qtx QA400 Power Amplifier 400W

Fully agree with with what others have written about the fan noise. It is extreme - there's no way the amp could be used in a studio - or even home music area in my opinion as the fan noise is too loud. I knew this when I purchased it - I had read the reviews. Managed to get the amp for £70 delivered from Amazon and thought I'd install it and assess the unit myself. After first day, I agreed with the assessment of other buyer - the fan was too noisy and distracting for every day use, so I ordered the Noctua NF-A8 ULN. Like another reviewer, I fitted it with the sound reducing resistor. It was an easy job to open the unit and remove the existing fan - it plugs into a two pin socket on the main PCB board. Two wires only - red and black. I both of these wires at their half way point so that I could keep the same two pin PCB connector. To fit the Noctura, I added the low noise resistor cable, felt where the resistor was in the sleeve and snipped the cable AFTER the resistor. You'll find 3 cables inside the sleeve - yellow, black and black cable after the resistor. From the original two pin PCB connector, solder black to black of the Noctura cable; red to the black wire after the resistor; finally, ignore (tape back) the yellow cable. I used heat shrink sleeving over the solder joints to ensure a tidy and safe installation. I ensured the unit was not connected to the power before commencing the work and wore an earthing bracelet just in case there was any residual charge in capacitors. Unsure how QTX think this unit is sellable and fit for purpose with the factory fan installed. Factoring in my low purchase price and £20 for the new silent fin, I have a great amp now that is totally silent. Real crisp sound that sounds good over most frequencies.

Delighted with the amplifier, performance is excellent, much better than the previous amplifier I was using, would highly recommend it.

It's a stereo power amplifier and does what you expect in that department. I got this version because it has XLR inputs which I wanted to interface to my mixing desk and that is worth the extra money over the non-XLR version. It sounds good to my ears. Internally it's fairly bog-standard (yes, I've already busted the warranty (if there is one) by opening it up for a poke around). There's quite a lot of room in the case and a standard linear power supply running off a 36 volt toroidal transformer. The stereo amplifier is a single PCB with 2SC5200 output transistors, mounted on a chunky fan cooled heatsink. Which brings us to the fan, which is incredibly noisy; the fan in mine is some untraceable far Eastern brand, standard PC fan style (80mm, 12V, 180 mA). So I swapped that for an Arctic F8 and solved the noise problem, but that's only an option if you're comfortable with electronics and opening up the case type of stuff. So I can't recommend the item as shipped without this caveat. It's fine of course if your amp is just going to sit in a rack in a rack room somewhere and then this wouldn't be an issue. Documentation by the way is minimal; you get a single sheet of paper with no specifications or description of the amp at all, just how to plug it in and the uselessly obvious "troubleshooting" of the "is it switched on?" variety. So I dithered over awarding 3 or 4 stars and went with 4. It's otherwise a good amp for the price. If this review appears below various models by the way, mine is the QA 400, which is 70W into 8 ohm and 200W into 4 ohm RMS.

Brilliant little amp as I use as a pre amp to push my bass pin from main amplifier

Bought for a small home studio setup. The fan is far too loud. Already sold it on.