Simple Symetrical Amplifier

[Riff]

Originally Posted by naf

Thank you Shaan,
my first channel using 47pf and this second channel i try using 33pf
my measure so far is good:
vas bias at 14 ~ 15 mA
offset -0.2 ~ 5 mV

my second channel "the red one" is lit

hi kang nafiri...can i replace pair of output with irf540/irf9540?

[shaan]

Hi riff.

No, you can't.

540s are vertical fets and the peeceebee was designed for lateral fets only.

[masood]

dear shaan,
what is the different between vertical fet and lateral fet.thanks

[shaan]

Vertical FETs a.k.a. HEXFET etc. need almost 4V between gate and source pins to conduct and the Vgs vs Id curve is so steep that they are almost impossible to bias for Class-AB without Vbe multiplers. They need large source resistors because they have extremely low on resistance, need sophisticated current clamping circuitry to limit max current! Also they show positive temperature coefficient(PTC) often at a bias of more than 10Amps! So for Class-AB the second-breakdown protection is unavailable. Ideal for SMPS and Class-D amplification. For use in Class-A the Id is usually limited with a constant current source.

Lateral FETs have simple bias requirements and they start conducting often at less than 0.2V between gate and source. Also they show PTC at much lower Id(~150mA) and has high on-resistance so can be biased using only small signal diodes or resistors and don't need source resistors for bias stability, a pair of zener diodes are enough for max current limiting. Perfect for Class-AB setup. And most of the available Lateral Power FETs are designed for use in audio as their datasheets suggest. Their on-resistance increase as they heat up, automatically lowering the bias and preventing thermal runaway.

This is as much as I know.

Edit: Both are blazing fast devices so both must be used with some kind of oscillation protection, usually a gate stopper resistor ranging from a few ohms to 1K or so.

[Lazy Cat]

Thank you Shaan for a proffesional guidance and explantions to dear DIY friends. Keep up the good work, will help if needed but really short in time lately.

[shaan]

[Salas]

Easy way to know a Mosfet is lateral is when pin order is g s d. Verticals are g d s.

Shaan a friend has made your version P2P. Just without the input cascode base trimmers, DC input, still steady he says. He used an IR led and small trimmer instead of your 2 biasing diodes between drivers in the end, so to can match the channels output bias and take it to 200mA. 25mA through drivers and 5mA through input BJTs he tells me over the phone. He is not as happy yet as with the one we had battled with early in thread for some aspects of sound, although much easier to be DC stable over the bridge. He will add our JFET CCS from the older amp idea for first stage to compare. When I will meet him and examine I will tell you more.

[JOHN BALI]

Originally Posted by shaan

Hi John. I think the following place has what you want!

Bigun's TGM5 - The All BJT SSA

Have fun!


shaan

edit:- None of the configs is best. The one that suits your needs is the one for you...

Ok, thanks Shaan
I've been there a while ago, I must be forget that all bjt SSA is in another thread
For the Mosfet I have four pairs of
K811 & J142 (TO 220)
So if they are hexfets we can not use it right?
I don't check it yet what it is type actually.
I have info about the lateral, it is not cheap & not so expensive either

Regards

[Jay]

Originally Posted by Salas

He used an IR led and small trimmer instead of your 2 biasing diodes between drivers in the end, so to can match the channels output bias and take it to 200mA. 25mA through drivers and 5mA through input BJTs he tells me over the phone. He is not as happy yet as with the one we had battled with early in thread for some aspects of sound,

The bias stability I think is the characteristics of Shaan's SSA circuit. But for sound quality I'm afraid the 2 biasing zeners are also the determinant factor. I guess that Shaan biased the input stage more than 5mA, but at least 10mA, most probably 12mA (I don't know if Shaan has mentioned about this).

The previous Nico's circuit focuses on THD hence biases the front end with lower current. One important characteristics I found with Nico's circuit was that, with certain setting, the 2nd order distortion can be very dominant, giving a very lifelike sound.

[JOHN BALI]

Originally Posted by JOHN BALI

Ok, thanks Shaan
I've been there a while ago, I must be forget that all bjt SSA is in another thread
For the Mosfet I have four pairs of
K811 & J142 (TO 220)
So if they are hexfets we can not use it right?
I don't check it yet what it is type actually.
I have info about the lateral, it is not cheap & not so expensive either

Regards

I download the datasheet & it can't be used (hexfets)
Maybe could be used for another amp.
Ok it's time for searching the lateral one, thanks to you all
great thread & I will keep looking for any good news

Bye