Mosfet AMP 200W very simple

[leojavier11]

I have this circuit that I found in a forum in Spanish and already many users have made it with very good results.
i wanted to know what modifications there would be necessary to do in order that it could work to +/-65v???

Thanks!!!

 

[JonSnell Electronic]

The output FETS will stand 200v so no need to replace them. I would change the BD135 for MJE340 and the pair of 2N2904s for a matched pair of KSA992. Replace the four 220u with two 100u 160v. Place a 22R 2W resistor in parallel with the output choke to stop resonance.

 

[leojavier11]

Thank you Jon!...i will tray to do!

 

[diyralf]

Very very simple amp. I wouldn't build it. Moreover without protection circuit very dangerous.

 

[meanman1964]

Most amplifiers here at Diyaudio have no protection circuit

 

[thimios]

Very very simple amp. I wouldn't build it. Moreover without protection circuit very dangerous.

Why not?

 

[leojavier11]

i tried to simulate in Multisim but i have problems...can someone check my simulation and detect errors please?

 

[leojavier11]

and this is other version with some changes that works good in the simulation but when the input is about 1.1 or 1.2 vP the wave in the oscilloscope is bad

 

[jaycee]

Vgs multiplier (T4) not on the heatsink, no miller compensation, driving 2 pairs of vertical mosfets straight off the vas... no thanks!

 

[minek123]

Thank you Jon!...i will tray to do!

Zobel circuit looks funny, 10 Ohm resistor with 68pF cap?
The capacitor should be more like 100nF...

Also, I would put a cap (1uF ?) in the input, so it's not DC coupled.

820 k resistor in sequence with BIAS trimpot also looks weird.
820 k ??? More like 8k or 800 Ohm...

Overall I wouldn't trust this design. Too many errors/mistakes already...

 

[xrk971]

Why not?

We live on the edge

I think mostly it's because we build amps, not complete amp systems. We move on from one amp to next. If you settle on one you want to use in a permanent (a real case) setup then protection is good. Most 50w amp don't need protection as speakers can take full rail fault for a moment if rated appropriately.

 

[diyralf]

The part values are random. Horror!

 

[Svitjod]

You will have to change the 1.2k and 2.7k resistors that sets the various currents. The values must be slightly higher.
Exactly how much will be a good practice to figure out.

 

[Kay Pirinha]

Why not?

Good question!

Best regards!

 

[bwaslo]

Since you'll be approximately doubling the power out, you'll also probably need to go from 2 sets of output devices to 4 sets.

BTW, did anyone notice that the 2N2904 are already being operated outside of their voltage limits in the original schematic?