Need help

[catcat]

Need help making an audio amp that runs on a 9-12 vdc power supply for an 8hm: speaker.

 

[ljcox]

Need help making an audio amp that runs on a 9-12 vdc power supply for an 8hm: speaker.

You could buy a kit. See the kits section in www.jaycar.com.au they have an outlet in the USA.

 

[Hero999]

https://www.electro-tech-online.com/custompdfs/2006/11/LM386.pdf

 

[mramos1]

electronickits.com. I spent $16US on a 2 channel (stero) unit that works very well. Sure they will have something.

 

[audioguru]

While you are in Australia buying that cheap kit, can you get a couple of baby kangaroos for my daughter?

A cheap little audio amp operating from only 9V will have an output power of only 400mW into an 8 ohm speaker, about like a small clock radio.

With 12V then a cheap amplifier will have an output power of 500mW and a good amplifier IC will have 1.5W into an 8 ohm speaker, or 3W into a 4 ohm speaker. A bridged car radio audio amplifier IC will have an output of about 11W into a 4 ohm speaker, or 17W with a 14.4V supply.

Philips has an audio amp IC for cars that is bridged and doubles the supply voltage on demand. It has an output (RMS power, not peak power) of 60W into a 4 ohm speaker.

Your choice. Puny 400mW or pretty loud 60W.

 

[catcat]

I dont really need more than 80dB but more would be better.

 

[audioguru]

A sound pressure of only 80dB can easily be exceeded with headphones with only 60mW of power.
My clock radio has a max loudness of 80dB when it is close to me.
My pc speakers have an average loudness of 80dB and a max loudness of 90dB from its 3W per channel amplifier.
The stereo in my living room has a loudness of 80db in my kitchen.

How much power do you need from an amplifier?

 

[catcat]

1w would be enough.

Is it possible or practical to make a bridged amplifier with a single polarity supply?

I could use a 4hm: speaker.

 

[audioguru]

In the "good old days", normal sized audio amp IC were made and I made many. Now they are all in tiny surface mount packages made for cell phones.

Texas Instruments have some nice little ones that maybe you could use and one has an output of 1W into a 4 ohm speaker with only a 3.6V supply. TPA6211A1.

National Semi used to make many audio amp ICs that I made. Now they are all very high power (and very high quality and very high price) or tiny little things. One has "bumps" on its bottom for a machine to solder with hot air.

Philips and ST Micro make many normal size bridged car radio amp ICs that have 12W into a 4 ohm speaker with a 12V supply.

 

[Nigel Goodwin]

Is it possible or practical to make a bridged amplifier with a single polarity supply?

Yes, more than practical, there's no reason to use a split supply for a bridged amplifier - it provides no real advantage. Most 'bridged only' amplifiers only use single supplies, but if it's switchable it's very likely to use split supplies.

 

[catcat]

What IC's can you recommend?

Can you make a bridged amplifier by connecting the speaker terminals each to the output of an amplifier ic and running oneIC through the regular input and the other one through the inverting input?

 

[audioguru]

You can't bridge two little LM386 1/2W amps because with an 8 ohm speaker then the current will be twice as high as their max rating so instead of the speaker getting the power, the amps will melt instead.

A good bridged audio amp made for cars that is still available is the TDA2005. Its output is 11W or 12W into a 4 ohm speaker with a 12V supply, or about 6W into an 8 ohm speaker. Its absolute minimum supply voltage is 8V so it can't be powered from a little 9V battery that would quickly drop to 6V.

 

[Hero999]

Why not just a single LM386?

The datasheet says it will deliver 700mW into 8hm9V, whould it not be unreasonable to assume it might be able to give 1W@12V?

Either way, I can see why it isn't a good idea since the THD is a bit too high so it won't sound very good.

What about the TDA7052? The maximum output at 12V isn't shown on the datasheet but there's nothing stopping you adding a voltage regulator to the supply.

 

[audioguru]

Why not just a single LM386?

The datasheet says it will deliver 700mW into 8hm9V, whould it not be unreasonable to assume it might be able to give 1W@12V?

Semiconductor manufacturers play the numbers game with the power ratings of amplifier ICs.
They turn up the volume way past where clipping begins to where the output is an awful-sounding square-wave with 10% distortion.

The LM386 has very low distortion up to clipping. A graph in its datasheet shows that clipping begins at an output of 180mW into 8 ohms with a 6V supply. But they rate it at 325mW!

Therefore their rating of 700mW into 8 ohms with a 9V supply calculates to only 388mW at clipping.

With a 12V supply I think the poor little IC will melt at full power. Most of the power will be heat with the speaker getting only a little.

I didn't remember the TDA7052 because its distortion is too high for me.