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Better than LM386 on batteries?

Discussion in 'Electronic Basics' started by phaeton, Dec 18, 2007.

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  1. phaeton

    phaeton Guest


    I intend to build a stereo headphone mixer/amp type device for mixing
    bass guitar signal and the output of an mp3 or cd player. The preamp
    will be a couple of TL082s or similar dual opamps (plus various stereo
    pots and filter circuits, etc), and for the power section my first pick
    was going to be a pair of LM386s. I was going to run it at 18V for the
    clean headroom, and I was going to leave the gain set at 20 instead of
    200 (pins 1 and 8 not connected).

    IIRC, even in this state, the 386 is actually overkill for headphone
    operation, and it tends to consume a lot of power. I would prefer this
    device to be battery powered (so I can walk around with it wirelessly).
    Are there any newer, more efficient, or
    lower-powered-but-adequate-for-headphones type of chipamps that anyone
    could recommend?

    Or is battery life just the price you pay when you want to physically
    move stuff with electricity?


  2. Eeyore

    Eeyore Guest

    How loud do you want it to go ?

    You can drive headphones from an op-amp output (typically via 100-150
    ohms) if you don't need deafening volume.

    I wouldn't suggest a TL082 for that stage btw, a 5532 would be a better

  3. LAB

    LAB Guest

    TDA7053 for a battery powered headphone amp;

    NJM4580 or NJM4560 give more power if you have +/- 12 or 15V. You can
    also use the two sections of a TL072 for each channel (FidoCAD, :

    [FIDOCAD ]
    LI 65 70 65 55
    LI 65 55 90 55
    MC 95 75 0 0 080
    LI 90 75 95 75
    LI 65 80 65 90
    LI 65 90 90 90
    LI 90 90 90 75
    SA 90 75
    LI 110 75 105 75
    MC 95 35 0 0 080
    LI 90 55 90 35
    SA 90 35
    LI 90 35 95 35
    LI 110 40 110 75
    LI 105 35 110 35
    LI 110 40 110 35
    SA 65 30
    SA 65 40
    LI 110 55 125 55
    LI 125 55 125 60
    MC 125 80 0 0 045
    LI 125 75 125 80
    SA 125 75
    SA 125 65
    LI 125 60 125 65
    TY 20 30 5 3 0 0 0 * OP AMP inputs
    TY 130 65 5 3 0 0 0 * Headphone
    SA 110 55
    TY 70 45 5 3 0 0 0 * TL072
    MC 65 70 0 0 580
    TY 75 70 5 3 0 0 0 * b
    MC 65 30 0 0 580
    TY 75 30 5 3 0 0 0 * a
    TY 90 25 4 2 0 0 0 * 100 or 150 Ohm
    TY 90 65 4 2 0 0 0 * 100 or 150 Ohm

    Hash: SHA1
    Various places do specially designed headphone power amplifiers. National
    do a nice looking headphone amp: LM4882. I haven't tried it out but the
    specs look great. Furthermore, you can run it off 5volts if you want - no
    need for a noisy charge pump.

    - --
    Brendan Gillatt
    brendan {at} brendangillatt {dot} co {dot} uk
    PGP Key:
    Version: GnuPG v1.4.3 (MingW32)

    -----END PGP SIGNATURE-----
  5. LAB

    LAB Guest

    you can run it off 5volts if you want - no need for a noisy charge pump.

    Yes, charge pump is very noisy. For audio I use NE555 / push pull
    2SB1166+2SD1723 / a little toroidal transformer / fast diodes @120kHz... No
  6. Clint Sharp

    Clint Sharp Guest

    You can drive headphones from an op-amp *and* have deafening volume if
    you really want! Think LM48 and L165B plus any number of newer devices.
  7. PhattyMo

    PhattyMo Guest

    Google for "CMOY headphone amp" That should get you one such example.
    I've actually built a CMOY,not bad at all,for such a simple amp. It
    might have troubles driving low impedance 'phones to insanely high
    volumes,but it doesn't have any problem driving my 32ohm Panasonic's to
    ear-splitting levels. (well above any 'normal' listening level!). But
    I'm using +/- 9V rails,delivered by two small DC-DC converters.
    (salvaged from old 10meg Ethernet cards.)
  8. Eeyore

    Eeyore Guest

    Where do yoiu get the little toroidal transformer ?

  9. LAB

    LAB Guest

    Yes, charge pump is very noisy. For audio I use NE555 / push pull
    I salvage switching components everytime i get broken PSU's. I measured
    inductance of a few turns and chosen the core, only the core. Diameter is
    about 16mm. Primary is 24 turns 0.7mm, secondary is 80 turns 0.4mm, then I
    get +/-15Vcc rectifing + and - separatly. Primary L is about 120uH,
    frequency is 120kHz.

    There is NO feedback. I thought: when I connect a transformer to 240Vac
    I rectifier the output, nothing else. Let's do the same... Negative feedback
    introduces low frequency (audio) noise due to the correction delay. If I
    have no feedback, I can't have noise before the switching frequency, that is

  10. phaeton

    phaeton Guest

    Thanks everyone! Hopefully this long holiday weekend will afford me
    some time to breadboard up some bridged opamps. I presume that
    they'll automagically run like a Class AB. Special thanks to LAB for
    the link to FidoCAD. Excellent program! It's the stripped-down no-
    nonsense SPICE I've been looking for.

    Graham, are you unrecommending the TL082 for the headphone driver, or
    just the whole circuit in general? And, why?

    Also, *could* opamps drive a typical 4 or 8 ohm speaker without
    blowing up?

    I had looked at the CMOY once a couple years before, and forgotten
    about it until PhattyMo just mentioned it. I forget why I didn't
    build it then, maybe because (at the time) I thought the opamps it
    lists are "special" somehow and they aren't carried by my fave
    distributor, or something. Maybe I should just try it out with the op
    amps I have.

    Thanks again!

  11. Eeyore

    Eeyore Guest

    Not the TL082 since its current drive isn't that good but a 5532 or
    4560/4580 op-amp can drive headphones quite effectively if you use a 100
    ohm series resistor.

    Because the LM386 has rubbish audio performance ! It's real dog of a chip.

    They won't 'blow-up' because they have internal current limiting. They
    would however be entirely unsuitable as speaker drivers as they can only
    deliver some 30mA or so.

    His choice of op-amp is somewhat esoteric. You certainly don't need the
    OPA2132. Try what you have but the TL07/8x series isn't a good choice in
    this instance.

    Hash: SHA1
    Oh they are special - they're spectacularly expensive ;]
    The Burr-Brown parts have fantastic specs, however, if you need it.

    Furthermore, if your distributor doesn't carry them you can always
    request a couple of samples. From my experience TI seem pretty good to
    their customers, samples included.

    - From my memory of building a CMOY, I recall that the specs for the part
    he chose have an enormous current handling capability - ideal for driving
    speakers/headphones without clipping.

    Saying that, most regular op-amps will drive earphones to a decent level.

    If you are going to build a CMOY don't don't don't use a 9v battery - the
    life through a pair of 64ohm 'phones is, perhaps, 3 hours! Use some good
    NiMH AAAs or consider looking at lithium polymer batteries.

    - --
    Brendan Gillatt
    brendan {at} brendangillatt {dot} co {dot} uk
    PGP Key:
    Version: GnuPG v1.4.3 (MingW32)

    -----END PGP SIGNATURE-----
  13. Eeyore

    Eeyore Guest

    It has insanely low THD figures (0.00008%). Somewhat better than the LM386's
    0.1% or so.

    It's only +/- 40mA actually. A mere 2mA better than a 5532.

    Don't forget the 100 ohm series resistor.

    Hash: SHA1
    My bad memory then! I thought it was in the range of 150-200mA.

    - --
    Brendan Gillatt
    brendan {at} brendangillatt {dot} co {dot} uk
    PGP Key:
    Version: GnuPG v1.4.3 (MingW32)

    -----END PGP SIGNATURE-----
  15. phaeton

    phaeton Guest

    A 3 hour practice session on the guitar or bass probably should be
    followed by a break anyways.

    That said.....Oh how i pine for the days when we will have small,
    safe, and adjustable nuclear power cells that will put out a constant
    amount of power and last forever. That may be lofty, but i sure hope
    that some huge revolution in battery technology is within the decade.

    For this device, I was probably going to use rechargeables. Or just
    plug it in and deal with the lack of mobility. I even mused taking
    apart an old sony Discman, identifying the necessary circuit bits, and
    kitbashing my circuit and the Discman all into the same housing with a
    single power supply, but I guess I'm not that ambitious.

    The Burr-Brown chips are significantly overspec'd for my application,
    at least as far as the THD figures are. Especially since I'm kinda
    sorta planning a distortion circuit for the instrument input anyways.
    Ideally, it would have that and some sort of mid-hump tone control,
    but the more I think about it, the more features I want to add, and I
    tend to overcomplicate everything I do. I've been trying to practice
    the K.I.S.S. philosophy. Just go back to the original plan of 3
    simple audio channels each with their own separate volume and pan
    control. In any event, I've got 3 RC5532s in my parts collection.
    I'll still have to use TL082s or some other opamp for the rest.

    Hash: SHA1
    While you're building effects might I point you to a very neat little

    Works great and definitely goes along with the KISS mindset =]

    - --
    Brendan Gillatt
    brendan {at} brendangillatt {dot} co {dot} uk
    PGP Key:
    Version: GnuPG v1.4.3 (MingW32)

    -----END PGP SIGNATURE-----
  17. phaeton

    phaeton Guest

    Excellent circuit! Looks like it will be a lot of fun.

    Say, btw... is there anything else I should be using to search for
    100K stereo pots w/ audio taper? I'm completely striking out at the
    following places:

    with permutations of "stereo potentiometer" and "dual ganged pot" and
    "stereo volume pot" and such. Even rifling through the hits of
    "potentiometer" doesn't seem to show them. Radioshack has it, but
    they're a last resort.

    I could swear I bought one online once before, and I would expect
    these to be a fairly standard item. Did someone cut down the last
    stereo pot tree?

  18. --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  19. Eeyore

    Eeyore Guest

    TL082s will be good for the high input impedance input stage you should have to
    avoid destroying the 'tone' of your guitar. Mind you it's less of an issue with
    bass guitars.

  20. phaeton

    phaeton Guest

    Thanks for the links. Mouser's website search feature is pants, but I
    forgot that the PDF catalogue is the way to go.

    Btw, in that FidoCAD example, (I could provide a jpg if necessary), I
    can hook up the top opamp like a normal inverting or non-inverting
    gain stage, right?


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