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Topic: Small Class D amplifier (Read 4984 times) previous topic - next topic

permnoob

If this isthe wrong forum and this should be in electronics, please move, but this seems right...

So I need to amplify a small pulse, with modestly high peak power and low average power.  Battery life is concern #1 so I am looking at class D amps.  Power needs are still up in the air, but probably on hte order of 5W.  I am currently using a TDA2030 which is a lovely but obsolete monolithic AB amp that is super easy to use, but I want to try and up the efff w./ a class D.  The catch is since it is battery powered, I want to stick with a single +13v supply to keep things simple and not have a neg source eating up power.  THe pulse itself is only positive going, so there is no need for a negative supply anyways.  output will be into a speaker network, i am hoping I can put several in parallel to dropthe eff resistance to whatever the minimum the amp can handle will be to try and boost the power, otherwise I will need to boost the amp voltage which is not a thing i want to have to do.

So tell me, does anyone know of a low power class D amp that comes as an all in one chip, and can be run from a single supply?

retrolefty

Maybe search out the datasheet for the PAM8610  chip used in module like this:

http://www.ebay.com/itm/Digital-Amp-Audio-Amplifier-Module-10W-10W-2-Channel-Class-D-/221239184525?pt=US_Home_Audio_Amplifiers_Preamps&hash=item3382e20c8d

CrossRoads

Single supply amps for driving speakers:

http://www.parts-express.com/2x8w-at-4-ohm-tpa3110-class-d-audio-amplifier-board-only--320-329
http://www.parts-express.com/pam8610-2x10w-class-d-audio-amplifier-board--320-604
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

JChristensen

Adafruit has several, the one I looked at has very low standby current.

http://www.adafruit.com/search?q=class+d

DVDdoug

Quote
i am hoping I can put several in parallel to dropthe eff resistance to whatever the minimum the amp can handle
A Bad, bad, bad, idea! :(   The general rule is NEVER connect outputs together. (That's why you use an audio mixer to mix audio signals.)   Solid state amplifiers have very low internal source impedance (often less than one Ohm).   The output of one amp "shorts out" the output of the other.

The most common "trick" is to make a bridge amplifier.    That doubles your peak-to-peak output voltage (theoretically 26V P-P = 9V RMS) with a 13V power supply) and that gives you 4 times the power into the same load.  Doubling the voltage doubles the current, so an 8-Ohm speaker "looks like" a 4-Ohm speaker to each amplifier.   In theory you can get about 10W into 8 Ohms, but there is some voltage drop across the transistor/MOSFET and you can't actually get the full power supply voltage across the speaker.

High power automotive amplifiers have a voltage-boosting power supply.


retrolefty


Quote
i am hoping I can put several in parallel to dropthe eff resistance to whatever the minimum the amp can handle
A Bad, bad, bad, idea! :(   The general rule is NEVER connect outputs together. (That's why you use an audio mixer to mix audio signals.)   Solid state amplifiers have very low internal source impedance (often less than one Ohm).   The output of one amp "shorts out" the output of the other.

The most common "trick" is to make a bridge amplifier.    That doubles your peak-to-peak output voltage (theoretically 26V P-P = 9V RMS) with a 13V power supply) and that gives you 4 times the power into the same load.  Doubling the voltage doubles the current, so an 8-Ohm speaker "looks like" a 4-Ohm speaker to each amplifier.   In theory you can get about 10W into 8 Ohms, but there is some voltage drop across the transistor/MOSFET and you can't actually get the full power supply voltage across the speaker.

High power automotive amplifiers have a voltage-boosting power supply.




And for 'bridging' to work the audio signal input must be inverted 180 degrees in one of the amps.

permnoob

wow that's a lot of sources quick, thanks guys!  I'll take a look at em now. 

@retrolefty and DVDdoug:  I meant put the speakers in parallel, not the amps, so I can drive more power at the same voltage.  However since class D amps are 'digital' I figure they are a bit harder to predict how they will behave outside of thier rated range of loads compared to AB amps.  Gotta dig into the datasheets to konw for sure.  stupid low voltage supply, BUT since it is so close to automotive range, I know there must be devices out there specifically for it.

retrolefty


wow that's a lot of sources quick, thanks guys!  I'll take a look at em now. 

@retrolefty and DVDdoug:  I meant put the speakers in parallel, not the amps, so I can drive more power at the same voltage.  However since class D amps are 'digital' I figure they are a bit harder to predict how they will behave outside of thier rated range of loads compared to AB amps.  Gotta dig into the datasheets to konw for sure.  stupid low voltage supply, BUT since it is so close to automotive range, I know there must be devices out there specifically for it.


Well keep in mind that 'digital' class D amps are still analog as seen by the speaker loads as there is a low pass filter output stage on any audio class D amp.
Also halving the speaker impedance does not automatically double the output power unless the amp is rated for the increased current demand for the decreased speaker impedance. The datasheet for the amp chips should always be studied to determine what actual power output you can get at a give device voltage and speaker impedance. There is more to it then simply ohm's law.  ;)

CrossRoads

Did you look at the specs on the others?
Specifications:
• Output power: 3W x 2 @ 8 ohms (<0.1% THD+N), 5W x 2 @ 8 ohms (<10% THD+N), 6W x 2 @ 4 ohms (<0.1% THD+N), 8W x 2 @ 4 ohms (<10.0% THD+N)
• Frequency response: 20 Hz to 20 kHz (±3 dB)
• Signal to noise ratio: 100 dB (A-weighted
) • Recommended power supply: 10 to 16 VDC

Both 4 & 8 ohm, 12V supply.

Specifications:
• Power output: 2 x 10 watts @ 8 ohms
• Efficiency: 90%
• Signal-to-noise ratio: 90 dB
• Frequency response: 20 to 50,000 Hz
• Signal input: 3.5 mm stereo jack
• Signal output: 4 wires
• Power requirements: 7-15 VDC

Quote
Power needs are still up in the air, but probably on hte order of 5W.
Quote
The catch is since it is battery powered, I want to stick with a single +13v supply to keep things simple and not have a neg source eating up power.






Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

permnoob

true, but as most amps are in the 15-30 watt range, with only a 12 v supply we are talking 10 watts peak RMS, maybe 1-2 watt average RMS on an 8 ohm speaker. (yeah its a wierd wave, normal math need not apply)  so I should have plenty of overhead to play with.  Most amps are rated at higher power to 4ohm, but if I need even more kick I don't think I've ever seen more than one datasheet that spec's to 2ohm.
as for class D being analog, yeah I get that, hence the quotes, but some qty of noise must get thru, and there are strange things that can happen when you are not playing by all the normal rules, which I am.  And when a problem is harder than you are smart, the best thign to do is just build the damn thing, take some measurements, and see if you need to worry or not then, not earlier! lol.

oh and no, II have not yet looked at the specs of ANYTHING posted here, bookmarked em to look at after lunch.

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