My latest lovely journey with external PSUs

[Sam Spoons]

I have a Peterson Strobostomp pedal, it's a great tuner, super accurate, and also has a DI output so pretty useful. I made the mistake of plugging a non-regulated 9V DC PSU into it (from a Roland MicroCube amp FWIW) and it fried the regulator. I did manage to find a local tech to repair it and, on checking, the PSUs no load voltage was 13VDC so high but not stupidly high (I'm pretty confident my Boss pedals would not bat an eyelid...) so IMO some pedals are a bit fragile when it comes to PSUs.

[adrian_k]

I can confirm that Sam then clearly labelled that Roland microcube PSU. I was using it yesterday

[The Elf]

So... right format (ac/dc), right polarity (connector), right voltage, but any higher current or wattage (within reason).

This is the part I'm clinging to!

Thanks.

[Kayvon]

There's more to power connector specs than just the diameter. There's inside diameter, outside diameter and barrel length. If you're intending to solder a new connector on, there's also the maximum cable diameter the connector will take.

This is one thing that often bothers me when I use the couple of variable power supplies I have. Check the power supply can supply enough current - great, switch it to the correct voltage - fine, check multiple times the polarity is lined up the right way - well I guess what these arrows is telling me is right, choose from the 20 different barrel connectors I have from 3 different power supplies - ermm, well I guess it fits...

Pretty sure that somewhat often I've not used exactly the correct one but it's worked. Most often I get the feeling that the outside diameters might be a bit small whilst ensuring a snug fit on the inside.

Any tips / words of caution there?

I feel the 2 or 3 variable power supplies i have could be labelled up in a more foolproof way with regard to the polarity pins orientation. I have a Maplins one, then two others that came with used gear. All wall warts.

[ef37a]

It is indeed a huge cluster**** and in dire need of rationalization. Mention was made of the vast variety of DC plug dimensions. Can I suggest that the size that most guitar pedals use be taken as a standard? I have not of course tried them all but it does at least seem that that industry has fixed on dimensions to some degree and I think I am right in saying that all their 9V supplies use a positive barrel polarity? (**** knows why!)

Now, I know SoS reviewers are hard pressed folk but could they take a mo' when presented with gear that take a DC* supply to try a standard pedal plug COLD! to see if it fits? Then comment on that if not in a negative (Boom!Boom!) way? Bit more to write but then the real wall rat haters always seem to find time to have a canter on THAT hobby horse!

The 'over voltage' unregulated issue is certainly one to watch. This can damage old 'Bucket Brigade' chips in chorus/flanger pedals. One nominally 16V 800mA AC supply I know of delivers over 22V on a light load.

Polarity is the biggest killer if you get it wrong. Many devices have 'S**** or Bust' polarity protection i.e. a parallel diode that blows a fusible resistor. That requires a tech to fix but in fact the idea is also flawed in that it does not protect the circuits downstream anyway in many cases. I urge everyone to buy a cheap voltmeter. A ten quid jobby from Halford will do.

Can I also enter a reminder to the 'rat knockers' that these supplies have made possible millions of clever devices that could never have existed if needing onboard mains power...at least not at affordable prices to most of us? Modern SMPSUs are also doing their bit to save the planet (see *) although we COULD do with a lot less of everything!

*An EU directive (I think it was) many years ago outlawed small, unswitched AC-AC supplies. Reason being these consume a good percentage of their rated power even when unloaded. Modern SMPSUs run stone cold when you diss' them from the kit.

Dave.

[Folderol]

It is indeed a huge cluster**** and in dire need of rationalization. Mention was made of the vast variety of DC plug dimensions. Can I suggest that the size that most guitar pedals use be taken as a standard? I have not of course tried them all but it does at least seem that that industry has fixed on dimensions to some degree and I think I am right in saying that all their 9V supplies use a positive barrel polarity? (**** knows why!)

"Hysterical raisins"
The early ones all used PNP transistors, so it was logical. Later, it became 'traditional'

[Sam Spoons]

Nearly all 9V guitar pedals use the Boss 'standard', 9VDC centre -ve 5.5 x 2.1 mm plug. Those requiring higher voltages seem to have different plug dimensions and a 5,5 x 2.5 plug will fit into a 5.5 x 2.1 socket but won't make the centre connection (or may do but unreliably).

I can confirm that Sam then clearly labelled that Roland microcube PSU. I was using it yesterday

I did indeed...

[The Elf]

Nearly all 9V guitar pedals use the Boss 'standard', 9VDC centre -ve 5.5 x 2.1 mm plug.

This is like the "i before e except after c" rule. I seem to find more exceptions than the rule!

[Sam Spoons]

I must have about 20 9VDC guitar pedals and they all use the same 5.5 x 2.1 DC plug

[James Perrett]

It is indeed a huge cluster**** and in dire need of rationalization. Mention was made of the vast variety of DC plug dimensions. Can I suggest that the size that most guitar pedals use be taken as a standard? I have not of course tried them all but it does at least seem that that industry has fixed on dimensions to some degree and I think I am right in saying that all their 9V supplies use a positive barrel polarity? (**** knows why!)

"Hysterical raisins"
The early ones all used PNP transistors, so it was logical. Later, it became 'traditional'

It was a widely used standard in consumer electronics at the time Boss pedals first came out. Certainly Philips used that connector with the same polarity for all of their gear that accepted external DC power.

[MOF]

For the last 15 or so years I've been backing up all my files, photos, sounds, music library - everything - to an external USB hard drive. I have never filled it up it was so unimaginably spacious when I got it. However.... On Sunday it went missing. No reassuring spinning noise, no alluring glow. NO DATA!! Gaa!! Sysadmin hell!

Anyway; ray of sunshine point 1 - I managed to find someone in Oakham who ACTUALLY REPAIRS STUFF yesterday morning. He works out of his shed. He confirmed the power supply was dead with a meter and Amazon was the place these days.

Ray of sunshine point 2 - Amazon did indeed have a generic 'Amazon's Choice' power supply of exactly the right specs and 4 ADAPTOR PLUG END PIECES for different things! It was £11.99 I now have all my tunes and holiday snaps back since the dawn of digital media. I have renamed myself El Smuggo.

El Smuggo, not so fast there. I hope you’ve backed up the back up, if data doesn’t exist in at least three places then it doesn’t exist at all!!!

[amanise]

For the last 15 or so years I've been backing up all my files, photos, sounds, music library - everything - to an external USB hard drive. I have never filled it up it was so unimaginably spacious when I got it. However.... On Sunday it went missing. No reassuring spinning noise, no alluring glow. NO DATA!! Gaa!! Sysadmin hell!

Anyway; ray of sunshine point 1 - I managed to find someone in Oakham who ACTUALLY REPAIRS STUFF yesterday morning. He works out of his shed. He confirmed the power supply was dead with a meter and Amazon was the place these days.

Ray of sunshine point 2 - Amazon did indeed have a generic 'Amazon's Choice' power supply of exactly the right specs and 4 ADAPTOR PLUG END PIECES for different things! It was £11.99 I now have all my tunes and holiday snaps back since the dawn of digital media. I have renamed myself El Smuggo.

El Smuggo, not so fast there. I hope you’ve backed up the back up, if data doesn’t exist in at least three places then it doesn’t exist at all!!!

Oh yes! I'm El Cuatriple Smuggo now. Its copied everywhere! You might even be seeing it on Sky TV in the near future!

[ef37a]

Yes, I have heard of the "PNP transistor" argument before but since most if not all pedals were battery only (PP3) to begin with it makes little sense to me?
Then I have a very old compressor pedal that uses a 1/8" mono jack for power. Now THAT makes sense not to have the tip at +9V.

Germanium NPN transistors followed pretty shortly AC128s say and when Silicon arrived PNP was rare to start with and more expensive. I will admit however that there is virtually no industry more conservative about circuitry than the guitar one and pedals even more so!

But, too late to change now just have to be vigilant and I say again..."If you don't have one yet..Get a friggin' meter!"

Dave.

[Wonks]

Then I have a very old compressor pedal that uses a 1/8" mono jack for power. Now THAT makes sense not to have the tip at +9V.

I think you mean 'Now THAT makes sense to have the tip at +9v' (or whatever the power supply voltage is), the standard way for 1/4" / 3.5mm jack power to be supplied.

Or maybe 'you' meant 'sleeve' rather than tip (same difference)?

[ef37a]

Then I have a very old compressor pedal that uses a 1/8" mono jack for power. Now THAT makes sense not to have the tip at +9V.

I think you mean 'Now THAT makes sense to have the tip at +9v' (or whatever the power supply voltage is), the standard way for 1/4" / 3.5mm jack power to be supplied.

Or maybe 'you' meant 'sleeve' rather than tip (same difference)?

No? Well, unlikely to happen but if there is a chance of it brushing a chassis a +ve tip could blow the supply. If -ve...err. not!

As things are we have co ax sleeves which can be shorted to a case and the bit at normal chassis potential well protected. But, as I say, have to live with it now.

Dave.

[Wonks]

All my old pedals have positive tip jack plug supplies. And as more often than not, they are metal jack sockets, then the sleeve is connected to the metal casing, so it needs to be ground/0v.

[Folderol]

How old is 'old'?
The earliest one I saw was using OC71s. That was in the mid 1960s. I didn't think anyone would have used such a clunky thing as anything in the AC series - they didn't just leak, they cascaded!

[merlyn]

Any tips / words of caution there?

I have a Mesa Boogie V Twin pedal, and it needs a 12VAC 1Amp power supply. It's no longer made, and Mesa stopped making power supplies for it, but they were good enough to publish the exact specs :

https://mesaboogie.zendesk.com/hc/en-us ... r-Supplies

It has a 2.5mm inner diameter, which means the usual Boss type power supply won't fit, which is actually a good thing, as we don't want 9VDC into this pedal.

If a pedal can take a battery then the usual Boss type power supply is probably right. Other than that it would be best to find the exact specs of the power connector.

[DGL.]

Alesis liked AC supplies for some reason with a few different ends, makes getting a new power supply for something like a Miniak/Micron a fair bit more difficult.

[Folderol]

AC supplies were generally liked by those wanting the cheapest possible split rail. The kit then needed just two rectifier diodes and two caps a bit bigger than normal.

[ef37a]

AC supplies were generally liked by those wanting the cheapest possible split rail. The kit then needed just two rectifier diodes and two caps a bit bigger than normal.

This is very true Will and the technique is not as 'crude' as some tend to make out. Yes, each 'side' is only half wave rectified but as far as the transformer is concerned it is full wave rectification. As you say, the filter caps need to be bigger than with a bridge but they are cheap compared to a decent 3 pole connector and a more complex transformer. Then there is the issue that there still is no 'industry standard' for low voltage connectors, at least I know of none?

Dave.

[Hugh Robjohns]

In the pro audio world of portable gear, the XLR4 and Hirose HR10 4-pin dominate for 12V DC supplies. Both locking, too.

[merlyn]

As far as I'm concerned 'they' have totally lost the plot.
Originally your wall wart could supply a relatively low voltage and current (hence low power) from a totally enclosed unit. This was safer for users, and cheaper for kit makers as they no longer needed to go through extensive (and expensive) certifications.

USB 1 followed along the same track, 5V, 500mA, which is just 2.5W. Then the current rating got bumped up to 3A - 15W which raised a few eyebrows as this could do some real damage. Now while starting fairly low, via a negotiation system, that can go up to 48V @ 5A, which is 240W. Regardless of the current, under some circumstances 48V is potentially lethal. You could also make a mini welder with that @ 5A. In any case faulty kit could very easily catch fire. Oh, and a DC arc is far more dangerous than an AC one.

I think you're over egging that. 48VDC is generally considered safe. Sure, someone will have electrocuted themselves with 48V, but then in the history of the world it's statistically likely that there has been a fatal accident involving a teaspoon.

240VAC is potentially fatal, yet we have wires carrying it all over our houses. Why do you think 240W PD is going to be dangerous?

[Folderol]

240VAC is potentially fatal, yet we have wires carrying it all over our houses. Why do you think 240W PD is going to be dangerous?

First, there is perception. People are well aware that AC mains is dangerous, but low voltage is 'safe'... that is unless they short out a car battery.

Then there are the actual regulations and certifications. In most of the world there are serious constraints on what you can do (and who can do it). Not so with low voltage kit - the main reason why manufacturers prefer to use wall warts. It's much simpler and cheaper!

Once you get down to USB leads people throw all caution to the wind. Maybe I'm missing something - I'm a bit out of the loop these days, but I'm not seeing any tightening up for this extended voltage and power.

I've seen the amount of damage that 'just' 24V at 3 or 4 amps can do... in a metal industrial panel.

Before anyone talks about fuses, a fault situation with mains, will most usually blow the fuse, or trip a circuit breaker / RCD. I've never seen low voltage kit with an RCD, and the fact that it is low voltage means often you don't get the quick catastrophic failure that blows a fuse. It's far more likely to be heating up until something catches fire, and even then could be some time before any kind of protection kicks in.

[Wonks]

'Extra low voltage', not 'low voltage', Folderol, please. Might as well do it right as people should know the correct terms to avoid dangerous mistakes. 'Low voltage includes mains'. Extra low voltage is below 50v AC or below 120V DC.