Amplifier circuitry-4 ohm vs 8 ohm

      YEP (GS beat me to it)!

       Here are two references, that may illustrate/shed more light on the subject:

                                   and (under ’Output Tranny Types’, parameters):

                      https://education.lenardaudio.com/en/14_valve_amps_5.html

The single amplifier at some point splits the signal going into either one of these Ports. What differences are there in the circuitry?

Maybe this will help me better understand the difference between these two taps. I believe 4 ohms is a wider more open path for voltage to flow. So when you’re speaker attempts to go lower, which requires more power, the 4 ohm more easily allows this to happen with a better outcome. Or maybe I got this wrong.

@emergingsoul 

You did.

As pointed out, the one output transformer for each channel has taps in a single winding for 4 and 8 Ohms. If the 4 Ohm tap is used with an 8 Ohm loudspeaker, the power tubes will be loaded at too high an impedance (transformers get their name from the fact that they transform impedance, and that goes both ways) and so will not make nearly as much power as they are supposed to.

If the 4 Ohm tap is loaded with 8 Ohms the transformer will also ’ring’ which is to say it will make distortion of its own. If the amp employs feedback, it might be able to compensate for this. But it will be lower distortion if the transformer is simply loaded correctly- so if an 8 Ohm speaker put it on the 8 Ohm tap!

If a 4 Ohm load is put on the 8 Ohm tap, the transformer will again be improperly loaded and so will the power tubes- they will have a load too low, causing some of the power they make to be dissipated in the tubes themselves, causing them to run hotter! In addition, the output transformer will be rolled off in the highs, although feedback might be able to compensate for that. However the power tubes will make more distortion, so you can see this is a Bad Idea. If a 4 Ohm load, use the 4 Ohm tap!

@atmasphere 

What if the speaker has a nominal impedance of 6 ohms? Which tap (4 or 8) should be used since the load is right in the middle of the two windings?

Wilson has their trained representatives setup their speakers and the Sabrina X list nominal impedance as 4 ohms at 135 Hz and it spends much of the time around 5 ohms. When they set up the speakers they used the 8 ohm terminals and I asked if 8 ohms was the correct terminals and they said yes, but I didn’t understand why they chose 8 ohms. I’ve not changed to the 4 ohm terminals. The MA-12000 has a solid state power amplifier, so I’m guessing that the only downside to this would be the amplifiers working harder for a given SPL.

What if the speaker has a nominal impedance of 6 ohms? Which tap (4 or 8) should be used since the load is right in the middle of the two windings?

@dspringham Try it on both. If you have access to the impedance curve of the speaker, look at the impedance it presents to the amplifier in the bass region. That's where the energy is and will have the most effect on the interaction between the amp and speakers. If it seems more like 4 Ohms than 8, use the 4 Ohm tap...