Parallel reverse polarity protection diodes... yes, please!

[JaviCAP]

Hi mates,

Just to comment and ask what you think about the controversial reverse polatiry protection diodes in parrallel with the power supply.

If you put the diode in series with +9v, you get a small voltage drop in the supply, from 0,2 to 0,7 volts, so if the pedal is not designed with these values in mind, the lowered voltage can affect the pedal tone.

If you put in parallet and set a wrong polarized supply or an AC instead of an correct DC one, the diode is prone to explode and, surely, blow near components too, but........

Here you can see what happens if you plug a 12v AC to a center negative Danelectro Free Speech:




Well, the diode was blown, same happened to two electrolitics and the dc jack was melted, a real mess, but... I put a new diode, two caps, a new dc jack, did use a wire to recreate a burnt path.... and the pedal works great again.

Yes, It was a mess, and I had to spend some time redoing the circuit and soldering new components, but the pedal survided, thanks to this parallel diode.

If there wouold have been no protection diode, the whole pedal would have been burnt, except resistors, but no doubt that all caps, transisitors and opamps would have been killed in a few seconds.

So, maybe the parallel diode is not the best solution, but is always better to have it on your circuit.

J.

[dbat69]

Good point Javi - board looks a little frazzled

Maybe possible to consider mounting on a small daughter board, away from the main components etc

[IvIark]

Totally agree mate, parallel protection diodes without a fuse are just completely stupid and yet so many manufacturers do it, even ones with strong engineering plaudits like Cornish.  I always find that bizarre.

[JaviCAP]

Yeah, don't know how the board could survive. The former owner told me that he lent it to  a friend, and was returned this way.... it seems that until the friend noticed some burnt smell in the room was wondering why the pedal did not fire up :P.

I used to omit the paralel diode, even the series one if does not appear on the original schematic, but after getting this pedal, in all my builds there's a protection diode :)

I'm wondering if as you say, and Mark has done in a few boards, it would be a good idea to have a separate daughter board for the power section of the effect.

J.

[rocket88]

man, that tells me that i should never lend one of my pedals to one of my buddies. lol

but seriously, i can't believe that board survived and that actually happened. it does make me think twice about reverse polarity protection in my builds.

[Frank_NH]

Here are your options.  I'm assuming that option three is the minimum?

[JaviCAP]

Yeah, It survived, but I wasn't really sure about it until I re-built the burnt tracks, using diode and caps legs to  create the new path, and so on. Once I plugged it (with a correct PS :P) and could see that led was lit and the internal speaker was hissing, i pluged the guitar, and nearly all ok :P There was just a mini track burnt for the out jack ground, so I sldered an aerial wire, and pedal working.

NIce little talk box by the way, with a good mic, of course, not the crappy ones included:




J.

[dbat69]

JaviCAP wrote

NIce little talk box by the way, with a good mic, of course, not the crappy ones included:

I got one of these a long time ago but could not get on with it - I was using the 'crappy ones'.  Maybe that is where I went wrong - I'll have to dig it out again.  Did you plug the mic back into the pedal or take it to another amp/pa?

[JaviCAP]

Back to the pedal, but I see no problem sending the mic output to a dedicated amp (as the real talk box works).

And yeah, the mic isthe main thing in this pedal, te internal speaker works quite well. I  didn't heve any expectations about this pedal, so that's maybe why I finally liked it :)

J.