Good (cheap!) source for complete SMPS modules?

[armstrom]

I'm contemplating building a very small 40W head using a TPA3106D1 class D chip. This is the same chip used in the "44 Magnum" amp "pedal" that EH sells. My plan is to build something a bit more complete that has an interesting, useful preamp, tone controls and some digital effects for good measure. I want to cram it all in the smallest enclosure possible. The power amp, preamp and digital effects are really not a problem. They can all be be crammed on to a small PCB. The power amp, being class D, doesn't require a real heat sink and can use the ground plane of the PCB itself to sink waste heat...  The part I'm struggling with is the power supply.

I'm sure that to keep the weight and size of this project down I will need a SMPS of some sort. I'm starting to realize that I'm likely going to have to use an external power "brick" just to keep the costs down. 24V DC is a somewhat common voltage for consumer electronics so there are a few sources of 2.5-3.0A 24V power adapters at reasonable prices. I would REALLY like to have the power supply built in to the amp head itself though. Several companies make SMPS "modules" that are already CE certified and save me from trying (and ultimately failing) to design a build my own SMPS. However, these things are CRAZY expensive. I would prefer a fully sealed PCB mouted "Block". 85-250V AC goes in one end, 24V DC comes out the other. These seem to be very common for lower power and/or voltage ratings but not so common for what I need.

Does anyone know of a source for these modules that doesn't cost an arm and a leg in small quantities? Or even a good source for external power bricks that are small in size? I know they can be built... just look at the power supplies that are available for netbooks and other types of laptops. I have one at home with a footprint not much larger than 3" x 1.5" but while it's rated at 60W it only puts out 18V. To get ~40W out of the amp I really need to run it at 24-25V.

Any thoughts? Suggestions?
-Matt

[R.G.]

Mouser, 675-CENB1060A2403F01, $29.25, 43 in stock, 24V 2.7A.

[AdamM]

In the UK you can get replacement laptop PSU's for around £5-£10 on amazon. They're typically around 20V/3.5A although it should be relatively straightforward to trim the voltage up a touch

[DavenPaget]

Just search for 24V (Make sure they are quite large) laptop chargers
And just take a IEC wire and use only the female plug , leave the 3 bare wires and terminate on a IEC plug , if you need a separate power supply for the preamp , just get a cheapy 12V smps wall plug ( router plug preferable , just remember to use a regulator and tons of filtering ) and hack it !

[armstrom]

Thanks for the info guys. I have found a number of cheap external bricks, the issue is that they're larger than what I was hoping for. Here's one from Amazon http://www.amazon.com/24V-Power-Supply-Adapter-Monitor/dp/B004P1PCXA/ref=sr_1_12?ie=UTF8&qid=1330554585&sr=8-12

My hope was to be able to find either a small SMPS module that I can embed in my head (the amp head, not MY head ), or a TINY external brick. It would be kind of silly to have a tiny 40W amp just to require carrying around a power supply larger than the amp itself in order to use it My ideal solution would be something PCB mount and sealed... Like this: http://search.digikey.com/us/en/products/KMD40-1212/285-1761-ND/1827694
But for far less money I know, it's all about volume. But one can hope

R.G., if I may ask a slightly related question... I've found that some of these SMPS modules can introduce noise into the circuit. Usually through the DC ground being noisy and even elevated above "earth" ground by several volts. In the past I've tried to ensure that I only SMPS units with 3-prong IEC connectors (the one I liked above does not ) and that the DC ground is shorted to the ground lug of the IEC connector. If I can't be picky about my power adapter, how would you recommend isolating the noise of the power supply from the rest of the circuit? I know if I'm just dealing with ripple on the positive rail I can filter it out the traditional way... But what if the problem is on the ground rail? Some time ago I dug up an old post of yours where you describe a device you've been meaning to create one day.... Some kind of "battery simulator" or something to that effect. I can no longer find the post but you said such a device would isolate the effect circuit from the power supply with a capacitor. I never found a follow-up to this... could you describe what kind of circuit you had in mind?

-Matt

[R.G.]

My ideal solution would be something PCB mount and sealed... Like this: http://search.digikey.com/us/en/products/KMD40-1212/285-1761-ND/1827694
But for far less money I know, it's all about volume. But one can hope

Try this one: http://search.digikey.com/us/en/products/VGS-50-24/102-1937-ND/2045668 for $37.00.

I highly recommend not getting an open frame power supply for noise and safety reasons. The metal skin stops most RF radiation problems if the thing is properly grounded to AC power safety ground.

I've found that some of these SMPS modules can introduce noise into the circuit.

Yeah... 

Usually through the DC ground being noisy and even elevated above "earth" ground by several volts. In the past I've tried to ensure that I only SMPS units with 3-prong IEC connectors (the one I liked above does not ) and that the DC ground is shorted to the ground lug of the IEC connector. If I can't be picky about my power adapter, how would you recommend isolating the noise of the power supply from the rest of the circuit?

It can be quite difficult. Take a look at a metal-enclosed supply like the one I suggested first. First off, be picky about your power adapter. Use a three-wire version, ground the DC secondary to the incoming AC safety wire at one and only one place. Use an IEC receptacle with an internal fuse. Be really, really, really scared of where and how the AC power wires are routed, attached to switches and fuses and things. This last sentence is not a joke. Dead is forever.

I know if I'm just dealing with ripple on the positive rail I can filter it out the traditional way... But what if the problem is on the ground rail? Some time ago I dug up an old post of yours where you describe a device you've been meaning to create one day.... Some kind of "battery simulator" or something to that effect. I can no longer find the post but you said such a device would isolate the effect circuit from the power supply with a capacitor. I never found a follow-up to this... could you describe what kind of circuit you had in mind?

Ground noise is best dealt with by either forcing all ground points to the same voltage by tying them to incoming AC safety ground, or by forcing the currents to flow on different wires, which is a form of star grounding. Switching power supplies make this worse by having switching harmonics well up into the FM and aircraft RF bands, so the noise can simply radiate over to where it will cause the most irritation.

Having misdirected your attention to grounding subtleties, I'll admit that the capacitive ground isolator did not work well so far. Don't be thinking about that as a possible way out just yet. 

[armstrom]

Thanks for the great info. I've used those metal framed supplies in the past (DC-DC converters from Mean Well). They're a bit larger than I would like but as you said, I don't want to deal with an open frame module due to noise issues. I guess I just need to stick with the ole power brick for the time being. If I were able to find a PCB mount, sealed SMPS module at a decent price then I wouldn't route AC wires at all . I would use a PCB mounted IEC power entry module. The ideal IEC socket for me would have an integrated power switch and fuse in addition to being PCB mouted I look forward to seeing if you work out the issues with your capacitive ground isolation circuit.
-Matt