AFAIK, the reflected impedance will push the loadlines for the output tubes more horizontal, resulting a higher didt and more dissipation. The output transformer will get hotter as well, since it delivers more current into the load.
Ian Finch and DJK have the answers about the MI amp way.
To be more precise I get slightly over 200W into 8 ohms and slightly over 300 into 4 , with just +/-63V (raw) rails, and that with only 5000uF caps per rail.
With my own wound low loss EI transformers.
But I just wanted to post a generic comment based on rail voltages you expected and tried to play it very conservative. 🙂
You will probably get more 🙂 , but that's not the main point, which is: don't worry about numbers, you'll get what your PSU can give you and not a Watt extra.
To be more precise I get slightly over 200W into 8 ohms and slightly over 300 into 4 , with just +/-63V (raw) rails, and that with only 5000uF caps per rail.
With my own wound low loss EI transformers.
But I just wanted to post a generic comment based on rail voltages you expected and tried to play it very conservative. 🙂
You will probably get more 🙂 , but that's not the main point, which is: don't worry about numbers, you'll get what your PSU can give you and not a Watt extra.
Now that you have thought about the effects of using a lower impedance load, go back and review your post 1 questions.
You need to broaden your outlook 😀
The standard in Germany for example was 4 ohms for decades, don't know if it still is or not?, and of course 4 ohms was, and is, the standard for car audio.
Historically 15/16 ohms was the standard for valve amps, and as you mentioned it didn't matter because you simply wound the transformer to match your speaker.
But before 8 ohms became the standard for home SS speakers there was no real standard at all - and any decent amp would be specced to feed from 4 ohms to 16 ohms.
Yes, I suspected it coming down to dissipation and PSU strain, just like tube based amps. But thought there might be more to it. And things like secondary breakdown are new to me.
Great idea to halve the rail voltage for two ohms use while maintaining the same power output as well.
P.S. Beautiful country, Scotland! I've visited it for the third time by motorcycle last june.
The APT Model 1 has a switch for the transformer for when you need to run 2Ω, it reduces the voltage by a factor of 0.7 (roughly).
you are right about the output tube power dissipation getting exceeded...
the OPT? it depends....😉
the pioneer Spec2 likewise had a switch if you wanted to run 4 ohm speakers...http://www.hifiengine.com/manual_library/pioneer/spec-2.shtml
I presume you're talking about small cheap units?, Sony ones also often have 6 ohm speakers - presumably it's just a matter of getting the most available power from the chips and PSU's used? (presumably the chips won't handle 4 ohm?).
a 6 ohm secondary can handle both 8 and 4 ohms load...i did it in my opt and can not decide it was bad, actually i like it...
A good example - Monitor Audio RS-8, rated by manufacturer as 6 ohm.
I own a pair of those.
Except that some 6ohms speakers are not a combination of two nominal 6ohms drivers.
They are more usually a combination of a 4ohms Bass/Mid driver and an 8ohms Treble driver.
This is more like a 4ohms load as far as the amplifier sees in terms of the output current that the amplifier has to pass.
I reckon the output stage should be designed for 4ohms duty when driving one of these 4/8ohms two way that is called a 6ohms speaker.
They are more usually a combination of a 4ohms Bass/Mid driver and an 8ohms Treble driver.
This is more like a 4ohms load as far as the amplifier sees in terms of the output current that the amplifier has to pass.
I reckon the output stage should be designed for 4ohms duty when driving one of these 4/8ohms two way that is called a 6ohms speaker.
My electronics teacher in high school always said if you lower the resistance the speaker , crossover distortion becomes more evident. I'm not sure if that's actually true but in theory I could see it at lower volume levels.
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