Vintage Electric Mistress power supply

[SpaceProphet5]

I'm about to land a vintage ("green") Electric Mistress, but I'm wondering how I'm supposed to power it safely. I've heard that I only need a 12 v adapter, since the pedal limits the 18 volts down to 12 on the inside anyway, but I'm unsure if my adapter cable works. I got a Boss-style-to-1/8"-audio-plug adapter with a power supply I bought a couple of years back (Godlyke Power-All). However, the Mistress requires a "tip positive" plug, and I'm pretty sure a regular pedal power supply is tip negative. Is the polarity reversed within the adapter cable, or do I need to put anything in between?

I just want to make this absolutely sure, 'cause if you're gonna take risks with your gear, an irreplacable vintage pedal isn't exactly the optimal place to start.

[lefort_1]

I cannot find a schematic that I can guarantee is the same era as your pedal, but I can state that some older power supply designs might not be happy at all with 12 volts if it is expecting 18. If you aren't willing to risk the polarity, why risk any other part of the power equation?

I'd email EHX and see what they reco. Also, the mA rating will be critical. Older pedals often draw more than you'd expect (due to the design-of-day for power supplies and logic families).

 

 

[Mr.Grumpy]

From looking at the schematic, it's apparent the E.M. needs more than 12 volts. It has an internal voltage regulator, but they need at least a couple of volts above the regulated voltage (12 - 13.5 volts) to work. So a power supply between 16 and 24 volts should work, provided it's the correct polarity and supplies enough current (mA). 

[eti313]

Back in the day, I hooked up two 9-volt adapters with battery clip connectors to the internal dual 9-volt battery clips. Of course, that makes for a tight squeeze to get the adapter cables inside a closed pedal.