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[mike_ss]

Thanks a lot audioguru. What I really wanted to make was an amplifier that would be able to power car speakers. Pretty much If I wanted to throw the amp in my truck and listen to the radio it would sound better. Are there any IC's that could do this? How about MOSFETS? I have heard a lot about MOSFETS being good audio amplifiers. Thanks again

 

[mstechca]

The op-amp (LM386) as Audioguru pointed out is an IC.

I don't use op-amps, because I want to control my gain, not go overboard with it, and with transistors, I can be more flexible with circuit board space.

 

[audioguru]

What I really wanted to make was an amplifier that would be able to power car speakers. Pretty much If I wanted to throw the amp in my truck and listen to the radio it would sound better. Are there any IC's that could do this?

All car radios use IC power amplifiers. Philips has about 76 of them, ST Micro and National Semi have more.

Many car radios use an IC similar to Philips' TDA1554 which is a quad amp that is usually used as a medium-power bridged stereo amp. They claim 20W per channel but it is actually only 14W per channel without distortion.

 

[audioguru]

I don't use op-amps, because I want to control my gain, not go overboard with it

The gain of an opamp circuit is determined by only two negative feedback resistors, used as a voltage divider. The gain is very controlled and can be just about as much as you want.
Simple transistor circuits have severe distortion, simple opamp circuits don't have distortion (except for a few very old opamps).

with transistors, I can be more flexible with circuit board space.

Each transistor needs a supply, ground, many resistors and a few capacitors.
A single opamp has only 8 pins, a dual opamp also has only 8 pins and a quad opamp has only 14 pins. A single pin is the supply and another single pin is the ground for all of them.
Most opamp circuits use very few resistors and capacitors.

 

[mstechca]

Each transistor needs a supply, ground, many resistors and a few capacitors.

I was able to pull off a simple common emitter amplifier design with only 2 resistors, 2 capacitors and an NPN transistor.

But if you are talking about high-quality, extra-low distortion amplifiers, then I can agree with you.

 

[mike_ss]

The tda1554 looks like an easier circuit than the LM386 I had first. As always my posts come with questions... What is the non-inverting input? Does the capacitor make it an inverting input into Pin 2. Also, what is the supply voltage ripple rejection? Are the positives of both speakers connected to the IC or the negatives? Thank you

 

[mike_ss]

ooh, another question I have with the transistor amplifiers. Can you switch a regular NPN or PNP transitor with a MOSFET? If are there different types of MOSFETs?

 

[audioguru]

What is the non-inverting input?

It is the input to each bridged amplifier channel.

Does the capacitor make it an inverting input into Pin 2?

The capacitor to pin 2 feeds the inverting input of the 2nd power amp for the 1st channel. Then the speaker is fed opposing signals which effectively doubles its voltage swing. Since the speaker's voltage swing is doubled, then its current swing is also doubled, therefore the amplifier's output per channel is nearly 4 times the power of a normal non-bridged amp.

Also, what is the supply voltage ripple rejection?

It is the amount of reduction of noise that is on the power supply voltage that is heard at the speaker.

Are the positives of both speakers connected to the IC or the negatives?

The IC has 4 power amplifiers. The speakers are connected so that the + of a speaker connects to the 1st amplifier and the - of that speaker connects to the 2nd amplifier. Then the two amplifiers are connected in a bridge to effectively nearly quadruple the power to each speaker. The 3rd and 4th power amps are connected in a bridge for the 2nd speaker.

 

[audioguru]

ooh, another question I have with the transistor amplifiers. Can you switch a regular NPN or PNP transitor with a MOSFET? If are there different types of MOSFETs?

A completely different amplifier design is needed for Mosfets.
Mosfets are N-channel or P-channel, something like NPN and PNP transistors.

 

[audioguru]

BTW, the TDA1554 is 14W with low distortion per bridged channel from a car battery, only if 4 ohm speakers are used. The power to 8 ohm speakers is only about 7.5W per channel.

 

[mike_ss]

Can you connect two of these circuits together to make double the power or will the distortion be too great? Can you look at the picture I have below to see if it is correct. Thanks again

 

[audioguru]

The left side of the amplifier is its two inputs from a stereo CD or MP3 player. The right side shows the two 4 ohm speakers connected to its outputs. Additional speakers will overload it.

I don't know why you want to connect more speakers at the amplifier's inputs. They won't work. Speakers connect to an amplifer's outputs, not inputs.
Actually, the speakers you added are across the input capacitors so the amplifiers will be totally messed-up.

I don't know what two circuits you want to connect together.
This is a stereo amplifier for two 4 ohm speakers. If you want more power then use a second amplifier with its own two speakers, or a much more complicated high-power amplifier.

 

[mstechca]

I don't know why you want to connect more speakers at the amplifier's inputs. They won't work. Speakers connect to an amplifer's outputs, not inputs.

This is a different amplifier circuit.

What I do suggest in order to prevent short circuits is to add a coupling capacitor between the speaker and the input. Do the same with the output.

It seems that this circuit (to a point) allows you to take advantage of both polarities. What I mean is that if the input is positive, the speaker will work as if it was connected positively. If the input is negative, then the inverse happens. What you may notice with the speaker is the center moving out and in. Most available circuits that use a speaker tie one connection point to ground.

 

[audioguru]

What I do suggest in order to prevent short circuits is to add a coupling capacitor between the speaker and the input.

I suggest getting rid of the speaker at the amplifier's input.

Do the same with the output.

Why does it need an output coupling cap? Each channel is a bridged pair of amplifiers. The amplifiers all have the same output DC voltage so output coupling capacitors aren't needed.

It seems that this circuit (to a point) allows you to take advantage of both polarities. What I mean is that if the input is positive, the speaker will work as if it was connected positively. If the input is negative, then the inverse happens. What you may notice with the speaker is the center moving out and in. Most available circuits that use a speaker tie one connection point to ground.

We don't know what you mean. Each wire of a speaker is fed an inverted signal from the other wire. Each amplifier's output is push-pull and drives positive or negative from its half-supply reference voltage. Since both ends of each speaker are driven with opposing signals, the speaker's voltage swing is doubled.

The speakers don't have a DC voltage across them so their cones move normally in and out, except twice as far as with a normal amplifier.

 

[Nigel Goodwin]

It seems that this circuit (to a point) allows you to take advantage of both polarities. What I mean is that if the input is positive, the speaker will work as if it was connected positively. If the input is negative, then the inverse happens. What you may notice with the speaker is the center moving out and in. Most available circuits that use a speaker tie one connection point to ground.

It's a 'bridged' amplifier, a very common configuration, particularly in car audio - it effectively doubles your supply voltage. This gives double the power into double the impedance. So each of the four amplifiers in the chip can provide 8W into 2 ohms, when bridged you get two amplifiers that will provide 16W into 4 ohms.

As you noticed, a bridged configuration doesn't have one side of the speaker connected to ground, and doing so will blow the amplifier.

It's also commonly used in PA amplifiers, for example my Behringer PA will provide 400W per channel into 4 ohms (stereo), by selecting bridged mode in will provide one channel of 800W into 8 ohms (mono).

But the original post makes no sense, he needs to explain far more what he's wanting to do - I 'suspect' he's trying to feed the amplifier from the output of a power amplifier?, but he's going about it completely wrong!.

 

[mike_ss]

ooh I messed up! I didnt mean to put '+ speaker' Just '+' (what I really mean is the output from a CD player). I dont want to connect the amplifier after the speaker (that makes no sense) Sorry I screwed you guys up. So non-inverting input #1 is from the CD player to the left speaker but goes through the amp first and non-inverting input #2 is the same but for right speaker. I can't believe I did that. I'm still confused as to what supply voltage ripple rejection connects to. As for the more power, I was wondering if you could connect the outputs of one amp to the inputs of a second one. I see now that you cannot because there are four outputs and only two inputs. Sorry again for confusing everyone.

 

[Nigel Goodwin]

ooh I messed up! I didnt mean to put '+ speaker' Just '+' (what I really mean is the output from a CD player). I dont want to connect the amplifier after the speaker (that makes no sense) Sorry I screwed you guys up. So non-inverting input #1 is from the CD player to the left speaker but goes through the amp first and non-inverting input #2 is the same but for right speaker. I can't believe I did that. I'm still confused as to what supply voltage ripple rejection connects to.

Why not consult the datasheet to find the connections?, which (on a VERY brief glance) appears to show it only being used for a four channel application?.

As for the more power, I was wondering if you could connect the outputs of one amp to the inputs of a second one. I see now that you cannot because there are four outputs and only two inputs. Sorry again for confusing everyone.

There would be no point in putting power amps in series, you would only get the same amount of power out - and it would be horribly distorted. If you had an extra set of speakers you could use seperate power amps for each set, and get more power that way.

 

[audioguru]

Is this wiring diagram clearer?

 

[mike_ss]

Yes, thanks audioguru