I have a 20+ years old technics SU-Z400 amplifier still working well,
however I need to change the speakers because the rubber around them
is disintegrating and the the sound is distorted.

I noticed on the back of the amplifier a 2-positions switch for
impedance settings: one for main or remote 4-6 ohm (and main AND
remote 8 ohm) and the other for main or remote 8-16 ohm (and main AND
remote 16 ohm).

I suspect the switch has always been on the wrong setting (4-6 ohm) as
I have only a pair of speakers (main) with 8 ohm written on them. (The
impedance is always referred to each speaker, right??)

So if I buy another couple of 8 ohm speakers, should I set the
amplifier to the 8-16 ohm?

Thanks in advance

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"Legambiente" wrote in message

I have a 20+ years old technics SU-Z400 amplifier still working well,
however I need to change the speakers because the rubber around them
is disintegrating and the the sound is distorted.

I noticed on the back of the amplifier a 2-positions switch for
impedance settings: one for main or remote 4-6 ohm (and main AND
remote 8 ohm) and the other for main or remote 8-16 ohm (and main AND
remote 16 ohm).

I suspect the switch has always been on the wrong setting (4-6 ohm) as
I have only a pair of speakers (main) with 8 ohm written on them. (The
impedance is always referred to each speaker, right??)

So if I buy another couple of 8 ohm speakers, should I set the
amplifier to the 8-16 ohm?

It probably doesn't matter that much one way or the other. These 8-16 ohm
switches generally changed the voltage applied to the output transistors.
The 4-6 ohm setting might put 35 volts on the output transistors, while the
8-16 ohm setting might apply 45 volts. If you don't really stress the
amplifier, the difference is mostly noticable on the test bench, not in
actual residential use by a conservative consumer.

(Legambiente) said:

I noticed on the back of the amplifier a 2-positions switch for
impedance settings: one for main or remote 4-6 ohm (and main AND
remote 8 ohm) and the other for main or remote 8-16 ohm (and main AND
remote 16 ohm).

Correct.
Assume the switch is at 4 ohm.
It means when using 2 speakers, they may have an impedance of 4 ohm or
higher. When using 4 speakers (by means of e.g. pushing both speaker
"mains" and speaker "remote" together) all 4 speakers must be 8 ohms
or higher.
This is because essentially both main and remote outputs are wired in
parallel.

I suspect the switch has always been on the wrong setting (4-6 ohm) as
I have only a pair of speakers (main) with 8 ohm written on them. (The
impedance is always referred to each speaker, right??)

No speaker is just "8 ohms" , the impedance varies over the frequency
range. For the sake of brevity, I'll still refer to it as an 8 or 4
ohms speaker though.
What this switch does: when set at "4 ohms" it lowers the internal
supply voltage of the amplifier circuit, to ensure that when a lower
speaker load is used, the current through the amp isn't exceeded.
At "8 ohms", the supply voltage is higher, but the current capability
is lowered.
As long as you won't use a speaker load lower as 8 ohms, you can use
this 8 ohms switch position.

So if I buy another couple of 8 ohm speakers, should I set the
amplifier to the 8-16 ohm?

NOOOOO!!!!!!!
You must remember that a second pair of speakers will be put in
parallel, so this means 8/2= 4 ohms!
DEFINITELY use the 4 ohms position!

When I get amps in for repair, or have to install one somewhere, and
there's such a switch present, I ALWAYS put it in the lowest position.
And when using a tube amp, correct matching of impedances is essential
for good operation.

Hope this helps!

--
Sander deWaal
"SOA of a KT88? Sufficient."