This is really a long and memorable vacation ...
Mainly for well-known reasons ... I haven't released any measurements for a long time
Logistics was completely stopped ... R & D and manufacturing were also completely halted ...
God ... this is really a boring holiday ... I have been bored to spend the whole week to adjust one of the equipment I made before (for example, to make the THD+N vs Freq curve of the left and right channels basically the same, and the harmonic components are also consistent)
For the coronavirus, I was almost 600km away from the center of the outbreak. In terms of government's epidemic prevention measures, in fact, I could hardly find anything to worry about-----Good social order and basically good supply in the supermarket-one thing to complain about is that Coca-Cola in the supermarket near my house is always in short supply
well, let's get back to business……
Before the Spring Festival, I knew that Topping was developing a new headphone amplifier and made an appointment with them for measurement.
The thing was finally mailed to me two days ago (thankfully they started working).
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This is a compact unit. The workmanship is not exquisite, but there is nothing to complain about. Topping's family-style design (the size is the same as D90)
What I like very much is that the Power supply is built-in, making the whole system look simpler (it is always uncomfortable to hang a power adapter outside)
It's a headphone amplifier and preamp integrated product, this design may be very suitable for desktop users? (A small combination of active speakers and headphones)
First I will measure the headphone amplifier part:
I start with a medium gain, 4V input
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Wow! ... I was a bit shocked ...
I feel that it is not the device under test that restricts the measurement results, but APX555.
In the case of 5V input / UNBAL output, I got 123 SINAD!
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This is crazy!


For comparison, this is the AP Loopback:
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How does THD + N change with frequency?
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Attention! The bottom of this chart is not 0.0001% as usual, but 0.00001%!
Alright, let's get on the load! See the results under load!
SNR:
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THD+N vs Level
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I was having difficulty measuring the maximum output ... because the protection circuit is very sensitive, it cuts off all outputs at the moment of overload ...
I got a maximum output of 6.5W with 33R (BAL Out) in dashboard mode!
In this case, SINAD is still as high as 110db.
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The results of the previous test were so crazy that it made me feel boring to release things like frequency response (such a device is almost impossible to have problems in this area)
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Of course ... Since the volume is adjusted with a potentiometer, there must be some problems with channel balance.But it is said that the final version of the gain will be adjusted to -9 0 9 (the one I got is 0 6 12) should be able to adapt to various headphones.
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End of headphone amplifier measurement ... output impedance(0.37R):
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Preamp section: As good as the headphone amplifier section!