AC adaptor with negative center pin???

[10acErnie]

I need a power adaptor for my White 1998 Fullton Deja Vibe. I emailed Fulltone tech to see if they had any.
Here's the response:

>> On Thursday, September 29, 2005, at 12:58  PM, <tech.fulltone@comcast.net> wrote:

>> Any regulated 18VAC adaptor with negative center pin (2.5mm) will work for your white DV.
>> Hope this helps.

>> Tech Dept/ Fulltone

Is there such a thing as a regulated AC adaptor with "negative" center pin

[Mark Hammer]

Yes.  This is essentially another way of referring to the same sort of adaptor recommended for Boss, DOD, and other similar pedals.

To switch from battery to adaptor, the jack has to permit one contact to be pushed out of the way when the plug is inserted so that the power now comes from somewhere other than the battery.  Whether phone plug or barrel type plug, the "pushing" has to be done by the positive contact (V+).  On phone plugs, that HAS to be the tip.  On barrel plugs, that HAS to be the shaft or outside contact (making the inner contact negative/ground).

The reason why they always make a big deal out of plug orientation/polarity is that from a human safety perspective, it is safer to have the outer contact be ground than have it be hot, since if you happen to be holding yourself steady by grasping a grounded device with one hand while grasping the outside contact of the jack by the other hand, you basically turning into the appliance which the adaptor is supplying current to!!

If the appliance/pedal does NOT use/need a battery, then there is no need to push a contact out of the way and the manufactuer has a choice of whether they want to have outside as ground, or outside as hot.  If they don't NEED to have outside as hot, then safety suggests outside be ground.

The end result of all of this is that where adaptors that have a phone plug on the end are ALWAYS tip=pos, shaft=gnd,adaptors that use a barrel plug MIGHT be ouside=pos OR they  MIGHT be outside=gnd.  Since it's a 50/50 shot, the pedal manufacturers will make a big deal about telling you to buy ONLY THIS ADAPTOR.  The purpose is simply to make sure those with less electroics understanding don't inadvertently damage the pedal.

Fulltone's reply to you is absolutely 100% accurate.  It just wasn't as detailed as you needed to hear.

[vanhansen]

But Fulltone said 18VAC not 18VDC.

[10acErnie]

But Fulltone said 18VAC not 18VDC.

Hmmm, yes, the original adaptor output  is 15V AC 400ma.

[littlegreiger]

Isn't there no such thing as an 18VAC center negative jack. AC doesn't have polarity so it wouldn't matter as long as its 18VAC.

[Mark Hammer]

But Fulltone said 18VAC not 18VDC.

Note to Hammer: Read the blasted posting before you start rambling on!!

Yeah, an AC adaptor wouldn't be centre-anything.  Seems to me I'm not the only guy working on automatic pilot some days!

Just out of curiosity, does the chassis have a little wiggly line  (~) beside 18V?  I learned the hard way that this means AC.  Ran all over town trying to chase down a 10vDC adaptor, onto find out the pedal wanted 10vAC.

[vanhansen]

I guess the big clarification is does that pedal take AC or DC for power?  I'm gonna say DC considering that on the Fulltone site it says this:

"and because of the mini-DV's unique voltage doubling circuit you can use any standard 9 volt adapter or power supply (our FPS-1 is included) and inside the pedal the power is ramped up to the original Univibe's 18 volts DC!"

You should be able to find a 18VDC center negative adapter somewhere.

[vanhansen]

But Fulltone said 18VAC not 18VDC.

Note to Hammer: Read the blasted posting before you start rambling on!!

Yeah, an AC adaptor wouldn't be centre-anything.  Seems to me I'm not the only guy working on automatic pilot some days!

Ehh, you're just prepping for the weekend, Mark. 

[10acErnie]

But Fulltone said 18VAC not 18VDC.

Yeah, an AC adaptor wouldn't be centre-anything.  Seems to me I'm not the only guy working on automatic pilot some days!

Just out of curiosity, does the chassis have a little wiggly line  (~) beside 18V?  I learned the hard way that this means AC.  Ran all over town trying to chase down a 10vDC adaptor, onto find out the pedal wanted 10vAC.

This is what confused me. The original is 15V AC 400ma output.  I checked it with my DMM and it outputs about 18V AC. I didn't understand what they meant by the answer 18V AC with negative center pin. Here's a pic of a DV just like mine with the original adaptor.

[vanhansen]

Now I'm confused. 

[Mark Hammer]

I'm going to guess and say that:

a) The unit uses an incandescent light bulb,
b) The bulb and associated modulation circuit works off a different supply voltage than the audio circuit.
c) The circuit takes an input voltage and regulates it to provide one higher voltage (e.g., 15vdc) for the audio circuit, and a lower one (e.g., 6vdc) for the LFO and bulb.
d) It starts out with an AC voltage that, once rectified, can be any of a variety of DC voltages, as long as they fall within spec for the regulator.

You can tell me if I'm right or full of crap by doing the following:

a) take the bottom plate off and look for a small cluster of 4 diodes near where the leads from the wallwart socket go to the board.
b) near those diodes and what is likely the biggest electrolytic cap or caps on the board see if you can spot either a small 3-pin transistor looking device that starts with a 78 number, or a larger 3-pin device (same size as a power transistor) that also starts with a 78.

The numbers after the 78 will tell you what their regulated output voltage is (so 7812 is a 12vdc regulated output).  This would explain why you see conflicting numbers for what voltage the adaptor should be.  If the adaptor is supposed to be a DC voltage already regulated, then you should stick with that unless warranted.  If the pedal has onboard voltage regulators that will take a wide range of external supply voltages and magically transform them into the same regulated voltage, then as long as the adaptor delivers the required current and an AC voltage that is at least 2vac (rectified) greater than the desired DC output, you're fine.  So, a 12vdc regulator needs to get at least 14vac fed to it to behave well.  A 10vac adaptor just squeaks through that requirement.  If it's a 15vdc regulator. then a 12.6vac adaptor will work, and probably anything up to and including 18vac as well.  12.6VAC, once rectified, gets you 17.82vDC, and 15vAC gets you 21.21vDC.  The 15V regulator is comfortable with either.

[10acErnie]

Mark,

I don't see a cluster of 4 diodes near where the leads from the wallwart socket go to the board. There seems to be one diode tied to the power (black wire) and to the 2200uf cap. The board is epoxied to the standoffs so I can't see underneath too well. I don't see any transistor looking devices or larger 3-pin devices that start with a 78 number. There aren't any other parts soldered to the underside of the PCB.

To make matters even more confusing, the back of the DV says "use FPS-1 only." According to Fulltone's website the FPS-1 is a 9V "DC" 200mA adaptor. The original adaptor clearly says on it 15V "AC" 400mA.

I emailed this to Fulltone Tech but I haven't heard back yet:

"I'm totally confused!
According to the writing on the adaptor itself the original adaptor output is 15V AC 400mA. When I checked the voltage with my DMM it was outputting 18V AC.
The back of my DV says "use FPS-1 only" which is a 9V DC 200mA adaptor. The model of the original adaptor is AA-4115-04U.
This info seems to be conflicting.
Also, can an adaptor that outputs AC volts have a negative center tip?
If I use the FPS-1 which is a DC adaptor will it harm the DV which came with an adaptor that outputs AC voltage?"

[vanhansen]

Ahh, interesting.  I'm willing to bet that the design was changed so it would either work fine off 9VDC, or use a charge pump internally to get the voltage up to 15.

Does it happen to have a sticker inside somewhere that says when it was made?

[Mark Hammer]

Yeah, that is truly odd.  There is nowhere near enough regulation on the board to provide a nice hum-free sound using an AC wallwart.  This baby looks like it cries out for a DC adaptor.

I'm sorry if we've led you on a wild goose chase.  Though from what I can see here, it was Fulltone that fired the starter's pistol and gave you a mismatched adaptor.  It is quite possible that the adaptor was changed in subsequent or prior pedal issues.

FWIW, the side of my Boss Flanger says 9vdc on the adaptor jack.  The service notes say 12vdc.  The pedal is palatable with 9v but terrific with 12v.  So, it's not Fulltone's exclusive sin.  Even the big boys do it.

[10acErnie]

There are three different dates written on this DV.
The dates 12/9/96, and UPDATED 3/11/98 SH are hand written on the inside of the box. On the outside 5/98 is hand written and signed by Mike Fuller.

Also, in the pic, if you notice where the black wires are attached to the board there seems to be a spot that has been filled in. Maybe that's where the bridge rectifier diodes were and the unit was updated?

[10acErnie]

I'm sorry if we've led you on a wild goose chase.  Though from what I can see here, it was Fulltone that fired the starter's pistol and gave you a mismatched adaptor.  It is quite possible that the adaptor was changed in subsequent or prior pedal issues.

No problem Mark! Actually, this is a pretty good learning experience for me. Do you think using a DC adaptor would harm the unit?