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Class D Switching Power Amplifiers and Power D/A conversion

Best class D amplifier board for 9 Volt supply
Best class D amplifier board for 9 Volt supply
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Old 20th July 2019, 09:47 PM   #11
Bare is offline Bare  Canada
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Quote:
Originally Posted by Khron View Post
Well, the ready-made PBTL boards with TPA3118 can be found for under 2$ a piece, so...
Not to mention that TI wants ~4$ each for the chips individually and ~2$ in 4000 unit lots.
Fairly certain that those Chi Fi boards have their TI chips, Along with everything else .. as hand made in a Noodle factory.
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Old 20th July 2019, 09:52 PM   #12
Khron is online now Khron  Finland
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I've been using two of those small blue boards in my surround speakers, and 4-5 others in some small guitar amps i'm designing, and i've encountered no issues whatsoever.

With a 4x12" 4 ohm guitar cabinet, one of those little buggers got up to ~115dB around 2m in front of it. Without even breaking a sweat, i might add...

Khron's Cave: #28 Active full-range surround speaker project (BN96-12832 & TPA3118)
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Old 7th August 2019, 09:51 PM   #13
goodlionaudio is offline goodlionaudio  United States
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Default TPA3118 results on 9VDC

Finally got all the parts to build a test system and make some measurements. The carrier board contains a mono TPA3118 credit card style board (PBTL) and a DC/DC converter module (SIP-8).

The local power supply is the DC/DC converter, with 48VDC input and 9VDC @1A output. It is driven by a bench power supply set at +/-24V in series.

The maximum observed output in a 8 Ohm resister load with 1 KHz sine wave is 12VTT, which means a power output of 2.25 Watts. The power output is limited by the 1A max current of the DC/DC converter. I could not find a suitable 9V converter with higher current rating. My goal is to get 3-4Watt, so I have ordered a 12VDC converter with 20W rating (1.67A, DIP-24) and will try again when parts arrive.

The scope shows input and output signals; the measured gain is 32dB. The measured THD+N at this level is ~0.56% with the residual being mainly broadband noise.
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Old 8th August 2019, 12:45 AM   #14
Khron is online now Khron  Finland
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Since you have that triple-output power supply... Why not use the free channel to test the amp board, in the mean time?

(Although i kinda get it, i guess this test was meant to test the 9V power supply as well - right?)
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Old 8th August 2019, 01:01 AM   #15
goodlionaudio is offline goodlionaudio  United States
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That's right, I want an integral power supply with the amp board. The intent is to power the amp using power over ethernet (PoE), which supplies 48VDC.

As stated, I have done some measurements with the amp board already. There are a couple of things that need to be modified. I want to lower the gain to 12dB or so, and I want to have a balanced input rather than single ended. On my board the negative input is grounded.

I seem to have some stability issues (seen as oscillations riding on the sine wave) which may be related to the fact that the DC/DC converter is isolated and the test equipment, connected to input and output, are grounded. I am not to worried at this point because I can make them go away by adding another ground wire.
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Old 8th August 2019, 08:27 AM   #16
Khron is online now Khron  Finland
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The only way you can reduce the gain lower than the chip's minimum of 20dB (10x) is by adding some sort of (fixed) attenuator on the input. The former can be achieved by (carefully) removing the 100k R27 (3rd from the bottom in your photo).

"Creating" a balanced input is quite trivial as a concept, but perhaps a bit fiddly in practice. What you need to do is separate the "outside" of C21 (second component above R27) from the ground-plane (while ideally still leaving a bit of copper there, so you can scrape off the solder-resist and solder a wire to it), with the sharp tip of a box-cutter knife or something along those lines.

Just be careful not to get the solder blob all the way to the exposed edge of the remaining groundplane - ask me how i know
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Old 8th August 2019, 01:47 PM   #17
doctormord is offline doctormord  Germany
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Very nice.
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Old 8th August 2019, 02:03 PM   #18
goodlionaudio is offline goodlionaudio  United States
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@Khron thanks for your detailed response; it confirms my plans nicely!

The only difference is that I want to remove the 2 input capacitors all together and solder in some leaded ones. This would take care of the tricky part to separate the one capacitor from the ground plane and provide an easier way to attach the input wires.

The 12V DC/DC converter should arrive by the end of the day; so, I'll be able to continue my quest shortly.
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Old 8th August 2019, 04:12 PM   #19
Khron is online now Khron  Finland
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"Where there's a will, there's a way"

I used those to "active-ate" the pair of junky "surround" speakers i hacked together a while ago, and since they're on the other side of the room from where my computer & interface are (and the power brick's plugged into another mains socket) i figured running a balanced line couldn't be a bad thing.

Khron's Cave: #28 Active full-range surround speaker project (BN96-12832 & TPA3118)

I chose to not connect the shield to the amp's ground, to eliminate the chance of ground-loops.

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Originally Posted by doctormord View Post
Very nice.
That's fair enough, i suppose - i'd prefer to keep those leaded caps as close to the input side as feasible (if not even under the amp, so they're shielded by the amp board's groundplane on the bottom).
Just to minimize output switching noise coupling back into the input, since leaded caps will need to be off-board, no matter how you cut it.

Quote:
Originally Posted by goodlionaudio View Post
@Khron thanks for your detailed response; it confirms my plans nicely!

The only difference is that I want to remove the 2 input capacitors all together and solder in some leaded ones. This would take care of the tricky part to separate the one capacitor from the ground plane and provide an easier way to attach the input wires.
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Last edited by Khron; 8th August 2019 at 04:16 PM.
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Old 12th August 2019, 08:02 PM   #20
goodlionaudio is offline goodlionaudio  United States
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Default 12V supply update

The 12V DC/DC converter does the trick and easily provides the desired 4W output in 8 Ohms. The output now clips at 20Vtt; i.e. 6.25W.

The observed THD+N at 4W and 1 KHz sine wave is 0.15%.

I have removed R27 to lower the gain to 20dB and have added a TY-145P input transformer and passive divider to bring the overall gain down to 10dB. The transformer provides a balanced input into the single ended board (no board modifications needed). The frequency response is flat between 100Hz - 10KHz; sufficient for my application.
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