What do you think about this Amp

bostjancek · 11th June 2005, 05:10 PM

Hello !

What do you think about this 50W/8E Amp - it's worth to build it ? Do you sugest any modification ?

mikeks · 11th June 2005, 06:11 PM

Quote:

Originally posted by bostjancek
Hello !

it's worth to build it ?

No...Both gain stages are not optimised for high gain at low distortion....

Even worse, the output stage employs a simple current limit...Which limits output current when it isn't necessarily required, and doesn't when it is needed....Bad!

bostjancek · 11th June 2005, 06:38 PM

Thanks for your oppinion !

Cheers

amplifierguru · 11th June 2005, 09:57 PM

Yes,

I would not operate a BJT amp (unless dedicated to a known load) without at least 2slope SOA VI limiter. that could be fixed with 1 more resistor,2 diodes and a couple of small c's for lagging.

Mikeks could do it in his head I'm sure?

rest of the cct is pretty ordinary but functional.

darkfenriz · 11th June 2005, 10:21 PM

I wonder what is 6.8k||0.1u for.

amplifierguru · 11th June 2005, 10:29 PM

Hi darkfenriz,

The 6K8//100n is to equalise dissipation in the diff'l pair, as the other one is cascoded and not seeing full rail voltage. Matching the dissipation helps minimise DC drift.

Greg

darkfenriz · 11th June 2005, 10:44 PM

my question was rather why not casode the second diffy transistor or use a zener?

11th June 2005, 06:38 PM	#3
bostjancek diyAudio Member Join Date: Aug 2003 Location: Koper	Thanks for your oppinion ! Cheers __________________ Some are born with more and some born with less so don't take for granted the life we've been blessed it's hard to understand thet we're only a guest and each one of us shall be put to life's test.

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11th June 2005, 09:57 PM	#4
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Yes, I would not operate a BJT amp (unless dedicated to a known load) without at least 2slope SOA VI limiter. that could be fixed with 1 more resistor,2 diodes and a couple of small c's for lagging. Mikeks could do it in his head I'm sure? rest of the cct is pretty ordinary but functional.

11th June 2005, 10:21 PM	#5
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	I wonder what is 6.8k\|\|0.1u for.

11th June 2005, 10:29 PM	#6
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Hi darkfenriz, The 6K8//100n is to equalise dissipation in the diff'l pair, as the other one is cascoded and not seeing full rail voltage. Matching the dissipation helps minimise DC drift. Greg

11th June 2005, 10:44 PM	#7
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	my question was rather why not casode the second diffy transistor or use a zener?

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