Mixing PC Speaker Out into TDA2005

Discussion in 'General Electronics Chat' started by BReeves, Feb 28, 2014.

  1. BReeves

    Thread Starter Member

    Nov 24, 2012
    I am building a replacement circuit for an existing kiosk because the audio chip the kiosk originally used is no longer available. The original audio circuit used a stereo amplifier but only used the Right output of the Computers audio into one channel of the amp. The other channel was not used and had the input shorted to ground. What I would like to do is combine the two channels of the PC speaker output into the input of a TDA2005 wired for Mono.

    The attached schematic kinda shows what I have in mind. The Volume Control pot is an existing component in the kiosk and is wired as shown. (Have no idea why they didn't tie the bottom of the pot to ground). It looks like from the data sheet the input impeadance of the TDA2005 is 70K at 1kHz. I really have no idea what the output impediance of the Speaker out of a typical PC audio board is, 600ohms?

    Looking for ideas on how best to utilize the existing volume pot without rewiring it and resistor values for my combiner circuit. Thanks...
  2. MrChips


    Oct 2, 2009
    The resistor values are not critical.
    Try 100Ω for starters.
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    If you have copied the bridge amplifier setup from the data sheet you should be safe regarding that part. Is the input stage copied from the old amp? In most cases the main output of PC sound card, will be able to drive a 32 ohm headphone without problems
  4. BReeves

    Thread Starter Member

    Nov 24, 2012
    Thanks for the quick responses, what I'm not sure about is how well the volume control will function as a simple series resistor and how the input resistor values might effect how well the control works.

    Yes the schematic is a copy from the TDA2005 data sheet, all I added was the input and output. I didn't try to draw a circuit of the existing input, the chip they used has a 220nf cap on the input and assumed it had a fairly high input impedance compaired to the TDA2005.

    I would bread board the thing but the TDA2005 won't directly plug into a breadboard which would make it dificult. I am going to have boards made once I get it nailed down.
    Last edited: Feb 28, 2014
  5. luvv


    May 26, 2011
    Just pulled apart five sets of pc speakers,four of them where 4 ohm,one 10 ohm.

    Could I ask why you decided to go w/ a diy amp opposed to one of the many 8-12$ complete amps on ebay?

    Most of them make use of the same line of amp ic and come with all the other bells and whistles.

    I ordered two of these for 18$ with free shipping,you get two ic(s) per device.
    One TDAxxxx that handles L/R and one basic push pull for "super bass".
    That, along with volume,bass,treble,power nobs it's a steal.
  6. BReeves

    Thread Starter Member

    Nov 24, 2012
    Ya, I looked at the eBay amps but decided because I need specific connectors to accommodate the existing wiring it would be better to build it myself. I have 10 of these things to retrofit and once I get the board layout done and have boards made it won't be too bad.
    luvv likes this.
  7. BReeves

    Thread Starter Member

    Nov 24, 2012
    Reviewing the schematic again.. I'm thinking I need to move R10 to Pin-1 of J2. With R10 tied to ground on the input of the IC when the volume pot is set to max resistance it will help shunting the audio. Still may not be able to turn it down far enough to turn it off but that isn't really a problem.