The mysterious death of two effects...

[john1056]

This is a strange one I think.  I have two effects, one I built (a Ross compressor and a Distortion+ in one chassis) and a Barber Tone Press.  They both worked recently but now both are dead.  Both pedals have continuity between the +9v power input and ground (which explains why they don't work) with nothing pluged in (input or power).  If I plug them in to a shared power adaptor (a daisy chained One Spot) all the other effects go off too, becauase of the short.  The only that I can think of that could have killed both is another cheapo power supply that I use that's unregulated.  Any ideas?  If it was the other supply what likely got fried, the transistors?

Thanks!

[gez]

Did they have diode protection, the type where the diode is reverse biased across the rails?

[gez]

The only that I can think of that could have killed both is another cheapo power supply that I use that's unregulated.

Do they have both have large electrolytic caps across the rails, if so what is the voltage rating?

[R.G.]

Yep - it is likely to be either a reverse protection diode shorted or a power supply bypass cap shorted.

[robbiemcm]

If you have a regulated power with caps across the rails and all, should you still have this protection diode in your circuits?

[R.G.]

Rhetorically, if you have an electrician inspect your house wiring for fire safety, do you still need fire insurance?

Yes, you still need the protection diode, because it only takes a moment for your bass player or the lead singer's girl friend to disconnect the regulated supply and connect it up to some other power supply of the wrong polarity.

[john1056]

Hello, Thanks everyone for their suggestions  I just looked at the schematics for the Dist + and the DynaComp/Ross compress on Tonepad.  It looks like the DynaComp/Ross has a 10 uF cap across the rails.  I guess I can just desolder this part to see if it's the offendind component.  I'll have to look when I get home to see what the voltage rating is.  This was my second build, so it's very possible I used a value that's too low (sub 16 V I guess?)

Don't know about the Barber Tone Press, I'll take a closer look when I get home to see if there are diodes on the board or a large electrolitic.  The board is glued in so I'm pretty limited with what I can do to fix it myself.

I don't have diode protection on any of my pedals, can someone like me to a schematic I can look at that has the protection?

[gez]

Don't know about the Barber Tone Press, I'll take a closer look when I get home to see if there are diodes on the board or a large electrolitic.  The board is glued in so I'm pretty limited with what I can do to fix it myself.

I don't have diode protection on any of my pedals, can someone like me to a schematic I can look at that has the protection?

I think there's an article at Geofex on diode protection, but don't have a direct link so you'll have to rummage around a bit to find it.

Don't know anything about the 'Barber Tone Press', but it might have a reverse diode across the rails and it could well be this that is shorted.  Should be easy to trace on a board.

[gez]

I think there's an article at Geofex on diode protection

Link at top of page for Geofex.  Go there and scroll down for 'Advanced polarity protection with MOSFETs'