Cheap "Wall Wart" power supplies

FenderBender

I had a customer bring in some DIs for repair that are creating a hum on the desk.
The first thing I noticed was that each one had a switchable wall wart power supply connected to the battery terminals.

I decided to do a few measurements to check the supply itself, since I was certain that this was the cause of the noise.
The supply has a switch for 3, 4.5, 6, 9 and 12 volts.

I tested only the 9V, 7.5V and 6V output. I loaded the supply lightly with the DI and measured the DC output with a Fluke 115 multimeter and the AC ripple with a Philips PM3230 oscilloscope.

The 9V output produced 14V DC and the AC ripple was around 600mV!

The 7.5V output produced almost 12V DC and the AC ripple was a fraction under 600mV!

The 6V output produced 9.7V DC and the AC ripple was around 450mV!

What does this mean?

The gear on the other end of the power supply is running at too high a voltage and this could stress the components.
The massive AC ripple will induce nasty hum on your signal path.
Batteries are the best supply for your pedals and gear, but...
If you want to use AC power, your wall wart must be destroyed and you must use a good supply!!

Boss power supplies and the like are not cheap, so I have been looking around for a good alternative. I have found a really good (on paper), low cost, reliable PSU that I will be testing soon. It delivers a regulated 9VDC at up to 2A with very little ripple. It will handle two to three digital pedals and lots of other analogue pedals at the same time. I will post here again after the tests!

IceCreamMan

excellent ...will keep an eye out for that power unit and price.

arjunmenon

I thought it funny that the wall warts in the pics have the word JUS on them ?

But thanks for the info Greame. Much appreciated.

MikeM

Interesting.. Would love to see how my 1Spot compares..

Someone was talking to me about making a tiny power filter type box.. Can't remember who but would those be worthwhile in the war against hum?

AlanRatcliffe

Most decent DIs should run from phantom power from the desk, which is usually a nice clean 48V that gives them plenty of headroom. Quite frankly, the idea of having a wart for each is scary.

Q from the semi informed - is it true that the voltage of those supplies drops a bit when under load? If so, does your multimeter simulate a load?

Q2 - is the ripple caused by inadequate smoothing caps?

I'd be interested in your findings on the Roland warts some time - especially the non-regulated ones. I know they work alright, but somehow I've never believed them to be all they are cracked up to be.

nick

Alan Ratcliffe wrote: Q from the semi informed - is it true that the voltage of those supplies drops a bit when under load? If so, does your multimeter simulate a load?

Im also curious about this as my Boss PSA adapter measures over 13v with no pedals plugged in to it but is rated at 9v 500mA

FenderBender

@Arjun - Yeah you gotta be JUS to use them!

@MikeM - Line filtering can help for noise in the AC mains supply, but in this case the wall wart is the troublemaker!

@Alan - Yes, these do allow for phantom power. I'm not sure why they are using a separate supply for each DI.
A - Yes, being an unregulated power supply, the voltages would drop under load. I used the DI box as a load in each case as a reference.
A2 - Inadequate smoothing caps and other bad design calculations (or lack thereof) ?
It's easy to check, next time someone is here with a Roland, I'll grab it and take it off to the torture room!
@Nick - If it's unregulated, then the open circuit voltage would be high.
Not something I'm crazy about, because then the DC voltage becomes inversely proportional to the current supplied.

Squonk

Without Hijacking this thread, What are the better Power Supply's to buy?

IS it worth paying extra cash for a Boss/ Line 6 PSU, I would just need to power up my Pocket Pod which has the following specs:

DC Input – You can power Pocket POD here using the optional Line 6 DC-1
external power supply. The optional DC-1 provides 9.6 volts DC, 200 mA and has centernegative
polarity.

Those cheapies (Ellies I think) would they be no good?

FenderBender

*Collapses behind his laptop*

@Squonk - Wait for me to test the new PSU I found ?

Sean

Graeme Parfett wrote: *Collapses behind his laptop*

@Squonk - Wait for me to test the new PSU I found ?

hahaha, I think that's a "NO" Squonk ?

AlanRatcliffe

Squonk wrote: Those cheapies (Ellies I think) would they be no good?

To quote Brave Sir Robin: "Run away! Run away!". The better digital gear refuses to even power up on the Ellies supplies because the voltage is so far off spec. They also have a depressing affinity for the transformer to short primary to secondary, allowing a brief but lethal dose of 220V through to your nice, expensive and sensitive electronic devices on the other side (which, for their part, tend to say "Poof!" or "Pop!", and immediately release the magic smoke of legend.

PeteM

Alan Ratcliffe wrote: and immediately release the magic smoke of legend.

And that distinctive smell that seems to linger for days.

CDee

A friend of mine ruined my perfectly good Boss DD3 with a similar power supply. That power supply has since been "recycled"... ?

matta

I use the same supplies that Graeme is talking about, DARN low noise for a switching unit, heaps of juice and I've installed them onto several floor boards for clients and no complaints yet, and VERY cost effective.

RE the BEST power supply, well in an ideal world it would be linear in design, isolated outputs with their own taps off a torrid (which has much less stray EMF radition over conventional C and E core types). Several 9V taps and a couple varistor/trimmerable rails that can be 'preset' to various voltages with adjustable regs (317/337 etc), in practical terms that would cost a few thousand rand... in which case we revert to a super cool, low cost switching supply. :-\

P.S: Graeme, love that scope's ripple, gets me all edgy, LOL

Matt

Bob-Dubery

This is so cool. Graeme's OP I mean. It contains priceless stuff like hard facts and scientific method. Karma (or whatever it's called these days)

Squonk

Waiting with anticipation for Graeme's test findings.
I need to buy a Power supply soon ?
The batteries are quite expensive ☹

FenderBender

Thanks for all the kind words guys. All in a days work for me. I just took the opportunity to test a cheap wall wart as I have none in the house myself. Glad I could shed some light on power supplies. I will post soon after I get the new supply in my sweaty paws ?

Squonk

Thanks Graeme

I could of blown up my pocket pod, even if you had to duck behind your computer ?

Bob-Dubery

IT's the Line 6 owners who are the 2nd class citizens of the world. Those modelers want an AC wall wart.

TomCat

It would be interesting to know how any microphone inputs they've blown on their mixer over time by using the wall warts on their DI's.... ??? ???