Andrea Ciuffoli Mosfet Amp

[DieterD]

Has anyone built the 350 Watt Mosfet amp as shown in Andrea's Home Page? It,s in Italian (a copy from an electronics mag) but seems to be detailed enough to build without translation. I like the look of it, and it give a good enough to use PCB layout etc.
I would appreciate any comments, ideas etc as I have made the board and will start building as soon as funds permit.
His web page is http://www.geocities.com/researchtriangle/8231

[wuffwaff]

I´ve had a look at Andreas homepage but couldn´t find a 350W amp. Could you be a bit more precise?

william

[DieterD]

Try http://www.geocities.com/researchtri....html#DOC_AMPL

It,s in a section right at the bottom of his page under "documentation: amplifiers". Just scroll down and you will see the heading plus pages to download. His page contains a lot of advertising and it all needs to open before you get to the real meat of his page.
I found some of the scanned article pages did not download properly, and got him to mail them to me. If you want copies I can mail them to you.

DieterD

[wuffwaff]

Hello DieterD,

this amp looks like one I build many times with good results. It´s just like the old crescendo from elektor slightly modified (the original used 2 + 2 2sj50/2sk135)
I would suggest some minor changes:

swap the bf drivers for BD139/140 or better MJE340/350. This makes a big improvement in speed/attack, clarity and bass performance.

don´t use a capacitor in the feedback loop. A simple servo with an OP77 will do a lot for bass performance.

separate the power supply for the driver and output section. You can use a pair of LT317/337 set at about 3-4 volts above the output section voltage.

I ´don´t know how the mosfets used here sound but you can still buy some 2sk135/2sj50 (although named differently nowadays).

Are you sure you need all the power? With a 40-50 Volt supply you could go for a higher bias (200-250mA per fet) and BC550/560 in the differential stage wich would also improve the sound. You just have to change a few resistors to get the thing running again.

regards,

william

[DieterD]

Hi William,
Thanks for the info, I see from your reply that you have a lot more knowledge about amps etc than I have, and if I get stuck I will mail you direct (if you dont mind)
I need the power as my son plays in a band and wants to use his equipment to do live performances in halls etc. Unfortunately we dont have the money to buy factory made amps, eg Peavey or Crown, as the exchange rate here in South Africa makes importing goods very expensive, so I want to try & build a few "biggish" amps and use those. I have built a few ESP amps, bridged them and now want to try my hand at something bigger, and this one seems to be the logical next step. I assume one could bridge two of these and get a fair amount of power out of it?

Thanks again,
"sprechen sie Deutch?"

[djk]

http://meltingpot.fortunecity.com/br...plifier_p6.jpg Same amp as here http://users.swing.be/edwinpaij/ampli_mosfet.htm

[wuffwaff]

Hello DieterD,

if you want to bridge then have a look at an old elektor project called the "kilowatter". It´s almost the same design with 2 x 4 mosfets bridged. I think this would be what you need including ventilator cooling. I´ve got the original article and I believe they´ve brought out a cd with all the articles and layouts.

regards,

william

[Dirk]

For what it's worth, I heard from a designer from Elektor that they don't consider the "kilowatter" as a very good amplifier. More recently, they published the "Titan" amp which they find very good (and which is quite complicated).

Regards,

Dirk

[wuffwaff]

Hello Dirk,

I think you´re right concerning the audiophile qualities if you want to go for the very best(all those zener diodes can´t be good) but for a PA system this wouldn´t hurt.

Elektor (elektuur) designers often talk about good and bad in terms of measured performance. A few years ago they (one) told me the kilowatter was a lot better than the crescendo.....
I haven´t ever heard the kilowatter but looking at the circuit topologie it can´t sound that bad. I suggested DieterD had a look at the article cause there are a lot of nice and usefull features (balanced in/ bridging mode / fans / layout) he can also use for the 350 watter mentioned above.

william

[DieterD]

Hi William,

Is there an Elector home page where these articles are available?

DieterD