[Patrick Turner]

Phil Allison wrote:

"Keithr"
" The Turneroid Menace "

Both said that if they used the transformer to make a 4 ohms speaker
appear to the amp as an 8 ohm or 12 ohm load, the music sounded better.
That's because the distortion becomes lower and damping factor becomes
higher.
Exactly how does the damping factor become higher? If you use say the 8
ohm tap on the OPT, then an autotransformer to step this down to 4 ohms,
provided both transformers do what they say, nothing is changed from using
the 4 ohm tap in the first place.

** Contradicts the proposition you are commenting on.

Which was about deliberately UNDERLOADING the amplifier.

The output stage sees exactly the same load impedance

** Not when the speaker remains the same - pal.

and the damping factor is unchanged because the speaker still sees the
same source impedance.

** Still wrong on both counts.

These transformers may be fine if you do not have an output tap to match
the speakers, but it is hard to see what they bring to the table if the
correct tap is available.

** PT never said they did -

the ****wit OP suggested that nonsense.

...... Phil

If one uses a step down matching tranny after an amp you are
"deliberately UNDERLOADING the amplifier" as you say.

But the load match you may actually get when you do this might in fact
be a better one for fidelity for the power you want.

There isn't anything wrong with using a 16 ohm speaker plugged into the
"4 ohm" labelled output of a tube amp if the levels obtained are high
enough, and assuming that the makers have made their amp unconditionally
stable, ie, it won't oscillate with the higher value ohm load.

Many tube amps oscillate at LF and perhaps HF with a high value load, or
no load connected, ie, with a load equal to an infinite number of ohms,
ie sitting there without speakers plugged in.

Most tube amps will produce better fidelity at least for the first few
watts of power if the load value is higher than the outlet label says.
This is because the output tubes are working in a more linear manner
with more class A1, output tube voltage gain is higher, and thus the
amount of applied global NFB is greater, because the amount of applied
NFB depends on the open loop gain. The higher load also means the
leakage inductance causes less HF attenuation and the damping factor is
raised.

Many listeners have heard better sound using Zero Impedance transformers
even when the load match was OK in theory; ie, when the load value was
raised higher than "it should be" and the load is "underpowered", the
music sounded better, and so it should have because the THD was lower,
and DF higher. The "underpowered" load match means less maximum PO is
available abd in SE amps it means clipping is asymetrical because the
wave clips onj one side due to grid current before cut off occurs. But
who cares how the amp clips if there is **enough** power before clipping
occurs?

Patrick Turner.