Let’s try this again… running ONE amp through TWO inputs and TWO Speaker Outs

Stage & Studio ZMACS
1

I tried asking this EARLIER with zero response. Perhaps the question needs simplified.

One Plexi (having 4 Inputs and 2 Speaker Outs).

Want to run 2 of the 4 inputs as if EACH input was an independent AMP preset on the 4 available slots on the ZMACS.

Wiring seems simple: ZMACS Ch1 (To Plexi Ch1 Hi Input > Left Speaker Out to ZMACS); ZMACS Ch2 (To Plexi Ch2 Hi Input > Right Speaker Out to ZMACS).

The issue is impedance setting

If this was ONE speaker out in use, Amp simply would be set to say, 16 ohm and ZMACS would match at 16 Ohm.

Since TWO are in use, would the Amp be set to 8 Ohm (for one 16 ohm Active ZMACS channel and one 16 inactive/dummy load ZMACS channel) or what?

2

The limitation here isn’t the ZMACS or the wiring. It’s the Plexi’s output stage. On a Plexi, the two speaker outputs are simply paralleled connections from the same output transformer, not independent amp outputs. Because of that, there’s no way for the ZMACS to see two separate amp returns from a single head, regardless of how they’re routed.

That’s also why the impedance question doesn’t really resolve cleanly. The amp only ever “sees” a single combined load across its output transformer, not one active and one inactive return in the way you’re describing. Changing the impedance selector won’t make the two outputs behave independently.

In short, this setup requires separate amp output stages to work as intended. A single Plexi can only function as one amp from the ZMACS’s perspective.

Julian

1 Like
3

I don’t think the ZMACS needs to see or understand anything beyond it having 4 “amp in” bays it can match impedance with.

Correct me if I am wrong…

  1. Four Amps each set at 16 to ZMACS.. ZMACS provides appropriate 16 Ohm resistance to all 4 amps despite the fact only ONE can be actively used.

  2. If I changed one of those 4 amps to 8ohm and added an additional 16 ohm cab to the amp’s second output, it would be as if the amp was pushing two 16 ohm cabs- the 16 Ohm ZMACS and the 16 Ohm Ext cab. ZMACS needn’t know what’s going on with the other output at all. It provides its 16 Ohm, the Ext cab provides its 16 Ohm, the amp is set to a balanced 8 Ohm

  3. The very same should be true If I set the amp to 8 Ohm and ran the ZMACs at 16, using the other speaker out instead for a dummy load set for 16. The amp is set for 8, it has 2 16ohm loads and is in balance. ZMACS should neither know nor care if the other speaker out is in use at all, or running a cab or dummy load… as long as it is matched to the Amp’s output.

With all that said ,how is it any different setting the amp to 8, and running two inputs to 16 on the ZMACS? One should be active, and one should be dummy with either selection of the “amp channels.”. Even if both are dummy loads because another amp is in use, the operation would be the same as if the amp was running two 16 ohm dummy loads..

4

It does, it must prevent potentially dangerous operating conditions that could damage the connected amplifiers. For this reason, it is not possible to switch on two amp returns simultaneously. Unused amplifiers (returns) are put into a protective load state. This becomes a problem when you connect your plexi, whose output jacks are wired in parallel internally.

Julian