Hybrid Single End Power Amp - ECC99 Tube+IRF540 MOSFET >10 Watt

[lineup]

Here is the schematic.

The bias of ECC99 is like 21mA.
The bias of MOSFET is 2A.

The output at 1 Watt is fairly low THD. Like leass than 0.02%.
Also at 10 Watt is the THD less than 0.10%.

Welcome with critic and improvements 🙂

 

[jan.didden]

Nice!. 2A in class-A - that'll get warm!
But be careful with that LM334 - it's just at the edge of max voltage.

Jan

 

[ra7]

Nice and simple!

Presumably, R5 or R6 is a pot and you adjust to put U2’s source at 20V, right?

 

[jan.didden]

Its relatively simple to calculate those two R's for mid-voltage - @lineup showed that.
A pot would degrade the reliability with no advantage.

Jan

 

[indra1]

Better safe than sorry, use IRFP140 instead of IRF540 same chip with TO247 package.

 

[andyjevans]

I know very little about solid state amps except for looking at the Pass designs and the MoFo.

Those who know a lot more about these circuits might like to make a comparison?

 

[lineup]

Nice!. 2A in class-A - that'll get warm!
But be careful with that LM334 - it's just at the edge of max voltage.

Jan

I know. LM334 max 40V According to PDF.
But there is a drop like 4-5 Volt with the CS MOSFET.

 

[indra1]

might like to make a comparison?

Personally I prefer Sue Parker's topology.

 

[lineup]

Regarding R5 and R6.
It turns out that the lowest distortion at 1 Watt into 8 Ohm is when R5 and R6 are equal.

Here is Revision 1.
There are a few changes.

 

[lineup]

Nice!. 2A in class-A - that'll get warm!

Jan

I did not think of that.
In SPICE there is no heat or heatsink 😀
You are of course right.

IRF540 is a TO-220.
It is specified 150 or 120 Watt dissipation. What number varies form PDF to PDF.
At 175 degrees max.

 

[lineup]

Better safe than sorry, use IRFP140 instead of IRF540 same chip with TO247 package.

IRFP140 is a good alternative.
The distortion stays almost the same.
And will take a lot of heat with the IRFP140.

How about the IRFP240?
Would that be suitable?

 

[Marcus Halberstram]

Personally I prefer Sue Parker's topology.

Seems like I've seen that a few other places ...

 

[indra1]

How about the IRFP240?
Would that be suitable?

Sure. But the schematic is not yet complete, still needs provisions to protect mosfet gates and speakers against turn-on and turn-off transient/thump.

 

[ra7]

Its relatively simple to calculate those two R's for mid-voltage - @lineup showed that.
A pot would degrade the reliability with no advantage.

Jan

There is part variability in the MOSFETs. A pot is necessary at least to start and then can replace with resistors.

 

[lineup]

I have to add zeners at the Gate of MOSFET.

 

[andyjevans]

Would this work with Exicon ECW20N20? Laterals seem the current favourites?

 

[lineup]

Would this work with Exicon ECW20N20? Laterals seem the current favourites?

It would be perfectly alright.
That model is a rugged device. Takes 250 Watt!!! That is much.
I have some SPICE models of EXICON transistors. But not ECW20N20.

 

[lineup]

Revision 2

I added protection Zeners for the MOSFETs.

I added a Power Up Delay. The delay is set on 12 seconds.
I am not sure how many seconds the delay should be?
Will 12 seconds be alright?

 

[vinylkid58]

Personally I prefer Sue Parker's topology.

Could we have a link please.

jeff

 

[Marcus Halberstram]

Sue Parker's audio site is here.