does this mosfet schematic looks promising?

[abeteer]

I found this scanned schematic in the net, I got interested and would like to construct it (for the reason of low power and parts availability), i was hoping my 200w 8ohm speakers won't blow
[IMG]file:///C:/DOCUME%7E1/Abet/LOCALS%7E1/Temp/moz-screenshot-1.png[/IMG]
Seriously does this schematic looks promising?
[IMG]file:///C:/DOCUME%7E1/Abet/LOCALS%7E1/Temp/moz-screenshot.png[/IMG]All of your comments, recommendations is very much appreciated

[wahab]

Crescendo Millennium offset problem

This will help in case of problem..
The schematic is the same , apart from the output devices since
this is an evolution of the one you are interested in..
Of course, both are from elektor mag.

[nigelwright7557]

The 8M2 ressitor in the relay circuit might be a problem in a high humidity area.

At Plessey Electronics they werent allowed to use a resistor bigger tham 1 meg ohm for this reason.

[abeteer]

thanks for the tips! that was duly noted

[dennismati]

Isn't this is the Elektor (Giesberts) Hexfet amp published in the december 1993 edition? There's also another higher powered version with IGBT's published in sept 1995. I have built the IGBT version 12 yrs ago, and experienced some stability problems (oscillations).

You might find a lot of information in this thread :

http://www.diyaudio.com/forums/solid-state/112426-hexfet-amp-please-help-me-fix.html

[AndrewT]

Hi,
this uses a FET CFP output stage.
It could have oscillation problems.

The BD139/140 used for VAS are attrocious for VAS duty. They are good for drivers in the next stage.
However, I notice only a little stability compensation added elsewhere.
The use of the high Cob VAS transistors may be a way of incorporating Cdom without fitting/buying extra components.

[nikwal]

Good topologies, but I would look elsewhere as it's not an unusual one.. also, I prefer sourcefollower output with irfp series.

[abeteer]

That scared me dennismati thank you for bringing that up...........anyway
I got another one from the net (attached) both had the same circuitry and the same power requirements and was designed by swagatam innovasion from brighthub site. I overlooked the first schematic it looks to me that the resistor values are of the 5 band type. They are hard to find here, but of course putting a no. of resistors in series will also do but that would be impractical for it will only take a lot of pcb space.
This one had the average resistors you can always find, but it has missing parts (i have to wait for the authors feedback yet) perhaps it was overlooked when posted in the site. Values for R18, Voltage trimmers P1& P2, Transistors T9-11 were missing from the parts listing (below).
Parts List
All resistors are ¼ watt CFR unless otherwise specified.
R1 = 1M, R2, 27 = 47K, R3, 20, 21 = 470Ω, R10, 11, 12, 13, 28, 17 = 1K, R6, 7, 8, 9 = 56Ω, R29, 30 = 330K, R14, 15 = 270Ω, R26 = 4K7, R16, 19 = 100Ω, R22, 23 = 0.25/2W, WIREWOUND R24 = 1Ω, R25 = 10Ω, C1 = 2µ2, C2 = 1 nF, C3, 4 = 10 Pf, C5 = 47 nF, C6, C7 = 100µ/50V, C8, 9 = 10,000/63v, D1, 2 = LED RED, D3, 6 = 1N4148, D4, 5 = 12V/400mW Zener, Power Supply Diodes = 6 Amp. 300V T1 = MAT 02, T2 =MAT 03, T3 = BC 560C, T4 = BC550C, T5 = BF 470, T6 = BF469, T7 = 2SK 135, T8 = 2SJ50
In this case, I was hoping you can help me out guys here and figure what was the missing values!!!
Will these values do ?– T10=2SK170 (its a FET right?), T11=BC550C, R18=1k, P2=500ohms. Also can a couple of BC550 & BC560 can replace MAT02/03 for the differential amp? Two in one transistor packaging is much harder to find.
Honestly this is my first attempt to build a mosfet having built bi-polars so far, until I got a copy of Anthony Holtons 2SK1530/2SJ201 1994 Mosfet design, I never built it, it was a huge amp with -/+70v rail & a 500VA power requirement. However, my colleague built it and made it to work. Me, so far was looking for a medium power at the least.
All feedbacks is very much welcome or you can e-mail me at cjames_lco@yahoo.com

[jaycee]

The first amp makes a good oscillator. Avoid it.
The second amp's schematic has several errors too.

Quasi's NMOS amps are good designs - Quasi's DIY Audio Site

[Mooly]

You could always build mine which uses Lateral FET'. It's all here but you would have to make your own boards. Super stable design due to the topology used.
My MOSFET amplifier designed for music.

Alex MM did a great looking PCB.