midiverb power supply 16V CT?

jondog · #1 12-29-2004, 05:18 PM

I've got an original midiverb w/ no power supply. It has an odd 3 tine connector. Does anybody know what 16V CT means? Yes 16 volts, but will it be AC or DC?

Freaky Fender · #2 12-29-2004, 05:42 PM

Maybe you can only power it in connecticutt?

Passinwind · #3 12-29-2004, 10:38 PM

That CT means center tapped, which strongly implies AC. This means that ground is likely at the halfway point of the transformer winding, which is common when powering a +/- DC internal supply from AC.
Looky here: http://www.alesis.com/support/faqs/general_power.html as well. A good tech could double check this for you quite easily.

jondog · #4 12-30-2004, 05:32 AM

Thanks, I'll look for a 16V AC adapter then. The link is interesting but not helpful, they don't even list the original Midiverb. I assume the adapter I'm looking for is P1 since they just start at P2. I'll probably just find an equivalent power supply and solder directly to the tines.

nashvillebill · #5 12-30-2004, 06:04 AM

A standard 16V "wall wart" wouldn't work because it only supplies two wires of AC at 16 volts. You need a transformer that puts out 8-0-8. There's three wires (or terminals) coming out. From output 1 to 2 measures 8 volts, from 2 to 3 measures 8 volts but opposite polarity (the sine wave is inverted compared to 1-2), from 1 to 3 measures 16 volts AC. A standard 16 volt wall wart woun't have the center tap.

Center-tapped transformers are commonly used for the linear power supply of power amplifiers. In conjunction with a bridge rectifier and appropriate filter capacitors, a DC power supply is generated that will have both +DC and -DC measured with respect to ground....

Mouser Electronics ( www.mouser.com ) carries the Hammond 187C16 for about $10. It's Mouser's part #546-187C16. It's only good for 800 milliamps, though that should be enough current.

jondog · #6 12-30-2004, 08:08 AM

Wow, you guys are awesome! Here's a pic of the inside, can you confirm that this is the part I need? It's pretty cheap so no big risk, but I'm not even sure this unit works so I'd like to know my odds are pretty good before ordering from Mouser.

nashvillebill · #7 12-30-2004, 10:23 AM

The transformer I listed is just a plain, open transformer with exposed terminals. So you'll need a chassis (case) to mount the transformer in, an AC cord to plug the transformer into the wall, a fuse holder for the incoming AC, wire to go back to the Midiverb, and grommets to protect the wires where they enter and exit the case. And a soldering iron to solder the wires.

Sure it isn't easier or cheaper just to get the power supply from Alesis? Did you check Ebay?

And if you buy the correct power supply, but your Midiverb doesn't work, you could sell the stuff on ebay and get your money back, whereas you're pretty much stuck with the transformer if you buy it from Mouser.

jondog · #8 12-30-2004, 10:35 AM

Yeah, Alesis says Part No Longer Available and I don't see anything on ebay. The chassis and other parts are no problem, the soldering sounds easy, the only thing I've never done before is the fuse, does it just go in line before the transformer?

Joe P · #9 12-30-2004, 10:38 AM

I'd be careful with the AC-or-DC question. I don't think you'd want to hit it with one, if it needs the other! A tech could probably pretty easily tell by looking at the components on the board if it's AC or DC (there'd be rectifiers).

Either way (I have a feeling it's DC, actually), I'd imagine that just to test it at least, you could use TWO straight 9V supplies. They're isolated; if DC is what the unit requires, there shouldn't be any problem with just connecting them in series to get 18VCT.

Can any other techs confirm that? I'm almost sure I've strung together wallwarts like this to power two-rail op amps before.

Joe

Passinwind · #10 12-30-2004, 11:03 AM

Quote:

Originally Posted by Joe P

I'd be careful with the AC-or-DC question. I don't think you'd want to hit it with one, if it needs the other! A tech could probably pretty easily tell by looking at the components on the board if it's AC or DC (there'd be rectifiers).

Either way (I have a feeling it's DC, actually), I'd imagine that just to test it at least, you could use TWO straight 9V supplies. They're isolated; if DC is what the unit requires, there shouldn't be any problem with just connecting them in series to get 18VCT.

Can any other techs confirm that? I'm almost sure I've strung together wallwarts like this to power two-rail op amps before.

Joe

If it's DC, it's the [only] Alesis power supply that is, according to the FAQ I linked to. Still, better to be safe; let's keep the smoke inside, eh?

Jon, they did list the original Midiverb (look hard, I had trouble seeing it), with "not available".

The second picture seems to show a lot of diodes, and possibly DC regulator chips, all very near the power supply jack. That'd imply AC as well. I can't read the numbers off the picture, but if Jondog can PM me we can probably figure it out. If you were here, I could figure this out in a matter of seconds, most likely.

Edit: Thanks to Nashvillebill, I'm deleting the picture I just posted.

If it had happened to be DC, stringing two supplies could've worked, but you still need to determine polarity. Reversed polarity can be a real killer.

nashvillebill · #11 12-30-2004, 11:15 AM

I Googled "midiverb power supply" and hit a picture of the Midiverb AND ITS ADAPTOR!!!

The adaptor clearly says Output 18VAC, CT, 15VA

So the Hammond is slightly underpowered. Mouser's part # 553-VPS161600 is rated 25VA and would be about $16

Yes, the fuse is on the incoming AC line but it's also a good idea to fuse the two secondaries.

PM me and i'll email you the picture.

jondog · #12 12-30-2004, 01:36 PM

Awesome! PM sent. Parts Express has a wall wart that's 18V AC, but that still won't work for me because of the center tap, right? Maybe if I keep looking I can find a wart that does have 18v AC and 3 wires coming out of it.

nashvillebill · #13 12-30-2004, 04:14 PM

Right, if the Parts Express doesn't have a center tap you're outa luck.

Email with pic sent.

jondog · #14 01-12-2005, 05:10 PM

I think this one might work, can any of you second that opinion?

http://cgi.ebay.com/ws/eBayISAPI.dll...774092908&rd=1

nashvillebill · #15 01-12-2005, 05:34 PM

Looks like it should work. If voltage is a tad high, maybe put a couple of zeners on it.

jondog · #16 01-12-2005, 05:50 PM

I think the voltage will be fine, the amperage is what concerns me. The original midiverb PS appears to say 15VA on it, whereas this Rane is 750mA. I don't know what VA is supposed to mean, I've only seen A and mA.

nashvillebill · #17 01-12-2005, 09:18 PM

For a transformer, VA is just the product of current and voltage. 18 volts times .750 amps equals around 13.5 VA...That's a tad under the 15 VA requirement, let me amend my last post from "it should work" to "it'll most likely be OK"

Sorry I didn't have a calculator handy last post so that's what I get for multiplying in my head.

For $16 you could get the transformer from Mouser that'd be 25VA, definately no question it'd work. I'd still get the Mouser transformer.