If you like transistors why not build the circuit I posted in #119. It uses parts you have on hand as you requested in post #1.
The circuit has been assembled and verified with the components listed. If you are planning on using a 4 ohm speaker at 12 volts that will provide about 2 watts output. 18 volt supply will deliver about 4.5 watts.
SG

 

Well I don't mind using an opamp. I'm quite open to it. I was just trying to get the jist of basic transistor only amp circuits before I jumped into using opamps.

Geez. Why didn't you say so in the first place? That opens up a whole range of possibilities.

 

If you simply want an efficient audio amplifier for around the house, go buy a class-D for under $5 as already suggested in post #5.

 

If you like transistors why not build the circuit I posted in #119. It uses parts you have on hand as you requested in post #1.
The circuit has been assembled and verified with the components listed. If you are planning on using a 4 ohm speaker at 12 volts that will provide about 2 watts output. 18 volt supply will deliver about 4.5 watts.
SG

I probably overlooked it. I'm not getting alerts like I did at the start. Been missing a lot of posts on here.

Geez. Why didn't you say so in the first place? That opens up a whole range of possibilities.

I suppose I'm a learning to walk before I run sorta guy. Felt like I needed to learn basics of how and why instead of just building things without knowing how it works or dont work. But absolutely. I suppose an lm386 would work correct?

 

I probably overlooked it. I'm not getting alerts like I did at the start. Been missing a lot of posts on here.

Did you click on "Watch Thread" at the top of this page?

 

I suppose I'm a learning to walk before I run sorta guy. Felt like I needed to learn basics of how and why instead of just building things without knowing how it works or dont work. But absolutely. I suppose an lm386 would work correct?

The LM386 was designed as a single chip low power audio amplifier, not as a driver for a more powerful amp. Did you ever try the circuit on post #34 at higher supply voltage and heatsinks on the transistors?

 

MrChips, I tested a slightly modified version seen below. With the two bias diodes in the original circuit the idle current was over 100 ma. Replaced one of the bias diodes with a 1K pot to set bias at 15ma.
EDIT:
Output power just .6 watt at 12 volts. Using a LM386-4 at 18 volts 1.3 watts, same as with the LM386 alone as expected but without the dissipation.
SG

 

You wouldn't need fans or air holes. With the circuits you are considering a fairly large (maybe 6" by 12" by 1") would be enough without a fan. You would need to check that because I am not an expert in heat sinks. But you really should heat sink the transistors now so you make sure you don't fry them. A $15 heat sink is good

 

Is an lm386 capable of providing enough negative feedback or am I to upgrade my opamp?

No. An LM386 is not hifi and cannot use a supply voltage high enough to make much power. It is made for kids toys and clock radios.
A few around your house would sound good enough if the speakers are good enough. If an LM386 drives a pair of TIP transistors then the resulting losses results in very low output power.

Only enough hole for the speakers to function without blowing a case apart

A half decent small speaker in a sealed enclosure produces poor bass. When a port is tuned to the speaker's free air resonant frequency then the port produces pretty good bass.

 

We are going to wrap up this short tutorial with a working example of a four-transistor audio amplifier circuit. The purpose of this exercise is to demonstrate that it can be accomplished with commonly available components. It is not intended to be a high quality amplifier. As pointed out before, there are superior ways of driving the output stage with multiple transistors.

Q1 is a basic class-A common-emitter pre-amplifier with a voltage gain of about 18. An opamp circuit will do even better here. The output of this preamp is AC-coupled to the driver stage Q2 so as not to disturb the DC biasing of Q2. Proper attention must be paid to the biasing of both Q1 and Q2. Negative feedback is supplied from the output stage via R7.

 

Did you click on "Watch Thread" at the top of this page?

It's selected. I do get alerts but sometimes it doesn't show all of them. I still scroll through to make sure I don't miss anything.

The LM386 was designed as a single chip low power audio amplifier, not as a driver for a more powerful amp. Did you ever try the circuit on post #34 at higher supply voltage and heatsinks on the transistors?

I had completely missed it. See! Not getting all my alerts! I didn't realize it until around page 4.

No. An LM386 is not hifi and cannot use a supply voltage high enough to make much power. It is made for kids toys and clock radios.
A few around your house would sound good enough if the speakers are good enough. If an LM386 drives a pair of TIP transistors then the resulting losses results in very low output power.


A half decent small speaker in a sealed enclosure produces poor bass. When a port is tuned to the speaker's free air resonant frequency then the port produces pretty good bass.

That's fairly sad news. What opamp would you recommend and how do I increase my voltage gain with my ab class? Also the case will have holes for the speakers. Just not the components. Plan on sealing the off enough so to much dirt doesn't get in. This will be an around the job site item.

You wouldn't need fans or air holes. With the circuits you are considering a fairly large (maybe 6" by 12" by 1") would be enough without a fan. You would need to check that because I am not an expert in heat sinks. But you really should heat sink the transistors now so you make sure you don't fry them. A $15 heat sink is good

I shouldn't need any at the moment. I'm learning to build a proper circuit first so I can advance to a higher power one that will likely need cooling.

 

That's fairly sad news. What opamp would you recommend and how do I increase my voltage gain with my ab class? Also the case will have holes for the speakers. Just not the components. Plan on sealing the off enough so to much dirt doesn't get in. This will be an around the job site item.

There are many audio opamps available. An older one but still available is an NE5532 that costs $1.53US at Digikey today. Its typical gain is 100,000 which is plenty.

A TIP pair driving 6.25W into an 8 ohm speaker has a peak output current of 1.25A and since its minimum current gain is about 20 then its input needs 63mA.
But the opamp and most other opamps cannot produce that much current so compound TIP transistors (a total of 4) are needed. Compound transistors have a current gain of 400.
The compound transistors allow the opamp to work with a supply as high as its maximum which is 44V then the maximum output of an amplifier that uses compound TIP transistors and this opamp with a 40V supply is about 20W into an 8 ohm speaker or almost 40W into a 4 ohm speaker with very low distortion.

 

There are many audio opamps available. An older one but still available is an NE5532 that costs $1.53US at Digikey today. Its typical gain is 100,000 which is plenty.

A TIP pair driving 6.25W into an 8 ohm speaker has a peak output current of 1.25A and since its minimum current gain is about 20 then its input needs 63mA.
But the opamp and most other opamps cannot produce that much current so compound TIP transistors (a total of 4) are needed. Compound transistors have a current gain of 400.
The compound transistors allow the opamp to work with a supply as high as its maximum which is 44V then the maximum output of an amplifier that uses compound TIP transistors and this opamp with a 40V supply is about 20W into an 8 ohm speaker or almost 40W into a 4 ohm speaker with very low distortion.

That is awesome. Might I ask what do you mean by compound? Also, and I know Ive asked before, why do Bluetooth and car radios get so loud on only 12 volts of input voltage? Not meaning manufactured consumer amps. Just the radio 12volts or BT speaker on much less than 12volts have a fairly high output? Is that to do with it possibly being digital or using toroid's? That's where I keep getting hung up is everything gives me watts but also needs such a high voltage. I have batteries but I'd hate to carry my BT speaker setup on a dolly because it has 400lbs of batteries in it.

 

Consumer audio stuff is very likely to utilize the Class D amp configuration that everyone keeps mentioning.
Cannot be beat for size / efficiency / cost reasons.

 

Little Bluetooth and car radios produce loud sounds when powered from 12V because:
1) Bridged amplifiers are used that produce almost 4 times the power of an ordinary amplifier.
2) 4 ohm speakers produce 2 times the power of 8 ohm speakers.

Here is a description of a "compound transistor" that has a lot of current gain, and how they are used as the output stage of an audio amplifier:

 

Consumer audio stuff is very likely to utilize the Class D amp configuration that everyone keeps mentioning.
Cannot be beat for size / efficiency / cost reasons.

Yea I figured as much. Seems like it was the standard even back in the 90s. Was looking for something manufactured, not class d, to trace it's circuitry.

 

Car amps are loud because they employ a DC-DC converter to boost 12V to 80V.

 

Of course if you boost the DC voltage then you can have lots of amplifier power.
Here is a VERY powerful subwoofer for a car. Its weight is so much that two strong guys can barely carry it:

 

Car amps are loud because they employ a DC-DC converter to boost 12V to 80V.

Now that makes more sense. Still I don't think anyone has explained how to increase voltage using an ab circuit. Only that it increases current.

 

Now that makes more sense. Still I don't think anyone has explained how to increase voltage using an ab circuit. Only that it increases current.

And what you just wrote doesn't make any sense.
A class-AB amplifier doesn't increase the voltage beyond what is supplied by the power supply.
If the power supply delivers 12V then 12V is the max voltage you can get (assuming we are not employing a boost converter).
You increase the current by decreasing the resistance of the load.

 

Very high power car amplifiers use a voltage boosting circuit so that the high power amplifier has an 80V power supply.
If the power supply voltage is 80V then the voltage swing across the speaker will be max 75V p-p which is 25.5V RMS that produces 88W in an 8 ohm speaker or about 150W in a 4 ohm speaker. If you bridge two of these amplifiers then the power in a 4 ohm speaker will be about 525W.