[Ikrit42]

I'm currently putting together an order for parts for a Millett Hybrid, but I'm having trouble finding a good AC adapter. I'm also planning on upgrading to a TREAD at some point.

If I were to get, say, a 24V wall wart adapter, then plug it into the TREAD, would I be able to get 24V out of the TREAD, or does some voltage get lost?
I'm relatively new to electronics, so I don't really know how the efficiency would work: since nothing's 100% efficient, would the TREAD just lose some power or some voltage? If it loses power (wattage), then it could be configured to just lose some current capability, right? (P=VI)?

 

[FallenAngel]

If you get a 24V AC wallwart, you should have no problem getting 24V DC out of the TREAD.

 

[headphonejunkie]

You should try and find a 30 volt or 28 volt walwart. The tread won't regulate if the input is the same as the output. You need a differential between the two. Also, this way you could adjust to 27 volts which is what a lot of people are running there milletts at. I would try and find a 30 volt. I had a 24 volt elpac and I could not use my tread just because of that problem.I got a toroid and the tread worked fine. Unfortunately, I got too big of a toroid so my regulator would get very hot. I had to get a big heatsink to compensate.

 

[n_maher]

I don't think I've ever seen a DC wallwart higher than 24V, so unless you like hunting through junk/surplus stores I'd take Fallen's advice. Just get a 24V AC wallwart and you'll have plenty of headroom to run it up near 30V.

 

[tomb]

Here's how it works:

The Millett uses ~350ma, so you might buy a 500ma walwart minimum.

An AC walwart is rectified by the TREAD. The act of rectification - chopping off some of the waves, bringing up the valleys, etc., actually increases voltage by 1.4x (round numbers). This has to do with the relationship between AC Volts peak-to-peak vs. RMS, but the details don't matter. The 1.4x does.

Now, the rectifiers also burn up some of those volts, but not nearly as much as were increased with the 1.4x: subtract about 1.4V.

So now, with a 24VAC walwart, after rectification, you're already at (24*1.4)-1.4 = 32.2V, now DC.

You are correct that the regulator will burn some power - approximately 3V, times whatever the eventual current is, but we know that from the top: ~350ma.

So now, you have a max voltage capability after the TREAD of 32.2 - 3 = 29.3V. Most people turn it back down to 27V for the Millett.

The down side is that all of this voltage reduction is wasted in heat. How much? Power = Volts x A. So, 32V-27V = 5.2V wasted. Then 5.2V x 0.35A = 1.82 Watts. That's where the power goes. However, looking back at your walwart's power: 24V x 500ma = 12 Watts. So, after the TREAD, you still have over 10 Watts of power left. At 27VDC (your new voltage), that's more than ~370 ma.

As long as you put a heat sink on the regulator, you'll be fine - something bigger than a postage stamp, though. However, as many people find out, a 500ma walwart is cutting it kind of close with a Millett.

EDIT: Nate's right. The key is to purchase an AC walwart with a TREAD. If you buy DC, it's already been rectified and you don't get that voltage jump advantage.

 

[headphonejunkie]

That is what happened to me. I was trying to use a 24 volt dc elpac with my tread.

 

[Ikrit42]

Great!
Thanks everyone- Now to hunt through Mouser for a good one.

P.S.- Nate, were you at the Marlboro meet last summer? I think I remember talking to you for a while. I was the really tall teenager with the MS-1s.

 

[The Monkey]

Quote:

Originally Posted by Ikrit42 /img/forum/go_quote.gif Great! Thanks everyone- Now to hunt through Mouser for a good one.

EDIT: Nate correctly noted that these are DC supplies. Exactly what you do not want for this application. Apologies for the misinformation.

http://www.jameco.com/webapp/wcs/sto...56&pa=191556PS

or

http://www.jameco.com/webapp/wcs/sto...35&pa=163635PS

 

[n_maher]

Quote:

Originally Posted by Ikrit42 /img/forum/go_quote.gif P.S.- Nate, were you at the Marlboro meet last summer? I think I remember talking to you for a while. I was the really tall teenager with the MS-1s.

Yes, I was. Can't say that I remember any particularly tall young folks - of course I'm not that old (31) and I run about 6'-1" so my perception may be skewed. Or it could be the fact that I generally don't remember squat from a year ago.

Vincent, those two wallwarts you linked to are 24V DC supplies and will leave the user a bit short when it comes to the Millett. The best you could hope for (and I've actually done this) is to squeeze about 22V on the output of a TREAD from one of those. And that's if they run on the high side and output more than they're specified. I greatly prefer Digikey's MT7172 or Mouser's 412-224054 both of which are direct from the TREAD parts list.

 

[The Monkey]

lol, oops. Right you are, Nate. Exactly what you and tomb explained NOT to do.

<slinks away>

 

[splaz]

However you don't get higher than the AC voltage with half wave rectification, unlikely it would be used in an audio power supply though anyway.

 

[Ikrit42]

What about Mouser's 553-WAU24-1000?

The difference from the one Nate mentioned is the current- It can't hurt to have more current capability than necessary, right? Plus it's like $2 more, so I figured why not. Would more current be potentially damaging? I would think not, but just wanted to make sure (I'm going to be ordering in a couple hours).

 

[tomb]

As long as you have that heat sink, you'll be OK. Like you, I think more current is better than less, within reason.

The downside is that all the walwarts we're talking about here are unregulated (the purpose of the STEPS or TREAD). What that means is that the voltage is rated only for the stated current. At less current than the rating, that voltage will climb and will not come back down. Thus, you will be burning more voltage off through the heat sink.

For instance, most 24V walwarts will give you ~27-29 unloaded. The walwart with more current capacity will tend to stay up on the high side of the voltage (29V+) even after you get everything hooked up. Your TREAD or STEPS will still regulate it down to the voltage you select, but there will be more left over to be burned off through the heat sink (hopefully). (sorry if that was redundant)

I still think this is better. A walwart/transformer closer to the current rating of your amp will not perform as well. The transformer gets saturated above 80% and will throw out a lot more noise. Some quote an even lower percentage of load than that (50%) as the maximum the transformer should ever see. So, you're still better off with more current, IMHO.