Important: Keep all unused taps isolated from each other. Touching any two
taps together is essentially the same as shorting out the amplifier.
Using the ZEROs will not affect a speaker's efficiency, and it has been found
that when paired with an OTL amplifier, the speakers will play at about the same
(if not greater) volume level with the ZEROs installed and the volume control
left unchanged.
The ZEROs have a very low DC resistance value of about 0.3 ohms. This allows
for a very efficient transfer of power and has the added benefit of protecting
the speaker as it will bypass almost all of the DC current in the unlikely event
of a tube short. This low DC resistance will alter the offset voltage meter
reading (Atma-Sphere OTL amplifiers) in a similar way, but to a greater extent,
as having a low impedance speaker connected. I recommend that you set the
amplifier's bias and offset voltage prior to installing the ZEROs, and then view
the bias and offset voltage reading again after the ZEROs are installed, so you
can see the effect. Be aware that the ZEROs do not change the bias nor the
offset voltage , just the meter's ability to display the actual readings.
The ZERO autoformer holds its impedance charter down to 2Hz. But still, the
low 0.3 ohm DC resistance may cause trouble if using a Solid State amplifier
with excess offset voltage. As little as 300mV of amplifier offset voltage will
cause 1 amp of DC current to flow. Also, if the SS amplifier's offset voltage
changes dynamically with the music, a large amount of DC current can flow as
well. Because of this, I recommend that a 3A fast blow fuse be installed in
series between the SS amplifier and the ZERO. The ZEROs will protect the speaker
from DC, the fuse is there to protect the amp from itself if it does try to push
DC. I give this fair warning for caution, yet I have many guys using the
ZEROs (without extra fuses) with solid state amplifiers for many years, and so
far no amplifiers have been damaged.
I recommend that you install the ZEROs close to the speakers so that there is
essentially no speaker wire run from the ZERO to the speaker. This is the low
impedance / high current side of the autoformer. The longer speaker wire run
should be from the amplifier to the ZEROs, which is the higher impedance / lower
current side of the ZEROs.
This may seem to cause a problem if your speakers are bi-wired. Yet the
advantage of using the ZEROs to reduce the current in the speaker wire run may
be comparable to bi-wiring. You may want to first install the ZEROs at the
amplifier and continue to use the bi-wire run to your speakers. After using this
configuration for a few weeks, re-configure the set up so the ZEROs are at the
speakers and a single speaker run goes from the amp to the ZEROs as described in
the above paragraph for comparison. I get better sound in my system this way, so
I have abandon using bi-wires and I was able to upgrade my speaker wires for
half the cost.
Finding the best speaker impedance multiplication factor is not difficult.
Start by using the 2x and then the 4x multiplication factors to get the feel of
the ZERO's effect. As the speaker's impedance is increased you will notice a
decrease in distortion, an increase in resolution, and a tightening of bass
control. Start with a low multiplication factor and step up to higher
multiplication factors. You will know when you have gone to far when the system
starts sounding dry. This happens when the amplifier has over damped the
speakers. When this happens, the multiplication factor needs to be reduced
again. Trust your ears, and when you achieve the best sound possible, you are
done. It is likely that you will find that the best sound is achieved when
running the OTL amplifier in its maximum power transfer region. This will be
loading an Atma-Sphere MA-1 with 8 to 10 ohms, Loading a M-60 with 14 to 16
ohms, and loading a S-30 with 22 to 26 ohms.
After you have found how best to utilize the ZEROs for your system, you can
now effectively change the number of output tubes without affecting the optimum
impedance relationship (and optimum sound) that you have established. For
example if you have found that you get the best sound using the ZEROs as a 4x
impedance multiplier, then you can try removing half of the output tubes, but
compensate for it by using the ZEROs as a 8x impedance multiplier, so that half
as many tubes are presented with half as difficult of load to drive. The system
should sound about the same but will play at 3dB less volume.
A number of ZEROs owners have asked if there are any other multiplication
factors available. In fact there are. The Yellow and Blue leads are designed to
be connected to either the speaker or the amplifier, which opens up a variety of
interesting configurations. I have pulled together all available configurations
into 3 different groups. Many of them are ridicules multiplication factors, and
will not sound good at all. Others are quite interesting possibilities. For
example, if you are currently using 2.75x, you will find a 2.9x in "Group 3
Configurations" that you may want to try. There is also a 2x configuration in
all three groups. They may sound slightly different from each other, so find
which one works best for your system.
