Hearthrob capacitors in backwards!?!?

[yodude]

I love my hearthrob (thanks MarkM!), but have been wrestling with a nasty switch pop for a long long time.  Took it out again to mess with it and um ... I think I put all the electros in backwards.  Will someone please confirm:
- The silver end of an axial electro is negative.
- The square pad is positive. http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Hearthrob_Tremolo_LAYOUT.gif.html
- The pedal will work just fine with all the electros in backwards, except for a persistent and loud switch pop.

Thanks.

[Taylor]

The electro has a line down one side, which is negative. It's not possible to say what color this is as it depends on the brand.

The square pad is positive, yes. The negative side is also marked with a line in that layout, though it's a little hard to see because of the transparency.

That layout does not have any pulldown resistors. Adding them would be the place to start to fix the popping.

[yodude]

Thanks Taylor!

The electro has a line down one side, which is negative. It's not possible to say what color this is as it depends on the brand.

These are axials and the stripe doesn't have any arrows.  One end is black and the other is silver.  I read some random website that said the silver end is always negative.

The square pad is positive, yes. The negative side is also marked with a line in that layout, though it's a little hard to see because of the transparency.

Word.

That layout does not have any pulldown resistors. Adding them would be the place to start to fix the popping.

I've played around with pulldowns a ton.  Still popping.

[Taylor]

Is there a dimple in the cap?

[yodude]

Unless the schem and the layout are wrong I've got them all in backwards.  WTF indeed.

Seems odd that the effect would work fine except for the popping.  Oh well.  I'll flip them around and report back.  Thanks again for the help!

[Taylor]

I've always been a little unsure about that myself. There are definitely situations in which it doesn't matter how you orient a cap. If it's reverse-biased but there's not significant current flowing the wrong way I think it's ok. This means in the audio path. The only time I've actually blown up a cap this way is in the power supply filtering, and this layout doesn't seem to have any power supply filtering. But this is one of those spooky mysterious things to me, maybe I'll simulate it to understand better.

[yodude]

ok:
- reversed the input and output caps
- removed all previous attempts at pulldowns
- added single pulldown from output to ground on the board

... and no more popping.  Sweet.

Effect works great, even though all the other caps are in backwards.  Weird but it works, so back in the rotation it goes.  Thanks again for the help, T.

[MikeH]

I would correct the orientation on all of the caps, not just the input and output caps.  Otherwise they are doomed to FAIL. 

[PRR]

Axial caps: "usually" the can is negative. One lead is welded to the bare can; this may be what you mean "silver". The other lead is insulated from the can by a rubber plug; held-in by the "dimple" in Taylor's post.

Radial caps: both legs come out the rubber plug. These sure better have a ->->-> mark pointing to the negative lead. They may also be identified by length, but if I could not tell at a glance I'd be real unhappy.

Common electrolytics can stand about 1 Volt reverse bias. More, and they leak. More, with real power available, and they burst. In this case, some may work, others may leak enough to upset the circuit. I am surprised it "worked".

It is perhaps real educational to work on BIG systems. When a soup-can size cap explodes pulp all over the room, because you connected it backward, you remember.