Welcome to Per-Anders Sjöström's hifi pages.

QRO - The MOSFET Power Amplifier 2 x 300 Watts

In the mid 80's I started to write for the swedish hifi magazine called 'Audio-Video'. My first design was a power amp which was a hybrid of many good solutions but gathered into one product. I got the inspiration from the swedish 'Radio & Television' and their RT75 (2x75 W, 8 ohms) and the dutch magazine 'Elektor' and theirs Crescendo (2x180W, 8 ohms) (boy, what an oscillator!). The good parts were taken from these sources and the bad ones removed. I also tried to make a 'whole product' with everything that makes an amplifier complete i.e DC-protection, inrush current suppression, startup delay and VU-meter.

The Crescendo is now out in a new version and I must say that the design is very balanced. Now they have soft start, DC-servo and short circuit protection. Take a closer look at the Crescendo Millennium Edition, Allt om Elektronik no 4/2001 (the swedish edition of Elektor) or one or two issues back in Elektor.

My article in "Audio-Video" was in 50 pages! Some day I will publish the whole article in english but I don't promise when.

The amplifier at the pictures does service at home and have been doing this since 1989!

I have a similar amp at work, built 1984, which have been switched on (day and night) since 1988 and works still. The only thing which have broken down is the run-time counter.

The reason why the amp is always on is because it has no "soft start", the fuses goes every time the amp is switched on. 230V/77A in inrush current!
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The Crescendo Millennium Amplifier by "Allt om Elektronik" and "Elektor"
Per Hägglund built my amp with help from the article. He succeeded quite well as you can see.
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The QRO Amplifier built by Per Hägglund, Sweden
people have viewed this page since 2000-07-11.

Per-Anders Sjöström 2024-12-15