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Adding an Amp into Thin-Client PC
Adding an Amp into Thin-Client PC
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Old 30th March 2018, 11:44 AM   #1
phofman is online now phofman  Czech Republic
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Default Adding an Amp into Thin-Client PC

Perhaps this will come useful to someone...

A small fanless thin-client PC (FS Futro, HP Txxx, Dell Wise etc.) powered by a typically 20V adapter, for nothing from ebay, ideal for home audio (Daphile). Some models offer room inside, integrated Intel HDA soundcard codecs have improved a lot, digital amp boards are small, efficient and use single-voltage power - let's make a small dirt-cheap all-in-one machine.

Sounds good, but my try with tripath amp Home * pavhofman/plabs-player Wiki * GitHub was a bit disappointing. The ground loop within the PC board and the amp was just unfixable. Every CF card access, every letter typed on screen, every mouse move, all was clearly audible no matter what I tried. I ended up with two adapters External Relay Activated Power Supply for the Amp * pavhofman/plabs-player Wiki * GitHub - one for the PC and another one for the amp. Clumsy.

Then I learned about the TPA3116 chip which (unlike tripath) offers balanced inputs. Most TPA3116 boards do not pull out the negative inputs from underneath the heatsink but there are some which do, e.g. Click the image to open in full size.

Just disconnecting the -IN capacitor from ground makes a perfect balanced input.

Unbalanced connection + power from the PC adapter proved just as disappointing as the tripath.

Then I connected the amp in the usual way for unbalanced-balanced interface, using shielded microphone cable, powering the amp directly from the jack power socket of the board:

Click the image to open in full size.

Click the image to open in full size.

Voila, the noise was completely gone, dead silent at full volume. Amp for 8 dollars, thin client incl. the adapter for 10 euro, 18W/8ohm THD-N 0.05%, reasonable performance even for 2.7ohm.

I did some measurements ( Headless Amplifier Measurement Workstation ), they fit the amp datasheet http://www.ti.com/lit/ds/symlink/tpa3116d2.pdf very close, which means the noise from the ground loop is eliminated. All the figures are available here Player v.2: TPA3116 with Single Adapter * pavhofman/plabs-player Wiki * GitHub

Perhaps some daphile or other small audio PC builders will find this useful. It works :-)

Last edited by phofman; 30th March 2018 at 04:19 PM.
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Old 30th March 2018, 07:08 PM   #2
CharlieLaub is offline CharlieLaub  United States
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Hey P, very nice!

Is that TPA3116 board 2 BTL or 4 SE channels? It's not my favorite amp for sure, but it definitely fits your application well.
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Last edited by CharlieLaub; 30th March 2018 at 07:11 PM.
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Old 30th March 2018, 07:48 PM   #3
phofman is online now phofman  Czech Republic
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Thanks. It is a regular stereo board, with bridge switches at each channel output.

Its performance in absolute terms is doubtlessly quite inferior compared to good analog amps. But these do not come with single supply voltage, tiny footprint, high efficiency allowing use of the PC adapter + low heat losses. Not even talking about the price :-)

The project is done by a few school boys here who are building a piece each for themselves to use it at home. Another piece plays in kitchen. There is really no ambition to replace a living-room setup.

Yet the question is how such device would fare against a full-blown hifi gear in a blind listening test at normal listening levels...
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Old 15th September 2018, 05:46 PM   #4
Think is offline Think  Netherlands
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Adding an Amp into Thin-Client PC
Nice project! Just using them for the powersupply and case is allready nice.
But this is used as a media player? What software do you run on it? Voyage Linux?
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Old 15th September 2018, 09:08 PM   #5
phofman is online now phofman  Czech Republic
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Thanks. Yes, it is a media player with CD drive and internet radios. Based on voyage linux + python. The github repo Home * pavhofman/plabs-player Wiki * GitHub is not updated with the balanced TPA3116 version (+ flash plaback) yet.

Click the image to open in full size.
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Old 18th September 2018, 09:46 PM   #6
MAAC0 is offline MAAC0  Portugal
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It works because the power adapter has only two pins, so no ground connection.
That's a common problem on laptops for Djing. I cure it usually using a 3 to 2 prong mains adapter or a non grounded PSU. Many new laptops come nowadays without ungrounded PSUs.
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Old 19th September 2018, 04:23 AM   #7
phofman is online now phofman  Czech Republic
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Join Date: Apr 2005
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Quote:
Originally Posted by MAAC0 View Post
It works because the power adapter has only two pins, so no ground connection.
If you look at the diagram, the same power adapter is powering both the PC and the amp. This ground loop is not related to mains ground (PE wire), but to the common ground line of PC and the amp. The common-mode rejection of the amp's balanced inputs eliminates the common-mode noise voltage of both soundcard outputs against the common ground. Logically no elimination occurs when using an amp with unbalanced inputs.
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