EMG-Pi2 active phase reversal

[rbkxiiowe]

I've just got a set of EMG pickups (SA/SA/81 set) and would like to reverse the phase of the middle pickup.

EMG sell the Pi2 for this, but what does it actually do? And why is it better than using a dpdt switch to do phase reversal by switching the hot and ground wires of the pickup?

Cheers.

[ChrisK]

The SA/SA/81 set are all active electronic pickups. These have a supply input lead, a signal/power common lead, and a signal output lead.

While internally "just" a two lead coil before the internal OP AMP circuit, these are not passive pickups and hence a DPDT switch cannot be of use in phase reversal.

The power supply input and signal/power common must remain the same for all pickups sharing the same power supply system/battery. This leaves the signal output lead for which there is nothing to switch it with.

As a result, an electronic means such as the PI2 must be used to invert (Phase Inverter 2) and not "reverse" the signal of an active pickup. This inversion results in an effect most similar to passive pickup phase reversal although there is no passive component interaction as there is with passive pickups.

[rbkxiiowe]

Thanks Chris, I understand. What I was looking to do was to have a dpdt on-off-on switch for a pickup to do on/off/reverse phase. As the Pi2 is built onto its own two-way toggle switch, it looks like that might not be easily done.

Does anyone have any experience hacking one of these? It could be as easy as simply unsoldering the switch and refiddling my on-off-on switch onto it I suppose. Only problem is I can't find any schematics or even a close up picture of one.

[newey]

It could be as easy as simply unsoldering the switch and refiddling my on-off-on switch onto it I suppose

I'm not sure how that qualifies as "easy". A separate on-off switch would be easy, and you could then let the PI2 do its thing unmolested.

[ChrisK]

What I was looking to do was to have a dpdt on-off-on switch for a pickup to do on/off/reverse phase.

This could be done depending on the circuit topology used in the PI2.

If there are two signals; a buffered one and its inversion with the appropriate one being selected by the EMG switch (a SPDT), then a SPDT Center-OFF could be used with no signal being conveyed in OFF.

If there is a buffer and a selectable inverter/non-inverter stage, with the mode being selected by the EMG switch (a SPST), one pole could be used for this and the other pole could be used for the coupling of the common output (SPDT Center-OFF as above).

As the Pi2 is built onto its own two-way toggle switch, it looks like that might not be easily done.

Easy is directly related to what's known. After all, any sufficiently advanced technology is indistinguishable from magic.

One (not me) would have to procure (a fancy word for buy/get) a PI2 and trace the circuit. EMG will not publish the schematic since that would mean that it's not magic.

Does anyone have any experience hacking one of these?

No, other than a brief lapse of judgment that led to my procuring a DG-20 kit a few years ago during a GC clearance sale, I've no great interest in their stuff. I built the The MellowCaster Project, but haven't yet brought myself to the point of putting a battery in it.

Pssst, anyone interested in a DG-20 set?


That being said, since it isn't magic, one could ascertain the operation fairly easily.

The instructions indicate the number of connections.
www.emginc.com/content/wiringdiagrams/EMG-Pi2_r0230-0017A.pdf

The picture shows 6 terminals used on the embedded toggle switch.
www.emginc.com/products/category/143

It would appear that the green output wire is connected to one of the switch poles and is switched from either the input signal to an inverted signal, or from a buffered input signal to an inverted signal.

Either way, a DPDT Center-OFF could do the same, with the output being disconnected in the Center-OFF position.

No guarantees; this is an educated observation.

Since you're replacing a DPDT with a DPDT Center-OFF, if you rewire it exactly the same, things will work exactly the same except in the middle (unknown) position. ;D ;D

It could be as easy as simply unsoldering the switch and refiddling my on-off-on switch onto it I suppose.

Hmmm, that's a firm maybe............ ;D

Don't you have to fiddle before you can refiddle?

[rbkxiiowe]

A separate on-off switch would be easy, and you could then let the PI2 do its thing unmolested.

I already have three holes in the guitar ready for mini toggles and wanted to have neck on/off, middle on/off/phase, bridge on/off.

Don't you have to fiddle before you can refiddle?

I was planning on both fiddling and refiddling.

I think I'll buy one and then get fiddling.