The ZEROs are the
simplest type of transformer called an auto-transformer or autoformer. They
are used to multiply the impedance of any speaker so that it "feels" like
the optimum load for the amplifier being used. They are very helpful in
matching speakers to amplifiers. By adjusting the speaker's impedance, both
the damping factor and the maximum power transfer of the amp/speaker can be
tailored for the best sound.
Dick Olsher called the
ZEROs "an important new product category that allows music lovers to
actively modify and control the amplifier-loudspeaker interface".
The ZEROs are a great way
to get better amplifier performance when driving low impedance speakers.
What is wrong with low impedance speakers? They suck...
That is they suck a lot
of current. Using the ZEROs to increase a speaker's impedance, decreases the
current demands on the amplifier. Super large amplifiers are not necessary
needed for their ability to produce 200-300 watts of power, but rather, to
be able to source the current demands of low impedance speakers at 20-30
watts without sounding stressed.
The ZEROs are an
alternative approach to spending mega bucks on a mega amplifier to drive low
impedance speakers. The ZEROs can give your sweat sounding low to mid sized
amplifier the low distortion and authority of a mega sized amplifier.
What is considered low impedance?
Even 8-ohm loads are not
optimal. Half of the ZEROs owners used them to increase the impedance of
their 8-ohm speakers. Multiplying the reported best sounding ZEROs
multiplication factor times the original speaker's impedance, and then
averaging the results, I found the average reported optimal impedance to be
14.6-ohms. Speakers rated 8 ohms and lower typically produce benefits.
What are the Multiplication factors available?
The multiplication taps
are: (2x), (3x), and (4x), so a 4 ohm speaker can be made to look like an 8,
12, or 16 ohm speaker. This, in most cases, will take care of your needs.
There are actually other
multiplication factors available (ie 1.3x, 1.78x, 2.75x, 8x, etc.), but it
gets a bit messy and confusing. If you are fairly technical and like
experimenting you can check out these three schematics to see what is
How will I know which multiplication factor to chose?
Start by using the 2x
factor, then work your way up 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.
What is Damping Factor?
The damping factor is
simply the ratio of the speaker's impedance over the amplifier's output
impedance. For example if a 4 ohm speaker is being driven by an amplifier
that has a output impedance of 2 ohms, then the damping factor is 4/2 = 2.
Now using the ZEROs to
make the 4 ohm speaker look like a 16 ohm speaker, the damping factor
becomes 16/2 = 8.
A woofer that is "under
damped" will sound uncontrolled and boomy. A woofer that is "over damped"
will sound thin and lean. A speaker's woofer will sound best when it is
"critically damped", This is where it will extend lowest in frequency
without "ringing". The ZEROs allow you to freely adjust the damping factor
for best sound.
I'm afraid of that huge coil of wire. How does the music get through it?
The large coil of wire
wound around the toroid shaped (round) core can look a bit fearful to anyone
wanting get "closer" to the music, so maybe this will help: The music is NOT
spinning around the core through the winding wire hundreds of times before
it comes out the other side. That would be true if the autoformer was
electrically used in series between the amplifier and the speaker (like an
inductor...one wire in, one wire out). Fortunately, the autoformer is a
parallel wired device, like the voice coil of a dynamic speaker.
What improvements can I expect to hear by adding the ZEROs to my system?
Both my experience and
reports from many many ZEROs users have these common results:
- A) Lower distortion
"sounds cleaner" (due to an easier load on the amplifier)
- B) Firmer bass (due to
an increased damping factor)
- C) Higher resolution
(due to an easier load on the amplifier)
- D) More extended and
better focused high frequency.
The ZEROs don't sound quite right. What should I do?
What happens if I run them backwards?
Most everybody uses the
ZEROs to MULTIPLY the speaker's impedance by connect the BLACK and WHITE
leads to the speaker, and connecting two of the other four leads to the
amplifier. In contrast, you can use the ZEROs to DIVIDE the speaker's
impedance. This can be used to optimize your speaker's impedance to the rare
amplifier that prefers a low impedance speaker, like the Decware Zen tube
amplifier that has only a 2 ohm output tap. This can be done by connecting
the BLACK(-) and WHITE(+) leads to the AMPLIFIER, and connecting two of the
other four leads to the SPEAKER.
impedance by 2 = YELLOW (+) & BLUE (-) to Speaker (ie. 8 ohm speaker becomes
impedance by 3 = YELLOW (+) & BROWN (-) to Speaker
impedance by 4 = GRAY (+) & BROWN (-) to Speaker
You will notice the only
thing that changed is that the connections to the speaker and to the amp are
FLIP-FLOPPED...thus making it an impedance DIVIDING autoformer, instead of
an impedance MULTIPLYING autoformer.
Please experiment for
best sound. As your speaker's impedance is reduced, the Zen amplifier will
be able to source more and more power into the speaker down to the maximum
power point of 2 ohms (Zen amp). Best sound will be achieved when a balance
between most power and "critically" damping the speaker is achieved.
Reducing the speaker's impedance to low will under damp the drivers causing
an overly blooming bass. Trust your ears, and when you achieve the best
sound possible, you are done. An interesting article on critically damping
your speakers can be found here:
Who is using the ZEROs?
The ZEROs are used world
wide. I have shipped ZEROs to the Netherlands, Hong Kong, Israel, Egypt,
Canada, England, Guatemala, Turkey, Sweden, Scotland, Australia, Portugal, Holland,
Puerto Rico, Malaysia, Italy, Mexico, India, Thailand, Greece, Spain,
Switzerland, France, Norway, and the United States.
The most common users are
running OTL amplifiers. Many are using them on SET and Push-Pull tube amps
with great results. There are guys using them
with their solid state amplifiers as well.
What is the difference between the ZEROs autoformer and a typical tube
The ZEROs have a few
advantages over "typical" tube amp transformers:
A) The music comes out on
the same winding wire that it goes in on so the music does not have to pass
from a primary winding to a secondary winding.
B) There is no DC current
to contend with. When a transformer is made to accommodate a DC field, its
audio transparence is compromised.
C) The impedance ratio is
very small (16 ohms to 4 ohms, compared to a few thousand ohms to 4 ohms).
This simply means that it is much easier to achieve things like, frequency
response extremes, than with a "typical" tube amp transformer. The ZEROs
sport a frequence response of 2 Hz to 2 MHz.
Doesn't adding the ZEROs to my Output-Transformer-Less (OTL) Amplifier
defeat the benefits of the OTL design?
The ZEROs were originally
designed to maximize the full benefits of the OTL amplifier by changing the
speaker's load impedance to the Maximum Power Transfer Region of the
amplifier being used.
The ZEROs are not an
amplifier fix, they are a speaker fix. It is a great disfunction to music
loving audiophiles for speaker manufactures to be making 4 ohm speakers with
3 or 2 ohm impedance dips, and then expect amplifiers and speaker cables to
be able to transfer music into a load approaching a dead short. The ZEROs
simply multiply the impedance of the speaker in use, and do it so
transparently they provide greater benefits than the "penalty" of an added
Should I add the ZEROs close to my speakers or close to my amplifier?
Placing the ZEROs close
to the speaker typically provides best results. Adding the ZEROs close to
the speakers means that not only does the amplifier benefit from the higher
impedance, but the speaker cables benefit as well. This benefit was not
expected by me, yet is very real. The inductance and resistance in a speaker
wire run is 1/4 less of a problem into 16 ohms as it would be into 4 ohms.
What is with those skinny red leads?
The leads are made of one
solid piece of continuously cast copper. They might look skinny, but that is
because the insulation is a very thin coating of enamel, instead of the
typical thick plastic insulation (ie PVC or Teflon). They are actually 12
gauge wire even though they look much smaller. After spending a few months
buying and evaluating (by listening) many different lead out wire options
from many different companies, these were found to be the most neutral and
transparent sounding. Below is my opinion why:
- They virtually
eliminate the three most common sources that give speaker cable their
- The solid core wire
eliminates the complex conductive and magnetic interaction that happens
between the many individual strands of stranded wire.
- Keeping each lead
separate eliminates the magnetic fields of the leads from interacting with
- Beyond the extremely
thin enamel coating, there is nothing left but air. Next to a pure vacuum,
air the best insulation dielectric! Air is also why break-in time is
short. Great big fat speaker cables with thick insulation need a long time
to break-in because there is so much dielectric material to absorb and
What will the ZEROs do for my already transformer coupled tube amp?
It has been really fun is
to hear for myself, and hear reports from others, that transformer coupled
tube amps sound better driving higher impedance speakers (made so with the
ZEROs autoformers) as well. Since I trust my own ears, I have to ask myself
why did adding the ZEROs autoformer to the speaker and moving the
transformer coupled tube amp off of the 4 ohm tap, on to the 8 ohm (or 16
ohm if available) tap improve the sound? It really doesn't make sense at
first, adding another component to improve the sound when a 4 ohm tap is
already available for the 4 ohm speaker. Again I can't prove anything, but I
speculate that it is possible that the transformer coupled amp sounds best
when the entire secondary winding is used, provided that it is driving the
impedance it wants to see (and the ZEROs do this). Maybe it is because the
feedback loop (if used) is usually not taken off of the 4 ohm tap. Maybe it
is because there is a smaller impedance ratio from a few thousand ohms down
to 16 ohms, rather than down to 4 ohms. Maybe it is only the speaker wire
that becomes a better transfer of music driving 16 ohms instead of 4 ohms.
Audio Research Corp tube
amplifiers typically sound best from their 8 ohm taps. I have many Audio
Research owners (including their own engineers) using the ZEROs to make
their 4 ohm speakers look like 8 ohms, so they can use the better sounding 8
ohm amplifier taps.
Why don't speaker manufactures just make speakers with 16 ohm impedance if
it will make systems sound better.
A 4 ohm speaker will draw
four times more current from a solid state amplifier than from a 16 ohm
speaker at the same volume setting, thus sucking four times more power from
the amplifier (again at a set volume setting). This helps make the speaker
play louder in the showroom when it is going up against competitors. I think
"perceived" efficiency helps sell speakers, and you got to sell them to stay
This has gotten so out of
hand that the speaker industry stopped rating a speakers "efficiency" and
started rating it as speaker "sensitivity", which is how loud a speaker will
play at a given voltage rating no matter how much current (and power) it is
sucking out of the amplifier.
This aspect of the
speaker industry has got to change back. After meeting with and then writing
a letter to the Editor of Stereophile on this issue, John Atikson has noted
in his "Measurements" sections of low impedance speakers, that the speaker
is actually drawing more power than the 1 watt standard. It's a start, so
good for him. Below are three examples:
- July 01, p.65, Martin
Logan Prodigy review:
"....indicates it to be, as specified, basically a 4 ohm load through much
of the audio band. This will mean the speaker will actually draw 2W from
the amplifier from that voltage level, not 1W."
- August 01, p.70, Krell
"However, as shown by its impedance plot, it is a 4 ohm design, drawing 2W
rather than 1W from the partnering amplifier to reach this measured
- August 01, p.79, Audio
Physic Avanti III review:
"...revealed it to a 4 ohm design; ie, it actually draws two watts from
the amplifier to raise the rated sound pressure level."
18 What about Bi-Wiring?
Bi-wiring as an attempt to off load the
speaker cables of the heavy current demands of driving a low impedance
speaker. The ZEROs remove this problem, and make bi-wiring essentially
unnecessary. Yet, I encourage people to try it both ways. First
connect the ZEROs to the amp, and run bi-wires from there to the speakers.
Live with that for a while. Then try connecting the ZEROs to your
speakers, with a single-wire cable from the amp to the ZEROs. Most
likely, you will find having the ZEROs close to the speakers and not
bi-wiring, a better sound.
Who is Paul Speltz and where can I ask more questions?
I'm just a music loving
Electronic Engineer, having fun with my hobby, selling a properly
implemented impedance transforming device that many people are enjoying.
Feel free to contact me with any additional questions at:
or call 651-735-0534