DIY Mic Pre Kits, Lunchbox Mic Preamp Kits, Power Supply Kits

What are the specs on this p/s? I mean if you use a 20-0-20 transformer as opposed to the 18-0-18 transformer you supply what are the highest outputs that we can use safely, amps and volts? I was considering purchasing a second 1848 to make as a bench supply for working with other DIY projects. If I turn down the trim pots to make it 9v will it work fine with most pedal projects for example?

You recently posted a sticky where you stated using more than 20-0-20 trafo was not a good idea because you would need bigger heatsinks on the regulators among other factors, but here you say you can use a 22-0-22... I'm confused. I guess I need to work on my fundamentals.

Using the above mods, with a 22-0-22 transformer, you'll get adjustable output from 1.24volts to 28+ volts.

Using a 20-0-20, you'd get 1.24 to about 24Volts.

> If I turn down the trim pots to make it 9v will it work fine with most pedal projects for example?

Yes.



I think you misread, or I mistyped... I said 30-0-30 will be too high.

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I was talking about the post titled "Transformer Voltage Rating" where you said at most 22-0-22 but the regulators will get hot and require larger heat sinks, etc. So 22-0-22 will not require bigger heatsinks?

Okay I see what you mean.

For an 18V output:
If using a 22VAC, the DC voltage will be around 31volts. Out of this 31 volts, you'd need to throw away 13volts to regulate it down to 18V. That's why I said it will generate too much heat and wasted energy, and thus require a bigger heatsink.

Now, if your wanted output is 25Volts or 24Volts, it's not so bad as you only need to throw away 6-7 volts.


Now, if you only use a 20VAC transformer for the 18-0-18 supply, the DC volts will be around 26 Volts, and you'd just need to throw away 8volts to regulate it down to 18v.

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So I received both my 22-0-22 trafo from digikey and my new PS-2848 power supply (thanks Ruel!!) and I now have some questions of course.

My intention for this is to use it as a versatile variable bench supply for small electronics projects and I'm trying to figure out how to best hook this up. I'm figuring if I put a switch to swap the secondaries between series on both secondaries or just one secondary coil I should be able to get up to +/- 26v DC while in series, and then around +/- 14v DC if I use just one. Will this work ok? I intend to replace the trim pots with panel mount pots as well.

I haven't worked out the effect of the higher trim pot values and the resistor change yet on the PS-2848 as opposed to the 1848 so I'm not how that would affect switching to the lower voltage. I'm basically interested in getting 9v to 15v, 18v to 24v outputs. If I can get away with not changing anything and still hitting those without ill effect to the PS-2848 then that would be better. But I'm afraid the voltage regulators will burn up if I try to run it at 9v for very long without halving the secondaries... Anyway, a little help steering me in the right direction would be appreciated.

If I should just buy another PS-1848 to use for lower voltages that works too, of course. This is really a project about learning fundamentals for me so feel free to point out where I'm wrong or how I'm an idiot. I've been studying a basic electronics book but sometimes its a little overwhelming if you don't have anyone to ask specific questions.

Yes, you can use it as a bench PSU. Of course you'll need a case, and some binding posts (4pcs) for the output voltages.

(Actually, my first project back when I was 17 yr old teenager is a regulated Bench PSU... 1.25V to 20V using... guess what... an LM317 chip.)

If I were you, I would not solder the PCB trimmers.... instead, get some pots of the same values as the trimmers (5K) and just wire it to the PCB from the front panel.

Now, since this is a bench PSU, and the amount of load this will be connected to will vary, I'll probably use a bigger heatsink. And since I designed all the regulators to be on the side of the PCB, it will be easy to install a big heatsink with fins... (and from there, you can even get fancy and also install a fan to blow on the heatsink, you can buy 110V fans... but I think it will be overkill.)

WARNING: If you'll be using a SINGLE heatsink to connect all 3 regulators to it, you MUST USE TO-220 insulators for both the regulator and the mounting screws. You can buy this at digikey and other electronic hobby shops. The insulator will prevent the back of the vreg from touching the aluminum heatsink and isolate the mounting screw also. Then, mount the aluminum heatsink to the case for further heat dissipation.

NOTE: Since the kit for use with the SC-1 does not require a big heatsink, and we're using separate heatsinks for each Vreg, and the heatsinks are not touching any part of the case, we're able to get away from not using any TO-220 insulators.

As I said, Using the above mods, with a 22-0-22 transformer, you'll get adjustable output from 1.24volts to 28+ volts.

Using a 20-0-20 trafo, you'd get 1.24 to about 24Volts.

So I don't think you need a separate PSU for +/-14V. Since the 24V outputs can be adjusted down to 14V (and lower) if needed. The minimum voltage is 1.25V. i.e. you can't reduce the psu to below 1.25Volts without any major changes in the design.

One mod you can do to your PSU is get one of those digital meters that you can hookup across your outputs. Then you'll have a digital readout of the output voltage. You can buy them at eBay.

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That is GREAT information thanks so much! I'm looking at the Mouser catalog at heatsinks and I'm a little overwhelmed. Can you give me an example of the TO-220 insulator and heatsink you are talking about so I can see a picture of it? I'm assuming you mean one huge big heatsink for all 3 regulators right?

Something like this... includes the Mica insulator and the plastic/nylon bushings for the mounting screws.

http://www.alliedelec.com/Search/Produc ... R=935-9422

But I found this... heavy-duty heatsinks for TO-220.
http://www.alliedelec.com/Search/Produc ... =specs#tab

You may have to wire the TO-220 off the board.

There's so many ways to do this project.

Other heatsink styles here.
http://apexjr.com/Sinks.htm

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Ah that helps a lot. So I would get one per regulator with that set, right? Are the regulators far enough apart to mount a heatsink that big? I will need to measure.

I'm not clear on what you mean when you say wire the TO-220 off the board. Doesn't the heatsink have to be physically connected to the regulator? Do you mean mount the regulator to the heatsink and case and run leads back to the board?

Yes.

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