Insulate the unused positions of your daisy chains!

[R.G.]

We had one of those periodic things come up where pedals died and a 1Spot was suspected. I always take these complaints seriously, so I dug in.

The owner of the pedalboard was kind enough to return the 1Spot, daisy chain, and damaged pedal to Visual Sound for examination. The first look through it found that it had a fair amount of 5V logic init, and all the power pins of the logic sat at 9V. These were supposed to be protected/fed by a 78L05 regulator. In this case, the regulator was shorted, letting 9V through.

Nothing I did to the 1Spot made it put out any dangerous voltage spikes, so I dug through the pedal schematic. The regulator chip did not have a shorted-input protection diode. When 3-terminal regulators have large capacitances on their outputs, an input short causes the capacitors to feed back to the shorted-to-ground input and can kill the regulator. This one had two 47uF caps on the output. I think that a spare position on the daisy chain shorted the outside (positive!!) barrel to ground, instantly grounding what should have been 9V and causing the caps to back feed and kill the regulator.

I've always put reverse-feed diodes on all my three terminal circuits for decades. You put the anode to the output, the cathode to the input of the regulator. A shorted input dumps the output capacitors harmlessly back into an input short.

The moral is:
1. Use anti-backfeed diodes on your three-terminal regulators.
2. Insulate the unused positions of any daisy chain with tape or something. Anything will work - duct tape, masking tape, electrical tape, etc. - but not aluminum or copper metal foil tape, I guess. 

[Mark Hammer]

Thanks for that.

I'm surprised that no one provides a little plastic insert to cover the plug, particularly given the risk entailed by having the outside positive.

[Rodgre]

I keep a snug bit of heat shrink tubing over the unused ends on my pedalboard daisychains. Easy to slip on and off when needed.

[R.G.]

Thanks for that.

I'm surprised that no one provides a little plastic insert to cover the plug, particularly given the risk entailed by having the outside positive.

Actually, we (VS) do; or we buy preexisting ones, don't know. But we include a number of them with our daisy chains. I'm trying to get a freebie covers program set up to give them away for the cost of the postage. It will take a while to find out if we can get a gross of buckets full of them to do that, but if I can get it going, I'll put notice here.

Mean time, get out the masking tape or duct tape.

[joegagan]

i can just see it now:
the great visual sound  "put a condom on that soldier" campaign of 2011.

thanks for the info, rg.

[RedHouse]

One should always use the protection diodes on 3-terminal regulators (we should sooooo know that by now).

Might be good if you're a DIY'er (like everyone here) ...to build yer own power support!.  

I found these on the bay the other day, just add a diode (or two) and you're good to go for $6.


http://cgi.ebay.com/LM317-DC-63-4-5V-Out-60-1-5V-Converter-step-down-Z-/150518335226?pt=LH_DefaultDomain_0&hash=item230b9786fa

these are a good DIY daughter-board for the ForumVibe and much other stuff. Use a LM317 and have adjustable voltage output.
(just make sure you feed them 3 more volts than you expect from them)

Might want a little bigger input cap (100uF-470uF) for low noise application.

Ya can't hardly make a PCB, and load it with parts for under the $6.
(plus your time, etc)

[g-sus]

If the unused plug happens to touch for example a metal jack it will AT LEAST cut off all power from the chain. Happened to me at rehearsals last week, learned my lesson..

[Processaurus]

The problem with the tubes that come with the daisy chain is they get lost... If some forward looking company that made daisy chains (wink wink) could make some rubber cap that was tethered onto the plug, it would keep track of them while they were plugged in, and in a month when you've decided to cut a pedal from the pedalboard, the cap is right there waiting to be stuck on the end of the spare plug.

I use bits of stripped insulation off guitar cables in the meantime, heavy but stretchy enough to stick on the barrel  of the plugs snugly.

Most guitarists don't know to stick something on the ends, and are always wondering what's going on when their stuff's shorting out...  But why should they need to know?   a plague o' the barrel positive standard.

[petemoore]

  Marketable power supply designs all adhere to failure prone design convention. They have to, all the pedals are designed with failure prone DC - or + barrel or pin, as well as DC or AC jacks.
 The new big company re-design I have here sparks on the side of the box pretty easy too.
 Seems simple enough, but we just don't get it, we get new design that sparks on the box, old designs where failure oversight is the case or the case is just that failure is simply deemed a pre-accepted-convention [which apparently can't be broken]
because it enables mass marketing, and has already been mass marketed.
  I bought a box from one of the most famous effect companies ever, it has a redesigned plug / jack system, the plugprong that sticks out sparx real easy on the rivet that holds the jack in the sheet metal.  
  Invitation to look at any new designs an stamp approval of 'not failure prone' goes out to anyone considering installing a DC or AC jack on anything.
  Not that hard to for me to see it, apparently very easy to overlook if there's insufficient field testing [took me like 10 seconds to find the flaw, and have extremely succesful thought experiment fix].

[Paul Marossy]

Yeah, I've always covered the unused barrel plugs on my power supply daisy chains so that sort of thing can't happen. Although all of my pedals are center positive and it would be highly unlikely that the positive portion could get shorted to ground, I still cover them up anyway. Can't be too safe AFAIAC. 

[wavley]

I wrap mine in this stuff because it doesn't leave a residue http://www.lowes.com/pd_158594-98-2242_0__?storeId=10151&Ntt=splicing+tape&UserSearch=splicing+tape&productId=3127861&N=0&catalogId=10051&langId=-1  I use it a lot for neatly bundling cables, wrapping around circuits so they don't touch things, all sorts of stuff... it filled the hole duct tape left in my heart.

[SISKO]

Good info in here!

R.G. (or any other), could you explain how or why a capacitor back-feeds when the input of the regulator is shorted?

I think that the charge of the capacitor goes back inside the regulator from output to input (thus killing the regulator), as there is a voltage diference, but i can not see how is it able to pass by. If this would be correct, then even a single transistor stage with a capacitor to ground at the output would die if its intput is shorted.

I need to re-look a regulator schematic..

-------------------------------------------------------------------------------------------------------
Edit: I think that a look at the regulator schematic did the thing.

Taking this http://www.datasheetcatalog.org/datasheet/unisonic/LM7824.pdf as guide, now I see that T14 (just to name one) can be easily damaged by an input-short. It would be something like putting a power transistor of an amp backwards. It would be killed instantaneously.

(I took the power amp example because, in a pedal, putting a transistor backwards rarely kills it  as it have 4 biasing resistors (normally), and they act as current limiters)

If Im wrong or someone wants to point/add something, please go ahead.

[Gordo]

I found this out the hard way.  Stage lights are coming up and I glance over and no lights on my pedal board    Saw the bare connector and nudged it and everything came back up.  Those 1Spots are tough!

Never understood with the standard is center negative....

[chi_boy]

This thread made me look for something to cover my plugs.  This probably isn't a perfect solution but for the price, I won't complain.  These things are $3.27 for a pack of 100.

This pictures show the plug covers and the link is to McMaster where I founds them.  To my eye the fit is perfect.  Tight but not difficult to remove.

Cheers,
George

http://www.mcmaster.com/#catalog/117/3719/=cc4v5a  The part number is 9753K12 

[caress]

the guitarist in my band was ALWAYS having issues with his stuff "not working".  especially when we were on tour... 
finally i realized that he had 1 or 2 extra daisy chain power pins loose under his board that were shorting stuff out.  a bit of gaffer's tape and we were off to the races!

[mistahead]

If you know a friendly network technician chances are you could also get a drawer full of these for free - they used to be on all the old fibre optic patch cables, I'm now kicking myself for throwing out a couple of hundred of these in various colours - I could have hooked people up for postage costs... 

[MoltenVoltage]

I've always questioned the wisdom of tip negative for this exact reason.  There is a very good reason that the positive is recessed inside the connector in power supplies for virtually all other consumer electronics.

Also daisy chain cables with covers already exist:

http://www.moltenvoltage.com/mvcart/index.php?main_page=product_info&cPath=70&products_id=236

Sorry for the shameless "plug".

[Renegadrian]

So what's the matter!? Take those pedals and daisies, tape them out and charge them big $/£/€!!!