voltage and reverse polarity protection

[nag hammadi]

it seems that most of the repairs that come through are shop are the result of improper voltage and polarity.

i know this has been covered here in some detail, but a lot of it is over my head a bit.

it seems like adding a simple bit of protection with either a zener setup and/or voltage regulator would be the thing.  i would rather change out a diode or regulator when it fries than repair a mess load of stuff on a board.

i always recommend to our customers the use of a regulated supply, but most of them give me the ol "it fit in the hole so i used it" routine.

does anyone have any simple suggestions for something i can offer to add to these pedals as a proactive fix?

i am really dumb, so speak slowly and use small words. 

[KMG]

Simpliest way is to use zener. Reverse-biased it protects from overvoltage, forvard-biased it protects from reversed polarity (limits voltage at about 0.6V).
To protect against excessive current and power supply/zener diode from damage, I use a resettable fuse (POLYFUSE) in series from the power connector to the zener and the other circuitry.
http://www.littelfuse.com/data/en/Product_Brochures/EC327-E_Polyfuse_PTC.pdf

[Canucker]

I started up half the threads on this topic...I'm still not sure....and I still have the question....what pedal companies actually have polarity protection built into they're pedals?

[Toney]

 Perhaps the simplest is to use a low forward voltage diode in series with the power.
Many regulated power supplies put out a little more than the stated 9v, so losing 0.3v is no biggie. Something like a 1N5817 Schokkty or 1n34a, 1n60 Germanium.
Simple flow/no flow valve.

@Canucker
All of them!

[Canucker]

Perhaps the simplest is to use a low forward voltage diode in series with the power.
Many regulated power supplies put out a little more than the stated 9v, so losing 0.3v is no biggie. Something like a 1N5817 Schokkty or 1n34a, 1n60 Germanium.
Simple flow/no flow valve.

@Canucker
All of them!

ALL OF THEM? since when? Nobody could name one when I asked before. Even in stuff as far back as the 60s? or since theres a power supply input and battery power as opposed to just the battery power option???

[Toney]

 Any modern major commercially available pedal will have reverse polarity protection.
Perhaps exceptions would be some  home made "boutique" things you might find on Ebay or the earliest battery only designs but any major modern pedal will have this.

If in doubt just follow the power input.

[Canucker]

Any modern major commercially available pedal will have reverse polarity protection.
Perhaps exceptions would be some  home made "boutique" things you might find on Ebay or the earliest battery only designs but any major modern pedal will have this.

If in doubt just follow the power input.

I like it when I can read an answer and it makes sense to me even before I go exploring further! Thanks

[ashcat_lt]

Horse hockey! 

The only thing protected by the diode across the power rails which Boss and the others install is their own warranty department.  Plug in a reversed polarity supply for more than a second or two and that thing will explode.  Unless it manages to take out adjacent board traces, everything downstream will be subjected to the reversed power.  Electrolytic caps will pop, ICs will burn out...  And the company can say "You obviously didn't use our official power supply.  Warranty voided.  Buy a new one."

[Canucker]

Horse hockey! 

The only thing protected by the diode across the power rails which Boss and the others install is their own warranty department.  Plug in a reversed polarity supply for more than a second or two and that thing will explode.  Unless it manages to take out adjacent board traces, everything downstream will be subjected to the reversed power.  Electrolytic caps will pop, ICs will burn out...  And the company can say "You obviously didn't use our official power supply.  Warranty voided.  Buy a new one."

It could just be the fact that hockey gets mentioned in the intro but again very convincing. If a single diode did the trick every time wouldn't it show up in every single layout/schematic/vero thats online? Why omit a single component thats potentially so important? It just seems more complex to me then that but again I'm as amateur as they come in this field...but why would there be more elaborate layouts for this sort of thing like this http://farm5.static.flickr.com/4034/4635974624_e8f3894336_o.jpg    Also I said "potentially important" because if it was death every time a wrong power supply was used or battery touched the wrong way wouldn't the world have a hell of a lot more dead pedals? 

[Mike Burgundy]

Those diodes are in almost everything, and they protect from a *short* polarity mistake - such as when accidentally touching battery terminals the wrong way round. If you hook up a powersupply (or battery for that matter) in reversed polarity, the protection diode shorts it out and a battle to the death between power supply and diode starts. Some advanced switching powersuplies will cut out, and everything is still ok. Most PSU's keep pumping current, fry the diode after a (rather short) while and reverse polarity sweeps through the circuit.
I think the reverse diode is often left out of some schems since it's not part of the actual audio circuit, just like flipflop-based bypass switching.
Factory BOSS schems all show the diode.
It's probably an economy thing that they don't use better, more thought-out protection such as RG's. One diode leads to "good enough" as far as damage claims are concerned, and they're done with it.

[ashcat_lt]

The series diode thing actually works for reverse polarity.  Period.  It also protects against accidentally connecting an AC adapter.  It can't fail unless the voltage supplied is extremely high, in which case you'd have much bigger problems.  The only reason I can think that it's not used universally is the one I supplied above.  Boss wants you to pay them more than necessary for their official PSU, and they want their pedals to fail catastrophically if you don't.

[Jdansti]

I've been interested in this for a while myself.  Here are a few methods I found just searching the Internet.  Maybe someone can comment on the pros and cons of each (there may be some redundancy in my selections).

A.


B.


C.


D.


E.


F.


G.

[rockhorst]

I was really really really impressed with the protection in my Boomerang Rang III looper. It's absolutely ingenious and yet a very simple idea that they came up with and I haven't spotted anyone else in pedalland doing it (probably too expensive or something?). Here it is: it runs on almost whatever you plug into it: 9V DC, polarity reversed and even 9V AC, all from the same jack.

Haven't checked how they did it, but I guess it could be as simple as a diode bridge rectifier circuit, i.e. 4 diodes (but not 4 diode drops) and a capacitor to even out the ripples.

[Jdansti]

I was really really really impressed with the protection in my Boomerang Rang III looper. It's absolutely ingenious and yet a very simple idea that they came up with and I haven't spotted anyone else in pedalland doing it (probably too expensive or something?). Here it is: it runs on almost whatever you plug into it: 9V DC, polarity reversed and even 9V AC, all from the same jack.

Haven't checked how they did it, but I guess it could be as simple as a diode bridge rectifier circuit, i.e. 4 diodes (but not 4 diode drops) and a capacitor to even out the ripples.

I used to have a cordless razor (shaver) that was like that. It had a straight AC cord for 120VAC and a cord with a 12VDC plug for charging in an automobile. The cords plugged into the same jack which was not polarized. The manual said you could use anything between 12V and 120V AC or DC.

[R.G.]

A long time ago I spent some time trying to make that work. The problem is that any kind of rectifier bridge offsets the ground of the pedal being powered from the negative (or positive, I guess) side of the power being supplied to it. If that same power is applied to other pedals and NOT offset by exactly the same amount, you get ground offsets, hum, noise, interference and clicks. I messed with it a long time, thinking that if I made the ground side low enough, it would be acceptable. You can get approximately to there with active diodes using MOSFETs in a synchronous rectifier type setup.

There's another thing that works - isolate the power supply inside the pedal. You can make a small switcher, run it through either a transformer or capacitive isolator, then make your DC power in the pedal, isolated from the supply. That lets you run a bridge on the supply and ignore polarity.

The complexity adds up fast.

[Seljer]

May I ask what the difference is between the C circuit shown above (PNP transistor + resistor from base to ground) and the cheap and intelligent polarity protection circuit on the geofex site (which has the NPN transistor on the base)?

[jubal81]

To protect against excessive current and power supply/zener diode from damage, I use a resettable fuse (POLYFUSE) in series from the power connector to the zener and the other circuitry.
http://www.littelfuse.com/data/en/Product_Brochures/EC327-E_Polyfuse_PTC.pdf

What threshold rating do you recommend?

[merlinb]

A long time ago I spent some time trying to make that work. The problem is that any kind of rectifier bridge offsets the ground of the pedal being powered from the negative (or positive, I guess) side of the power being supplied to it.

That's only if your power supply is being shared by other equipment, right? Provided the power supply is dedicated to that one particular pedal (and is presumably isolated from ground) then the groun reference would be on the circuit side of the bridge rectifier.

[R.G.]

That's only if your power supply is being shared by other equipment, right? Provided the power supply is dedicated to that one particular pedal (and is presumably isolated from ground) then the groun reference would be on the circuit side of the bridge rectifier.

That is correct. However, this is an esoteric point to most guitarists, in spite of power supply design being a fairly simple technical issue.

Historically, with only batteries for power, pedals in the First Golden Age of effects didn't have this problem because all batteries provide an isolated power supply. But whatever their other advantages, batteries are inconvenient and expensive. This precipitated the rise of wall wart power adapters, and the problems started. Wall warts provide convenience at the expense of power system complexity which could cause hum and other problems.

There are two main kinds of solutions to these issues: make the incoming power be clean and quiet to all pedals, or make the pedals immune to their power supplies.

I designed an eats-almost-anything 9V (or whatever volts) power supply for inclusion into pedals some time back. The design of an internal isolating switcher small enough to go inside a pedal is now feasible, given modern power controller ICs. Simplest is probably an isolating flyback. These things can take wide input voltage ranges and convert them to clean, isolated DC power. The difficulties are finding a controller IC that will take low voltage DC as an input, and making the design quiet enough to go inside a pedal.

Well, OK, making it small and cheap enough to go inside a pedal counts as an issue, too I guess. 

The complexity of a power supply like that often overwhelms the pedal.

What DIY effects makers want is a simple two-to-four part circuit that makes it all go away. Unfortunately, that's not really feasible. The good solutions aren't simple, and the simple solutions aren't good. This is why the complexity of powering pedals usually goes outside the pedal, not inside.

[pee-j]

[...]To protect against excessive current and power supply/zener diode from damage, I use a resettable fuse (POLYFUSE) in series from the power connector to the zener and the other circuitry.
http://www.littelfuse.com/data/en/Product_Brochures/EC327-E_Polyfuse_PTC.pdf

hi,

I think the MULTIFUSE solution has not been ruled out in any way....
and given R.G.'s memorable description of "the diode and the battery are engaged in a duel to the death",
a MULTIFUSE looks as the perfect intervention... doesn't it?

unless it creates a voltage drop itself
speaking of which,
as to the MF-R005-0,
https://www.hestore.hu/prod_10042279.html
its resistance looks very subtle... yet, at 50mA it might be 0,5v...
however, at 10mA only 0,1... and so on...

so, as I see (an outsider) see it, a multifuse + the parallel diode protection can be an elegant solution...
is something wrong in my dilettantish calculation?

I mean, KMG's suggested (applied) method seems great, doesn't it?
as well as Jdansti's solution "A"