HEXFET amp - please help me fix it.

[Beto]

Do you have a layout of this amp?

Ok meanman1964 below is the link for the layout of the project:

http://www.bas.plumts.com/LEGEND-StageMaster MK2-PCB.pdf

 

[meanman1964]

Thanks
Do have the silkscreen too?

 

[alex mm]

silk screen .......

here ... http://i43.tinypic.com/1zoc3ub.gif

regards alex mm

 

[Beto]

Who designed this amplifier Bora was the address of the site below where you will find more details about the amplifier.
http://www.bas.plumts.com/mojiprojekti1.html

a small correction before I sent the layout is wrong the correct and I am sending this now.

http://www.bas.plumts.com/leg-LAY.gif

http://www.bas.plumts.com/leg-stage_masterPCB.pdf

 

[meanman1964]

Re: silk screen .......

here ... http://i43.tinypic.com/1zoc3ub.gif

regards alex mm

Alex,
Thanks,what's the output power of this amp?

 

[Beto]

this layout posted by alex mm and the master-stage amplifier Legend MK2 has the power of a 500w load 8ohms.

 

[meanman1964]

Thanks,if I want to know more about this amp I'll mail you.This way we keep this tread clean for the Hexfet amp

 

[papacool]

hi guys,

here is better than hexfets of elektor, with excellent support work. these amps are very good and PCBs are available. amps are a symmetrical configurations

http://amplifredy.spaces.live.com/

 

[meanman1964]

Please don't hijack this thread it's about the Hexfet amp

 

[meanman1964]

Eddelarue,

Did you use indution free resistors or the regular white ones as emiter resistor and R31-30?

 

[EDDELARUE]

Eddelarue,

Did you use indution free resistors or the regular white ones as emiter resistor and R31-30?

Regular white with low inductance and I use metal filme as R30-R31 with higher wattage capacity.

 

[Coastben]

Any good for 4 Ohm use?

Ok So it looks like we have a winner here. Nice amp. Has anyone build one and done and specs on it?

Anyone keen to hazard a guess that it will run at 4R? Would expect 800 into 4. The devices are 150W so it should be alright????


Anyone?

 

[papacool]

Hi,


Here , some very good mosfet amplifier . You can contact the author, this is my Friend .
you can see amplifier of "Frédéric" and mine "Guy"
Sorry in French , but we can help for your choice.

For you the better is "Hexo3"

http://amplifredy.spaces.live.com/blog/cns/

 

[papacool]

I corrected this. The designer of these amps is Mr Dominique jacovopoulos. Who give permission for the blog see link

http://amplifredy.spaces.live.com/blog/cns/

 

[nigelwright7557]

I also would suggest the trimmer.

The bias has gone to a minimum value which will alos cause crossover distortion which is worst to hera at low levels.

 

[seppi0815]

Doesn't R3-4 need to be 33 Ohm and not 330 Ohm?

I did this amplifier based on the Elektor initial HEXFET version. To use the same version with IRFP240 and IRFP9240 on +/- 43V supply, one has simply to add one Miller-caps at the T8 and T9 from base to collector, 220p each, and a 22nF across R31 to get it stable.
All other mods have significant impact on the SNR performance, even the proposed 20k on T8 and T9 to ground.

 

[meanman1964]

I did this amplifier based on the Elektor initial HEXFET version. To use the same version with IRFP240 and IRFP9240 on +/- 43V supply, one has simply to add one Miller-caps at the T8 and T9 from base to collector, 220p each, and a 22nF across R31 to get it stable.
All other mods have significant impact on the SNR performance, even the proposed 20k on T8 and T9 to ground.

Did you made only the mod with the 22nF?

 

[seppi0815]

Did you made only the mod with the 22nF?

Finally, I removed the 22nF and the amp keeps still stable, again important are just these two Miller caps to move the gain of the oscillation frequency <1. Hence, the 20k resistors “damage” the design principle of this type of amp.

All other components are kept the same as proposed by Elektor in its initial Hexfet 540/9540 version. Be sure you have equal! components as described in the Elektor article.

My comments to the other modes given in the thread vs. stability:
a.) Changing the “gate stoppers” to higher values does not help a lot, just slowing down the slew-rate
b.) Changing the current feed-back on (R25,R28) has just influence on the open loop gain, but not on the gain at the oscillation frequency.
c.) Changing the bias current of the input diff-pairs from 2mA to 4mA ok, will have positive effect on the Miller caps, but not necessary.
d.) Changing the band limiting network in the input diff pairs ok, will have positive effects on the gain at the oscillation frequency, but not necessary.

 

[meanman1964]

Can you tell me exactly what you have chanced like resistors and what you've add?

 

[seppi0815]

Can you tell me exactly what you have chanced like resistors and what you've add?

See the figure below