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Old 14th February 2008, 06:05 PM   #21
latala is offline latala  United Kingdom
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Thanks Tim for your schematic I dont feel that your toplolgy will work I did ask for 30 watts or more !
I have got a problem with my scanner at the moment so can not put my proposed solution on as a schematic at this time !
However I will say that the inputs are a differantial pair with opto isolator transmitter diodes in the collectors these are then connected to totem pole darlington transistors with the receiver transistors connected to the bases of the darlingtons
I will try to get this on line this weekend !!!
I must stress I have not yet made the amp its only a design exercise at the moment
there will be stability problems to be sorted I am sure !
At this time I must say I had not thought of the solution when the challange was made but must say I have been stimulated via the challange to think about it on my dailey 3 hour commute to work and back
regards Trevor
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Old 14th February 2008, 06:35 PM   #22
poynton is offline poynton  United Kingdom
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Default Re: Here is a Challange

Quote:
Originally posted by latala
.................. Could any of you design a Dc coupled amplifier using NPN devices only !!!
Target power is 30 watts rms or more in 8 ohms at less than 0.1 % distortion midband
................

DC coupled - so no transformers or opto couplers !!!!
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Old 14th February 2008, 07:12 PM   #23
latala is offline latala  United Kingdom
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Poynton
I have all ready stated you can use opto or any device all that you can not use is a PNP device!
When I issued the challenge I had no Idea what the solution would be and to be honest still dont !!!
I have suggested opto,s as merely 1 solution
The use of opto .s would give an absoulute dc coupled effect any drift in output would be corrected by the diff pair
So come one where is your solution
Regards Trev
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Old 14th February 2008, 07:51 PM   #24
Tim__x is offline Tim__x  Canada
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I beg to differ, by design it's trivial to take a differential output from the second stage and use a push-pull class-ab output stage.

I did say the output stage needed revamping, being only one of the simplest NPN followers possible.

There nothing stopping it from going within a couple volts of either rail.
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Old 14th February 2008, 08:52 PM   #25
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Quote:
Originally posted by latala
The other one by steve eddy is interesting ! and very unexpected
lots of iron though!
Well sure. Why do you think Popeye ate his spinach?

se
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Old 14th February 2008, 09:50 PM   #26
latala is offline latala  United Kingdom
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TIm_ X
Please do not get me wronge I am not Knocking your design
However I feel that to get a practical design your output stage leaves somethingto be desired ! From what I can see it would have to be class A. Nice but not practical , now if it was Ab that would be a different thing!
The front end and driver of your design is ok, but as I see it would be the driver outputstage where we have a problem .
Please think again you at least have the courage to put your ideas forward for which I thank you .
The Idea is to see where an alternative/restrictive design concept would get us
Regards Trev
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Old 14th February 2008, 10:41 PM   #27
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Really guys, there's a ton of designs that fill this requirement.

The stupidest of them would be the Son of Zen - just throw some feedback around it for a distortion spec.

Other ones? Balanced versions of the PLH, ZV4 or ZV9, without the coupling caps.

Don't like that? I have a swell circlotron...
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Old 16th February 2008, 05:25 AM   #28
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Check this out guys
Its all NNNNNNN

Gate Driver supplies need to be regulated. A zener+resistor combination could also work from the main rail and mid rail for both drivers respectively.
Attached Images
File Type: jpg alln.jpg (40.3 KB, 417 views)
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Old 16th February 2008, 09:32 AM   #29
latala is offline latala  United Kingdom
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Workhorse I like your solution I thik it has potential !!! You have implimented a solution at the front end that to be honest I dont think I would have come up with .
Sorry I called you Trojan erliear got a little confused with your label.
Thank you Mr Pass for your suggestions and while I have built and do like class A designs I feel they are always difficult because of heat issues etc .
However I must admit that I have not listened to any of your designs
I have looked at some of your work but have not come across the Circlotron and will endeavour to find it .
I don,t think I was specific enough when I made the challenge but as ever the forum is a great learning aid in that it makes one think and attempt to be logical it not only knowing what are the answers but also what are the correct questions to ask
regards Trev
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Old 16th February 2008, 10:17 AM   #30
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Quote:
Originally posted by latala
Workhorse I like your solution I thik it has potential !!! You have implimented a solution at the front end that to be honest I dont think I would have come up with .
Sorry I called you Trojan erliear got a little confused with your label.



I just accepted your challenge and now rest is history.
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