Power Supplies

Power supplies are the bane of my existance.
They work one day and not the next for no particular reason.
Now I’m searching for a replacement, none of them work, even universal ones that state their compatibility.
And I’m pretty sure I’ve damaged my Studioprojects VTB-1 by plugging in a power supply of the wrong voltage.

Does anyone else have this trouble? I haven’t been able to record anything for months because I can’t power my preamps.

Hi Jow:
Is this power supply a WALL WART External power Adaptor? that powers your pre-amps? If so, you could have a major failure with your preamps… Or if there is a Voltage regulator circuit in them, you might have just a diode or Zenner diode or regulator device that has failed… ??

Bill…

The StudioProjects VTB-1 requires 12 volts AC, just as many Alesis devices do. Most wall-warts supply DC, including virtually all universal wall-wart replacements. The docs don’t make it clear if there’s any regulation of filtering in there. My guess is that there is some (RF and whatnot), but it’s probably minimal. The docs say to use the supplied AC adapter only for a reason…though if it’s strictly unfiltered AC you can get by with a simple 120v to 12v transformer. I don’t suggest trying.

I doubt you fried the pre-amp by hooking a DC supply to it, but it is possible. The filtering in the preamp should protect it, unless it’s a piece of crap.



http://www.studioprojectsusa.com/pdf/vtb1_feature_descriptions.pdf

There are two important specs when looking at power supplies… Voltage (volts) and Current (milliamps, mA, or amps).

My Dad who was an electrical engineer always taught me to think of the two like this…

Imagine a water hose. The pressure of the water is analogous to the voltage, and the quantity of water flowing down the hose is analogous to the current.

Now this is a little simplistic, but I find it useful (and I’ve now got a degree in Electronics so it must have helped).

Now then, imagine that the water sources supplying the water to the hose can supply the pressure (voltage), but can’t actually supply enough water to flow down the hose at that pressure… the pressure drops and the flow slows. Bringing this back to wall warts, voltage is important - too much and you run the risk of frying the thing it’s supplying; too low and you don’t get enough “pressure”.

As for current, the value stated on these devices is the maximum current that they can supply (at the stated voltage), so too high is OK, too low is bad (not able to provide enough flow). A wall wart asked to supply too much current will eventually give up the will to live and fry itself.

So in general… Voltage should match the required voltage of the device, and current should match or exceed what the device requires.

There are other considerations but we’ll ignore those for now, and as Phoo has pointed out, you need to make sure wheterh you need AC or DC.


HTH someone


Mark

A simple cheap AC/AC PSU will contain nothing more than a transformer; it will leave the rectification, smoothing, regulation and protection to the piece of equipment it’s supplying.

However, that protection is often one-shot, in other words, something will blow.(It’d be nice if it was a fuse, but usually it’s a diode or summat).

Hopefully, whatever it is that blows will be in the protection circuitry and not in the main part of the equipment, so if you have a multimeter, it’s not too hard to find and replace the blown component(s).

Ali

What Ali says is true, however in an attempt to reduce mains hum by separating the power supply from the unit, the filtering is often done within the wall wart case itself. That is part of the design advantage…to separate the unit from the mains through the use of a wall wart and a length of power cable.

Normally the input voltage/current requirements are printed on the unit back panel or in the OM as well as on the original power supply. Look for something like: 12VAC/250mA meaning it wants 12VAC at 250 milliAmp.

I looked at the unit and did not see a rear view but I did learn that it wants 12VAC and not DC. Very important point! Don’t subject it to 12VDC or you will be letting all of the smoke out! ???

This is one case were the warning: “Use original power adaptor only!” may have some merit. You need some knowledge of Electronics to substitute an after-market adaptor in this case.

HTH

Don

What sort of filtering is done within a cheap PSU that outputs AC Don? :p

And hopefully, the first thing in a piece of equipment that asks for low voltage AC will be a bridge rectifier, so I can’t see that feeding it DC makes much difference. Perhaps a wee bit of extra heat because only two of the diodes carry the load instead of all four and if the rectifier is working on the edge, then yeah, there might be smoke, but not on any decently built piece of gear. And of course the actual voltage will be a wee bitty different, but the regulation ought to handle that. Anyway, when does the claimed voltage on those things ever even approach the real one! :D

I’ve run my Boss SE50 on any PSU I’ve had handy at the time, AC, DC (both polarisations) and rated ranges from 9V to 18V, and it’s worked fine with them all. (It asks for 12VAC).

Mind you, I sometimes blow things up too! :(

But, that’s why good gear asks for LV AC, not only does it have its own high quality rectification, regulation and smoothing, but it makes it more or less idiot proof too.

Ali

EDIT: Note Jow, do not do it the other way round, i.e., using a PSU that outputs AC into a piece of gear that wants DC will definitely alert the Cheyenne that you’re in the area and are demanding a fight! :cool:

ANOTHER EDIT: PS, how ya doing Don? :)

Right, Ali. DC into a unit expecting AC probably won’t fry it, but it won’t work most of the time either (I have seen one that did (old crappy booster based on a class A amp), since the unit internally required only DC of the same polarity that the incorrect DC adapter was sending in - the rectifier just passed it through - and it worked. Most units will make use of a zero voltage ground and plus and minus DC, for balanced power).

This isn’t the reason the Boss unit worked. Those are smart and will detect the polarity of DC and switch to use whichever polarity is there. It’s nice. I’ve got a Roland MIDI controller at the office that does the same thing.

The AC filtering in some of these AC units would be low pass filtering to get rid of RF plus things used to block spikes it shunts them to ground and harmonics of the 60 hz, like buzz from a dimmer. All those can be filtered out of the AC. I’ve gone blank. Is a thyristor or zener diode what I’m thinking of that shunts spikes to ground? Lot’s power strips have them. Anyway, they are very simple and would be added to the transformer side side of the rectifier at little cost.

Ask me about this 30 years ago and I might know the answer.

Phoo, re filtering, I’m talking about cheap five quid boxes, and the ones I’ve opened up have nothing but a txfmr in the AC/AC units, and even the AC/DC ones, it’s just that plus a 4 diode bridge rec., and a (too small) cap. No zener regulation, so if you look at the off-load voltage compared to the on-load voltage, there’s a helluva difference.

Remember, I’m talking about cheap simple PSU’s here from Woolworths, not the good pro gear.

But, perhaps modernity has overtaken me. :D

As for the balanced thingy, again, on the gear I’ve got, they’re just a two wire cable, (no earth reference), and the equipment decides, (after rectification), which is earth. And split rails is easy to do without external reference; just use a 78xx/79xx pair; and again, it’s all done after rectification. You don’t have to centre tap a txfrmr, you just buy the right chip!

Anyway, ain’t switched mode the thing these days? Fault finding those feedback loops always gave me a headache. :(

As for the clever Boss SE50, you may well be right, I’ve never looked at it closely, and I’d always assumed it was just a bridge rec., but I’m probably wrong.

But, once again, technology is moving ahead a lot faster than I am.

There again, I’m probably having more fun than it! :D

A thyristor is just a fast solid state switch, and is sometimes used in PSU crowbar protection, but not for filtering.

The Zener is just a simple reverse biased diode as a regulator to keep the voltage constant, and it will shunt spikes to a certain extent. But you’re showing your age Phoo, :D Zeners were old hat even when I retired, the 78xx/79xx series of solid state regulators were commonplace way back then. OK, you might have a Zener to lift the voltage a wee bit, but not often. I hate to think what’s common these days, and as I said, I really don’t know anymore. But cheap is cheap and economics is economics, so cheap PSU’s will probably never have more than the absolute minimum of components.

But the best thing for spikes is a series inductance and a parallel tantalum cap plus fast regulation.

There again, for all I know, they probably use dilithium crystals these days. :(

Ask me about AC versus DC for valve filament heating, I can bore for hours on that! LOL

Ali

Thanks for all the info.

About damaging my VTB-1 preamp…I can actually power it now with one of the universal power supplies (I’ve never heard it called a wall wart before - but I guess it’s the same thing) but it outputs alot of noise now so it’s basically un-usable.
I assumed that this is because of damage caused while trying power supplies of the wrong voltage etc, but maybe the noise is just caused by using the wrong power supply (ie, it will work fine when i get a compatible power supply).

Which do you think is most likely?

A guy has to take careful consideration of the number of Wall-Warts he has in his collection, as he aquires more-and-more TOYS… If he has all of these adaptors in his collection, he may as well use the right one… For the job-at-hand… There are pluses and minuses to these adaptors… Well??

Scotty, in Engineering, is tellin Jim, on the Bridge… " I can’t hold’er… She’s brake’in up"… and… Scotty is telling Jim that the Ship is running Low-on-Power… and that that they need to replenish their supply of [" dilithium crystals"] or they wouldn’t be able to get to “Warp Speed”… How will all this be talked about in the year 2050??

Bill…

P.S. Oh yea… Go get the movie Back to the Future (the first one)… There’s some great lines in that movie… Ya gotta watch it three times…in a row… :p :laugh:

Hi Ali,

Yeah, I’m doing okay other than letting my alligator mouth overlap my tadpole butt! My Speech Pathologist is getting a “Talking Keyboard” for me next month so I can speak again. Yahoo!!!

You are right, of course, the AC/AC adaptor (Original) does nothing more than step-down the mains voltage. Rectification and hum filtering must be a part of the main board. Still, some noise advantage is had by moving the transformer (the hum source) away from the unit. It still makes good sense to me to do the rectification and filtering within the wall wart package. At least that is how I would approach the problem.

Best regards, bloke!

Don

Jow, what do you mean by “noise”?

Are we talking hum, clicks and pops, hiss, what? :)

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Quote
.S. Oh yea… Go get the movie Back to the Future (the first one)… There’s some great lines in that movie… Ya gotta watch it three times…in a row…


Nah, you only gotta watch it once Bill, and then, to get really clever, having learned how to do it by watching the movie, you hop in your Delorean, go back in time by 2 hours and wipe the tape before you watch it! :D

Nice to hear things are looking up Don. :) I was sorta wondering if we’d lost you there.

Anyway, after you get your talking keyboard, you ought to contribute to the “electronic voices” thread in the other forum. :D

Take care Don.

Ali

That Movie was my TEST Movie when I serviced VCRs. I played it so many times… I was able to Pick up the scenes from recall at any point in the tape… I liked the Skateboard scene… And the alarm clock sitting on the Dashboard of the Delorean, during the electrical storm scene… Ah well… it’s a classic movie… in my mind…

Bill…

It might be the other way around. Why did you need to replace the power supply in the first place? I’d be willing to bet that the original AC power supply is fine if the preamp stopped working and that the fault is in the filtering or rectifying in the preamp itself.

Good point, Phoo!

See why I need you young bucks to analyz(s)e the problem?

The original AC/AC adaptor is a go/no go device. It is either working or it’s dead! No in between.

Don (crawling back in my hole) Gaynor

As long as that hole has all your toys go right ahead and have fun. :)

Young bucks…uh hu…I hear you…my kids will be cackling when I tell them someone mention phoo and young buck in the same post. :D

By the way, I’m very glad you are back posting again!

Jow, buy a cheap multimeter. That’s something that’s just as essential in your studio as a good mic and a fast hard disc. And the first thing to do with it is check if the original PSU is good or not.

If it is good, can you directly monitor the output of the pre-amp? If so, and it still sounds crap, then you know the problem is in the pre-amp.

But if you can’t, then the fault may possibly lie somewhere further down the chain.

Anyway, as in all fault finding, you have to isolate and eliminate.

Don’t assume that the fault lies in one particular component, 'cos that’s a mistake we all make sometimes. So isolate and check everything!

It’s very embarrassing dismantling a piece of gear and spending a whole day checking it out, only to find that it was the lead that was dodgy all along. I know, I’ve done it! :D

Ali

Phoo,

I’m pushing 65 so that may give me the distinction of being the oldest n-Tracker in captivity. Sooooo, young buck, what do you have to say aboot (Canadian) that!?

It is good to be back. Just wait till I get my “Talking Keyboard,” I may even try to sing again!!!

Ali,

I have a story about a friend who asked me to repair a fancy digital wall clock. He left it for service and I wasn’t able to find anything wrong with it. In amaz(s)ement, he asked me what I had done to get it going. I said I just hit the switch and it ran beautifully. He said: "Switch? What switch!?"

How you coming on your music? Anything that I can listen to?

Don