Ltp ...protection ????

sakis · 6th March 2010, 06:36 PM

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 · 6th March 2010, 06:50 PM

maybe it prevents hard clipping.

AKSA · 6th March 2010, 08:12 PM

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

Nico Ras · 7th March 2010, 08:56 AM

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 · 7th March 2010, 09:39 AM

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

sakis · 7th March 2010, 01:21 PM

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

6th March 2010, 06:36 PM	#1
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	Ltp ...protection ???? 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 __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

6th March 2010, 06:50 PM	#2
Bigun diyAudio Member Join Date: Jan 2009 Location: K-W Ontario Blog Entries: 2	maybe it prevents hard clipping. __________________ "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

6th March 2010, 08:12 PM	#3
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	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 __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

7th March 2010, 09:39 AM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	you can also add Zeners to +ve and -ve references to avoid overloading the input transistors. __________________ regards Andrew T.

7th March 2010, 01:21 PM	#6
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	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 __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr


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7th March 2010, 08:56 AM	#4
Nico Ras diyAudio Member Join Date: Nov 2005 Location: Amanzimtoti - East Coast of South Africa	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.

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