Two Transistor Amplifier
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 4th May 2009, 02:07 AM #1 Stinger   diyAudio Member   Join Date: Apr 2009 Two Transistor Amplifier Hi everyone, Would someone please determine the components values for this simple amplifier? I need to run it with a 24V battery and also the sound quality isn't important at all! Thank you in advance Stinger.
Nelson Pass
The one and only

Join Date: Mar 2001
Re: Two Transistor Amplifier

Quote:
 Originally posted by Stinger I need to run it with a 24V battery and also the sound quality isn't important at all!
That is just too easy.

 4th May 2009, 03:11 AM #3 sawreyrw   diyAudio Member   Join Date: Apr 2006 Location: Minnesota R1=30K R2=2.4K R3=500 R4=900 R5=100 C1=100uF C2=100uF This circuit will have a gain of 10.
 4th May 2009, 03:18 AM #4 MJL21193   Account disabled at member's request     Join Date: Mar 2007 Load?
 4th May 2009, 12:29 PM #5 Stinger   diyAudio Member   Join Date: Apr 2009 Well, thanks again for the fast replies. The load is a 2...4 ohms speaker (2W). What should be the transistors?
JoelM81
diyAudio Member

Join Date: Jul 2007
Quote:
 Originally Posted by sawreyrw This circuit will have a gain of 10.
How do you calculate the gain? It looks to me as 2 common-emitter circuits connected with the output going back into the first stage to act as negative feedback, which in my simulations leads to more linear amplification than if there were no feedback, right? But I'm trying to do node analysis to find the gain as a function of R3, R4, R5 and not succeeding.

Circuit Wiring Diagrams says the gain is 1+(R4/R5) = (R4 + R5)/R5

So I'm confused, but 1+R4/R5 matches my simulations.

And if it doesn't depend on R3, then how do you set R3?

Last edited by JoelM81; 27th January 2016 at 07:55 PM.

 29th January 2016, 09:50 AM #7 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders You have searched for and found a bad circuit. It won't drive a 2ohm speaker, properly 2W into 4r0 requires a maximum output of 4Vac and that could be obtained using a supply of 12Vdc, not 24Vdc. It could be developed into a stage to drive line level signals into a 2k load. __________________ regards Andrew T.
JoelM81
diyAudio Member

Join Date: Jul 2007
Quote:
 Originally Posted by AndrewT You have searched for and found a bad circuit. It won't drive a 2ohm speaker, properly 2W into 4r0 requires a maximum output of 4Vac and that could be obtained using a supply of 12Vdc, not 24Vdc. It could be developed into a stage to drive line level signals into a 2k load.
I know it won't drive a speaker. My goal is improved linearity over a common emitter amplifier, and low noise. I was able to work through the analysis and confirm that the AC gain is 1+R4/R5, if beta >> 1.

Some variations are also shown here (but without any explanation), and here (fig 39).

Last edited by JoelM81; 29th January 2016 at 12:12 PM.

 29th January 2016, 12:02 PM #9 esgigt   diyAudio Member   Join Date: Dec 2013 Check Nelson Pass's ZEN amplifiers out... they use FET's instead of transistors.
 29th January 2016, 10:08 PM #10 llwhtt   diyAudio Member   Join Date: Jun 2008 Location: SoCal FETs are NOT transistors? Craig

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