What Power Supply Should I Choose for this Amplifier?

Discussion in 'Power Electronics' started by Zohar, Oct 12, 2016.

  1. Zohar

    Thread Starter New Member

    Nov 19, 2015

    I have 2 unused speakers that I was to use, e.g. to connect some Line Out to it.

    I took them apart from an old synthesizer that I had.

    This is how they look:


    They are 11cm in diameter,
    and as can be seen, they are 4Ω, and each is 3W.

    Currently they are not connected to any citrcuit,
    so I need to buy them an Amplifier If I want to connect some Line Out output to them.

    I saw this nice Amplifier:



    It is small, compact, and also enclosed in its own case which is nice for me.

    My question:

    I intend to use it at home, not in a car,
    and it requires a 12v power supply,
    so what AC Adapter should I buy for it?

    The reason I ask, is because some time ago, a friend told me that when powering an amplifier,
    I should not use a Switching power supply (the light weight ones), and instead use a Transformer power supply (the heavy ones with the double coil).

    Is that correct?
    Must I use only a Transformer based power supply here?

    Thank you very much
    Last edited: Oct 12, 2016
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Your amp states that it requires 12V @ 5Amp
    A SMPS or a transformer supply would suffice.
    If the Amp shuts down or sound distorts when using a SMPS would mean that your SMPS is not supplying 5A. Then you should use a high Amp capacity one.
    A transformer based one for that amp will be heavier and bulky.

    If the SMPS is a good design you won't habe any issues using it. Good design means, good transient response and low output noise.
  3. Zohar

    Thread Starter New Member

    Nov 19, 2015
    Hi R!f@@

    Thank you very much for your reply.

    Allow me to put the Current subject (5A) aside for a minute, because I have a question regarding it too, that I will ask later.
    I will focus for now on the Switching mode vs Transformer based power supply.

    So you say both Switching and Transformer based, are good..
    OK, good to know

    Do you maybe have a link for buying online a good Switching Mode power supply?

    And now for the question regarding the Current:

    As you said, the product page says that the Amplifier expects a 12V 5A power input.

    I have a small regarding this.

    The amplifier chip in this amplifier is TDA7297.
    TDA7297 is defined as a 2x15W amplifier.

    My speakers here are not 15W but 3W.

    So does it mean that I really need a 5A power supply?
    Or maybe because the 2 speakers are 3W, then I need less than 5A?
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    For that to decide, you would need a good power supply.
    Connect the amp and speakers and drive it maximum music volume you like and them measure the peak current draw.
    Without a a measurement it's not easy.
    Based on what you said you need max 6W from amp, so at 12V that would be 0.5A. Taking efficiency into factor I say you will be good at 12V @ 1amp PSU.
    More power requires more current.
    Find a 12V @ 2Amp PSU and try how the music sounds, and if you can measure current.
    One cannot be sure without a signal generator and DMM capable of measuring peak current spikes. A scope will help
  5. Zohar

    Thread Starter New Member

    Nov 19, 2015
    I think that your simple calculation (which resulted in 0.5A), plus the safety gap of x2 (which resulted in 1A) is quite a good decision.

    So it means that a 12v 1A power supply (or even slightly more, like 1.25A or 1.5A which are usually very common for 12v AC Adapters) is a good and sufficient choice, for the current speakers.

    Now the question remains is where to buy a good 12v 1A switching mode AC Adapter.

    Usually when you buy AC Adapters, they don't have any brand on them.
    And this is relevant not just when ordering directly from china (from websites like banggood, etc), but even if you buy in a local store (and pay a much more expensive price).

    Maybe there's a place online that sells branded AC Adapters, and there there is a brand that is known to be good design (good transient response and low output noise - as you said)?
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    I normally buy from China.
    I message the seller if the part does not meet per specification I will open a dispute.
    Once I arrive, I check, if it does not meet the specs I open a dispute and get my money back and then look for another seller.
    But Basically I design them, that is Transformer types.
    SMPS ones works most of the time.

    I search Aliexpress and look for good ones, I look for the specs and how well it is made from the picture. One cannot tell without physically testing the part but tht's how I go about it.
    Get a 12V 2amp one. It can survive. Since it won't be loaded to it's max, transients response might be good.
  7. MrChips


    Oct 2, 2009
    Switch Mode Power Supply (SMPS) vs transformer PSU

    There are a number of properties one must consider.

    A SMPS is likely to be voltage stabilized. Hence a 12VDC supply will give 12VDC output.

    A transformer, rectified and filtered, for 12VDC output could very likely give 15-18V output with no load, dropping to 12V at the rated load.

    For audio amplifiers, one would be concerned with the amount of ripple and the ripple frequency.
    The concern with a SMPS is the high frequency noise generated by the switching circuitry whereas a transformer supply is bound to have ripple at line frequency, 50 or 60Hz depending on where you are located on the planet. Line frequency ripple can be reduced by inserting large value filter capacitors, 4700μF aluminum electrolytics, across the power supply output.

    As you said, your speakers are rated at 3W. Your total consumption will be 6W.

    A 12VDC @ 1A will work in your situation. As noted above, a 12V transformer output will be higher than 12V. Check before installing. The advantage with a transformer PSU is when the audio output goes into overload. The sound would be more compressed as the PSU voltage drops. A SMPS will clip your output and you will hear noticable distortion. Hence it is better to have an unregulated power supply for audio output.

    Finally, the speaker is correctly called a transducer and constitute only half the speaker design. The other half is the speaker enclosure. The transducer must be installed on a baffle board and installed in a speaker enclosure. Most of the low frequency sound will come from the baffle board. The purpose of the speaker box is to prevent the back wave from cancelling out the front wave. When you enclose a speaker in an air-tight enclosure, you will increase the resonance frequency. You can suppress this resonance by porting the front baffle making the back wave cancel the front wave at the resonant frequency. This is the theory behind the bass-reflex speaker enclosure. For this to work at the correct frequency, the port must be tuned, usually by trial and error.
    Zohar likes this.
  8. tranzz4md


    Apr 10, 2015
    That 3W figure is pretty loose. That device will draw more than 3W, if you supply it. Who knows how much it would take to blow it?

    The same goes for your amplifier. 15W is not it's failure point, or its power consumption limit.

    You'll probably be able to get moderate to low level sound, even using a wall-wart type PS, but don't expect any sound pressure or fidelity out of your rig.
  9. Zohar

    Thread Starter New Member

    Nov 19, 2015
    Thank you MrChips, really interesting knowlege.

    tranzz4md: I understand..
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Get yourself an old atx computer psu from a junk shop...12V @ 10Amps easy...
  11. Zohar

    Thread Starter New Member

    Nov 19, 2015
    And it will also be quality one,
    but it's big and clumsy for this purpose