Amplifier for speakers - Electronic Circuits Projects Diagrams Free

pball_inuyasha · 2nd August 2008, 11:34 PM

I would like to build an amp for some old stereo speakers I have. I have tried looking up different amp schematics but don't know what kind to use. If I could get some simple direction toward a particular amp type or schematic that would be of great help.

I would be using this to amplify a computer or mp3 player source for use with un-amplified speakers. I don't know how many watts those output but a 20 or more watt amp would be good. I have a 24 V .5 A power supply laying around I could use. So if anyone has any good advice that would help.

I have experience soldering and working with electronics, just no experience in making circuits and really doing more than assembling them.

Mikebits · 3rd August 2008, 12:13 AM

Quote:

I have a 24 V .5 A power supply laying around I could use. So if anyone has any good advice that would help.

That supply is too small for 20W.

Hero999 · 3rd August 2008, 12:24 AM

That PSU can only output 12W so largest output your amplifier can give is just 8W.

audioguru · 3rd August 2008, 02:19 AM

The little 24VAC transformer will make a rectified and filtered 32VDC. A single power amp with a 32V supply will have a max output of about 28V p-p. 28V p-p is 12.3V RMS which is 18.9W in an 8 ohm speaker.

Get a much more powerful transformer.

rjvh · 3rd August 2008, 02:48 AM

8 till 10 Watt is already a lot of noise

i asume that you dont run a disco so for home use it would already be fine

Robert-Jan

speakerguy79 · 3rd August 2008, 02:56 AM

Use an LM1875. And get a beefier power supply.

Mikebits · 3rd August 2008, 03:20 AM

Go for a real man supply like this one.
http://www.lambda-hp.com/product_html/esspower.htm

Intended as humor only

Mikebits · 3rd August 2008, 03:40 AM

Just to give you an idea of a part you might use (Available at Digi-key)
http://www.st.com/stonline/books/pdf/docs/1478.pdf

Guru or someone else can probably suggest a better part. I don't do much audio.

pball_inuyasha · 3rd August 2008, 03:55 AM

Ok disregard any thing related to output power I said. I am not familiar with how that is calculated and amplifiers in general.

I don't really know what to say, If someone could just refer me to a good schematic of a stereo amplifier that can run off of anything 0-20V or so and has some volume control. I could work with that.

I can always get another power supply if needed. I'm just trying to do this as a project and hopefully cheaper than buying something.

Thanks for the input so far.

audioguru · 3rd August 2008, 04:43 AM

Quote:

Originally Posted by pball_inuyasha

If someone could just refer me to a good schematic of a stereo amplifier that can run off of anything 0-20V or so and has some volume control.

An amplifier with a supply of only 20VDC will produce a max output of about 17V p-p. 17V p-p is 6V RMS which makes only 4.5W into an 8 ohm speaker. A little louder than a clock radio.

All amplifiers have a volume control.

speakerguy79 · 3rd August 2008, 05:18 AM

[quote]I don't really know what to say, If someone could just refer me to a good schematic of a stereo amplifier that can run off of anything 0-20V or so and has some volume control. I could work with that.[quote]

Read the LM1875 data sheet. Everything you need to know (schematic, PCB layout, etc) is in there.

audioguru · 3rd August 2008, 05:27 AM

The datasheet for the LM1875 shows that its output power is only about 4.5W into 8 ohms when its supply voltage is only 20V.
That is flea power for people with rice-paper walls.

The LM1875 is designed for a 50V supply. Then its power is 20W for people with cardboard walls.

pball_inuyasha · 3rd August 2008, 04:51 PM

ok thanks guys I'll take a look at that then

El Kit · 3rd August 2008, 07:39 PM

http://sound.westhost.com/project72.htm

It´s possible to use a lower Voltage supply. The formular for the output power is:

P(out) = Vcc^2 / 8*R

The output voltage of the amplifier always is at least 3V lower then the input. With the formular you get the peak-power output. The continious output is lower because the supply voltage will sink if the current will get higher.

Example:
Transformer 24VAC
Voltage at condenser = Veff * SQR(2) = 24V * 1.41 = 33.8V
Rectifieing needs 1.2V
33.8V - 1.2V = 32.6V
Amplifier needs 3V or more
32.6V - 3V = 29.6V
29.6^2 / (8*8 Ohms) = 13, 7 W maximum peak power @ 8 Ohm
The minimum supply voltage (for continiuos power) will be at minimum 27V.

Hero999 · 3rd August 2008, 08:37 PM

That formula gives peak power, doesn't account for the voltage drop across the transistors and I don't know where you got 8*R from.

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2nd August 2008, 11:34 PM	(permalink)
pball_inuyasha	Amplifier for speakers I would like to build an amp for some old stereo speakers I have. I have tried looking up different amp schematics but don't know what kind to use. If I could get some simple direction toward a particular amp type or schematic that would be of great help. I would be using this to amplify a computer or mp3 player source for use with un-amplified speakers. I don't know how many watts those output but a 20 or more watt amp would be good. I have a 24 V .5 A power supply laying around I could use. So if anyone has any good advice that would help. I have experience soldering and working with electronics, just no experience in making circuits and really doing more than assembling them.

3rd August 2008, 12:24 AM	(permalink)
Hero999	That PSU can only output 12W so largest output your amplifier can give is just 8W. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

3rd August 2008, 02:19 AM	(permalink)
audioguru	The little 24VAC transformer will make a rectified and filtered 32VDC. A single power amp with a 32V supply will have a max output of about 28V p-p. 28V p-p is 12.3V RMS which is 18.9W in an 8 ohm speaker. Get a much more powerful transformer. __________________ Uncle $crooge

3rd August 2008, 02:48 AM	(permalink)
rjvh	8 till 10 Watt is already a lot of noise i asume that you dont run a disco so for home use it would already be fine Robert-Jan

3rd August 2008, 02:56 AM	(permalink)
speakerguy79	Use an LM1875. And get a beefier power supply.

3rd August 2008, 03:20 AM	(permalink)
Mikebits	Go for a real man supply like this one. http://www.lambda-hp.com/product_html/esspower.htm Intended as humor only __________________ Pay it forward.

3rd August 2008, 03:40 AM	(permalink)
Mikebits	Just to give you an idea of a part you might use (Available at Digi-key) http://www.st.com/stonline/books/pdf/docs/1478.pdf Guru or someone else can probably suggest a better part. I don't do much audio. __________________ Pay it forward.

3rd August 2008, 03:55 AM	(permalink)
pball_inuyasha	Ok disregard any thing related to output power I said. I am not familiar with how that is calculated and amplifiers in general. I don't really know what to say, If someone could just refer me to a good schematic of a stereo amplifier that can run off of anything 0-20V or so and has some volume control. I could work with that. I can always get another power supply if needed. I'm just trying to do this as a project and hopefully cheaper than buying something. Thanks for the input so far.

3rd August 2008, 05:18 AM	(permalink)
speakerguy79	[quote]I don't really know what to say, If someone could just refer me to a good schematic of a stereo amplifier that can run off of anything 0-20V or so and has some volume control. I could work with that.[quote] Read the LM1875 data sheet. Everything you need to know (schematic, PCB layout, etc) is in there.

3rd August 2008, 05:27 AM	(permalink)
audioguru	The datasheet for the LM1875 shows that its output power is only about 4.5W into 8 ohms when its supply voltage is only 20V. That is flea power for people with rice-paper walls. The LM1875 is designed for a 50V supply. Then its power is 20W for people with cardboard walls. __________________ Uncle $crooge

3rd August 2008, 04:51 PM	(permalink)
pball_inuyasha	ok thanks guys I'll take a look at that then

3rd August 2008, 07:39 PM	(permalink)
El Kit	http://sound.westhost.com/project72.htm It´s possible to use a lower Voltage supply. The formular for the output power is: P(out) = Vcc^2 / 8R The output voltage of the amplifier always is at least 3V lower then the input. With the formular you get the peak-power output. The continious output is lower because the supply voltage will sink if the current will get higher. Example: Transformer 24VAC Voltage at condenser = Veff SQR(2) = 24V * 1.41 = 33.8V Rectifieing needs 1.2V 33.8V - 1.2V = 32.6V Amplifier needs 3V or more 32.6V - 3V = 29.6V 29.6^2 / (8*8 Ohms) = 13, 7 W maximum peak power @ 8 Ohm The minimum supply voltage (for continiuos power) will be at minimum 27V.

3rd August 2008, 08:37 PM	(permalink)
Hero999	That formula gives peak power, doesn't account for the voltage drop across the transistors and I don't know where you got 8*R from. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.