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Understanding Speaker Output on Nikko NA-550

Hi,
I'm trying to understand this label on the back of my amp (Nikko NA-550). Specifically I'm referring to this image: https://vintage-audio-heritage.fr/download/file.php?id=57573 .

First off, are these two separate output channels or are they wired to the same channel and just allow switching between two sets of speakers?

Then I'm trying to understand the impedance rating given:
  • what does the notation A.B and A+B mean? I'm assuming different configurations of the speakers and/or wiring. Does it also apply to a single set of stereo speakers or only if using one set per output (4 speakers total)?
  • how do I interpret the impedance rating? Does "4 ~ 16 Ohm / speaker" refer to the allowed impedance range the speakers must be rated at?

Thanks a lot for your help.

jgruff
jgruff OP
2 posts
 
Hey thank you so much for your quick response!

So just to understand this better, the notation here is opposite to that in boolean algebra, where A*B would mean A and B, and A+B would mean A or B?

What is the reason behind these different ratings, i.e. what is different between the two configurations (maybe in terms of the wiring or other internal features) that would cause the different impedance rating?
imhififan's avatar
imhififan
2,181 posts
 
just to understand this better, the notation here is opposite to that in boolean algebra, where A*B would mean A and B, and A+B would mean A or B?
Forget about boolean algebra.
The top line " A.B-4Ω~16Ω/SPEAKER " means IF playing speaker A OR B only, the amplifier able to safely power 4Ω to 16Ω impedance rating speaker.
The bottom line " A+B-8Ω~16Ω/SPEAKER " means IF playing speaker A AND B together, the amplifier able to safely power 8Ω to 16Ω impedance rating speaker.
What is the reason behind these different ratings, i.e. what is different between the two configurations (maybe in terms of the wiring or other internal features) that would cause the different impedance rating?
Nikko NA-550 is designed to safely power speaker not less than 4Ω impedance. If playing two sets of speakers together (speaker A and B), both set of speakers are connected in parallel by the speaker switch and the total impedance apply to the amplifier will be less.

https://geoffthegreygeek.com/calculator-speakers-in-parallel/
jgruff OP
2 posts
 
Ah thanks that last paragraph makes perfect sense, thank you.
imhififan's avatar
imhififan
2,181 posts
 
Yes, I agree that the top line " A.B-4Ω~16Ω/SPEAKER " is confusing, this is much better to understand:

https://www.springair.de/media/image/79/22/65/h53466-5-53466e.jpg
chrisgreen
1 posts
 

I have a NA-550. I have a 6 ohm pair of speakers on A and an 8 ohm pair on B. I run A+B all the time. I think this is technically out of spec, but is it anything I need to worry about?

Also, the 6 ohm pair is much louder than the 8 ohm pair. Different speakers, obviously. Also different gauge, type, and lengths of speaker wire. Can anyone suggest why there is such a disparity in the volume of the two pairs?

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