Daisy Chain Powering on AC

[Baran Ismen]

I got 2 pedals that requires AC 9V's; Line 6 M9 and Digitech XP-100

I've made a very simple splitter with a small piece of stripboard, cut 3 lanes, removed the middle one's copper layer, soldered 1 female cable and 2 male cables side by side, isolated them well, powered both pedals, worked fine, BUT with a small difference.

When I initially did this, audio jacks were not plugged to Line 6 and all was good. When I plug either input or output jacks (or both) to Line 6, the voltage drops to around 5V on the line and both units tend to freak out, displays go on and off, and there's a massive humming sound I hear.

The adapter I use is the original Line 6 adapter, which is 9V 2000A AC adapter. As I checked, M9 needs around 800mA (even though it says under the unit that min. 2000mA is required), and Digitech needs around 700mA (I run that with a separate 9V 1A AC adapter normally). So theoretically, this adapter should be enough for both units, but there seems to be a problem.

My intention is to use a common AC power supply to feed both units. I wonder if its possible; if yes, what should I do? Upon a suggestion, I've tried half-rectifying this splitter by adding 2x 1N4001's, M9 worked, but XP did not because there was only ~5V DC on that end.

I'm all ears for suggestions.

[JTEX]

Pedal #1 most likely ties one of the AC power leads to its ground, while Pedal 2 leaves both leads floating and needs them to stay that way for its internal power scheme to work. When the pedals are grounded together by an audio cable, you're shorting one of pedal #2's AC leads to ground where it needs to float. Grab a ohm-meter and measure between each pedal's ground and both its AC leads to confirm this.

[Baran Ismen]

Pedal #1 most likely ties one of the AC power leads to its ground, while Pedal 2 leaves both leads floating and needs them to stay that way for its internal power scheme to work. When the pedals are grounded together by an audio cable, you're shorting one of pedal #2's AC leads to ground where it needs to float. Grab a ohm-meter and measure between each pedal's ground and both its AC leads to confirm this.

I guess i need to open their guts to check this right? If thats the case, is there any Workaround?

[R.G.]

JTEK is right. Exactly how the two pedals connect the 9Vac to the audio ground inside matters a lot. There are a few ways to get this wrong. Workarounds will something like using stone axes and clubs until the particulars are known. You could of course use an isolated 9Vas for each one.

[Baran Ismen]

JTEK is right. Exactly how the two pedals connect the 9Vac to the audio ground inside matters a lot. There are a few ways to get this wrong. Workarounds will something like using stone axes and clubs until the particulars are known. You could of course use an isolated 9Vas for each one.

Ill check the power input stages for both units today over their schematics and try to find anything different, which i suspect i would 

Note that, m9 works with 9v dc power as Well, whereas xp100 does not, i mean it powers up but no sound coming out.

[Baran Ismen]

Found them. M9 uses a full rectify whereas xp100 uses a half rectify. Thats my all knowledge 

[R.G.]

For full wave rectification, each of the two AC wires is alternately one diode higher than the rectified DC and then one diode lower than analog ground.

For half wave rectification, one side of the incoming AC is always connected to the analog ground. This is even more complicated by the particular setup for half-wave, as it is used to make both +DC and -DC. This limits your solutions a lot. With one of the AC wires permanently tied to analog ground, connecting the two analog grounds means that the analog grounds in the cables are trying to short out the negative-side diode in the full wave bridge alternately. This is ugly, as you have found out.

I can't see a simple solution for this, other than two separate 9Vac supplies. I can come up with more complicated solutions, but the use of the +/- half wave power in the ... whichever one it was ... forces a solution that isn't just "add a diode here" or something otherwise similar. There are always isolated switching converters, 1:1:1 power transformers, etc, but if you have both 9Vac adapters, use them both.