analysis for 100w amplifier ciruit

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mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

18 Oct 2009 12:57 analysis for 100w ciruit

Hi all
I found this ciruit on the net
most people say that it works very fine and with a good quality
here is the main link : http://europa.spaceports.com/~fishbake/amp/ca100.htm
I attached ciruit with transistors so it can be easily seen
I made simulation to it and it seems great
i want to make analysis to it so i can modify it
I have a little problem with it
in the positive peak the power is 113 watt and the negative peak the power is 111 watt
I think it will not be noticed but I am seeking to solve this
any suggestions for analysis and my problem

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pauloynski

Joined: 06 Oct 2004
Posts: 277
Helped: 34
Location: Brazil

18 Oct 2009 13:51 Re: analysis for 100w ciruit

Many people can´t tell the difference between AM and FM radio. For those people this circuit may sound fine. With this circuit you´ll get:
1- Bad frequency and transient response
2- Lots of distortion (class-B output, low open loop gain)
3- Less power than you are expecting unless you have a regulated power supply.
It´s a waste of time (just as horrible as the shown diagram).
Regards

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

18 Oct 2009 14:23 analysis for 100w ciruit

I made simulation and found the frequecny response is very good
the bandwidth is from 20Hz to 100k
the gain is high
when the input is 0.3V the output will be about 28v or more i think it is high
I think it is very big I can limit it to 20Hz to 20K using 0.1mH coil
doesn't it seem a good circuit
I think there is no problem to make the power supply mentioned in the circuit link

I can't understand the problem of distortion I can see the output signal without distortion and very smooth
could u plz explain?

pauloynski

Joined: 06 Oct 2004
Posts: 277
Helped: 34
Location: Brazil

18 Oct 2009 14:38 Re: analysis for 100w ciruit

I doubt you can get this freq. response but if the simulated result is good for you it is OK. The problem with distortion is that, as any class-B amp, the output transistors are not biased for low amplitude signals and crossover distortion will arise. Please refer to this post
http://www.edaboard.com/viewtopic.php?t=366478#1199166
Regards

FvM

Joined: 22 Jan 2008
Posts: 5157
Helped: 767
Location: Bochum, Germany

18 Oct 2009 15:11 Re: analysis for 100w ciruit

Quote:

I made simulation to it and it seems great

You apparently didn't simulate distortion. It's pretty easy with SPICE fourier analysis. I see about 6% THD at 1kHz/1V output voltage with 4 ohm load.

I agree, that the frequency response is O.K.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

18 Oct 2009 15:23 analysis for 100w ciruit

1khz and 1v this is a very large input signal
try any thing under 0.4v and see the signal quality
the circuit starts to clip the signal over 0.4v

FvM

Joined: 22 Jan 2008
Posts: 5157
Helped: 767
Location: Bochum, Germany

18 Oct 2009 16:58 analysis for 100w ciruit

Look sharp. I said 1 V output voltage. (Means 10 mV input)

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

18 Oct 2009 17:50 analysis for 100w ciruit

could u plz explain how did u simulate distortion??
is 6% huge number?

FvM

Joined: 22 Jan 2008
Posts: 5157
Helped: 767
Location: Bochum, Germany

18 Oct 2009 18:20 analysis for 100w ciruit

I apply a VSIN input source in transient analysis with fourier analysis of the output voltage. The total harmonic distortion is calculated directly.

6% THD is quite a lot. It's even higher with lower output voltage. As pauloynski pointed out, the class-B operation mode (zero bias current) and low loop gain are the reason for high distortions.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

18 Oct 2009 23:38 analysis for 100w ciruit

thanks a lot man
do u recommend any cheap good quality circuits??
I need 200W one with a good quality

can u help for that?

Added after 1 minutes:

I found this one : http://mycaramplifiers.com/200-watts-amplifier-tda2030-8.html
whats ur idea about it too Smile

Added after 4 hours 40 minutes:

FvM wrote:

isn't there any idea to solve this problem?

Added after 30 minutes:

I found something when i remove the Resistance
which is connected to the 45v and with 3.3k value
the distortion decrease at 10mv input to 4%
its name is R7 in the updated image here

Audioguru

Joined: 19 Jan 2008
Posts: 1147
Helped: 95
Location: Toronto area of Canada

19 Oct 2009 0:43 analysis for 100w ciruit

The simple amplifier has very high horrible distortion.
Make an IC amplifier or make a much better one.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

04 Nov 2009 20:20 analysis for 100w amplifier ciruit

I have modified the circuit
here it is :

the distortion now is around 1%
I think this is better
I want you idea about the new modifications I did
thanks in advance Smile

Audioguru

Joined: 19 Jan 2008
Posts: 1147
Helped: 95
Location: Toronto area of Canada

04 Nov 2009 23:38 analysis for 100w amplifier ciruit

A good power amplifier has distortion of 0.05% or less at any power up to full output at all audio frequencies from 20Hz to 20kHz.

The 200W car amplifier you found (a car with a 24V battery?) produces 200 Whats into 2 ohms or about 80 watts into 4 ohms or 50 Watts into 8 ohms.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

05 Nov 2009 9:36 analysis for 100w amplifier ciruit

0.05% Ohhhhhh
then is there any chance to enhance my circuit?
the other question
from where does the distortion come from?

Audioguru

Joined: 19 Jan 2008
Posts: 1147
Helped: 95
Location: Toronto area of Canada

05 Nov 2009 14:58 analysis for 100w amplifier ciruit

Your amplifier circuit is too simple.
The output darlington transistors are not biased enough so they produce crossover distortion.

The other transistors should make an opamp that has distortion of only 0.003% or less.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

05 Nov 2009 15:18 analysis for 100w amplifier ciruit

I can see the input sin signal very clear
i think the crossover distortion of the darlington is minimum as possible because of the negative feedback removes it
am I right?

pippone1987

Joined: 02 Nov 2009
Posts: 4
Helped: 2
Location: Padova

05 Nov 2009 16:09 analysis for 100w amplifier ciruit

In my opinion the distortion is minimum when you use a couple of Sziklai pair in the output stage (or CFP complementary feedback pair) which guarantee a 100% feedback

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

05 Nov 2009 16:17 analysis for 100w amplifier ciruit

ok i will give it a try
but which transistors should I use ?
could you give me some numbers?

pippone1987

Joined: 02 Nov 2009
Posts: 4
Helped: 2
Location: Padova

05 Nov 2009 16:22 analysis for 100w amplifier ciruit

Of course, but they are not so cheap. For the drivers you can use 2SC2238 and 2SA968 (respectively for pull-up an pull-down net) while for the outputs you can use 2SA1216 and 2SC2922.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

05 Nov 2009 16:26 analysis for 100w amplifier ciruit

could I use 2SC5200/A1943?

pippone1987

Joined: 02 Nov 2009
Posts: 4
Helped: 2
Location: Padova

05 Nov 2009 16:40 analysis for 100w amplifier ciruit

I think so. These Toshiba's are widely use and sound good!

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

05 Nov 2009 16:49 analysis for 100w amplifier ciruit

I couldn't find any of those transistors on Orcad 10.5 Sad

I don't know should i try multisim ?!!!
is it good in simulation ?

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05 Nov 2009 16:49 Ads

pippone1987

Joined: 02 Nov 2009
Posts: 4
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Location: Padova

05 Nov 2009 16:54 analysis for 100w amplifier ciruit

Yes, of course...but i don't know if in that software there are them...

Audioguru

Joined: 19 Jan 2008
Posts: 1147
Helped: 95
Location: Toronto area of Canada

05 Nov 2009 19:16 Re: analysis for 100w amplifier ciruit

mr_byte31 wrote:

I can see the input sin signal very clear
i think the crossover distortion of the darlington is minimum as possible because of the negative feedback removes it
am I right?

No.
Your amplifier is also missing frequency compensation which rolls-off the high frequencies so that phase-shift does not cause the amplifier to oscillate when it has negative feedback. Then at high frequencies where crossover distortion is bad the open loop gain is too low to reduce the crossover distortion.

LM358 and LM324 opamps have 3% crossover distortion (when they have negative feedback) because their output transistors do not have enough bias current so that their power supply current is low.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

05 Nov 2009 19:43 analysis for 100w amplifier ciruit

then how can I design the frequency compensation circuit?

Audioguru

Joined: 19 Jan 2008
Posts: 1147
Helped: 95
Location: Toronto area of Canada

05 Nov 2009 19:47 analysis for 100w amplifier ciruit

You need to know about electronic circuits to design an audio amplifier with frequency compensation.

All audio amplifiers and opamps have frequency compensation.

mr_byte31

Joined: 19 Oct 2005
Posts: 198
Helped: 1

05 Nov 2009 20:00 analysis for 100w amplifier ciruit

is it as simple as RC ?

Added after 10 minutes:

i think a coil on the output can stop oscillation
right?

Audioguru

Joined: 19 Jan 2008
Posts: 1147
Helped: 95
Location: Toronto area of Canada

05 Nov 2009 20:23 analysis for 100w amplifier ciruit

A capacitor with its value properly calculated in the correct position is used for frequency compensation on an amplifier circuit.

Your inductor feeding the speaker simply reduces high frequencies going to the speaker but the amplifier will still oscillate due to phase-shift and too much gain at high frequencies.