Lepai TP2020A+ and Computer power supply very strange issue!

[ruchirablog]

hello forum,
I have got lepai 2020A+ Amp today (without power supply) and since im using it with my PC I have decided to power it with my computer power supply.

So I have plugged it to computer power supply ( the same computer that im working on) and my problem is even when no signal present at the input, this amp produces strange hissing kinda noise, its changing noise and the most craziest thing is the noise changes when I scroll web pages, open folders etc.

And when playing music I can only turn the volume about 2/10 and relay starts to kick off. but when tone control turned off I can go up for about 6/10 before relay kicks off. I can hear the noise and distortion on all levels of volume.

I have tried changing the jacks and still the same.

I didnt had any 12V power supplys lying around than the little adaptor which powers my wifi access point. its 500mA and I have hooked it up with lepai and it sounds great with that little power supply. No noises until about 7/10 and after that it produces like HF noise and I guess its problem of power adaptor.

So guys do you have any idea about why that Im getting noise when Im using it with my computer power supply? And why I can hear strange noises when I do stuff with my mouse and keyboard?

Thanks
Ruchira

[Saturnus]

Originally Posted by ruchirablog

So guys do you have any idea about why that Im getting noise when Im using it with my computer power supply? And why I can hear strange noises when I do stuff with my mouse and keyboard?

Thanks
Ruchira

Easy. You're using your computer power supply. DO NOT EVER DO THIS.

[ruchirablog]

Originally Posted by Saturnus

Easy. You're using your computer power supply. DO NOT EVER DO THIS.

Hmmm can you please be more specific that why shouldnt I use that? Computer power supplies produce clean voltages and current to the best of my knowledge?
thanks

[Saturnus]

Originally Posted by ruchirablog

Computer power supplies produce clean voltages and current to the best of my knowledge?
thanks

Then your knowledge is severely lacking. Computer power supplies can supply a steady voltage at high current demands but they are the most noisy crap you can possibly get. Moreover, when you connect your amp to your computer and both are on the same supply you're making a ground loop. You should never do this. Please disconnect one or the other immediately.

Get a proper 3A+ power supply for your amp, and all your problems are solved. Usually a scrap 12V power supply from an old IBM et al LCD panel will work fine (and use the exact plug used in the Lepai).

[ruchirablog]

Originally Posted by Saturnus

Then your knowledge is severely lacking. Computer power supplies can supply a steady voltage at high current demands but they are the most noisy crap you can possibly get. Moreover, when you connect your amp to your computer and both are on the same supply you're making a ground loop. You should never do this. Please disconnect one or the other immediately.

Get a proper 3A+ power supply for your amp, and all your problems are solved. Usually a scrap 12V power supply from an old IBM et al LCD panel will work fine (and use the exact plug used in the Lepai).

Oh thanks for your details reply
I have used a variable linear power adapter (the cheapo ones that costs about $2.5) rated at 1000mA at 12V and it powers up the blue light on the amp but relay doesnt go on. I have measured and it got 12V im wondering why?

But when I used the SMPS power adapter which is rated at 500mA 12V and came for my wifi access point, it produced great sound as stated on my first post.

[Saturnus]

Yeah, 500mA is plenty to drive the amp at average power consumption (which is around 380mA at full power level). Unfortunately it's too little to cover the peaks and therefore a 3A+ power supply is recommended even though you'll never use more than about 12% of that.

[ruchirablog]

Originally Posted by Saturnus

Yeah, 500mA is plenty to drive the amp at average power consumption (which is around 380mA at full power level). Unfortunately it's too little to cover the peaks and therefore a 3A+ power supply is recommended even though you'll never use more than about 12% of that.

Thanks again Like I stated on my first post, Im getting a hum after turning more than about 60% of volume. Is that related to 500mA power supply im using? like its too low for this?

[Saturnus]

Originally Posted by ruchirablog

Thanks again Like I stated on my first post, Im getting a hum after turning more than about 60% of volume. Is that related to 500mA power supply im using? like its too low for this?

Yes. It comes because the power demand in peaks at higher power levels is more than your power supply can deliver.

Btw, here's one of those old LCD power supplies that match. No matter where you are in the world you should typically be able to find them at $5 or less.

2wire Model CPA09-001A 12V 3A power supply adapter | eBay

[ruchirablog]

Originally Posted by Saturnus

Yes. It comes because the power demand in peaks at higher power levels is more than your power supply can deliver.

Btw, here's one of those old LCD power supplies that match. No matter where you are in the world you should typically be able to find them at $5 or less.

2wire Model CPA09-001A 12V 3A power supply adapter | eBay

Thanks for your help Saturnus I forgot to state that I got that hum even no signal present at the input. Is it happen because of your stated reason? 500mA isnt enough? or is it comes from SMPS like RF noise?

That one only ships for USA and Im in Sri Lanka Yeah I will be able to find one locally if I give a try. Else ill buy one from ebay