Source for a good but cheap power supply?

[pmc]

I need a 12V 1 to 2A DC power supply for a chip amp I am building. I can find laptop/LCD wall warts on eBay but it's hard to guess quality. If I go too cheap I might get humming or buzzing (or I might even fry the amp). But I don't want to pay too much because I'll probably build a nice power supply sometime down the road (once I figure out how to do it!). So the wart is only temporary.

Any idea for a good source?

-pmc

[Ken Layton]

Jameco Electronics, All Electronics, and MCM Electronics generally have those on sale.

[pmc]

Thanks Ken. I'll check 'em out.

-pmc

[Blanka]

Just grab a PC supply. At least go for a switching one, as they have much better efficiency and are way smaller/lighter.
http://www.arcadeshop.de/Miscellaneous-Power-Supply-130W-5/12/-5V_338.html
This one is too much already, but a nice option.
A very simple PC supply like this is way too much (15 amps!) but will work as well:
http://www.directron.com/m6320.html

What do you mean with I'll build a nice one myself along the road?
An old fashioned one with a torroid and big capacitors?
These cheap PC boxes will beat your DIY performance, and conform to EMC regulations. The torroid DIY will generate a lot of noise on the net. Not your problem, but if everyone would do it, the electricity companies go nuts.

Which chipamp do you use? I never seen models that just need 0 and 12V. They mostly need symmetrical supplies with negative power as well, and most work better at 2x30 volt. This because of speaker impendance. With 12 volt you cannot generate more power than 36 watt on a 4 ohm speaker. But with 2x 30V you can go in the hundreds of watts.

[mountain]

This because of speaker impendance. With 12 volt you cannot generate more power than 36 watt on a 4 ohm speaker.

Blanka, can you please explain what you mean by this?

[Blanka]

Know ohms law?: Resistance is voltage divided by current.
So 12 volt and 4 ohms means 3 amperes
And 3 amperes times 12 volt is 36 watt. There's probably some square root I forgot for seeing sinus-waves in relation to flat DC output, but I'm talking about the generic idea. 12V can never drive a 100 watt 4 ohm speaker! Or you need a clever switching D-class chipamp that makes a higher voltage internally.
With 2x30V on 4 ohm you could go to 900 watt in theory.

But on the other hand, the resistance of a speaker varies with the music played at them. My 4 ohm bass drivers can dive to 2 ohm in high power situations. During those peaks the speaker can drag much more than average power. Thats why an amplifier should always be capable of delivering peaks around 2 times the power of the speakers, as most speakers can go to half the impedance as stated during high power use.

[pmc]

Which chipamp do you use? I never seen models that just need 0 and 12V.

It's actually a T-Class amp. I was just trying to use generic terminology so I said "chip amp" but I may have beem misleading. It's not a gainclone. It's a Tripath TA2020 based amp and runs off a 12V supply. I'm told that it uses 0.25 to 0.5A typically, but can draw as much as 1.3A.  I think I can push it to 14.5V or so, but don't want to risk frying the chip because the board I'm building has minimal protection. Best to nail 12V and be happy.

I will, BTW, be driving 8 ohm speakers rather 4 ohms.

Just grab a PC supply. At least go for a switching one, as they have much better efficiency and are way smaller/lighter.
http://www.arcadeshop.de/Miscellaneous-Power-Supply-130W-5/12/-5V_338.html
This one is too much already, but a nice option.
A very simple PC supply like this is way too much (15 amps!) but will work as well:
http://www.directron.com/m6320.html

The first one is much more expensive than a wall wart type which I can get for $10-$20. But I suppose it's better. I see several of those on eBay (although not always with 12V output). I'm not sure what makes them better than a wall wart. I understand that the wall wart types are switching as well (SMPS) and work very well to drive a T-Class amp.

The second one (the ATX PS) is an interesting idea. It generates way more amperage than I need but I guess that's OK because my amp will just pull what it needs, right? But it also has a fan which will generate alot of noise that is not welcome while listening to music!Hmmmm..... and I just gave away a 300W ATX power supply too. Oh well.

What's the benefit/drawback of each of these types of power supplies? They will all produce enough amperage at 12V and they are all at a different cost level. I'm willing to pay a little more for better quality, stablility, and performance; but I'm still going be a cheap bastage.

What do you mean with I'll build a nice one myself along the road?
An old fashioned one with a torroid and big capacitors?

Yes. Or I can use a traditional transformer instead of a torroid. The benefit, from what I understand (which isn't alot) is that I can get better sound from the amp and I can contain the PSU parts in the amp chassis -- so I can plug a 110V AC line directly into my Amp. No other boxes and good sound. And I can modify it to improve the sound if I want. And I can build it and instead of buying it so I can control quality and cost. A wall wart seems simpler, but if I can bump up the sound quality by changing the PS I'll consider it. And I want to learn how to do it for when I start to play with tube amps.

These cheap PC boxes will beat your DIY performance, and conform to EMC regulations.

If they aren't good for the application, then why do people do it? That's a serious question BTW.

Thanks for your help Blanca. I'm learning a lot through this process.

-pmc

[Blanka]

Why DIY still use torroids?
Because of the weight! If an amp is not weighing like 10kg at least, it is not taken seriously.
A good switching amp can deliver much more stable voltage (<1% difference) than a traditional one (which can change on loads in a 10% range), and if high frequency noise is filtered out in a good way, it will not affect sound either. The T-class amp makes more noise itself than most switching amps. And switching amps don't need fans for the 100watt audio use, but most available PC ones have so much power crammed into a small box that even the low 10% loss of these supplies means a lot of heat.
You can buy any PC supply. They all have 12 volt if they have hard drive power cables.

[pmc]

OK. It seems common for people to use laptop / LCD power supplies because they are "cleaner" than wall warts. But that seems to be the route that people go.

It sounds like the whole Toroid / power supply board thing is unnecessary if I get a decent laptop power supply in the first place.

-pmc

[richms]

Laptop psus are normally 15-19v - most I have seen off ebay are chinese counterfeit ones that are total crap.

IMO, start to look at the power bricks off 3.5" external HDDs. If you get a case that would give you the PSU, a case and other stuff for minimal $$$. Perhaps look for an old external dvd burner case since the PSU is normally internal to them?

[whammoed]

MPJA is another source for economical power supplies:
http://www.mpja.com/products.asp?dept=3&main=1

[Dermbrian]

www.partsexpress.com has many wall warts to choose from.  I like that place.

Let us know how your tripath board comes out.  I own three of the original (ie. cheap) Sonic Impact T-Amps.  Amazing units.  The other night I brought one of those and some car speakers in Folgers plastic coffee cans over to a backyard movie night.  I use one of them for our projector for movies in the living room.  The third was the heart of a stereo on my motor scooter...now wrecked.

Brian

[pmc]

Yeah... I need to order some stuff from Parts Express anyway so I was hoping I could find something there anyway. I couldn't initially, but I'll try again. And I'll check out MPJA (thanks whammoed).

The problem with the stuff on eBay is that you can't tell if they are good bricks or not. Everyone says "get a heavy one" but you can't tell. So many are from China (all of them?).

What's wrong with something like this? It's only $19. It looks sturdy. But I can't tell one PS from another.

As for the Tripath: I was torn between the Charlize(2), the Autocostruire, and the 41Hz boards. I decided on 41Hz because it's cheapest and there's no indication that it's not similar audio quality. And I get to build it. 

I'll let you know how it turns out. If it turns out good, I'll be doing more. But I won't be using Folgers coffee cans for speakers.

-pmc

[pmc]

www.partsexpress.com has many wall warts to choose from.  I like that place.

This one looks very versatile (i.e. I can use it for lots of stuff since I can set the output voltage) and it's as cheap as a Chinese laptop/LCD brick on eBay. In the review section, someone cites that they are using it to drive a T-amp. Good sign.

Hmmmm..... maybe someone can tell me what a "regulated" power supply is? Sounds like a feature I want.

-pmc

[richms]

Regulated will hold output voltage between no current drawn and max current across the whole range of input voltages. Unregulated are just a transformer, a recitfier and a smoothing cap that is normally too small. If you supply voltage drops from 240 to 220 then your output will drop by about a volt if its a 12 supply, also if you are taking no current the voltage will be high, so if you have a higher voltage then normal, and are not using the amp you may have 16-17v on the output, which will toast a t-amp.

Almost all switching power supplies are fully regulated, but some will have a minimum load which if you are below, the voltage will go up and then they will shutdown. PC powersupplies are usually happy with just the fan in them as a load, but some of the open frame ones need a few 100mA of load before they will work properly.

[Blanka]

Go and get a decent PC psu and stop drooling! Cheap Chinese crap you showed over there!

[pmc]

Regulated will [...]

Wow. Your're like a human wikipedia.

Thank you for the information. It seems to me that I would want a regulated supply for two reasons:

1) to ensure a stable target voltage. I think my amp will fry at 14.5 and my board has no voltage regulator.

2) To keep the voltage steady as I increase volume. I understand that without regulation, the voltage will temporarily vary as the current draw varies.

Go and get a decent PC psu and stop drooling! Cheap Chinese crap you showed over there!

Hehe. You're right of course. I picked this one last night. It's cheap, regulated, has overvoltage protection, the right size connector (5mm/2.5mm), a ferrite bead (noise), and even an LED.

-pmc

[Blanka]

Which TA 2020 Amp is it that you use?

[pmc]

Which TA 2020 Amp is it that you use?

Yup. The TA2020 chip. It's the 41Hz Amp-6. I'm building the non-surface mount version. If it works out, I'll consider building another Tripath with an onboard regulated power supply or I might go try a gainclone.

Next summer, I plan to build either an audiophile grade stereo tube amp (maybe a Bottlehead) or a AX84 guitar tube amp for a Fender Champ styled cabinet. I'm working my way into this step by step because I have tons to learn and don't want to get in over my head too quickly.

-pmc

[richms]

I was looking at getting one of the sureelectronics boards for my arcade machine, but they have doubled the price of them recently so spending a bitmore on a 41hz is sounding like a better idea the more I think about it.

Hope it all goes well for you

[pmc]

I was looking at getting one of the sureelectronics boards for my arcade machine, but they have doubled the price of them recently so spending a bitmore on a 41hz is sounding like a better idea the more I think about it.

I've seen that 15 watt TA2024 stereo amp board on eBay shipped directly from China. But I don't know if it's cheaper than the website.  The 41Hz kit is more expensive.

For me, this is more of an audiophile application so I wanted something better. the problem with 41Hz is that it comes from Sweden so the weak dollar hurt my pocketbook. No better with the Autocostuire (Italy) or the Charlize (Malaysia). But all three are supposed to have fantastic sound.

And of course, you need to assemble the the 41Hz stuff.

Hope it all goes well for you

Thank you.