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.

2) 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.

3)) 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.

4) 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 possible:

http://www.paulspeltz.com/zero/group1.jpg

http://www.paulspeltz.com/zero/group2.jpg

http://www.paulspeltz.com/zero/group3.jpg

5)) 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.

6) 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.

7) 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.

8) 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.

9) The ZEROs don't sound quite right. What should I do?

• A) Make sure they are wired properly.
• B) Let them fully break-in.   
• C) Run them overnight with a demagnetizing sweep CD.
• D) You might need to re-adjust the speaker placement after adding the ZEROs.
• E) The 2x setting is the most commonly used. Run them a long time at 2x. This way you can get very familiar with the sound. After a few weeks remove the ZEROs. That will give you a good feel for what the ZEROs are doing. Some people don't realize the improvement until they have fully broken in, and then are removed from the system.

• F) There is a small chance your system is a candidate for running the ZEROs backwards.

10) 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.

-Divide speaker's impedance by 2 = YELLOW (+) & BLUE (-) to Speaker (ie. 8 ohm speaker becomes 4 ohms)

-Divide speaker's impedance by 3 = YELLOW (+) & BROWN (-) to Speaker 

-Divide speaker's 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: www.otlamp.com/articles/tomcik/index.html

11) 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.

12) What is the difference between the ZEROs autoformer and a typical tube amplifier's transformer?

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.

13) 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 component.

14) 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.

15) 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:

1. They virtually eliminate the three most common sources that give speaker cable their sonic signature.
2. The solid core wire eliminates the complex conductive and magnetic interaction that happens between the many individual strands of stranded wire.
3. Keeping each lead separate eliminates the magnetic fields of the leads from interacting with each other.
4. 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 releases energy.

16) 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.

17) 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 in business. 

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:

1. 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." 
2. August 01, p.70, Krell LAT-1 review:
   "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 sensitivity." 
3. 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. 

19) 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: paulspeltz@hotmail.com or call 651-735-0534

Enjoy, Paul