[philodox]

Hey Guys,

Just wondering if anyone has a schematic for something that would be roughtly equivalent to all the Elpacs which are so widely used on here? I need something to charge my recently acquired PINT. It would not be running off of this, so it doesn't need to be anything fancy.

Thanks,

Jason

 

[n_maher]

Jason,

If it's just to charge the battery I think any old wall wart will do, provide the voltage specs meet what you're looking for. The noise issue of an unregulated PS shouldn't be an issue as far as I can tell.

Is your PINT running one or two 9V's?

Nate

 

[philodox]

Hey Nate,

Thanks for the response.

I was told: "All you need is a regulated, isolated, power supply that can deliever 18 to 24 volts DC and has a center positive 2.5MM barrel plug."

I guess that would be if I was running it off of wall power? If I am just chargin I don't need to worry about it being regulated as long as it is between 18 and 24 vdc?

My PINT is built with a single 9V battery and the LM6172 OPAMP.

 

[n_maher]

From Tangent's PINT guide:

Quote:

First, if you want the wall supply to charge a NiMH battery, its voltage should be at least 1.45× the number of cells in the battery, plus 3 V to account for the drop across the regulator. The 1.45 number is the peak voltage per cell that you should see during charging. If you're using "9V" NiMHs, divide the rated battery voltage by 1.2 to get the number of cells; common configurations use anywhere from 6 to 8 cells. Let's say you're using two 8.4 V NiMHs in series. Each one has 7 cells, so that's 14 in total, giving a minimum charging voltage of 23.3 V. A 24 V supply would be sufficient.

The way I read that you probably need a PS that's putting out 15V to adequately charge the single 9V. I'd need to research it further to tell you if going much higher than that would be a bad thing.

Quote:

An unregulated power supply's output voltage will fluctuate as the wall voltage fluctuates. Also, unregulated power supplies tend to be cheap all around, so they'll have a lot of ripple on their outputs. If you're just using the wall supply to charge your battery, that's not a problem, but it is if you're going to listen to the amp while it's on wall power. See my Op-Amp Power Supply Quality Considerations article for the reasons why.

So, I think since you're in the "charge only" camp you can be more flexible with your PS choice, which is good since it means more, cheaper options. The isolation portion of the equation is handled by whatever jack is used on the PINT case, I'm going to assume that whoever built the PINT used the right jack.

HTH,

Nate

 

[cetoole]

Quote:

Originally Posted by n_maher The isolation portion of the equation is handled by whatever jack is used on the PINT case, I'm going to assume that whoever built the PINT used the right jack. HTH, Nate

Nate, by "Isolated", I believe Tangent is referring to the property of the transformer, as opposed to the DC jack, which should be isolated so that it is floating, so as not to cause issues with the virtual ground on the Pint. Of course, the dc jack also must be isolated.

An easy solution to your question philodox would be an unregulated wallwart, followed by something like a 7815. The Pint just has a trickle charger, so will not be pulling too much current at all to charge its batteries. It should be well under 100mA draw, even if you are using it while charging, especially with the LM6172.

 

[philodox]

Thanks guys, hopefully I have a suitable wallwart lying around.

 

[mono]

DIY Tread-like regulator board to fit inside a wall wart casing. Pick a different resistor value for different output voltage and complimentary wart default voltage and current as required. It's close to being do-able on perfboard if you wanted to go that route instead of etching a board.