iPod Lineout to Speaker Amp

Discussion in 'The Projects Forum' started by blah2222, Dec 7, 2012.

  1. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Hi,

    I have a hacked iPod lineout cable giving me access to R and L channels that have between 1-2 V swing. I would like to have that audio play clearly thru my 4ohm 8W speaker and was wondering what IC amp is recommended. The LM386N doesn't budge past 1.25W and sounds pretty bad.

    Any suggestions?

    P.S. Is a JFET preamp recommended with this input?

    Cheers!
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    This works well for me; no preamp required. Powered by a regulated 12 VDC wall wart. Or did you want mono?
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The TDA1517 IC has flea power.
    With a 14.4V supply its output into 4 ohms is 5W at fairly high distortion (0.5%).
    Into 8 ohms and with a 12V supply its output is only about 1.5W, like a cheap clock radio.

    A Jfet preamp is used with a very high impedance guitar magnetic pickup.
     
    blah2222 likes this.
  5. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    I only have room for the one speaker in the enclosure I'm using so I'm going to be combining L and R into one signal, so mono.

    I've got 8ohm 10W (6") and 4ohm 8W (4") speakers at my disposal. Is the sound quality just a question of matching speaker power with a suitable amplifier IC?
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    I have also built this, and it sounds good to me.
     
    blah2222 and absf like this.
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Speaker power is simply loudness, not audio quality.
    A speaker produces good audio quality when it has a flat wideband frequency response and low distortion. Most little speakers like your 4" and 6" need an enclosure designed for their detailed spec's. those spec's and the size of the enclosure determines the low frequency response.
    A little 4" or 6" speaker cannot produce deep bass sounds.
     
    blah2222 likes this.
  8. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    So for my speakers, I understand that the impedance of 4 or 8ohm is most likely an average but what is the power rating? Max or min? I'm assuming it's a fairly conservative maximum.

    Is there a rough power amount that would allow for one of my speakers to give off decent volumes to hear in a bedroom? As in what wattage: 0.125W, 0.5 W, 1W, ... would need to be met to receive decent volume levels?
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The power rating of many amplifiers and speakers is the momentary peak power (not continuous power) that damages the amplifier or speaker then it is multiplied by the age of the person making the rating. It is a useless rating.

    An amplifier with a truthful rated output power of 1W to 5W is fine for background music or TV sound in a bedroom. If you know the supply voltage to the amplifier and the impedance of the speaker then it is easy to calculate the truthful power output.
     
    blah2222 likes this.
  10. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Thank you!
     
  11. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    If anyone is curious I managed to get a really nice sound out of my iPod's line-out passing its through an LF411 with a gain of roughly 1/3 to bring the signal down for an LM386 wired for a gain of 20.

    Using my 8ohm 6" speaker at 75% volume I'm getting around 0.75W output power (closer to 0.9W at max volume).

    LM386N has a max of 1.25W, so this has some breathing room.
     
  12. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    I have been using an LM386 amp with my MP3 player for several months. It's set up for a gain of 50, and I just turn the MP3 player down.

    I also have a guitar practice amp that uses a MPF102 and an LM386 that sounds quite good to me. Despite what some think, I like the LM386. Not everyone wants or needs high power and huge speakers.

    And I suppose you know that it's possible to reduce the gain on the LM386 to less than 20.
     
  13. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Yeah, the MPF102 and LM386 are my go-to's for guitar/audio stuff for around the house and I am content with the sound as well.

    I have seen some articles on it but isn't the signal fairly unstable sub 20?
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The datasheet for the LM386 bshows that it overheats if its speaker is 8 ohms, its supply is 13V and output at clipping is 0.55W.

    The datasheet says it is stable with a gain greater than 9.
     
  15. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    I see the comment about stable gain >9. But how are you determining your second point about the overheating.

    Is that based on the second last plot of Dissipation vs. Output Power (DS006976-18)? Not sure if I see that as clearly.

    EDIT**

    Are you seeing the flat response >=0.55W for the 12V supply as overheating? Hm interesting, I didn't know that.
     
    Last edited: Dec 8, 2012
  16. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The graph of Peak-to-Peak Output Voltage Swing vs Supply voltage shows that when the supply is 11V or more the output voltage swing does not increase higher than about 6.5V p-p with an 8 ohm speaker when the supply is increased higher. Therfore the IC simply heats more. The output power at clipping is about 0.55w.

    The graph of Device Dissipation vs Output power - 8 ohm load shows that with a 12V supply and an output of 0.55W the heating is 0.8W. With a supply of about 13V or maybe 14V then the heating is about 1.1W when the output power into 8 ohms is 0.55W.

    The spec's say that the chip will be at its max allowed temperature of 150 degrees C in an ambient of 30 degrees C when the heating is about 1.1W.
     
    blah2222 likes this.
  17. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Ah, I see now. Thank you for the clarification.

    I am using a 9V battery along with an 8ohm load.

    Max Output Power = (\frac{6Vpp}{2\sqrt{2}})^{2}(\frac{1}{8}) = (\frac{36}{8})(\frac{1}{8}) = 0.5626W

    That puts the IC at roughly 0.5W dissipation.

    Max Junction Temperature = (107)(0.5) = 53.5C

    Looks okay to me with a 9V.
     
  18. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The distortion is horrible at the max p-p voltage swing. I multiply the resulting power by 0.8 to get the max low distortion output power.

    You probably will not play continuous organ sustained tones which will slowly heat the IC, instead you will probably play regular music with an average power of 1/5th to 1/10th the max power thenb the IC will be warm instead of hot.
     
  19. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    This is true. The IC was hardly warm with continuous play for ~20minutes.
     
Loading...