another beautiful class-b from mastertech

mastertech · 21st November 2005, 06:52 PM

any comments, critisism, suggestions, please do

cheers

AndrewT · 21st November 2005, 07:23 PM

Hi,
tell us why your decision to insert 2 input caps and keep the bases of the LTPs separate?
The feedback to the left side inverting LTP seems wrong. There is a missing DC block on the lower leg and an extra pair of caps in line with the feed.
Why do you call it ClassB? Depending on output pair Iq it could be A, AB or B
No input RF filter, no output Thiel network to reject RF and load the output at high frequency
How about a cap bypass across the Vbe multiplier
The DC block on the input could be non electrolytic with some advantage.
Output offset adjustment? LTP emitter resistors? Stability control components?
Decoupling? Separation of clean and dirty grounds?
Overall not much thought so far, or is this a leg pull?

anatech · 21st November 2005, 11:50 PM

Ditto.

mastertech · 22nd November 2005, 12:05 AM

hehe what is that mean

AndrewT i keep the two stages isolated because it gives
better dynamics, thanks for all your kind suggestions

cheers

amplifierguru · 22nd November 2005, 12:27 AM

HI Mastertech,

If you combine the input stage(s) at their bases you can have up to 90% cancellation of bias current for those bases - and with unity DC gain (your C to GND in the feedback leg), you could leave out input capacitors altogether. It my belief that no C is the best C.

This is what I have done in the S.K.A where bias current cancellation results in Ib nett of only 0.1uA. The input C (provided for on the board) is linked out for normal operation.

Cheers,
Greg

mastertech · 22nd November 2005, 12:45 AM

Hi Greg
"no C is the best C" , you could be right
i still use them , i know what you mean
good luck with the S.K.A
and thank you for taking time out of your busy schedule
to comment here

regards

Workhorse · 22nd November 2005, 03:39 AM

Hi Class-A specialist,

What are you doing with Class-B amplifiers? These dont fall under your surviellance domain....

regards,
K a n w a r

Greg Erskine · 22nd November 2005, 04:26 AM

Quote:

Originally posted by Workhorse
Hi Class-A specialist,

What are you doing with Class-B amplifiers? These dont fall under your surviellance domain....

Hi K a n w a r ,

I think OUR Class-A specialist is moving through the alphabet.

yesterday, class-A .... today. class-B ..... tomorrow, class-C ..... can't wait for class-Z

regards

Workhorse · 22nd November 2005, 04:59 AM

Hi GreG1,

I think Mastertech is revising his alphabetical Skills these days....

regards,
K a n w a r

mastertech · 22nd November 2005, 08:52 PM

Hi my friend Kanwar, youve been absent for a while it's great
yo see you back on the forum, what is going on these days
with classes i read on the forum that class-d is going to
dominate the whole amplifier domain even the high-end
I am primarily focused on class-a at present but this doesnt
mean that ive given up on all other classes, it is intresting to
see other people making progres or rather so they claim

Hi Greg all classes have pros and cons depending on the application and class-a to me is the most challenging from
the engineering point of view i think it has not been fully
developed for obvious reason i see great potential in class-a
in terms of evolving for high-end

regards to both of you

cheers

22nd November 2005, 03:39 AM	#7
Workhorse diyAudio Member Join Date: Dec 2004	Hi Class-A specialist, What are you doing with Class-B amplifiers? These dont fall under your surviellance domain.... regards, K a n w a r __________________ It's a fruitless endeavor to try and educate a fool that rejoices in ignorance

22nd November 2005, 04:59 AM	#9
Workhorse diyAudio Member Join Date: Dec 2004	Hi GreG1, I think Mastertech is revising his alphabetical Skills these days.... regards, K a n w a r __________________ It's a fruitless endeavor to try and educate a fool that rejoices in ignorance

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21st November 2005, 07:23 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, tell us why your decision to insert 2 input caps and keep the bases of the LTPs separate? The feedback to the left side inverting LTP seems wrong. There is a missing DC block on the lower leg and an extra pair of caps in line with the feed. Why do you call it ClassB? Depending on output pair Iq it could be A, AB or B No input RF filter, no output Thiel network to reject RF and load the output at high frequency How about a cap bypass across the Vbe multiplier The DC block on the input could be non electrolytic with some advantage. Output offset adjustment? LTP emitter resistors? Stability control components? Decoupling? Separation of clean and dirty grounds? Overall not much thought so far, or is this a leg pull?

21st November 2005, 11:50 PM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Ditto.

22nd November 2005, 12:05 AM	#4
mastertech Banned Join Date: Mar 2005 Location: Australia	hehe what is that mean AndrewT i keep the two stages isolated because it gives better dynamics, thanks for all your kind suggestions cheers

22nd November 2005, 12:27 AM	#5
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	HI Mastertech, If you combine the input stage(s) at their bases you can have up to 90% cancellation of bias current for those bases - and with unity DC gain (your C to GND in the feedback leg), you could leave out input capacitors altogether. It my belief that no C is the best C. This is what I have done in the S.K.A where bias current cancellation results in Ib nett of only 0.1uA. The input C (provided for on the board) is linked out for normal operation. Cheers, Greg

22nd November 2005, 12:45 AM	#6
mastertech Banned Join Date: Mar 2005 Location: Australia	Hi Greg "no C is the best C" , you could be right i still use them , i know what you mean good luck with the S.K.A and thank you for taking time out of your busy schedule to comment here regards

22nd November 2005, 08:52 PM	#10
mastertech Banned Join Date: Mar 2005 Location: Australia	Hi my friend Kanwar, youve been absent for a while it's great yo see you back on the forum, what is going on these days with classes i read on the forum that class-d is going to dominate the whole amplifier domain even the high-end I am primarily focused on class-a at present but this doesnt mean that ive given up on all other classes, it is intresting to see other people making progres or rather so they claim Hi Greg all classes have pros and cons depending on the application and class-a to me is the most challenging from the engineering point of view i think it has not been fully developed for obvious reason i see great potential in class-a in terms of evolving for high-end regards to both of you cheers