Me = Super Dumb

[madbean]

I've been putting my new prototyping rig together over the last week. Basically, bigger, better, faster. Since I had the room, I decided to add a little DS0138 O-Scope right on the board. I've been without a scope for a couple years now and figured this would be perfect since I don't have space to have a full sized scope set up all the the time. Having one on my breadboard would be super-convenient.

Anyway, bought the DSO138 off Amazon last week. I found one that was pre-built, was only a few dollars more, figured I'll save myself some time. Got it, didn't work. So, returned it and exchanged it for a kit version instead figuring "it'll work this time because I am the one building it". Built it, didn't work. Very frustrated I started probing and voltage testing. Found the problem: it's center tip positive 9v, not negative. I am dumb. Hooked it to a battery and it fired right up.

Always think before jumping to conclusions!

[Yahoo67]

Hahaha had the same problem on a pre-build chinese transistor tester. I was sure for days it was a scam until i tried a positive center tip power supply^^

[TFZ]

In almost all cases the sleeve is the negative for other appliances. Only guitarists are stupid enough to put the positive voltage outside .

[EBRAddict]

Let that be a lesson to all of us, lest we forget the protection diode at the power input of our designs...

[bluescage]

I had a similar problem with an EQ 505R which is a 3 band pre-amp for acoustic guitar ( built it in my Squier, to make this: http://singlecoil.com/docs/active_strat.pdf). Luckily they are cheap on e-bay, but it took three that didn't work, before I finally took my DMM and discovered that the red wire was "-" and the black wire was "+"......... .

[selfdestroyer]

Been there buddy!

[lars]

In almost all cases the sleeve is the negative for other appliances. Only guitarists are stupid enough to put the positive voltage outside .

I've always thought it was very strange that all modern guitar effects are negative tip. I think it has to do with Boss having such a huge influence on the AC power option, because until they came along, pretty much all guitar effects were either battery-powered or had the AC cord built-in. Then Boss decided to inflict us with their backwards wall warts, and no doubt tons of guys fried their pedals either hooking up a regular wall wart to a Boss pedal, or hooking their other brand pedal to a Boss wall wart. But it is a fact:  negative tip is backwards, wrong, incorrect, and dumb. Thankfully Boss never made guitar cables...imagine that mess.

[alanp]

lars -- Boss used tip-ground power because you can get sleeve-switching power jacks (for the battery to disconnect from circuit when external power is used), but tip-switching jacks are a bit more uncommon.

[peAk]

Did the exact thing when I built my Synare 3.

I fried a component in the process, smoke and all.

[reddesert]

lars -- Boss used tip-ground power because you can get sleeve-switching power jacks (for the battery to disconnect from circuit when external power is used), but tip-switching jacks are a bit more uncommon.

Yes.  Back in the 80s, say, lots of people used 9V batteries in pedals (many people also owned just a few pedals), and the battery power had to be switched off by the usual input jack arrangement of using the sleeve and ring connections.  That switched the ground. In order to lift the battery from the circuit when a wallwart was used, the positive connection had to be broken. If you look at how a barrel jack works, it's a lot easier to push the outside connection away to break the sleeve connection, so the sleeve became positive. I think this design drove Boss to use a negative tip adaptor, that is I think the negative tip adaptor started with the classic Boss mini pedal series and did not exist before, but I could be wrong.

Also back in the 70s or 80s, wallwarts were more expensive and people had fewer devices/gizmos, so one really didn't have a lot of wallwarts and the chance of grabbing the wrong one was probably smaller.

[TFZ]

I don't know who started it. But you're both right, the battery switching is the reason for it. It just annoys me, because standards are a good thing. And it also means we are doomed to use crappy plastic jacks instead of metal ones, because you obviously don't want the whole casing to be on 9V. Or are there metal jacks with an isolated sleeve contact that I am not aware of?

[lars]

lars -- Boss used tip-ground power because you can get sleeve-switching power jacks (for the battery to disconnect from circuit when external power is used), but tip-switching jacks are a bit more uncommon.

Huh. Back in the late 70's, Electro Harmonix, DOD, and MXR were easily able to solve the battery to AC switched power problem without having to create a reversed tip sleeve arrangement (they used 1/8" jacks, positive tip). The simple fact is, Boss decided to create a proprietary way of powering their pedals in order to force users to buy their specific wall warts. It was a marketing move. $$$. For some reason, other manufacturers followed suit. There is no implied superiority or lower cost considerations as to why everybody didn't just stick with the 1/8" positive tip jacks that were already established and readily available. It wasn't like there was some magic, huge, free stash of switched "Boss style" jacks laying around in 1978 that forced Boss's hand to use that option. Negative tip is dumb, period. It forces people to use cheap plastic jacks instead of metal ones because we can't have a positive sleeve in contact with the negative-grounded case of the pedal. There is no logical reason for it.

[Aentons]

I thought it was that the 1/8" plug type power was deemed bad because both postive and negative contacts are exposed and can be shorted when unplugged. Also, as you plug it in, the tip contacts the sleeve, which, for power, is prob not the best thing. Isn't that why we can have phantom power with an XLR type connector and not a TRS type.

[alanp]

There's also the problem that it IS an audio jack, and eventually some... person... is going to try plugging the 3.5mm power jack into an audio socket somewhere.