This amp is Good or Not?

[Bushulo]

I am wondering if any one has built this amp. Output power is 360 Wrms under 8 ohms or 550 Wrms under 4 ohms Any Comments and suggestions?

http://users.swing.be/edwinpaij/ampli_mosfet_360_w.htm

Bushulo

[kubeek]

see this thread: Mosfet amp - bridged?

I built a few of these, they work fine, but I had to do some minor changes in design.

[darkfenriz]

For such high powers I would add some short circuit/SOA and DC protection.

[parsecaudio]

Hello Bushulo

I viewed the schematic.

Some considerations on this.

1) the zener diodes are not a good idea to use for voltage drop or biasing like this circuit.A simple resistor is much better for noise and distortion.

2)in this configuration,the supply voltage on first and second stage must to be higher respect to the mosfet stage(4-5 volts) and stabilized

3)the circuit have no protection.For this high power a DC and SOA foldback protection are needed

4)the amount of NFB is high.Take care on oscillations and stability problems.

5)you do not use the IRF mosfet type but only the 2SK-2SJ.This devices are thermal stable when the quiescent current are across 200 mA each.200mA x 12 mosfets is a very high heat to be dissipate at no signal input

6)more important:the circuit have no value for the components.For this you should to be pay.


I think that a more correct schematic can also built.

I don't like this

Regards

[anatech]

Hi parsecaudio,
I don't like this design either.

The zeners are used to keep the transistors within their ratings, and without an AC voltage drop. Adding resistors would lower the amount of AC signal to the next stage.

I do agree with the rest of your comments.

-Chris

[parsecaudio]

Hi Chris
Sorry for my mistake.
You are right:the D1-D6 in this circuit are necessary because the Vcb max of the BC550-BC560 are lower than your respective supply voltage rail.The zener cause a DC voltage drop.
Why not use the low noise 2SC2240-2SA970?
They are 120V max and the zener are not necessarily.

Vittorio

[kubeek]

I can offer you a better schematic, I have this amp like a project from some magazine, including DC servo, current and DC protection and limitation detector. I also have the driver circuit + DC servo in Eagle on one board.

[anatech]

Hi Vittorio,
It is possible that the power rating may be exceeded as well depending on the tail current.

Why not use the low noise 2SC2240-2SA970?

Maybe the same reason they didn't provide a regulated supply for the front end with a 5 volt level over the main supplies. I don't think the driver stage can properly handle the gate charge anyway.

-Chris

[parsecaudio]

I agree Chris
This is for the T9 and T10 moreover.

Many years ago I have built a similar (Dynaco) amp.
Symmetrical dual differential input stage and second cascode stage with power mosfets on output stage.
In my first power on the amp it did not work because I forgotten to mount the two passive load resistors across the collector of the two transistors(named in this circuit T9 and T10) and the output of the amp .
An oscillation it was produced.
I had to add some compensations before that you noticed me of this error......

[anatech]

Hi Vittorio,
If we all listed every one of our mistakes ..... We can look back and laugh now.

Symmetrical dual differential input stage

Don't like that input stage.

Give me J-fet differentials any day. Cleaner sound.

-Chris