Single supply Low Power MOSFET Class A/AB amp

[Deleted member 550749]

Trying to build this Schematic, do I need Compensation? Or is it gonna work without that, or any changes u suggest

 

[lineup]

What is the supply?
15V Regulated?

 

[Deleted member 550749]

No, which one would b good regulated or non?? For this??

 

[lineup]

It has to be 15V regulated.
Because you have the input connected to the supply.
If you have unregulated, then will be hum coming from supply direct to the input.

One other solution if you have unregulated, is to have a capacitor between the two 100kOhm resistor to ground.
This will filter the supply and make it clean.

To your question.
I think you need a compensation cap. Across T5.

 

[Deleted member 550749]

Thanks 👍

 

[Elvee]

The quiescent current will be difficult to control: it critically depends on the ratio of the 4.5K to the 1+2K, the supply voltage and the MOS threshold voltages.
Something will need to be made adjustable, and some kind of temperature compensation will also be required

 

[Deleted member 550749]

Yes, I will use 2k preset for biasing current

 

[Deleted member 550749]

Is it ok?

 

[HAYK]

JLH type output can function in class A. I doubt it can in classAB. The drain resistor is more useful on the source to have the same gm as the upper. For thermal stability you need to parallel the gate resistor with NTC screwed upon the MOSFET.
Why you don't use simulator?

 

[Deleted member 550749]

Ok, wil simulate it with ur suggestion, thanks 👍

 

[HAYK]

I simulated with 140ma bias on jlh, it works.

 

[Deleted member 550749]

Oh😱 nice , thankyou ❤️ 🙏

 

[Deleted member 550749]

Hi, HAYK, 2days ago I made this jlh 69 mod , everything working fine but my problem is after few minutes of song listening output offset changes , is this just because of MOSFET behaviour or heating causes?? Or need more fine work for more stability? Or this is anykind error?

 

[HAYK]

As I told you, you need an NTC in parallel with the gate resistor R15 to keep the bias constant. The temperature drift of the MOSFET is about -3.5mv/°C. Look on Wikipedia how to calculate NTC value with series and paralleled resistors.

 

[Deleted member 550749]

Can u draw it for me or give link🙏

 

[HAYK]

NTCs have 2 parameters, resistance at 25°C and coefficient K.
https://en.wikipedia.org/wiki/Thermistor.
Use Tina simulator (free download from TI) it has models to simulate.

 

[Deleted member 550749]

Thanks, 👍

 

[HAYK]

About 2 years ago, I posted a 4 transistor, 40W, 0.0004%THD @7W1khz classA amp on EEVblog website using lm334 as temperature compensation element. The output stage, I have tested it for several months using step up transformer.
I replaced the lm334 by NTC and here is the amp that might interest you. The first 3 transistors have the same circuit as yours, the fourth is an SRPP. The outputs for low power can be replaced with cheaper IRF640/9640.

 

[Deleted member 550749]

Nice, appreciate , 👍😃 thanks for this schematic 🙏