Auna AV2-CD508 HiFi Amplifier: start-up power supply repair

The Auna AV2-CD508 is a quite nice and affordable amplifier, the case is pretty solid, aluminum front, steel case, and the controls are all easy to operate.

It’s a “600 W” peak amplifier, but won’t take more than 80 Watts, so it is more likely a 2x 40 W amplifier – still, 40 Watts are a lot of sound power.

Unfortunately, this set reached my workshop for repair, symptom: it doesn’t switch on, no signs of any activity. After some measurements, the fault is found it the auxiliary 5 V power supply, this is always on, to power-up the main power supply and the rest of the circuit. The auxiliary supply is controlled by a SF5922S switchmode controller, SO-8. Unfortunately, this part is only available in China, and doesn’t seem to last anyway, so I removed the power supply control, and added some wires to an external supply.

… the external supply, a 5 V power supply. Also used it to measure the current. Turns out, the auxiliary supply only needs to provide some 100 mA of current, not a lot.

With the lab supply connected, and the Auna plugged in, it powers up OK and all working!!

That’s the amplifier board, solder side. The auxiliary pwr supply controller marked in red.

With such a device, better not lose too much time, and I decided to add a completely new 5 V supply, from a leftover 5 V power adaptor.

These are the main amplifiers – CD1875 aka LM1875. These are not bad, and can reach -60 to -70 dB distortion, and are generally known as reliable parts.

Some distortions measurement, at two power levels…

… not too bad!

Gain, it’s not quite flat, but OK for the purpose.

Finally, with the new power supply, the Auna has a second life, most likely, even longer than its first.

2 thoughts on “Auna AV2-CD508 HiFi Amplifier: start-up power supply repair”

  1. What? You replaced the whole standby supply with a cellphone charger? OMG, I wouldn’t do that. It may work, but it’s not very serious. I have received another amp like this, same symptom. Did you check [R98] in primary side? Open. Should be 10MΩ. This is plain bad and cheap chinese design, using a so high resistor to reduce mains voltage. This is the solution, at least in my case. No bad SF5922SSG. I bet others will fail or have failed the same way.

    You say CD1875CZ = LM1875 by National Semiconductor / Texas Instruments? These are cheap chinese clones made by Wuxi China Resources. These guys do cheap imitations of well known ICs designed by serious USA or japanese makers. Other examples: CD6282CS = KIA6282, CD2030ACZ = TDA2030A, CD1691CB = CXA1691BM, and so on. They don’t invent anything new, just copy-paste.

    All in all, this amp is plain chinese CRAP, and nobody says it. When have you seen a HiFi amp consisting of 4 cheap amp ICs? Even good Sanyo STK ICs weren’t very respectable in the 80’s and 90’s. It’s OK for some computer speakers, but not for a serious amp. I know this amp costs less than $100, but that doesn’t mean that it’s good. They still sell it as «600W», LOL. «brushed steel front», while it’s just aluminium.

    1. You are right, these are rather cheap amplifiers and the low end, but there seems to be a market. The parts are only functional equivalent, the are not from Texas Instruments but Chinese copy, but distortion and power seems fine as per test. The power supply it is not a phone charger but a regular switchmode supply of intermediate quality. Sure you could fix the original supply but it will cost more time and needs the special parts that may fail again, so it seemed better to put in a more reliable solution than to fix the mediocre original design.

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