Need to build a Linear Regulated 24v Power Supply
Mar 12, 2015 at 11:38 PM Post #16 of 29

MisterX

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25VA is an awful lot for a Cmoy.
No datasheet so we don't know the unloaded output voltage from that transformer, which means we can't accurately calculate the thermal load on the regulator.
 
Less then $7 though...
Tough call.
 
Mar 13, 2015 at 12:03 AM Post #17 of 29

badmojo

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  25VA is an awful lot for a Cmoy.
No datasheet so we don't know the unloaded output voltage from that transformer, which means we can't accurately calculate the thermal load on the regulator.
 
Less then $7 though...
Tough call.

well, there's a bunch of others with lower VA http://connectronics.com.my/index.php?route=product/category&path=89_163 but as far as the voltage goes you think using a 24v transformer will work ok with the LM7824? My question is in regards to the dropout voltage, is the 24VAC from the transformer too low to work well with the regulator.?
 
Mar 13, 2015 at 1:37 AM Post #19 of 29

badmojo

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  Yep, 24 volt secondaries are enough to keep the regulator regulating.
Whats the current draw of the amplifier?

I couldnt find that info specifically about the CmoyBB but in general I'm using what Tangent wrote on his site: "The amount of current your supply can put out really doesn’t matter for this application — even the crummiest little wall wart can supply 100 mA, whereas your CMoy amp shouldn’t ever draw more than about 20 mA"
 
Mar 13, 2015 at 3:05 AM Post #21 of 29

badmojo

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  Is there a reason you can't just measure it?
I wouldn't take on a PSU if you don't a have meter that can SAFELY measure current....

Thanks! Your question was the first clue that I could use a basic multi-meter to measure the current draw :wink: I just did it! While playing music at max volume with large headphones. The max draw measured was 0.06 at a 10Amp reading, I did'nt have a setting between 200ma and 10Amps for a finer reading, so it could be anything from 600ma to 690ma. 
I suppose the 20ma Tangent was talking about is the consumption by the cmoy circuit itself. Where do I go from here?
 
EDIT: here's the thing though. the adaptor I was using during this test has a output of "24V 0.3A 7.2VA".
 
Mar 14, 2015 at 5:01 AM Post #25 of 29

badmojo

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  Selecting a suitable transformer is much easier now that you have an idea how much current you need.....
The 3VA model looks like the best option if you're limited to ordering from Connectronics.

Awesome! I've already ordered the LM7824 Regulator from here http://www.ebay.ca/itm/Positive-24V-DC-Voltage-Regulator-Module-Board-High-Quality-/201237830997?pt=LH_DefaultDomain_0&hash=item2edab59d55 thanks to Ocean7, (it has a datasheet: http://www.audiowind.com/pdf/D-1000.pdf) now I just need an enclosure which will fit everything. There are also good electronic stores near my house but they dont have websites. If I go looking what should I look at in a transformer that will make it a better bet than the "No-Datasheet" Connectronics ones.
 
Why get a cheap and noisy switching power supply and then regulate it with the LM7824?

Build the whole power supply straight yourself. Get this and a small toroidal transformer and put the whole thing in a nice enclosure. Done.

If you want to be more into DIY the same eBay seller also sells the bare PCB but it will cost you more in the end and maybe will not look as nice (I got a bunch of those modules and they are really well made).
 

Also at this point adding anything is not going to be easy, but do you know of any solutions that is not too "involved" when it comes to isolating the power source? But also since Ocean7 has already reported how its well made hopefully it wont really need anything else.
 
Mar 14, 2015 at 4:58 PM Post #26 of 29

MisterX

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If I go looking what should I look at in a transformer that will make it a better bet than the "No-Datasheet" Connectronics ones.

In addition to a data sheet?
biggrin.gif

A toroidal with dual secondaries would be nice.
 
do you know of any solutions that is not too "involved" when it comes to isolating the power source?

We're discussing building a linear power supply so electrically isolating the inputs from the outputs is pretty straight forward.
If you're going to use an aluminum enclosure make sure the safety ground lead from the IEC is not connected to the ground terminal on the DC jack.
If you're using a center tapped transformer don't connect it to the case. And so on....
 
Mar 15, 2015 at 4:55 PM Post #27 of 29

badmojo

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  In addition to a data sheet?
biggrin.gif

A toroidal with dual secondaries would be nice.
 
We're discussing building a linear power supply so electrically isolating the inputs from the outputs is pretty straight forward.
If you're going to use an aluminum enclosure make sure the safety ground lead from the IEC is not connected to the ground terminal on the DC jack.
If you're using a center tapped transformer don't connect it to the case. And so on....

Ok, thanks for all the help MisterX and everyone, once I have completed the job, will post back summary with some photos.
 
Mar 15, 2015 at 5:10 PM Post #28 of 29

amb

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Yes, a 24V transformer will work, because after rectification, the voltage gets multiplied by a factor of 1.4142, enough to account for the regulator's voltage dropout and variations in line voltage. The transformer you linked is a EI core type, which emits strong magnetic fields in certain directions. Keep it far away from the amp circuitry to avoid interference.
 
Mar 15, 2015 at 5:14 PM Post #29 of 29

badmojo

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Yes, a 24V transformer will work, because after rectification, the voltage gets multiplied by a factor of 1.4142, enough to account for the regulator's voltage dropout and variations in line voltage. The transformer you linked is a EI core type, which emits strong magnetic fields in certain directions. Keep it far away from the amp circuitry to avoid interference.

thanks for that piece of info. if i cant find a well priced toroidal one than that will be it, and the plan is to house it in a plastic enclosure will sit on the floor about 3feet below the cmoy on the table.
 

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