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Old 7th November 2012, 11:29 PM   #1
PGM1975 is offline PGM1975  Canada
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Default Amplifier with USB port for MP3s

Hello. I'm new on this forum and I'm looking for someone to shed some light on a few things for me.

I'm looking to buy an amplifier with a USB port to play MP3s directly off of a USB stick. The unit would power two bookshelf speakers in my room in order to produce "white noise" during my sleep. I found several units, but this one caught my attention:

50W Audio Digital Power Amplifier MP3 Player with USB Host/AUX - Black - $59.49 : BuyOnMe.com, wholesale dropship

Here are my questions:

1. Why would someone pay $60 for this one, when you can buy a Lepai for $20? What's the "added value" associated with this unit?

2. The frequency response is 58hz to 20khz. I've never seen an amplifier that only goes down to only 58hz. What will happen if I play a some soft music (sound of waves) and some of the frequencies are below 58hz (my speakers go to 50hz)? Will I hear those low frequencies anyhow?

3. Based on the specs, does this seem like a good product?

If someone with more experience than myself could answer these questions, it would be greatly appreciated.

Thanks
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Old 8th November 2012, 01:01 AM   #2
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1. They might like the accessories. This unit includes remote control, cables, a snazzy stand holder, etc.
2. We have to assume the bandwidth is spec'd at the 3dB points. Whether frequencies below 58Hz are heard at all depends on several factors: circuit design, volume setting, steepness of cutoff (the speaker response cutoff will add to the amp response cutoff), etc. FWIW, I wouldn't expect a lot of bass power with one of these little class-D amps and bookshelf speakers anyway.
3. Not to my mind; the Lepai seems a better value. I note that the specs say, "Output power: 20W@4 ohm,10%THD+N,13W@8 ohm" yet they still stretch that to "50W amp."
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Old 8th November 2012, 01:18 AM   #3
mikje is offline mikje  United States
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Parts Express has this one that is said to be a good value. Plus, there are a lot of folks who know these amps very well and have a lot of info on mods and repairs.
Lepai Digital 2x15W Amplifier with Remote USB MP3 SD FM 310-302
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Old 8th November 2012, 02:31 AM   #4
PGM1975 is offline PGM1975  Canada
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Thanks for your answers.

Well, I thought I found a winner when I saw figures like Dynamic range: 98db and SNR 90db and above. My understanding is very elementary though and I'm sure there are more aspects to consider when assessing the overall performance of an amplifier.

I was also thinking of actually building an amplifier myself using parts on Parts Express. I'm assuming I'd get better quality per dollar spent. I'd have no problem buying a board and a few connectors, and putting it all together. The only problem is that I really want to have an integrated USB MP3 player port. I could get one like this:
MP3 Hardware Decoder w/ FM/Remote Controller/USB/Mini USB/SD Slot - Black (5V) - $6.96 : BuyOnMe.com, wholesale dropship

My problem is that I wouldn't know how to connect the MP3 player to the amplifier board (connect the audio signal and the power supply to the board). Would this require lots of skill and expertise?
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Old 8th November 2012, 03:21 AM   #5
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Those specs aren't unusual for this range of class-D amps. Connecting the MP3 DAC to the amp would be pretty easy to do. Just a half dozen wires to connect. If it is any good at all it looks like a fair deal to me - I wish I had one here to play around with.
This is the diyAudio forum after all, so I won't even attempt to steer you away from a homebuilt amp. That is up to you, after considering the pros and cons. Either way, I strongly suggest you invest in a multimeter if you don't already have one. If you're on a budget a $5-10 model will pay for itself in no time.
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Last edited by sofaspud; 8th November 2012 at 03:33 AM. Reason: accuracy
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Old 8th November 2012, 04:34 AM   #6
PGM1975 is offline PGM1975  Canada
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I really feel like giving this DIY project a shot. I'll get the multimeter and call it an early Xmas present.

So what exactly would I need to order/buy to connect this MP3 player:

MP3 Hardware Decoder w/ FM/Remote Controller/USB/Mini USB/SD Slot - Black (5V) - $6.96 : BuyOnMe.com, wholesale dropship

...to this amplifier:

2x25W @ 4 Ohm TDA7492 Class-D Audio Amplifier Board Only 320-332

Which wires? Can you provide me a link?

I read on Parts Express that there's a 5V output on the amplifier board. I think I see the "+5V" sign on the board (near the center beside the heat sink) where the power would come from. But how the heck do I get that power to go to the MP3 player? What do I need? :S

Thanks
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Old 8th November 2012, 05:14 AM   #7
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I'm not sure the 5V from the amp board will power the DAC. It is designed to power the rotary encoder + volume control p/n 320-318. Parts Express has the MP3 decoder also, p/n 320-350. They also have a multimeter on sale for $4.88, p/n 390-500. I'd seriously consider purchasing all this from PE.
My understanding is the decoder comes with hookup wire, so you need a couple RCA plugs to solder to the ends, or if it's OK for your application you can just solder the wires to where the RCA jacks are on the amp (you decide whether you want to remove the RCA jacks first).
You need a power supply for the amp, something like 18VDC @ 5A. Then you can add a 5VDC regulator to it to power the decoder.
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