siliconchip.com.au Australia’s electronics magazine May 2019 43
Yuanjing Left/RightChannelCrosstalk 22/12/18 13:52:0120 50 100 200 5001 k2k5k 10k 20k
Frequency ()Hz-60+20-50-40-30-02-01+0+10Relative Amplitude (dBr)+30+40+50+60
Left channel (undriven)
Right channel (driven)Fig.9: crosstalk for the Yuanjing amplifier isn’t exactly great
but it’s significantly better than the cheaper one. You’re not
likely to notice this coupling when listening to ordinary
program material with stereo speakers.
to-DIP adaptors) but the improvement
in performance was so minor as to be
insignificant. If you must change the
op amps, don’t forget to fit them in the
right orientation!
Getting one
There are many similar modules
available with a different size, layout,
components, connectors and so on.
You may want to look for one that’s
visually identical to ours, since it is
at least a known quantity. There are
many possible sources but here is one
to get you started: http://www.aliexpress.
com/item//32810347968.html
The Yuanjing module
Since we noticed so many other
similar modules were available, we de-
cided to try a second one, specifically,
one with built-in Bluetooth support.
The one we’ve chosen has no ob-
vious model number but since it has
“Yuanjing” written in copper tracks in
the corner near the Bluetooth module,
and this is presumably the manufac-
turer, that’s how we’re referring to it.
You can find this module for sale
at prices from about $US28 to $US50
on eBay and AliExpress, although the
latter has a better selection. Search for
“tpa3116 4.1” and look for a blue PCB
matching the one shown in this article.
This one appears to be the best deal
at the time of writing: http://www.aliexpress.
com/item//32799510099.html
We’re guessing that this module is
designed for motor vehicles given that
it has two pairs of essentially identical
left/right outputs – these could be used
to drive front and rear car speakers.
The four pots along the front control
overall volume, subwoofer volume and
front and rear volume independently.
Even if you don’t need the extra
channels, there are two big advan-
tages to this module. One, we didn’t
need to make any modifications to get
good performance out of it; it appears
to have the correct output filter com-
ponents from the factory. And two,
the built-in Bluetooth audio receiver
is very handy for wirelessly playing
audio from a mobile phone or tablet.
It works seamlessly. When a Blue-
tooth device is connected, it switches
a relay to divert the Bluetooth audio
to the amplifier chips. With no Blue-
tooth connected, audio comes in via a
three-way pin header. The subwoofer
signal is generated by mixing the left
and right channel signals and then
feeding it through a low-pass filter.
Like the XD172700, the subwoofer
output on this module does not ap-
pear capable of the claimed 100W. We
think that in both cases, they simply
have not wired up the IC correctly for
BTL operation. It’s merely using one
of the two available channels and so
is only capable of driven 4-8Ω loads to
the same power levels as the left and
right channels.But still, overall, the performance
isn’t bad, especially considering the
price and the convenience of running
off a single, relatively low voltage DC
supply rail!
Figs.7-9 show how the performance
of the Yuanjing module compares. It’s
certainly usable as-is and is compa-
rable to, or better than the XD172700
module in most areas.
Just one point to note: while this
module comes with the appropriate
pot nuts and washers (as seen in the
photo) it doesn’t include the stand-offs
nor the cute knobs which the other
one has. Oh well – can’t win ‘em all!Conclusion
These fully built and ready-to-go
modules are very flexible and would
have many useful applications such
as in cars, TV soundbars, computer
sound systems, amplifiers for smart-
phones etc. They should be very reli-
able due to their comprehensive pro-
tection against short-circuits and im-
portantly, against overheating.
The fact that they only require a
single DC supply and can run from
5V to nearly 30V makes them even
more flexible. You can even get a few
watts of audio output using a small
USB charger!
The distortion, frequency response
and crosstalk could all be improved
but for the price, we didn’t expect su-
per hifi performance.
These modules can easily be mount-
ed inside a cheap Jiffy box or metal
amplifier chassis. It’s so straightfor-
ward, we aren’t even bothering to give
any instructions. Just mount them in
the chassis, wire them up and away
you go.As noted in the article, the inductors on the 172700 unit had
way too high a value to give a good frequency response. Not
wanting to spend any money on new inductors (they would
cost more than we paid for the whole module!) we tried
partially unwinding some of them. That worked, but it was a
lot of work. So for the remainder, we shorted out 15 turns by
soldering thin wires in place (after scraping off the enamel
insulation from the wire), as seen here. This dropped their
inductance down into roughly the right value.SC