Andrea Ciuffoli Mosfet Amp

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
 
Try http://www.geocities.com/researchtriangle/8231/doc/index.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
 
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
 
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?"
 
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
 
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
 
Elektor Kilowatter

Hi Wuffwuff,

I've built both the original Crescendo and the Kilowatter. I think the Crescendo sounds better. The Kilowatter has very good drive giving my Kefs 105s a good run for what they're worth but the sound especially vocals is not very open although bass is a killer. Could be due to capacitance from 4 pairs of parallel Mosfets. The original Crescendo is very reliable. It's still going strong after more than 10 years of service and measures quite well against middle level commercial units. Excellent for AV!
Anybody tried the recent updated Crescendo or the Titan Amp from Elektor?

ckt
 
Hello CKT,

I´ve also build lots of crescendos with 2,4 or 6 mosfets and various voltages for friends. The oldest one is about 15years old and still seems to work.
The one I use myself has undergone quite a few changes over the years. It uses 6 fets with MJE340/350 as drivers (a big improvement over the BF ones), DC coupling throughout with a servo, BC550/560 instead of 546/556, a seperate power supply for the input/drivers with LT317/337 (42 volts), main power supply with 500VA transformer (30 volts) and 2 x 50 x 1000microFarad per side. It´s biased at about 1A. At the moment it drives a pair of Thiel CS6.
For a design thats about 25 years old it´s still very nice to listen to and compares very well with commercial units in the higher price sector (€5000-10000). A friend of mine has a hifi shop and I do a lot of "testing" for him so I can hear a lot of new amps. Some are good, most are not and this isn´t even directly related to the price.

Never heard the recently updated Crescendo but there are a few things I tried in my amp (the drivers, higher bias in the input/driver stage). I don´t really like the new power mosfets they use (positive temp coefficient) and a bit more power would also be welcome.

At the moment I´m building an Aleph5 I plan to use for a small system but of course I will try it with the Thiels.

william
 
Hi William,
Thanks for all the info, I however do not quite understand your comment about separating the supply. I have previously built an amp where they had a zener diode/resistor arrangement over the supply rails between the drivers and output, and this effectively kept the supply for the drivers and input stable but at a lower voltage than the output.

"You can use a pair of LT317/337 set at about 3-4 volts above the output section voltage. "

Can you please explain the above comment in a bit more detail as this is new to me. (Like I said I am not a pro):eek:

DieterD
 
Hello Dieter,

I use a completely separated supply to power the input/driver stage. This has three advantages:

1. you can leave the input/driver stage on all of the time and shorten the warmup time considerably.
2. you can use high quality regulators/caps etc. and have absolutely no influence from the output stage
3. You can go for a 3-5 volts higher supply voltage than the output stage to compensate for the voltage drop from gate to source

william
 
350 Watt Mosfet

Hi William,
Thanks for the reply, just thought I would let you know the amp ran first time at +/- 35 volts (test bench power supply) last night, only one set of mosfets but it sounded ok. ( I love it when something works first time)

I am on leave for the next two weeks and will spend some time bringing it up to full power, still need to sortout a decent power supply.

I will let you know what happened.

Happy Christmas & a prosperous new year to all

DieterD
 
DieterD,
Congratulations. U have got the amp working. The supply voltage was +/- 35V with single mosfet output pair. Please tell me have u made any changes to the circuit or not? Or otherwise give us ur total story for new like me to follow & to be successful. Hoping of ur consideration for other DIY members.
Mahendra palesha
 
Hi palesha,
Esentially I built the amp as described in the article, except I changed the drivers to BD 139 & 140's, as suggested by William. I have now added the extra output trannies and the next step is to build the power supply.
I have a lot of 25 volt (ac) tiroidal transformers that I got for nothing and will use 4 in series to get to about +- 60 volts, and then see how the amp works.
Once I have done all this I will let you know how it all worked. I have Emailed you a copy of the complete article.

DieterD