Mobile Mono Amplifier

Discussion in 'The Projects Forum' started by luvv, Feb 1, 2012.

  1. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Hello AAC,

    I'll start by describing the project goal.

    Friend of mine wants a extremely loud predator call, coyotes to be exact.

    He purchased a battery powered call, it's just not loud enough and it sounds

    as if the recording was made on a sound board not a actual recording.

    So together we came up w/ the idea of using a cheap mp3 player from ebay

    and a actual recording playing on loop.

    Problem is,the thing can barely push a set of headphones...

    Having never made a audio amp, my friend and i went looking for a amp in

    other devices.

    Looked at a usb powered speakers..lil complicated for me,so i dug around

    and found a amplifier from a X Rocker chair.

    The board contains 2x amp chips each is capable of up to 4 watts in

    bridged mode.

    Problem is the board contains alot of stuff i don't need or want to power .

    Was wanting to pull one of the chips and build a simpler, more compact

    amp .
    And there is the root of my issue, i found BTL application note a little too

    simple for my taste .

    Was hoping someone could give me idea how best to implement this chip

    for my needs.

    Power Supply :9v battery(s)
    Signal :MP3 Player (mini jack)(it's weak to say the least)
    Speaker:(1) 8ohm, 10 watt

    If it helps i can upload a pic of the board as is now,just say so.

    Thanks in advance,

    -luvv-
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,734
    759
    To get real loud out put u need to a mega horn like those used in PA system.

    U can run a mega horn with a step up audio transformer.

    I believe u need to get rid of ur idea and use this approach. It is fairly simple. All u need is a push pull stage with a preamp to drive the primary of an audio Tx. The secondary will produce HV that can drive the mega horn.
     
    luvv likes this.
  3. wayneh

    Expert

    Sep 9, 2010
    12,087
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    I think that's going to be a limiting factor. A bunch of AAs in series or a car battery would give a LOT more power.

    You might also want to look here. They've got a number of DIY amp kits as well as ready-made units.
     
    luvv likes this.
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    FoxPro callers have excellent results. Look at the horn design and their audio output specifications so you have an idea of what you are looking for in an amplifier and speaker.
     
    luvv likes this.
  5. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Thanks for all the responses

    @R!f@@:the PA style system while surely would be effective, is perhaps a lil overkill for my needs.
    I have tried to explain same thing to my friend after he started suggesting car audio equipment, it's coyotes not Florida retirees we are trying to call .

    But, the megaphone horn and box is a good way to get better coverage and travel, i'll see what i can find the fits the bill.

    @wayneh:i think you are correct in power being a limiting factor,i considered this and figured i would use some 9v's parallel,buuut..i do happen to have few 12v SLA batteries as UPS back ups.

    @thatoneguy:very nice calls they got there,tho i don't think i have a chance of even approaching that kind of quality w/junk i have laying around.

    Ultimately, i feel this amp IC can be made to suit my purpose my only real issue is the redesigning of the circuit to eliminate the second IC,LED power,switch components,
    rectifying diodes etc.

    All i need is a mini jack input, a resistor to limit it from max output, and away we go.

    According to the data sheet a single external resistor is all that's needed to adjust volume, tho it dosent show one in the bridged circuit.

    The whole suggested application circuit just looks hokey to me,no resistors,all e-caps not single ceramic decouple?
    But hey my limited circuit experience comes from building circuits others have designed(nearly all of bill mardsen's 555 stuff) and automotive.

    Maybe someone can tell me if the circuit is plausible as is, or does it need serious improvement.

    IF so what do you suggest?

    Thanks

    -luvv-
     
  6. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Here is the board im working w/ maybe that will give you guys a idea of what im working w/
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    What is the number on the IC, and what is under that silverish colored heat sink?
     
  8. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    YD 20255
    vh1.z
    it had a matching heatsink i removed for the picture

    i assumed that there was a matching IC under the other heatsink...
    was very wrong .

    it is a STsj2206b
    s5801
    wasn't able to find the data sheet for it:confused:

    I've been pulling the components and working on a layout based on the YD IC's data sheet.

    There is a pic of the original board, YD IC removed and E-caps removed

    Second pic is the YD IC loose mounted in one of my super generic protoboards.

    Rather this IC works for the project or not, i would like to give a go at getting to work.

    Any help is greatly appreciated.

    Thanks,

    -luvv-
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    No.
    A re-entrant PA horn speaker is 8 ohms like most speakers. A transformer can be used for each speaker if you have many speakers in parallel in a PA system. The transformer does not make a horn speaker sound louder.

    The amplifier produces only 4.7W maximum into an 8 ohm speaker when it is clipping like mad with 10% distortion. Even a horn speaker might not be loud enough.

    The little 9V battery is 9V only when it is new. Its voltage quickly drops to 7.2V then drops slower to 6V when it is almost dead. The battery voltage will not last long enough.
     
    luvv likes this.
  10. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Thanks for the response Audioguru,

    Hadn't really planned to run the lil amp at max, think at 2w it will be a major improvement over what we have now.
    I'll ditch the factory heatsink in exchange or a copper one w/ twice the area, perhaps that will allow a little more flexibility.

    The 9v was just a base idea, i have access to a wide assortment of battery choices
    12v SLA(s),6V lantern(s),9.6v Li-Po(s) and all the stand bys D's C's etc etc.

    Would like to see the thing run 3-4 hrs w/o needing a charge/change out.

    Further more, even if this lil amp sucks buttermilk, i still would just like to see it work.

    Any ideas, rough schematics or just general pointers for implementing the IC ?

    Thanks,

    -luvv-
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You said, "Friend of mine wants a extremely loud predator call" but a few Watts in a speaker is not extremely loud. A re-entrant horn speaker will be much louder than an ordinary speaker but still might not be loud enough with an input of only a few Watts.

    The little Chinese amplifier IC seems to have a heatsink "stuck" on top of its plastic case?
    Then the heatsink won't do much. The IC will be at its max allowed temperature with a 9V supply and a pretty big heatsink so forget about using a 12V supply that might melt it.

    You must find out how much power you need and the battery voltage that produces it. Then calculate a battery size that lasts long enough.
     
  12. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Thanks again Audioguru,

    Yes, i did say a friend of mine want's a extremely loud call..

    But the same friend suggested a set of boxed 15s and 500w amp...

    This is what I have settled on..

    This lil cheap Chinese amp made XRocker chair "bump" once upon a time and had a max draw of 10v @1.2A

    That is w/ all the LEDs and 3 speakers, figured using it @ 1/2 pwr and 1 smaller speaker 0 leds, power would be manageable.

    Anyhow at this point, i just want to see it make noise.

    If someone w/ a little knowledge of circuitry could have a look at the application notes and tell me if there BTL setup is feasible, perhaps how i could improve on it?

    Thanks,
    -luvv-
     
  13. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I recently bought a Sylvania 2.1 powered speaker system for $24.99 as a "special buy" at a local store. It sounds great, looks good and is fairly loud. I use it for the TV in my computer room and the digital cable TV converter also plays many FM radio stations.

    In the ad it says 150W. On the box and owner's manual it says 75W RMS. On the power label it says 75W (so it is 100% efficient!). Inside it has a small power transformer labelled 9VAC/1.1A (9.9W). The amplifier is probably 50% to 60% efficient but might be a modern class-D switcher that is 90% efficient.

    Its amplifiers are two 16 pins DIL ICs with a small heatsink glued on.
    One IC is probably a stereo amplifier feeding 1.5W to 2.0W real Watts to each 4 ohm satellite speaker.
    The other IC is probably bridged and feeds 4.0W to 5.0W real Watts to the 6 ohm sub-woofer.
    So the total output power is 5.5W to 7W.

    Each satellite speaker has two 1.5" 2 ohm speakers with foam surrounds and the "soft-dome tweeter" is not a speaker but is actually a vent covered with a soft dome.
    The sub-woofer is a 5" long-throw speaker with a foam surround in a pretty big wooden ported enclosure. It lights up with 6 blue LEDs.

    The amplifier and power supply are built into the sub-woofer enclosure and has a volume control and bass and treble tone controls.

    I have played it loudly for hours and it doesn't smoke. I have never heard its amplifiers clipping. I tested its frequency response with my 66 years old ears and it plays from 40Hz to 18kHz smoothly and very well.

    It probably uses the same ICs as yours.
     
    luvv likes this.
  14. Experimentonomen

    Member

    Feb 16, 2011
    331
    46
    A few watts indoors is pretty loud, but outdoors you need many times the output power for the same loudness at the same distance.


    I built an amp once that in my room at home was deafeningly loud at only a fraction of its powe which was a few watts at full power, but when i took it to school, u could barely hear it over the ventilation system and that turned up to hard clipping.

    So you may end up needing something like a 500+ watt amp and a large PA speaker box in order to make the call audible far enough away for them coyotes to hear it without destroying it with clipping and distortion.
     
  15. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    FWIW, I don't think the coyote's voicebox can generate 500W, since that's 2/3 of a horsepower. But your point about outdoors versus indoors is quite valid.

    I can't help but recall the Hitchhikers Guide to the Galaxy scene where the rock band Disaster Area uses so much amplification that they destroy entire planets.
     
  16. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    @ Experimentonomen, Valid point, i am hoping to supplement the small electronic amplfication w/ a larger chamber for the speaker, think 5 gallon bucket.

    @wayneh, yea i tried to explain just how sensitive a coyote's hearing is to my friend.
    They can hear mice chewing seeds under a foot of snow from 20 feet away, i imagine they can hear a call as loud as a man yelling from a mile or more

    His thinking is atleast semi valid, he wants to call coyotes from neighboring counties lol

    But, at this point i am more interested in just makeing something "work" more for my own satisfaction , then the slaying of a invasive species

    Thanks,
    -luvv-
     
  17. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A large enclosure for a speaker allows the speaker to produce low frequencies as low as the speaker can go. A small enclosure increases the resonance of a speaker and the speaker performs poorly below its resonant frequency.

    I have never hear a coyote but doesn't it bark like a large dog? Then the frequencies are not very low so a large speaker in a large inclosure is not required.
     
  18. luvv

    Thread Starter Member

    May 26, 2011
    186
    31

    Well all the "calls" iv e heard range from a howling to a yaping sound.

    Along w/ the standard coyote calls we have assortment of predator calls ranging from bunnies squalling to wounded birds.

    Figured the chamber would serve two purposes,1 to offset the higher pitch noises inherent w/ smaller speakers 2. create a space to house the electronics and power supply.

    I was planning to incorporate a horn of some sort for amplification as was suggested earlier.

    Seen some pretty shoddy equipment sound decent when put in custom boxes,but that may or may not apply in my case.

    Again tho, all the design considerations are for naught if i don't get that lil IC making noise rather then smoke.

    And as i am unable to breadboard the chip because of the large heatsink/ground tabs, it will be going straight to solder, worrisome to say
    the least...

    So i guess i'll ask some more direct questions regarding the BTL app notes.

    1.Why is there no ceramic decoupler on the BTL Vin. vs. the stereo setup?

    2. Why isn't there a single resistor used anywhere?

    3. The app notes mention using a resistor to limit gain, where and how would that implemented .
    4. not related so much to the schematic but,in a mono setup,i can see the input which i assume is the insulted wire contained in the 2 wire mono jack
    where does the second un insulated wire connect? common ground w/ the power jack? sounds lil scarey to me..but idk..

    Think i had more questions but it is getting late and my mind getting squishy..

    Thanks.
    -luvv-
     
  19. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    I can call in yotes using a "squeaker", basically a little rubber bulb with a toy noisemaker in it, give it a squeeze two or three times, then wait. You wouldn't think it would be audible more than 10 feet away, but I've had coyotes trotting toward me from 200 yards and more.

    The FoxPro I use I play at about 1/2 volume with "dying rabbit", and a little louder for crows. It really doesn't take much power to get them in, just patience.

    Turning it up too loud will only scare them away. This is a common mistake for beginners, they might get lucky and find a dumb or starving yotes, but not peg 5 or more a day. Start low, wait half an hour, turn it up a little bit, wait, etc. You'll get the hang of it, but when it is calling them in effectively in the northern plains, you can still hear yourself crunching grass if you move.

    Make sure you are far away from your vehicle as well, no use even calling if you are obviously not a rabbit or mouse.

    In other words, volume isn't everything, it isn't even most of it. Clarity is very important, and most all of the audio is in the midrange two low tweeter spectrum, no bass. I've never seen a wounded rabbit or raccoon that could shake the ground with it's cry, anyway, so coyotes haven't either. It goes back to scaring them instead of attracting them.
     
  20. luvv

    Thread Starter Member

    May 26, 2011
    186
    31
    Hey myself ..im all for live trapping the lil boogers,but after they attacked my friends prized Shepard.. he wants blood.

    I am in no way a hunter,zero time for it,he wanted a idea to make his pre recorded mp3's louder, that's as far i care to look at it.

    From what i understand he has man powered call he had no luck or patients for.
    and he had a electronic one he gave to me because he said it was junk...
    it's called Varmit Call made by ALL ABOUT GAME inc.
    it has 5 calls "distressed fawn" "distressed rabbit" "coyote howl" "distressed mouse"
    "baby rabbit"
    honestly can't see why it wouldn't do the trick but hey..im no hunter..

    i do know that he is using estrus and i do know if he don't find a call to his liking he plans to hunt over a corpse(which is legal here)

    where he plans to obtain said corpse i can say would cause whole throngs of PETA activist die from shock...

    So in the interest of sparing the world that..i would like to make something suitable.

    Again i am no hunter,i would kill only what i can eat..and i don't eat dog...
    All i know of the calls is what this lil box makes and what i have heard on his iphone.

    By telling everyone of the intention of this lil proposed device, ive gotten far of topic which was the exact opposite effect i was hoping for.

    So for now lets assume i want to listen to the grateful dead in glorious 4 watt mono sound.

    If somone could look at the attached pdf BTL application notes ,and tell me if the thing should work as is i would be most apreciative.

    Thanks,

    -luvv-
     
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