Ltp ...protection ????

[east electronics]

I HAVE SEEN one yamaha schematic that features a classic AB design with an ltp in the front but there is a couple of 1N4148 in parallel ( one reversed from the other ) from input transistor base of ltp to the "output " transitor base of ltp

does any one knows the reason ???
is there to protect from something ???

thanks ....sakis

 

[Bigun]

maybe it prevents hard clipping.

 

[AKSA]

Protect the be junctions of the LTP from reverse bias when either the output goes to rail with a fault, OR the input exceeds 5Vp.

Not often used, but seen on sound reinforcement amps where ANYTHING can happen.

Hugh

 

[U102324]

This protection is to pass international EMC criteria. From memory, susceptibility is tested at 30V/m from 10kHz to 3 GHz. DIY does not care about these issues since compliance to regulation is not enforced.

 

[AndrewT]

you can also add Zeners to +ve and -ve references to avoid overloading the input transistors.

 

[east electronics]

thanks everybody ...got the meassage

How are you Nico ???? very good to see you around
all the best for you and family

kind regards sakis