Construction a 20W Jean Hiraga class A amplifier advice needed

[patrick101]

Hi, all,

I constructed several Class AB amps before but never construct a real Class A amp, it is because Class A amp needed big heatsinks and high volume of power supply caps stop me.

Now I start planning to construct a 20W Class A amp, I want to use a pair of TO-3 power transistor 15023/15024(I have stock) per channel.

The reference Amp are Musical Fidelity A1 and Jean Hiraga 20W, I prefer Jean Hiraga amp more.

The Class-A Amplifier Site - Hiraga 20W Class-A

I want the amp with temp stable and balance in performance. For the Jean Hiraga schematic, I changed the 9v zener diodes to a transistor current source, I think it is more easy to matching 2 channels difference than using zener diodes, I changed the thermal resistor control to a Vbe multiplier and install it near the power transistor to compensate the temp.

I don't know how to use those simulation software, please help me and advice if the above change is suitable or having good ideas to construct the amp.

Thanks,
Patrick

 

[U130421]

The NTC compensates the driver's Vbe termal variations , not the outputs. The voltage multiplier over compensates and shunts very low impedance .

 

[patrick101]

The NTC compensates the driver's Vbe termal variations , not the outputs. The voltage multiplier over compensates and shunts very low impedance .

Thanks, understood.

Is it means that the Class A amp power transistors temperature no need compensate as a Class AB amp?

 

[knutn]

The VBE multipliers is a very bad idea. You are reducing the open loop gain heavily without really gaining something.

 

[tvi]

Thats the unmodified version
below is the more usual build

quite different

 

[patrick101]

The VBE multipliers is a very bad idea. You are reducing the open loop gain heavily without really gaining something.

Ok, I got your meaning. I will remove the VBE multiplier and change back to resistors.

I saw there is a thermal resistor in the schematic and I saw one Class A amp project which attach a thermal resistor to the output MOSFET, I though this a kind of thermo control, so that raise this idea of using a Class AB amp VBE multiplier here.

Thanks,
Patrick

 

[patrick101]

Thats the unmodified version
below is the more usual build
quite different

I use a current source to replace the zener diode is according to another thread "Jean Hiraga Super Class A 30w Build" which also using a current source. There is a schematic inside this ebay kit.

Hiraga super 30W class A w/ current source + kubota reg partial assembled kit ! | eBay

The rest of the circuit will be constructed very close to the original version.

Thanks,
Patrick

 

[amplidude]

So Patrick did you get it build?
I'm very curious about your impressions, im awaiting hiraga kubota, and theres next to nothing about it.