Will that amp be as good as the author pretends?

[canonnica]

Hi all,
I have a mosfet amp plan that I dream of building since more than 20 years. It has been featured in a french magazine called RadioPlans in 1988 and can be found on the Web here: >> HEXO-III <<

I wonder if it's worth building that amp or if a newer design would be better. I suspect some parts may be hard to find as the articles is quite old now.
Can someone have a look at the plan and comment its design and express his feelings? Maybe someone already built it on this forus. I did a search with no luck.
I plan to connect it to some speakers with foam mounted suspension that are not really self-dampened (think of a Cerwin-Vega type of woofer), so the amp should exerce good control on them. By looking at the plan, I see that there are resistors in-line with the output transistors, does that means that the damping factor of that amp is going to be low?
Should I care about the voltage and amperage of the output, and weather it's biased towards one characteristic or the other?
You can be technical, I should be able to catch it up. Please see my self-introduction here: >> SELF-INTRO <<

My needs are: an hi-fi amp with about 75-100W RMS with lots of headroom for peak program, load will be 8-ohm. That Hexo-III amp seems to fit the bill. It's gonna replace the amp stage of a Luxman receiver (with pre-out). I may connect it directly to my Beresford DAC's variable output.
Any though/advice welcomed!
Thanks
Martin.

[AndrewT]

Look for a newer design.
There are many designs that use Vfets and a few that use LatFets.

Unusually hexo uses current limiting. Even more unusually it has no over-voltage protection diodes across the output.
3pair irf630/9630 as an output stage is very unusual.

[Conrad Hoffman]

It is a bit strange but would probably be OK. It's just that there's so much more information available today about the best ways to build power amplifiers. Lots of circuits on this site, plus the excellent books by Doug Self and Bob Cordell. You just wouldn't do things today like they did 20 years ago, any more than you'd build a copy of the old Dynaco solid state amps with '3055s and inductors wrapped around the filter caps. There really has been progress and lots of it.

[frederic75]

Hi,

"3pair irf630/9630 as an output stage is very unusual." AndrewT


In 1987/1988, power mosfet were expensive in France.
3 pairs of IRF633/9633 INTERNATIONAL RECTIFIER were a very good quality/price and very reliable for a 100W power amplifier.
Many french auditorium were equipped with Hexo (Hexo 2, Hexo 3 and 4) in 90's, amplifiers designed by D JACOVOPOULOS.

Sorry but in french :
Hexo 4 test, Revue du Son (Jean HIRAGA)
Hexo 3 and 4 used same design.

[Bonsai]

Take Andrew's advice on this: build a newer circuit. I would suggest you look at a Bob Cordell design if you are looking for a FET output stage

[destroyer X]

We can forecast something, but the real thing can be different from our forecast... wanna really know?... sorry... have to build and try by yourself.

Maybe yes, maybe know, only real world testings can say.... numbers are not a good indication, also electrical precision in the design also does not help too much... sometimes mistakes sounds even better than correct designs... this is what 51 years building made me learn... what i have learned?... as i said.

- "We never know"

regards,

Carlos

[pinkmouse]

Hi Martin. Depends on what you want to achieve. If you just want to build one amp that will last you for a good few years, then I would agree with the other posters here, a newer amp might well suit you better. However, if you're planning on building lots of amps, then by all means build that design if you can get the bits. You will likely be able to use the expensive bits, (psu, case, heatsinks), for other projects if this one fails to deliver. Old designs can sound great, my KSA50 KrellKlone is still a personal reference, but others can be awful.