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Old 10th December 2014, 07:48 AM   #1
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Default Choosing a good amp

Hey everyone,

I have 2 of the these speakers:
Fountek FE83 3" Full Range Driver 8 Ohm
and a 5v, 2a battery.

Any recommendations on a nice amp under $25?

Thanks
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Old 12th December 2014, 02:15 AM   #2
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Amp board or an entire amp for under $25? Parts Express is now selling the blue/black Yuan Jing 3116 board for under $25. A favorite among many, but you'll need more than a 5 volt battery.
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Old 14th December 2014, 01:07 AM   #3
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Any would need a more than 5V to get more than ~5 Watts. Only enough for small laptop speakers or headphones I would say.
What do you mean with 2A? Maybe 2Ah? Or 2A max. max power rating? Both are not very much.
You would need to use a step-up booster and an electrolytic capacitor to get more than 5V out of a 5V battery, though 2Ah isn't much exactly. (5V 2Ah = 12V 0,8Ah etc. respectivly 5V 2A = 12V 0,8A)

12V 0,8A is not enough for an amp, you would need at least 1,5-2A@12V

I guess you have an 5V USB powerbank with 2A max output, right?
USB Powerbanks are generally LiPo-Cell based. If it has 3-4 cells (usually all 10.000mAh+ Systems) you could open it and remove the cells (usually 18650 cells with 3,7V each) and put them in a row instead of parallel - you would get 11,1V (with 3 cells) or 14,8V (with 4 cells) from it directly which is enough voltage for a nice output. See Attatchment picture - 18650 cell battery holders are available on Ebay.
If you do that, you could keep your powerbank as a charger for your ceels.
Btw., it's importat to add a little voltmeter (2$ or something) between batteries and amp, because LiPo cells don't like it to get fully discharged. Don't let them fall below 3V per cell (so 9V for 3 cells or 12V for 4 cells) und use the voltmeter to check left over voltage from time to time while hearing music.

18650 cells can be also slaughtered from most notebook batteries btw.
Of course you could also buy an 11.1V (An 2200mAh 11,1V does cost 8-10 at dx.com) or 12V (lead, they are cheaper but heavier and larger) battery directly. For them you would need an additional charger of course. I do recommend Imax B6 or Imax B6AC - they can charge almost everything.

To answer you question about which boards can be recomended, for small or medium systems I would recommend "Muse" amp boards with TP2020 Chip and if you want a small cheap cased amp I would recomend the Lepai 2020A+. Though they're both only working <~14,5V as far as I know (otherwise they might overheat), so you can only put 3 LiPo batteries in a for them.

There are many cheap really great sounding boards with TK2050 (needs more idle power so slightly less good for battery powered systems). They can be used up to 24-32V (depending on model) or something and are producing much more RMS output if such high voltage is used (~15W if ~12V are used, 30W wih 24V and so on). Best cheap ones with TK2050 chip I know can be bought from HiFiMeDIY.com. As alternative there are TPA3116D2 boards - but cheap boards with that chip often doesn't sound as nice as price-wise corresponding TK2050 and TP2020 boards for my ears, though they need less idle power than the TK2050 boards and but can be used in a much wider range of input voltage than the TP2020 boards I recommended above.

Another option for battery powered systems would be Lepai 808 - it doesn't sound as nice as the TK2020 or TK2050 boards but not bad and it's dirt cheap (~10-15), needs low idle power and can be used up to 18V if I remember correctly.
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Old 14th December 2014, 01:14 AM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by googlexx View Post
I have 2 of the these speakers:Fountek FE83 3" Full Range Driver 8 Ohm and a 5v, 2a battery.
Any recommendations on a nice amp under $25?
If you're stuck with only a single 5V battery, you could go bridged, for about twice as much output voltage swing and about 4 times the power.
The 2A would still be enough current for stereo.

Last edited by rayma; 14th December 2014 at 01:16 AM.
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Old 14th December 2014, 01:45 AM   #5
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@Admin - sorry for double posting, please delete post above!

Any amp would need a more than 5V to get more than ~three clean Watts mono directly, as power output of amps is usually limited by voltage input. 5V is only enough for small laptop speakers, headphones or small extremly effective speakers I would say.

What do you mean with 2A? Maybe 2Ah? Or 2A max. max power output rating? Both are not very much for usual amps.
You would need to use a step-up booster (and maybe an electrolytic capacitor for filtering noise caused by step-up) to get more than 5V out of your battery, though 2A/2Ah isn't much exactly. (5V 2Ah = 12V 0,8Ah respectivly 5V 2A = 12V 0,8A)

But also 12V 0,8A is not truly enough power supply for an amp, you would need at least a 1,5-2A@12V for useful stability, unless you're not adding (another) additional electrolytic capacitors (to reach something like 10.000F), than you might be able to get about more or less clean 2x8W on 4ohm speakers and half on 8ohm speakers (effective music, not RMS as RMS would be limited to about 9W mono or 2x4,5W in stereo) or something out of an amp, which is enough to listen to music on usual speakers like your linked ones - though I wouldn't recommend that - it's not worth the effort as there are easier ways.

I guess you have an large 5V USB powerbank with 2A max output, right?
USB Powerbanks are generally LiPo-Cell based. If it has 3-4 cells (usually all 6.000mAh+ Systems) you could open it and remove the cells (they usually contain 18650 battery cells with 3,7V each) and put them in a row instead of parallel- you would get 11,1V (with 3 cells) or 14,8V (with 4 cells) from it directly which is enough voltage for a nice output. See Attatchment picture! 18650 battery holders for 3- and 4- in a row are available on Ebay.
If you do that, you could keep your powerbank as a charger for your cells - i've done that as you can see in the picture - worked nice, depending on loudness and speaker impedance&effectivity 3-9 hours. You can get easily more than 2x10W clean RMS output with them without any need of step up booster or capcitors.
Btw., if you want to do that it's importat to add a little voltmeter (does cost 2$ or something) between batteries and amp, because LiPo cells don't like it to get fully discharged. Don't let them fall below 3V per cell (so 9V for 3 cells or 12V for 4 cells) und use the voltmeter to check left over voltage from time to time while listening to music.

Additional 18650 cells can be also slaughtered from most notebook batteries btw.. Don't buy cheap chinese 18650 cells from Ebay - they're all fakes with often 1/10 of their labeled capacity - only brand ones if you want to buy additional ones.
Of course you could also buy an 11.1V (An 2200mAh 11,1V battery does cost 8-10€ at dx.com) or 12V (lead, they are cheaper but heavier and larger) battery directly. For them you would need an additional charger of course. As additional charger I would recommend Imax B6 or Imax B6AC - they can charge almost everything, incl. all types of LiPo batteries and 12V lead batteries.

To answer you question about which boards can be recomended, for small or medium systems I would recommend "Muse" amp boards with TP2020 Chip and if you want a small cheap cased amp I would recomend the Lepai 2020A+. Though they're both only working <~14,5V as far as I know (otherwise they might overheat), so in your case can only used 3 LiPo batteries.

There are severaly cheap really great sounding boards with TK2050. They can be used up to 24-32V (depending on model) or something and are producing much more RMS output if such high voltage is used (~15W if ~12V are used, 30W wih 24V and so on). Best cheap ones with TK2050 chip I know can be bought from HiFiMeDIY.com - they sound better than many 10x more expensive mid-class amps and sound-wise the best amps I know you can get for <25€! Though I wouldn't recommend them for you at first place, as they need quite a lot idle power, so they're only efficient when running loud and efficiency is extremly important if you only have a few LiPo batteries.

As another alternative there are TPA3116D2 boards - but cheap boards with that chip often doesn't sound as nice as price-wise corresponding TK2050 and TP2020 boards for my ears, though they need less idle power than the TK2050 boards as far as I know and and can be also used in a much wider range of input voltage than the TP2020 boards I recommended first. If you wan't to buy an TPA3116 board ask other forum members for recommendations, there some good ones but also some not so good boards with this chip within your budget.

Another option for battery powered systems and very easy and cheap would be Lepai 808 - it doesn't sound as nice as the TK2020 or TK2050 boards boards but also not bad, better than bad designed TPA3116 boards, and it's dirt cheap (~10-15€), needs low idle power and can be used up to 18V if I remember correctly - so it does also work with 4 18650 cells in a row and comes ready in a case.
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File Type: jpg 20140709_205650.jpg (509.9 KB, 70 views)

Last edited by ForenSeil; 14th December 2014 at 02:09 AM.
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Old 14th December 2014, 03:30 AM   #6
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Little addition - if 2x3W (=max 93,5db@1m respectivly max 83,3db@3m with both of your linked speakers together) are enough you could use you 5V source straight with LM386 and PAM8403 boards - they're optimized for 5V and very efficient and 2A would be more than enough for them. They can be bought for a few $ on Ebay.

Though powerbanks do contain step-ups to make 5V from 3,7V cells and step ups often produce buzzing noise when attatched directly as powersource to amps. You might need to add a single electrolytic capacitor in parallel onto your cable to filter that noise.

Another idea - Does anyone here know if there are ultra low voltage optimized boards which can be used BTL safeley? Togther with an capacitor for more stable power supply the TA could conjure 2x6W effective music power out of his 5V 2A with two bridget mini stereo amps without much effort. I know that the PAM can't be briged but what about LM386 boards @5V@8hm? According this thread it does work @5V Parallel lm386 but it's hard to guess how long they would live without additional heatsink (years or minutes?). Might be worth a try, as lm386 boards are dirt cheap.

Last edited by ForenSeil; 14th December 2014 at 03:59 AM.
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