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Old 18th January 2009, 03:09 PM   #1
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Default New Amplifier design

Hi to all.

I made a schematic for an Amp (class AB or class A depents on biasing and supply) combining ideas from Nelson Pass F5 and Mosquito amps (first stage) and a litle bit strange symmetric output stage (a driver bjt for each output bjt). The output stage was tested in real circuit in the past with very good results).
The output DC is configurable and the bias can be altered through the vbe (bd139). The simulated Frequency response in pspice is exellent ( DC to 500 kHz).
Anyone wants to comment to the circuit is welcome. Do you think that it has potential?

thnx
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Old 18th January 2009, 11:26 PM   #2
Beto is offline Beto  Brazil
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congratulations on kzeprf22 project seems interesting and the circuit
I have some doubts:
Bias current of what used in your project.
which amount to R26 and R76?
I use the circuit with 36v?
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Old 19th January 2009, 06:05 AM   #3
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Hi thanks for commenting my circuit.
I use R26 & R76 (5k) for setting the dc offset (~ 5mv) and I use vbe multiplier with bd139 and R449 for the quiscient current (~150 ma / transistor, 300 ma total).
Are you simulating the circuit also?
Thnx
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Old 19th January 2009, 11:26 AM   #4
AndrewT is online now AndrewT  Scotland
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change BD139 to BD140, or swap location of pot and resistor.
Why use a k170 j74 front end and follow up with Tips for the remaining stages? What a waste.
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Old 19th January 2009, 11:42 AM   #5
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Thanks for the comments. The tips are just for simulation. I am planning to us MJE15034-34 MJL4281A (NPN) and MJL4302A (PNP). I used this compbination again with this kind of output stage and it was great.
When I tested this output stage (a drive bjt for each output bjt) in another amp I liked it to much. It was so warm like class A and tube sound. My impression any way. So I thought to combine two thinks that I like:
symmetrical fet input and this "strange output stage". I hope I will get something good.
As far as the bd 139 you are right, it is a mistake in this jpg.
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Old 19th January 2009, 11:49 AM   #6
AndrewT is online now AndrewT  Scotland
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and change the VAS to a low Cob device, 2pF to 3pF @ 10Vce?
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Old 19th January 2009, 11:57 AM   #7
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I am planning to use 2sc3423 2sa1360.
What is your opinion.
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Old 19th January 2009, 12:19 PM   #8
AndrewT is online now AndrewT  Scotland
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1360 - good, recommended by a few on the Forum.
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Old 19th January 2009, 03:55 PM   #9
ferencz is offline ferencz  Hungary
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Have you simulated the followings:
- OLG (open loop gain)
- phase response
- square wave response
- clipping performance
- stability with non cleary resistive (capacitive/inductive) loads
- IM (intermodulation distortion)
- THD
?

The frequency response alone tells almost nothing about an amplifier.

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Old 19th January 2009, 07:16 PM   #10
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Default Re: New Amplifier design

Quote:
Originally posted by kzeprf22
Do you think that it has potential?
Yes of course. Let us know how the real one turns out.

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