Shop OBEX P1 Docs P2 Docs Learn Events
12V speaker amplifier for 3.3V PWM — Parallax Forums

12V speaker amplifier for 3.3V PWM

ericballericball Posts: 774
in General Discussion
I'm hoping someone can point me to an existing simple & cheap circuit I can use or (even better) something prebuilt I can buy cheaply.

I want to take the 3.3V PWM audio output from a microcontroller and amplify it up to drive speakers (spec suggestions welcome) using a separate 12V 1A supply. External volume control would be nice.

I've seen some circuits, but they don't specify the input voltage range.

Comments

  • kwinnkwinn Posts: 8,697
    Almost any 12V or higher amplifier module should be able to do this. Most will be expecting a 0 - 1V RMS input signal so should handle the nominal 3.3V P-P signal from the prop without a problem as long as there is a series capacitor of at least 10uF on the output from the propeller.
  • Wuerfel_21Wuerfel_21 Posts: 5,053
    Note: You want the series capacitor to be bigger than 10uF if you want it to not sound tinny and bad. 47uF seems okayish.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    An adequate series capacitor size depends upon the input impedance of the amplifier. Higher impedance implies lower required capacitor value.

    -Phil
  • CircuitsoftCircuitsoft Posts: 1,166
    Look up the TDA7266M.
  • kwinnkwinn Posts: 8,697
    ericball wrote: »
    I'm hoping someone can point me to an existing simple & cheap circuit I can use or (even better) something prebuilt I can buy cheaply.......

    Sorry, should have put this in my first post but got distracted. Lots of inexpensive audio amplifier modules available from multiple suppliers if you google "audio amplifier module". Here is one example.
  • JRoarkJRoark Posts: 1,215
    If you want something low power, cheap, and dirt simple, its hard to beat an LM386. Available in an 8 pin DIP for breadboarding and also in small outline packages. Can be easily adapted to a single rail supply too. There are lots of reference schematics on the web.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2019-08-22 02:59
    JRoark wrote:
    ...its hard to beat an LM386.
    Well, no it's not. The LM386 is last century's news. It has a huge disadvantage of requiring a large series output cap ahead of the speaker. There are much better options available today that can drive a speaker differentially in efficient Class D mode without any output cap, e.g.:

    https://www.maximintegrated.com/en/products/analog/audio/MAX9744.html
    https://www.adafruit.com/product/1752

    -Phil
  • RaymanRayman Posts: 14,641
    Not sure what you're doing, but it'd be a lot easier to use a MAX4410 to drive a headphone jack that you connect powered speakers to...
  • JRoarkJRoark Posts: 1,215
    Phil Pilgrim (PhiPi) wrote: »
    JRoark wrote:
    ...its hard to beat an LM386.
    Well, no it's not. The LM386 is last century's news. It has a huge disadvantage of requiring a large series output cap ahead of the speaker. There are much better options available today that can drive a speaker differentially in efficient Class D mode without any output cap, e.g.:

    https://www.maximintegrated.com/en/products/analog/audio/MAX9744.html
    https://www.adafruit.com/product/1752

    -Phil

    Listen, ya young whippersnapper... dont make me whup ya with my cane. I’ve got 300 of ‘em rolled-up in leaded paper and cosmoline from back when Reagan was president... back when real men only needed 64K, 8 bits, and a toggle-switch boot loader!

    On a serious note, I love them for breadboarding. But yeah, there are definitely better options out there. I cant imagine a Propeller-heads junk drawer without at least a few rolling around in it. YMMV.

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2019-08-23 00:39
    JRoark wrote:
    Listen, ya young whippersnapper...
    I'm 70. You must really be old! :)

    But, yeah, I still have a few of those venerable chips, and breadboard one from time to time.

    -Phil
  • ericballericball Posts: 774
    @"Phil Pilgrim (PhiPi)" thanks for the links, I think the MAX9744 and the Adafruit board has definite potential. The one thing missing from the Adafruit board is a lowpass filter on the input as I suspect it is a bad idea to feed a PWM signal directly into MAX's HF modulator. However, the board includes a lot of other nicely thought out features (e.g. generating 3.3 VDD from the PVDD to avoid ground loops).

    The one thing I haven't been able to figure out from the available documentation for the MAX9744 is how the gain works. The datasheet says the amplifier has an internal 20dB gain plus the volume setting of -92.8dB to +9.5dB plus the gain set by the external feedback resistor over the input resistance. From pSpice I can get the input voltage swing and current, but I want to anticipate how much current it is going to try to draw from the 12V power source (assuming Adafruit #1732 speakers).
Sign In or Register to comment.