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gsuser 31st August 2006 10:14 AM

Squeezebox power supply
 
Hello, for my first DIY work, I would like to build a "audiophile" power supply for my squeezebox. 220v to a 5v 2.5A.
Has someone a good shematic fot that and advices about best components to use ?
Thanks from a real newbee :rolleyes:

gsuser 11th September 2006 08:12 AM

2 Attachment(s)
Please, just a good shematic for a power supply like this one...

FastEddy 12th September 2006 12:43 AM

here is one way to do it
 
... http://focus.ti.com/lit/ds/symlink/ua7805.pdf ...

A Linear voltage regulator with wide range input voltage and very well behaved output ....

My personal application notes:
* Note that the "tab" on the TO-220 type is the same as pin#2, the ground pin. This means that the tabs can be attached to a heat sink that is at ground potential, meaning that your metal case can serve as the heat sink.
* These linear regulators can be linked in parallel and I have done this many times. Using the common "tab" / ground / heat sink of each connected together, the outputs can be in parallel ... and so can the inputs !!. Use three of these for up to 3 amps, five of these for 5 amps output current. Any differences & variations of output voltage between two to five or more regulators in parallel is nominal, as after a breakin period, an array of these regulators tend to each seek a common output voltage ... the break in time being how long it takes for the thermal charicturistics of each regulator to stabilize to the same levels. (The warmist tending to self limit, waiting for the others to "catch up" as it were.)
* Best input voltage for the -7805 is between 8 and 14 VDC = ideal for automotive use = best ripple rejection. These will stand up to +30 VDC down to as little as 1.5 VDC above the regulated output voltage, but the higher input voltages can increase heat generation.
* Note the circuits on page 6 above (see the link). The most commonly used circuit is of course the top one.
* Additional filtering can be added to the output leg (pin 3). I usually use at least 10 uF electrolitic cap on both input and output and a 0.1 uF tantalum cap on the output(s) = very good ripple rejection = decent for audio. For high resolution audio work (like the Squezzer) add more micro Farads at the output(s) and another 0.1 uF tantalum cap to the input(s) (of each regulator). All Capicitor voltages should be greater than 35 VDC rated = protecting the -78xx from surges & RF, etc.
* As a matter of prudence for the best possible performance, I over engineer the circuit, using much more capacity than may be required. === For your 2.5 Amp requirement, I would use five or six of these regulators in parallel = 5 to 6 Amps worth. This will give double what you need and much less than half the heat generated ... AND each regulator will thermally stablize better, faster ... AND your ripple & noise rejection will improve by a factor of 10x (a detailed technical explaination for this on request) ===
* I keep several dozen of these in the parts drawers in my shop. I buy them in lots of 5 to 20 at a time. The -7805 = 5.00 VDC, -7812 = 12.00 VDC, -7815 = 15 VDC and the 79xx are negative regulators (7905 = -5 VDC, etc.) ... and they can be had for between US$0.50 each to US$1.00 each ....

(For your transformer, use a 25 VA rated, primary for your voltage = 240 VAC and a secondary of 18 VAC ... fast blow fused to 1 Amp on the transformer input / line cord / plug in the wall side. This will allow you to plug in just about everywhere = from 120 VAC to 240 VAC = 9 VAC secondary to 18 VAC secondary, respectivly. Feed it through a full wave bridge rectifier ...)

:smash:

pinkmouse 12th September 2006 12:57 AM

Do you really need 2.5A? Seems an awful lot to me, and you'll need more than a 7805 to provide it.

FastEddy 12th September 2006 01:19 AM

Yes = more = more
 
Pink: " ... Do you really need 2.5A? ..."

Gsuser set the requirement, I only offered a solution. And yes you will need more than one (1) UA7805 ... I recommended five (5) or six (6) lashed together in parallel for a steady, cool running, ripple & noise free regulator ...
:)

You are probably right about the Squeezers not needing quite that much ... My recollection is that they need about 10 to 12 watts ... which at 5 VDC is about 2 Amps ... Yes?
:smash:

leadbelly 12th September 2006 01:28 AM

Well, IMHO, stringing 5 or 6 7805's in parallel is unlikely to beat the performance of whatever supply the device came with.

If you are a newbie, a super-regulator might prove too difficult. If you look at the following post and built the +ve circuit with an LM338, you might be very happy in the end:

http://www.diyaudio.com/forums/showt...154#post356154

FastEddy 12th September 2006 01:41 AM

Oh yeah .... plenty good
 
http://www.diyaudio.com/forums/showt...154#post356154 ... plenty good enough for this case ... and you just build the upper half of that drawing = plenty 'o current and a better parts count than my suggestion(s).

(I would bet there isn't much difference between the above and my suggestion(s) as far as ripple, surge, noise rejection goes ... but I've been wrong before.)
:smash:

FastEddy 12th September 2006 01:43 AM

truth is one ...
 
... paths are many ...

The Squezze Box comes with a wall wart = switching supply in a small brick.

:angel:

leadbelly 12th September 2006 03:57 AM

Re: Oh yeah .... plenty good
 
Quote:

Originally posted by FastEddy
[B(I would bet there isn't much difference between the above and my suggestion(s) as far as ripple, surge, noise rejection goes ... but I've been wrong before.)
:smash: [/B]
There is. Those older fixed regulators are noisier because they use a cheaper voltage reference. Why do you think you see so much use of the LM317 on this forum? You think all those countless DAC designs use the LM317 for 5VDC because the designer is too stupid to figure out that a 7805 exists?

mrjam 12th September 2006 09:35 AM

Quote:

Those older fixed regulators are noisier
From ST Micro datasheets:
1) LM317 - noise .003% Vout - BW 10Hz-10kHz
2) 78M05 - noise 40uV - BW 10Hz-100kHz

So the output noise with 5V output is:
1) 1.5uV/sqrHz
2) 126nV/sqrHz

Quote:

Why do you think you see so much use of the LM317 on this forum?
The reason isn't noise :D :D


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