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Wondom AA-AB31471 1 x 30 Watt Class D Amplifier Board Review and Measurements

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pma

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Wondom AA-AB31471 1 x 30 Watt Class D Amplifier Board Review

1. Intro


I wanted to have a small audio system for my holiday trip, not to depend on usual TV set sound available at the hotels and pensions. As a speaker I would take my small JBL Control 1 Pro, so there was a question of the smallest but still good enough amplifier. I have excluded linear class AB amplifiers, even if I designed something it still would be too big and heavy. After some time spent with browsing I have decided to order this:


1 x 30W class D amplifier board at incredible price of 14.09 EUR (without VAT). I placed the order and my price was 17.04 EUR (VAT included) + 11.70 EUR shipment, 28.74 EUR total. Like a single restaurant dinner, here.

The amplifier is based on TPA3110 circuit, using BD modulation type. Let's talk about class modulation principles a bit, as a start.

AD (Traditional) modulation

ADmodulation_principle.png


I have borrowed 2 images from literature [1]. The first one shows traditional AD modulation type.

The traditional switching technique (AD modulation) modulates the duty cycle of a rectangular waveform, such that its average content corresponds to the input analog signal. The bridge-tied load (BTL) outputs are the inverse of each other. AD modulation has no significant common mode content in its output. The TPA312xD2 family employs AD modulation.

BD modulation

BDmodulation_principle.png


The BD modulation switching technique modulates the duty cycle of the difference of the output signals such that its average content corresponds to the input analog signal. The bridge-tied load (BTL) outputs (see Figure 6) are not the inverse of each other. BD modulation has significant common mode content in its output, which creates stronger EMI interference signals. However, as there is little energy at the output for the zero signal, this kind of modulation can work without the output LC filter, resulting in a filterless design. The module under test uses this BD type modulation.

The PWM signal for AD modulation takes only two values, e.g., plus/minus supply voltage, and hence it is also referred to as binary modulation. By contrast, the PWM signal for BD modulation takes three values, e.g., plus/minus supply voltage and ground, and so is named ternary modulation.

Below is the simulation of class D amplifier with BD modulation.

BDmodulation_plots.png


2. Wondom AA-AB31471 amplifier board

The amplifier has arrived in this neat cardboard box:

Wondom_box.JPG TPA_inbox.JPG

Specifications are as follows, per manufacturer's datasheet [3]

Wondom_specs.png


We only need a 10V – 19V dc single polarity power supply, input RCA cable and a speaker to start to listen to the music. I am using a PC notebook SMPS power supply as shown in the next image:

SMPS_19Vdc_3A.jpg


The amplifier uses no heatsink, only copper plate of the PCB board. It is the BD modulation and high IC efficiency that allows this approach. The amplifier board is very small, 76 x 50 mm only.

3. Oscilloscope measurements

Measuring this amplifier is a kind of challenge, as it has considerable common mode voltage with very fast edges at its PBTL output. I use an isolation transformer with only 120pF of stray capacitance to supply my oscilloscope, so it is floating with the CMV. Below is the measurement setup. We can see the amplifier, 4.7ohm/200W load resistor, 2RC lowpass filter and the oscilloscope (supplied from the IT transformer). On the scope screen we can see 32Vpp 1kHz sine voltage output from the amp, which makes 27W/4.7ohm.

Oscillo_setup.JPG


Another screenshot shows PBTL unfiltered output, when signal frequency is 20kHz. Please note the 3-state shape of the output signal.

BDmod_scope.JPG



4. Audio measurements, distortion measurements

Again, measuring this filterless class D amplifier with BD modulation is a kind of challenge, because of its full scale rectangular impulses that are always present at the output, both differential and common mode voltages. I have had to use my Focusrite 2i2 + my special measuring LC filter, it was more EMI resistant than my usual D10s + Cosmos combo. Below is the setup

THD_setup.JPG


Frequency response

TPA3110 frequency response into 4.7ohm at 5W.png


Frequency response is quite flat and does not depend on load impedance (because it is a filterless design). It has +0.5dB deviation at 16kHz and -0.8dB at 20Hz. Above 25kHz, the roll-off seen is because of the measuring LC filter.

THD+N at 5W/4.7ohm

TPA3110_5W_4R7.png


It is nothing to call home about, SINAD at 5W/1kHz is 60dB. It is related to intrinsic distortion of the BD modulation type, which is higher than in case of AD modulation [2].

THD and THD+N vs. Power at 1kHz/4.7ohm

TPA3110 THD and THD+N vs. power into 4.7ohm load at 1kHZ.png


THD vs. Frequency at 25W/4.7ohm

TPA3110 THD vs. fequency into 4.7ohm load at 25W.png


Multitone distortion

TPA3110_5W_multi_4R7.png

Sound

I made some listening of various kinds of music through my JBL Control 1 Pro speaker and I have no complaints.

Conclusion

Wondom AA-AB31471 is an incredibly small, 30W/4ohm class D amplifier with filterless output, sold at very low price. It is not a high-end amplifier, however good enough for a desktop use with smaller speaker. It is capable to yield the advertised 30W power. During testing, the little amplifier never shut itself down and the chip temperature remained moderate.

Literature

[1] TI Application Report SLOA119B–April 2006–Revised February 2015, Class-D LC Filter Design

[2] Stephen M. Cox, Jun Yu, Wang Ling Goh, and Meng Tong Tan: Intrinsic Distortion of a Fully Differential BD-Modulated Class-D Amplifier with Analog Feedback. IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS

[3] Wondom AA-AB31471 - Datasheet.pdf

[4] https://www.researchgate.net/public...ulated_Class-D_Amplifier_With_Analog_Feedback
 
Last edited:

solderdude

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If it is filterless how is the 320kHz filtered in the end ? .
I can see that there may not be much switching going on when there is no signal.
No crossover of any kind or asymmetry (H2) going on at lower levels ?

Have you measured the spectrum upwards to say 1MHz (or higher).
Is there no chance of RF transmission with longer wires acting as antennae ?

In most cases where filterless switching is used the output wires are not allowed to exceed a certain length (often 10-30 cm or so).
 
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pma

pma

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If it is filterless how is the 320kHz filtered in the end ? .
Speaker inductance makes the filtering of speaker current.

I can see that there may not be much switching going on when there is no signal.
This is a BD 3-state modulation and with zero input there is almost no output signal, only very thin impulses, with average level of about 10mV.

No crossover of any kind or asymmetry (H2) going on at lower levels ?
No. At higher levels, H5 is dominating. You might like to read this:


Have you measured the spectrum upwards to say 1MHz (or higher).
It is cleaner than that of AD modulation, however with high Fs amplitude.

Is there no chance of RF transmission with longer wires acting as antennae ?
I have only tried it with a small SONY AM transistor radio, it does not seem to catch and demodulate the signal.
 

Matias

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I swear I misread "condom" in the title lol.
 
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pma

pma

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Interestingly enough, the distortion measured at acoustical side (with microphone from the JBL Control 1 Pro speaker) is low and is not any worse than with the linear amplifier. Another myth seems to be debunked :).

JBL Control 1 Pro TPA3110 1kHz 3.3Vrms.png
 

solderdude

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So ... only really suited for active speakers with short wires and or screened enclosures ?
18V on an antenna in the several MHz range can generate quite some field strength with a few meter of cable I reckon
It might help if the signal on both wires is symmetrical though and/or twisted cable is used.
This will likely not pass EMC testing ?
Surprised it cannot be picked up my AM radio.
 

Jeromeof

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Nice review - Wondom seem to be an ambitious new company - I bought the BRU-5 a few months ago:


Mostly it's pretty good - love the inbuilt 20xPEQ DSP configuration
 
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pma

pma

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So ... only really suited for active speakers with short wires and or screened enclosures ?
18V on an antenna in the several MHz range can generate quite some field strength with a few meter of cable I reckon
It might help if the signal on both wires is symmetrical though and/or twisted cable is used.
This will likely not pass EMC testing ?
Surprised it cannot be picked up my AM radio.

TI TPA3110 datasheet says this:

1691314726936.png


1691314788449.png



 
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pma

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I am doing more listening, now with my CNO-T25


and I have to say that it sounds same as any other good amplifier. It is incredible, taking into account the price and ultra small footprint 3” x 2”.
 

solderdude

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Aaah so some decent sized beats and small value cap to lower the 10MHz + band may be all that is needed to pass EMC testing when you need a really small sized amp.
 

frabor

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Great review, tks.

PMA, I saw that you using the UTD2025C . Do you recommended it today for analog work or if you were getting the unit today, would you choose another model?
 
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pma

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Great review, tks.

PMA, I saw that you using the UTD2025C . Do you recommended it today for analog work or if you were getting the unit today, would you choose another model?
Hi, I bought UTD2025C 12 years ago and it still runs without any issue. It is good enough when I need to measure amplifier step response and stability. However, today I would buy a newer oscilloscope, like Rigol etc.
 
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