Figuring out what type of wallwart to use on vintage Chorus pedal?

[Burstbucker]

I just bought one of these cool vintage chorus pedals today, the name on the pedal is VOLZ and it was made in Japan in the late 70s.  It sounds great and pretty close to a Boss CE-2 IMHO. 

I checked the current draw on the battery and it's a very decent 8 mA, so it's pretty easy on batteries.  There is a 9V DC jack on the side but it doesn't indicate whether the centre pin's negative or not.  Is there a way to figure this out?  There's no label next to it.  I'm guessing that it'll be the same as Boss pedals but I don't want to take a chance and maybe cook something by connecting it reversed polarity.  Any ideas?

Here's a picture of it:
http://filters.muziq.be/model/volz/chorus

 

[Burstbucker]

I just bought one of these cool vintage chorus pedals today, the name on the pedal is VOLZ and it was made in Japan in the late 70s.  It sounds great and pretty close to a Boss CE-2 IMHO. 

I checked the current draw on the battery and it's a very decent 8 mA, so it's pretty easy on batteries.  There is a 9V DC jack on the side but it doesn't indicate whether the centre pin's negative or not.  Is there a way to figure this out?  There's no label next to it.  I'm guessing that it'll be the same as Boss pedals but I don't want to take a chance and maybe cook something by connecting it reversed polarity.  Any ideas?

Here's a picture of it:
http://filters.muziq.be/model/volz/chorus

Apparently VOLZ was built by the same guys that built the LocoBox pedals in Japan, if that's any help.

 

[GibsonGM]

What I'd do is probe the DC plug center pin with my meter on continuity test, other lead connected to the battery - clip terminal.  Then repeat for the barrell of the DC plug.   One should show continuity.  If it's a switching-type plug arrangement, you'll have to defeat the switch somehow, so the plug "thinks" it's got something plugged in. 
Anyway, the results should be that center pin or barrell are grounded...this will tell you which terminal is negative.   IF this is a negative ground system, lol.  I'd bet $50 it's a 'normal' negative ground, being a chorus it probably uses opamps configured normally.

Other clues are to see if there are diodes right by where the DC adapter plug is, and note their orientation.  Cap orientation, too - use them as clues.   The above should work fine, however.  Good luck, sounds like a cool pedal! 

[Burstbucker]

Hey GibsonGM,

Thanks for taking the time to give that detailed response.  Thank you!
8^)

[Meanderthal]

 One other thing- make sure the wart is labled as a regulated power supply, otherwise you'll most likely get one hell of a hum!

[Mark Hammer]

If it is a barrel-type connector, and if the unit can work with either battery OR external supply, then the only alternative is for the pin to be ground and the outer contact to be V+.  No way around it.

Why?

Because the only means for a barrel plug to dislodge a contact on insertion to the jack, and switch over the power supply from internal (battery) to external (wallwart) is for the outer (shaft) contact to touch something and move it out of the way of something else.  Ground, of course, always remains the same, but the V+ has to be switched over.  Ergo, the outer shaft is always V+ in such instances.

Of course, you are right to be concerned.  When the pedal doesn't use batteries and nothing has to be switched over via plug insertion, then it becomes the manufacturers choice whether to use outside positive or outside negative.  Moreover, it also becomes the manufacturer's choice whether they want to use a DC supply or provide onboard regulation and use an external AC supply.  Trouble is that a lot of folks don't distinguish between those contexts where there is some manufacturer latitude as to what goes in that barrel jack, and those ontexts where the manufacturer has absolutely no choice.

[puretube]

are you sure?

[Mark Hammer]

Well, when you ask it like THAT, maybe not.

But how many other types of barrel jacks have you seen?  The polarity of the plug will depend on the limited number of ways that the jack itself can work.  The only barrel jacks I have ever seen use a spring-leaf contact sticking out from the side of the jack.  When no plug is inserted, the contact touches the outside (the part that the outer shank of the plug would normally contact on insertion.  Stick the plug in and the contact is broken and replaced by that between the outside of the plug and the jack wall.

Are there other mechanisms for changing contacts that are commonly used?  If so, I will gladly retract my recommendation and urge people to check first before leaping, but it's the only style of barrel jack I've ever seen.

[puretube]

I am not 111% sure myself at the moment,
coz I can`t get to my (recently moved) stock;

but IIRC, I got some sockets,
which can be wired such,
that the minus of the battery is being dis-connected from
the socket`s non-isolated (grounded) "sleeve"-lug,
as soon as the wallwart`s barrell is being stuck into the socket.
[ wallwart: tip+ , sleeve- ]

[Mark Hammer]

One of many reasons why I generally use mini phone jacks for power on my homebuilt boxes.  There is only one way to switch power lines on a standard mono closed circuit phone jack and I LIKE IT!  Of course, because hot and ground have a way of being shorted out on insertion if you're not smart enough to plug the wallwart in AFTER inserting the plug into the external power jack, manufacturers tend NOT to like them.

I recommend to people to always have a spare 2.1mm barrel plug on hand for deciphering those cases where you don't know what plug orientation/polarity to use and can't get confirmation easily.  Insert the plug into the external power jack, connect your ohmmeter to the solder lug for shaft and see whether it connects to ground or not.  Then test the solder lug for the inside (pin) contact the same way.  That will let you know which way the plug is supposed to be wired.