Audio Amplifier. Which class should I use?

[Shayaan_Mustafa]

OK Thank you first of all

As I am going to design 50W audio amplifier, so what things (class of amplifier, etc..) should I need for this?

If you tell me those components which are necessary in order to design 50W audio amplifier then I will start a new thread for that.

 

[goldsmith]

Well , it depends on that , is your input , a microphone ? or it is just an audio card ? or both of them ?

 

[Shayaan_Mustafa]

My input is a PC.

I am designing it for a PC. A home personal computer.

 

[goldsmith]

Oh you brought me back ! to 9 years ago . it was , my first design . i designed it for my PC too !
Anywhere , no problem , your first stage will be a buffer and then a preamplifier , rather with op amp . by the way , it means that you need an stereo out put , right ? if yes , a TL074 will be a good choice for start , it consists for , opamps .
Wait , wait !! did you say at first , you decided to design 400 W ? and now you changed it to a 50 w . 400 w fo PC amp ?????
Do you know , that we are talking about real power ? an airplane ( jet ) when trying to break the audio wall ( the speed upper than sound ) , it will create the voice around 350 watts . i think 400 watt will be pretty dangerous for your ear and the mirrors in your home and in general words , for your healthy !

 

[Shayaan_Mustafa]

Hahahahahaha:-D

So I was going to design that huge amplifier. lol

Thanks you for your suggestion then.

Yes stereo of course. But tell me for mono what could then suggest me?
Now I want to know why did you choose TL074?

And I know about buffer. Its impedance matching circuit. Right?

And tell me some about preamplifier.

In university, we have studied 741 opamp. As it was basic.

Sorry for bad English.

 

[enjunear]

My input is a PC.

I am designing it for a PC. A home personal computer.

The next question should be, what output are you driving? i.e. How much power can your speaker(s) handle? From that value, you will know the maximum power that your amplifier should output, so you won't overdrive your speakers.

 

[goldsmith]

The 741 op amp hasn't enough slew rate , hence it isn't good for audio amplifier at large signals . and of course low BW and low CMRR . so 741 isn't good choice for your aim . if you use it for a sine wave around 10 KHZ according to it's low slew rate it will give you a triangular wave !!!!!!
TL074 consists 4 op amps , or if you want mono , TL072 , it consists 2 opamps . it has enough slew rate and BW for audio .
And a buffer will do impedance matching at first ,and my reason by buffer is , to increase safety for your PC . you shouldn't take over currents from that . so you can add a potentiometer after your buffer , to control the amplitude of voice .
By the way : if you need higher powers with simple circuits , you can use a bridge amplifier . my means is you can create the other amplifier but with create 180 degree phase shift in one of your amplifiers , and then your load will be float . but if you want take feed back from out put it will be hard , but i think you won't need feed back for this simple project .

---------- Post added at 02:29 ---------- Previous post was at 02:28 ----------

And about thing that "enjunear" said , yes he/she is quite right . you forgot to describe the specifications of your speakers .

 

[Shayaan_Mustafa]

@enjunear

My speakers should be capable of handling about 50W maximum power.

---------- Post added at 03:04 ---------- Previous post was at 03:00 ----------

@goldsmith

Thanks buddy.

I have understood why should I choose TL074. So Where should I start? Can you give me any block diagram for that?

And as we discussed previously that we are designing for 50W. So my speakers must be able to handle 50W. Isn't it?

 

[goldsmith]

So if you use a complementary stage in your out put , ( with simultaneous supply ) the out put power will given by VCC^2/2RL
Hence you should tell me about the impedance of your speaker . to select enough supply .

 

[Shayaan_Mustafa]

@goldsmith

As you know it is my first design. So I need much help in order to design. I am able to join circuits as well designing. But how much value should I choose, it is confusing for me.

So I think 8ohm speaker suits for PC speaker? Am I right?

 

[BradtheRad]

A typical resistance for speakers is 8 ohms. To drive it, say, to the loudness of normal conversation, requires 1 VAC (depending on how efficiency the speaker is). 1 VAC is 2.828 V peak-to-peak.

So the current is 1/8 A. Power is 1/8 watt.

Whatever supply V you use, the intervening resistance must be varied so the speakers receive a swing of 2.8 V.

The intervening resistance may consist of:

two transistors alternating on and off,
or
a transistor alternating with a resistor,
or
an H-bridge consisting of 4 transistors (2 of which are conducting at any moment),
etc.

Suppose you are using a 3 V supply, and class A amplifier. Your transistor(s) must vary between high impedance, and very low impedance (a fraction of an ohm). The transistor(s) will not get very hot.

Suppose your supply is 5.6 V. Then the intervening resistance can average 8 ohms.
With higher supply V it is possible to drive the speaker to a much higher volume. Then the transistor(s) will start getting hot.

Link to helpful article:

**broken link removed**

---------

I see more messages were being posted while I composed my message.

The same website has a many articles about constructing audio amps. This one discusses configurations of class A.

**broken link removed**

 

[Shayaan_Mustafa]

@BradtheRad

You mean I should choose class A for this?

And yes with higher supply we can drive the speaker to a much higher volume.

 

[BradtheRad]

@BradtheRad

You mean I should choose class A for this?

And yes with higher supply we can drive the speaker to a much higher volume.

Hi, I was editing my latest post while you posted.

Somewhere the writer admitted there are blurry lines of distinction between class A and AB.

It seems to depend on whether your supply is single polarity or dual polarity. Whether you use a capacitor inline with the speaker, etc. Whether you use class A during low volume, and shift to AB during high volume. Etc.

It appears class AB is the compact and efficient way to power speakers. It will probably work well, with the highest likelihood of success, as a homebuilt project.

 

[godfreyl]

I think a good way to start is to look at existing circuits to see how they work. Here's a few links:

• Douglas Self gives a good explanation of one popular kind of amplifier, and how to make it better here: http://www.douglas-self.com/ampins/dipa/dipa.htm.
• Greg Erskine has put together a nice collection of the the popular DX amplifiers here: **broken link removed**
• There are also some articles and amplifier projects on Rod Elliott's website here: **broken link removed**.
• More useful information and circuits (especially JLH's) here: **broken link removed**.

edit: I see I also missed a few posts while I was typing and collecting links.

 

[SUMIT_GAMBHIR]

For "mid Q-point", I think the OP means that the quiescent point of the transistor is in the middle of the potential range.

You can also look at Class D, if you want to add a lot of complexity but improve the efficiency dramatically.
http://www.irf.com/technical-info/appnotes/an-1071.pdf

As for the impact of efficiency, it should have no impact on the audio output, but it will impact the power consumption and how you handle heatsinking your active devices. If you want 100W of audio output from a Class A amp, you need to put in at least 400W of power form the outlet (Class A theoretical max eff = 25%, 100W / 25% = 400W, minimum). That means that you will have to dissipated 300W of heat into the air... that's like cooling 5 light bulbs, simultaneously.

I'd lean toward AB and get some efficiency improvement, and suffer a little distortion (most people can't hear less than 0.1% THD). AB will get you closer to 50% in a well-tuned audio amplifier... so 100W output needs 200W input and 100W dumped as heat.

Read the section on efficiency to get some good numbers on real world amp applications (audio amps are noted and discussed).
http://en.wikipedia.org/wiki/Amplifier#Efficiency

Class D can get you up to 90% efficiency. So 100W would need 111W input and 11W left as dissipated heat.

Using Class D is an excellent option, depending upon the circuit where you want to use it. The Class D are quite expensive than Class AB, but has much better efficiency as indicated above by my friend.

 

[goldsmith]

Hi again .
Well , lets continue our design . you can design an inverting amplifier , (Av=-Rf/Rin) . and buffer section , can made without any resistor .
So , you'll need a complementary stage , at the out put . you need large value of beta , hence , you should use darlington configuration for your class AB amp .
Good luck
Goldsmith

 

[Shayaan_Mustafa]

@goldsmith

If you prefer me any block diagram then it will be more easy for me.

In block diagram. we have 3 blocks. preamplifier, buffer and a complementary stage. Is that all?

@BradtheRad

Yes that's why I chose class AB.

@godfreyl

Thanks for links. I have much knowledge about analog electronics. But as it is my first design that's why I am confuse how to start? I just want me as a successful electronics engineer. I therefore, just need help verbally, don't want to look pre-made circuits.

@SUMIT_GAMBHIR

As discussed in previous posts that class D have much high efficiency but they are expensive and I didn't study them yet. I have just studied class A, class B, class AB and class C power amplifiers.
So I am trying to do my first project with these my knowledge.

Thanks for everyone.
Thanks a lot.

 

[godfreyl]

So you don't want to read any explanation that has already been written - you want somebody to write an explanation specially for you?

OK, let's start.
To make a power amplifier, you need a differential input stage, a transimpedance stage, an output buffer,and a feedback network.

The input stage produces an output current proportional to it's input voltage.

The transimpedance stage produces an output voltage proportional to it's input current, which is the output current from the input stage.

The output buffer is connected to the output of the transconductance stage. It does not have any voltage gain, but has a high current gain.

The feedback network sends a fraction of the output voltage back to the input stage, where it is subtracted from the input voltage.

There are other ways to make a power amplifier, but this is the most common.



---------- Post added at 18:13 ---------- Previous post was at 17:37 ----------

You also need a power supply, of course. For 50W output into 8 Ohms, the amplifier must deliver an output of 20V RMS, so a power supply of about +-30v to +-35V would be needed.

 

[Shayaan_Mustafa]

So you don't want to read any explanation that has already been written - you want somebody to write an explanation specially for you?

No. I don't mean this.

Actually I have read these. But never apply practically.

Now I want to say here that goldsmith said to use TL074. And TL074 has maximum and minimum Vcc=±18V. But you specified ±30V to ±35V.

And one last thing more. Kindly specify your all and even smaller calculations in each and every post and at each and every step. Because I am noting down all of these for future help. Thanks.

 

[goldsmith]

Hi again
A note about class D amplifier : it's size and price for this power isn't economical . and a beginner can't , draw it's PCB , because it is high frequency , and it has two grounds , and it need an expert grounding , hence , i didn't suggest this class to Shayaan .
Anywhere ,
I know you'll need at least +-30 volts , to achieve 50 watts , and i know that these opamps , are not designed for this voltage , thus you'll need the other stage before your complementary stage , but i just wanted that you start and in practice when you see any problem i try to give you more ideas and i tried to educate you many things in this project , it is my first reason , that i didn't say , all of things in a post .
Best Lucks
Goldsmith