Velleman K4010

[Filterlab]

Originally Posted by Sensimilia

My apologies for the cost, time and effort my replies could well be costing you.

I have plenty of reserves for all three.

[leo]

Never been a big fan of mosfets but it would make a decent first time diy project for the price, the price for the components alone would cost must more than what the current bid is

You could build it and probably sell it on for not no loss if you didn't like it, be a good bit of experience for you too

[Filterlab]

My thinking exactly mate, I'm not a complete novice but I'm nowhere near the same level as you! Would be fun to learn but I won't test it with my £2k speakers just in case I've bodged something.

[leo]

Well no better way to improve experience than getting the hands dirty
Could also make an interesting thread, if you struggle with anything I'm sure theres enough on here to give help/advice if needed

What I tend to do with amps is measure for DC offsets, set the bias and then soak test them on a pair of high powered 8ohm loading resistors, plug in the sig gen and have a look at the outputs on a scope etc.
Main thing to do though is check the voltages, DC offset and correct setting of the bias which can easily be done with a multimeter

[leo]

I'm trying to find the schematic for this amp, seems it has speaker protection on the output too http://www.esr.co.uk/velleman/products/index_kit.htm

http://www.esr.co.uk/velleman/images/k4010.jpg

[Filterlab]

Indeed, and a soft start too.

[johnrtd]

Those power fets from Hitachi are marvellous. But the guys designing the Crescendo spoiled the possible result. I think they had a problem with stability and decided to filter it so the bandwidth is rather small.
In the end the design is reliable but it surely is not a High End design. You may find a better one (with the same transistors) at A-50. There is full documentation available at the download pages of that site.

[leo]

The bidding ended at £114.55 , reserve not met.
So much for it being a cheap project

[Filterlab]

Listed again though, his reserve must be almost as high as the retail price!

[Richard]

Originally Posted by leo

Never been a big fan of mosfets but it would make a decent first time diy project for the price, the price for the components alone would cost must more than what the current bid is

You could build it and probably sell it on for not no loss if you didn't like it, be a good bit of experience for you too

I produced the first non Toshiba application note mosfet output power amp, the Tresham Audio SR402 in 1980. A high powered PA / studio monitor amp, and that in my opinion are the only applications they are suitable for. For high power and endurance applications they are perfect as they self protect, as in instead of decreasing resistance between base and emitter and going into thermal runaway the way a normal bi-polar transistor does when demanded to be used outside its operating envelope, resistance across the gate of a mosfet increases to the point where the device shuts down. So it self protects. But for hi-fi applications mosfets have serious deficiencies. It is impossible to produce balanced pairs due to crystal growing properties and problems, the *on* resistance and other properties are very different between the + and - devices. This makes class B or AB designs have non linear properties that are clearly audible. Class A is a distinct possibility and for single ended class A transistor work they are about the only safe option.