ZMACS + PS-100 Impedance Question: Mostly 16 Ω Amps/Cabs, Manual Front Panel Switching
I am looking for clarification on the safest and most practical impedance setup for my ZMACS 4x4 with a PS-100 in the attenuator loop.
My system is configured as follows:
- All four tube amplifiers connected to the ZMACS can be set to 4, 8, or 16 Ω.
- I currently have all of the amplifiers set to 16 Ω.
- Cabinet 1 = 16 Ω
- Cabinet 2 = 16 Ω
- Cabinet 3 = 8 Ω
- PS-100 is connected in the ZMACS attenuator loop.
- We are primarily switching amps and cabinets manually using the front panel buttons, not MIDI.
I understand from the ZMACS manual that when the AMP and CAB impedance selections are different, the ZMACS automatically engages its internal impedance matching transformer.
For example:
16 Ω amp selected + 8 Ω Cabinet 3 selected = ZMACS set to AMP 16 / CAB 8, so the matching transformer automatically engages.
I also understand that when the AMP and CAB settings are identical, such as 16/16, the ZMACS normally bypasses its impedance matching transformer.
The manual specifically recommends setting a Power Station in the attenuator loop to 8 Ω AMP IN and 8 Ω SPEAKER OUT, and engaging Bypass Override Mode when the selected amplifier and cabinet have the same impedance.
This creates a workflow issue for us because most of our equipment is 16 Ω. If we leave the PS-100 at 8/8, every time we manually select a 16 Ω amplifier and one of our 16 Ω cabinets, it appears we would need to make sure Bypass Override Mode is engaged. We would prefer not to have to manually engage or verify Bypass Override every time we switch amps or cabinets.
My questions are:
- Since all of our amplifiers and most of our cabinets are 16 Ω, can we simply set the PS-100 AMP IN to 16 Ω and SPEAKER OUT to 16 Ω and leave it there?
- With a 16 Ω amp, PS-100 at 16/16, and 16 Ω cabinet, can the ZMACS simply remain in its normal 16/16 Default Impedance Bypass Mode without using Bypass Override?
In other words:
16 Ω amp → ZMACS AMP 16 → PS-100 16/16 → ZMACS CAB 16 → 16 Ω cabinet
Is that the preferred configuration when everything is already matched?
- More importantly, what happens when we then manually select our 8 Ω Cabinet 3 while leaving the PS-100 at 16/16?
The configuration would become:
16 Ω amp → ZMACS AMP 16 → PS-100 16/16 → ZMACS CAB 8 → 8 Ω cabinet
Since the ZMACS sees AMP 16 and CAB 8, I understand that its impedance matching transformer will automatically engage. Is the ZMACS designed to correctly perform the 16 Ω to 8 Ω conversion with the PS-100 still sitting in the attenuator loop at 16 Ω input / 16 Ω output?
Or does the impedance compensation circuit specifically expect the Power Station to be set to 8/8, regardless of the actual amp and cabinet impedances?
- Put another way, which of these is Fryette’s recommended configuration for our particular system?
Option A
All amps = 16 Ω
PS-100 = 8 Ω IN / 8 Ω OUT
ZMACS = actual amp and cab impedances
Use Bypass Override whenever amp and cab impedances match
Option B
All amps = 16 Ω
PS-100 = 16 Ω IN / 16 Ω OUT
ZMACS = actual amp and cab impedances
16/16 amp/cab combinations operate with the ZMACS transformer bypassed
16/8 combinations automatically engage the ZMACS transformer
Our goal is to have the safest possible setup while also being able to switch amplifiers and cabinets manually from the ZMACS front panel without having to remember to engage Bypass Override every time we return to a matching 16 Ω amp and 16 Ω cabinet.
I would particularly appreciate clarification from Fryette on whether Option B is fully supported, including the 16 Ω amp → PS-100 at 16/16 → ZMACS conversion → 8 Ω cabinet scenario.