Small 2 x 35w amplifier board (import) does this look legit?

Discussion in 'General Electronics Chat' started by RogueRose, May 17, 2016.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
    189
    4
    I need a small amp for a set of speakers for a LCD screen. The output from the computer/dvd player will either be a headphone jack, component audio (Red/white), or USB is it can handle it.

    2 x 35watt amplifier

    [​IMG]

    [​IMG]

    It looks like the speaker outputs are on either side of the IC, Voltage input is at the front center and I guess the signal input is the " L GND R" towards the front right of the board. I guess the signal channels can share the same ground? (I never thought about that before, lol :) )

    This board is about $5.50, IDK if that is a good deal or not, or if it will be adequate for driving speakers on a 24 - 29" LCD (so it isn't a home theater, just something for a small room). I have plenty of heatsink options so that shouldn't be an issue unless I need to add a fan, that is always a little bit of a bother.

    So should this work alright?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,001
    3,229
    Looks like a good buy.
    Yes the inputs can share a ground (and typically do).
    You probably won't even need a heatsink if it's just powering a couple peak watts of TV voice audio.
    The lower the power supply voltage, the lower the dissipation for a given output.
    You probably could get by with a lower end voltage (9V or so) if all you need is TV audio.
    (How are you planning on powering it?}
    You can try it without a sink at a typical program volume level and see how warm it gets after a few minutes of operation.
    The worst-case would be if you listened to music at a high level.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Have a look at the datasheet.
    The PCB uses the 2 X bridged circuit.

    Bertus
     
    RogueRose likes this.
  4. RogueRose

    Thread Starter Member

    Oct 10, 2014
    189
    4
    So if my raspberry pi, or whatever I use to send audio signal to the amplifier connects to the amplifier, do I need a pre-amp like this?

    http://www.ebay.com/itm/Digital-Hifi-Amplifier-Stereo-Audio-Volume-Control-Combo-Kit-/141906952957

    BTW, I'm planning on using a Rasp pi for this setup to play video/music on this monitor. Someone asked about how I am going to power the device and I'm really not sure ATM as IDK what the best options are. I am pretty sure the monitors I'm using have a 5 & 12v power supply built into the "control box" in the back of the monitor.

    I'm really bad at reading the IC datasheets as all the numbers seem so far off from what is advertised, as to me it looks like this chip is designed for 2 channels x 6 watts.
    but if this device is putting out 2 x 35 watts, then I would need at least 70 watts of power correct?

    The datasheet says
    "Absolute Maximum ratings"
    -"operating supply voltage" Vod - 18v
    -"DC Supply Voltage" Vs - 28v
    -"Power Dissipation" Ptot - 36w (That is a lot of heat!!!)

    "Electrical Characteristics"
    -Supply voltage range - 8 - 18v
    -Output Power - Single Ended min 5.5w - Typcl 6w - Bridge min - 18x Typcl 20w


    So to me, it looks like if I am using 8 ohm speakers in stereo, then i'm getting MAYBE 6 watts / channel. But if I run mono/bridged, I get 20 watts (@ 4 ohm??). I could get 4 ohm speakers and bridge them to get 2 ohm, but I'm guessing I might get a lot of heat with that.
     
    Last edited: May 19, 2016
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,791
    1,103
    If the pi puts out a high enough signal and the amp has a sensitive enough input then you don't need a pre-amp; just a volume control (potentiometer).
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,001
    3,229
    The amp has a gain of 20 (26dB) when connected for a bridge output, as your circuit is, so to get a 10W output into an 8Ω speaker requires about 0.45Vrms input.
    You thus should not require a preamp.
     
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