Questions on using AC-DC w/TREAD

[sbelyo]

I want to build a power supply for a T-Amp project. The requirements are 12-14.5 VDC @ 1.5 - 2.0 amps

Has anyone seen an adapter that meets those specs?

 

[tangent]

If I had to do that, I'd get a +/-15V dual output transformer and run the secondaries in parallel. Forget wall warts. You might instead find a single-output 15V transformer that will also work, but those are rarer.

 

[sbelyo]

Quote:

Originally Posted by tangent If I had to do that, I'd get a +/-15V dual output transformer and run the secondaries in parallel. Forget wall warts. You might instead find a single-output 15V transformer that will also work, but those are rarer.

That sounds like a better solution...

I'm going to run it from a battery and see how much current it really draws at full volume into an 8 ohm load. Some have said they never saw it top out over 800 mah. If that's the case, then it opens up the options.

My initial thought was to buy a cheap wall wart and use a TREAD to regulate. Or use a STEPS if I wanted high end.

Here's an off topic question in reguards to STEPS. If that transformer can put out 1.5 amps and the regulator can handle 1.5 amps I should be ok as long as I don't pull more that 1.2 amps or so right?

 

[bg4533]

You should be fine as long as you have proper heatsinking.

You might want to use the LM338 regulator as it is rated to 5A. Might as well up the transformer a bit too.

If you check current draw be sure to use some music with heavy bass and watch draw at big dynamic peaks.

 

[sbelyo]

I was hoping I could upgrade the regulator. The amveco that would fit the steps board will give me 14V @ 1.7 amps I think.

 

[bg4533]

You might need a bigger heatsink than the Steps board will easily fit. Someone else who knows more about HS requirements should confirm though.

 

[steinchen]

depends on the voltage drop across the regulator and the current drawn from the psu

voltage drop = input voltage - output voltage

power dissipation = voltage drop * current

e.g., with input voltage ( = transformer voltage after rectification) = 15V and output voltage = 12V you get a voltage drop of 3V

power dissipation = 3V * 2A = 6W

With the 4K/W heatsink of the steps the heatsink temp will be 24°K above ambient temp, pretty warm but ok with a ventilated case.

For 2A you need to switch from LM317 to LM338 and make sure to pick adequate rectifier diodes.

 

[mono]

Quote:

Originally Posted by sbelyo That sounds like a better solution... I'm going to run it from a battery and see how much current it really draws at full volume into an 8 ohm load. Some have said they never saw it top out over 800 mah. If that's the case, then it opens up the options. My initial thought was to buy a cheap wall wart and use a TREAD to regulate. Or use a STEPS if I wanted high end. Here's an off topic question in reguards to STEPS. If that transformer can put out 1.5 amps and the regulator can handle 1.5 amps I should be ok as long as I don't pull more that 1.2 amps or so right?

The T-amp has great noise rejection, people have even been using any-random switching supply and report they work fine... though I took the safer route and built a somewhat-STEPs-like linear for my T-amp... and it works better than necessary, is overkill.

The supply does not need 14.5V, you're better off leaving it at 13.2V max as spec'd per Tripath docs. Further, latter productions of T-amp dont' have the amp chip 'sunk to the PCB anymore so you may not even be able to run it full-out at 13.2V either, unless you first (re)sink it.

The supply does not need 2A capacity, indeed you'll not be using over 800mA and maybe not that much except peaks. Thus, the most effective supply will have a lot of post-regulated capacitance near the amp, not remotely mounted on a power supply board.


Frankly, if you took a very basic LM7812, put 8000 mfd after it, and a 12V 1.5A transformer before it, you'd be done... there is nothing you can really hope to gain unless you have horrendous AC noise getting in then consider some line filtration and/or look at how things are routed, if they're picking up noise.

 

[motherone]

If you really want a wallwart, go for the 15VAC / 2AMP one from allelectronics:

http://www.allelectronics.com/matrix...nsformers.html

I'll be using that to feed a LM338 on a Digi01 regulator board for my line-powered T-amp.. Mainly just because they're what I have lying around.

You can probably just as easily get away with the standard TREAD/LM317, though. Unless you're running the t-amp into a 4 ohm load near clipping and for long periods of time, you probably won't be drawing even 1.5 amps from the regulator.

 

[sbelyo]

Thanks guys...

I found a few things on the all electronics site that should work. I'm going to try both regulated and unregulated and see what happens.