks Nisbeth, I read your posts.

Do you have prepopulated PCBs available?

I suppose it would be rise to regulate the output too?
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Old 23rd August 2014, 07:42 PM   #10
Nisbeth is offline Nisbeth  Denmark
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I have some blank PCBs left over, but nothing populated. This is diyaudio after all

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