Zed Audio Draconia Parts list manual

Instruction and Installation Manual
MINOTAUR
DRACONIA
DREADNOUGHT
LEVIATHAN
RA
Designed and manufactured in the
United States of America

Index
Introduction Page 1
Myths, Magic and Facts Pages 2 to 16
Setting Controls Page 17
Quality Control Page 18
Installation instructions Pages 19 to 20
Specifications Pages 21 to 25
MINOTAUR Pages 26 to 34
DRACONIA/DREADNOUGHT Pages 35 to 48
LEVIATHAN Pages 49 to 61
RA . . . . Pages 62 to 66
Suggested Systems Page 67
Trouble shooting Page 68
Warranty and Return Policy Pages 69 and 70
Registration Form Page 71
New Products Schedule Page 72

Zed Audio is proud to introduce our third line of innovative mobile amplifiers. The new
products were carefully selected to fill the need of the car audio enthusiasts.
The first is MINOTAUR an all new single channel (mono block) rated at 600w into 4 ohm and
1000w into 2 ohm. This is not your normal “run of the mill” mono block since this is actually a
full range amplifier with some unique features.
DRACONIA is the smaller of the new four channel offerings at 125w x 4 at 4 ohms and
DREADNOUGHT is the “Bad Boy”rated at 250w x 4 at 4 ohms. These amplifiers are suitable
for use in almost any system, small or large.
LEVIATHAN our six channel amplifier has been improved and some of the crossover
frequency selections have been updated.
RA the last of the new products is a remote control/pre amplifier whose features are
dedicated for sub-woofer duty.
Some facts about our amplifiers:
We use only high current large pack TO-247 MOSFETs in the power supplies. These are
superior to the smaller TO-220 packages in their ability to dissipate heat.
The power supplies are fully regulated and so the amplifiers are independent of battery
voltage (>12v).
Low ESR 105 deg C capacitors are used in the power supplies. Additional high frequency
bypass is done with ceramic capacitors (the best choice by far for this application).
High speed (35nsec) rectifier diodes are utilized for the secondary supplies and all low
voltage supplies use Schottky diodes which have zero reverse recovery time.
The main high current power supplies which feed the power amplifiers are choke type for
superior filtering and noise rejection and again low ESR 105 deg C capacitors are used.
All amplifiers feature a two stage power supply for increased efficiency.
New super high speed low noise IC chips are used.
The class D amplifiers utilize the latest generation of low gate charge, high current
MOSFETs.
MINOTAUR is an industry first with a
The pre-amplifiers in all our amplifiers run off independent regulated supplies and drive the
power amplifiers in a full balanced differential mode.
This method of internal connection eliminates ground loops which cause alternator whine.
It also eliminates the need for balanced inputs of which we see many manufacturers using
RCA connectors which were NEVER designed for balanced connection.
Clipping LEDs are featured on all amplifiers.
MINOTAUR has 4 LEDs each spaced at 3dB intervals. (0dB, -3dB, -6dB and -9dB)
All amplifiers which have equalizers use constant Q types for a more precise result.
RCA sockets are solid gold plated machined brass with teflon inserts.
The power connectors accept wire with a diameter of 7mm (0.275”).
Low noise 1% metal film resistors are used in all gain and frequency dependent circuits.
All our amplifiers feature the usual plethora of protection circuits, such as DC, thermal and
short circuit. The short circuit is auto resetting and requires no input from the user.
The ZED logo doubles as a power and a protection indicator, flashing in protect mode and
solid under normal operating conditions.
48dB/octave analog High Pass crossover.
Page 1

MYTHS, MAGIC AND FACTS
Amplifiers: What are they and what do they do?
ALL amplifiers are basically power supplies! This will shock almost all who read this.
Audio amplifiers are really a valve between the power supply and the speaker. This valve
is “instructed” by the incoming audio signal to allow a given amount of the voltage and
current from the power supply to reach the loudspeaker dependent solely on the
amplitude and polarity of the incoming signal. This blows away the pre conceptions of all
who read this of what amplifiers really are. Remember there are two main components in
any amplifier, a power supply which is the sole source of power/energy and the
“amplifier” which channels the power from the power supply by virtue of “commands”
given by the driving audio signal. With this said let’s see what’s cookin’ inside our black
boxes.
So with these facts established, our class A, class B or class D amplifier channels
POWER SUPPLY energy to the speaker but waste a lot or a little energy performing this
feat (depending on the class of amplifier used).
The task of the amplifier is quite simple really. Take the input signal, make it larger in
terms of voltage and supply enough current from the power supply to drive the
loudspeaker. Remember the speaker’s impedance is typically less than 8 ohms and
greater than 1 ohm.
The task of increasing the voltage and current levels to that sufficient to drive a typical
speaker is not difficult at all. The challenging part is how well the amplifier can do this.
The frequency response and phase must be unaltered, and distortion must not be added
to the signal. This of course is impossible to do perfectly but in the past 40 years we have
come a long way and there are many fine amplifiers.
Amplifiers can be of two types, a voltage source or a current source. 99.99% of audio
amplifiers are voltage sources. In other words the amplifier tries to hold its voltage output
constant (assuming a steady signal being a sine wave) no matter what the load
impedance. The ONLY way an amplifier can achieve this is to have zero output
impedance (ie an infinite damping factor) and zero losses in the output stages. The first is
somewhat achievable by introducing positive feedback which in theory will give the
amplifier a NEGATIVE output impedance. Zero losses in the output stages are impossible
to overcome. The prefect output transistor/MOSFET/tube has not yet been invented and
never will be!
A current source amplifier tries to keep the current through the load constant no matter the
load/speaker impedance. Some simple examples on the following page.
Page 2

MYTHS, MAGIC AND FACTS
Let us use a 50w amplifier as our example. We shall assume a lossless output stage and
a perfectly regulated power supply capable of tons of current and enough rail voltage to
supply 8 ohm loads..
The constant voltage amplifier will deliver 14.14 volts across whatever load we present to
it. So at 8 ohms power is 25w, at 4 ohms it is 50w, at 2 ohms 100w...you get the idea so
far?
The constant current amplifier will deliver 14.14 volts across a 4 ohm load (The design
centre point) and this means we are running 3.5 amps through this load and thus the
amplifier delivers 50 watts. OK now let us increase the load to 8 ohms. Cool things
happen. The amplifier will deliver the same 3.5 amps into the 8 ohm load. The power
formula is I x I x R (Current x current x load impedance). A “funny” thing has happened.
The power is now 98 watts, so it has INCREASED from the 4 ohm load (opposite to what
we are accustomed to with constant voltage amplifiers). Well now it is kind of downhill
when we throw on a 2 ohm load. The output is 3.5 x 3.5 x 2 = 24.5 watts!
So what can we conclude from all of this? Well constant current type amplifiers are sort of
distant cousins of tube amplifiers which traditionally have high output impedances. (Think
of taking your amplifier and putting great big 2 to 4 ohm resistor in series with the output).
A constant current amplifier behaves the same.
An interesting idea comes to mind to have a mixture of both constant voltage and
constant current in the same amplifier. Keep your ears and eyes open for some future
product from Zed with this feature.
Amplifiers, be they class A, B or D behave and sound better into higher load impedances
like 6 or 8 ohms. Class A amplifiers buy virtue of their design do behave better at lower
load impedances than the B and D versions but they are not immune to these ills..
This is the first time I bring up low impedance loads and it will not be the last.
The idea of trying to maximize the output power simply because the manufacturer states
that his amplifier can deliver 8.24 Zillion watts into 1 ohm means nothing to us at Zed.
Every one of these monster class D (They generally are not made as class B any longer)
amplifiers has proved to be unreliable and sound just as bad. More about this on the
following pages.
We rate our amplifiers at 2 ohms ONLY because we recognize that firstly 4 ohm speakers
have impedance dips at various frequencies and that as much as we try to steer our
customer to higher impedance loads, there will be a contingent that will insist on the 2
ohm route. We have done design to keep our amplifiers more linear into these 2 ohm
loads however.
Page 3

MYTHS, MAGIC AND FACTS
Class A and class B amplifiers do not have output filters and so the feedback network is
always taken off from the output node of the amplifier. Class D amplifiers have a “monkey
on their backs” in that they ALL have to have an output demodulator filter to get rid of the
high frequency carrier. Class D amplifiers are simply Pulse Width Modulated power
supplies where the modulation is the audio signal. How good or bad they sound depends
on how the whole design is implemented.
Our class D amplifiers are of the self oscillating type which has proved to be simpler and
better sounding than driven types (Where a fixed clock at some high frequency is used as
the carrier). Analogous to FM or AM radio where the signal is transmitted at some high
frequency, your radio picks up this signal (Which contains both the carrier and the audio)
and then finally demodulates ie. Filters out the carrier leaving just the audio.
The absolute vast majority of sub woofer class D amplifiers sold today come from Asia
and they typically use designs from one or two different companies. They all make one
error, their feedback is taken BEFORE the output filter. What does this mean? Quite
simply the deficiencies of the inductor and capacitor in the filter will contaminate the signal
and the response will vary with frequency.
The reactance (AC resistance) of the coil which after all is in series with the speaker is
calculated from this formula Xl = 2 x Pi x F x L.
Xl = Reactance = AC resistance
Pi = 3.14
F = Frequency at which we want to calculate Xl
L = Inductance of the coil.
Simple example: F is 100KHz and L is 150uH (150 micto Henry) typical of these amps.
Xl = 94.2 ohms at 100KHz
Xl = 0.0942 ohms at 100Hz
Xl = 0.0188 ohms at 20Hz.
The 94.2 ohms is great because at 100KHz we want it has high as possible for maximum
rejection of the carrier. However we see in the narrow range from 20Hz to 100Hz is has
varied by a ratio of 5 as to 1. We have not included the simple DC resistance of the coil
which must be added to the 0.0942 and 0.0188 numbers. A typical coil in one of these
amplifiers uses a mean turn length of about 50mm (2”) per turn and may have between 70
to 100 turns of wire. #15 wire (whether made from a single strand or many strands if finer
wire) has a DC resistance of 3.18 ohms per 307 metres (1000’). So we will have about 70
x 2” of wire = 140” = 11.66 feet call it 12 feet for round numbers. Well 12 feet have a DCR
of 0.038 ohms and this does not include the second series coil used in everyone of these
Far Eastern made amplifiers. So giving the benefit of the doubt to the second coil lets give
it a DCR of only 0.002 ohms so our total DCR of wire in SERIES with the speaker is 0.04
ohm. Well now what do we have here?
Page 4

MYTHS, MAGIC AND FACTS
What we have is a big old amplifier with a 0.04 ohm “resistor” in series with the output.
The DCR of the wire on the inductors is absolutely equal to a resistor with regards to
straight DCR. The output impedance of the amplifier is at best 0.04 ohms and this does
not take into account the output stage’s resistance which typically is at least 0.01 to 0.02
ohms. Rounding off let’s go for 0.05 ohms and this is at 20Hz. At 100Hz the value is 0.134
ohms.
Now I am not a big fan of the Damping Factor hoopla. What I object to is the claim of DF
values for these “mega watt” and other class D offerings of 300, 500 and 1000w etc. At
best the is 0.05 + 0.0188 (do not forget the AC impedance of the
coil) = 0.0688 ohms. Divide 4 by 0.0688 and we have a DF of 58 with a 4 ohm load, 29
with a 2 ohm load and just 14.5 with a 1 ohm load. at 4 ohm is 4/0.134 =
29.8, at 2 ohm it is 14.9 and at 1 ohm 7.46....mmm interesting is it not.
As the saying goes, “make my day”. Please read the specifications of all of these
amplifiers and I bet each and everyone will claim massive DF numbers and distortion in
the “double 00’s”. The THD of an uncompensated output filter is quite high.
These Far Eastern class D amplifiers typically use a switching frequency of 100KHz or
less. OK for sub woofer application but useless for full range (20Hz-20KHz) operation.
Unfortunately even at 100KHz one has to use a pretty aggressive filter to attenuate the
carrier. The inductors range from 80 to 200 micro Henry and the capacitors from 22mfd to
220 mfd.
Zed is not the first to use post filter feedback but it solves all of the above issues to a great
degree. Here is what we incorporate. The distortion of the filter is reduced by the feedback
factor and in our amplifiers is typically about 15 times. The DCR of our output inductors is
an order of magnitude lower than the above, even with Draconia having the skinniest wire
we use less turns as our inductors are in the 22-30uH range. We use switching
frequencies close to half a megahertz (500KHz) and so our filter parts are of lower values.
Now any DCR in the inductor is taken care of by the feedback network and so does not
appear as a series resistive element. Our DF values are modest even with reflected
inductor DCR of about 0.002 ohms.
Finally we have low THD as the imperfections of the filter components are almost
eliminated by the feedback being post filter. The frequency response of our class D
amplifiers is flat from less than 10Hz to 25KHz within 0.1dB and less than 2dB down at
55KHz..
DF with 4 ohm at 20Hz
At 100Hz the DF
Page 5

MYTHS, MAGIC AND FACTS
Class B amplifiers can be made more efficient by using some smart power supply
technology. The “enemy” of the class B amplifier is the value of the power supply voltage
required to deliver the specified output for that particular power.
The technologies available are beyond the scope of this manual but more about this issue
Is available on our website at www.zedaudiocorp on the Techtalk link.
Back to our class D (not digital) amplifiers. These, as our analog cousins, are again power
supplies BUT with a difference. They are Pulse Width Modulated (PWM) power supplies
whose reference voltage is the incoming analog signal, ie a variable signal being music or
sine waves which changed the width of the pulses. Sounds nice of course but due to the
fact that the PWM operates at a very high frequency of typically greater than 250KHz in
full range class D amplifiers, we use a reconstructive filter to remove the carrier
frequency.
I would like to find the people who listen to sine waves. I am still looking! We all listen to
music. Well music is transient in nature and the average signal level varies over quite a
wide dynamic range. Thus our cuddly class D amplifier is NOT being driven at its optimum
Please read this paragraph very carefully. When typical bench testing of amplifiers is
performed we generally use sine waves, a quite severe torture test for almost all
amplifiers. The stress on both the power supply and the actual amplifier is far greater than
with music or speech. Typically any amplifier driven to 1/8th of its absolute clipped power
(1% THD) with sine waves, expends the same energy as music driving the amplifier to
occasional clipping. Easy to verify, We use pink noise (Google it and see what it really is)
to simulate music and this proves, at least to us that pink noise driving the amplifier to clip
occasionally is the same as that 1/8th power deal. What this is all about is that the peak to
average ratio of music is between 10 to 15 percent. In other words your 1,000w brand
spanking new mega Dollar amplifier is only a very good 100 to 150w amplifier which is
capable of musical peaks of 1000 watts ASSUMING that just occasional peaks of the
musical waveform are clipped! You have all been duped over the years by the power
issue. Now I must add this: When playing certain types of music there are times where the
musical signal is remarkably similar to those brute force sine waves us engineers like to
use for testing. Pipe organ music, of which I am a fan is one of these. A sustained organ
note drives the amplifier much harder than typical music almost like a sine wave.
Now for another “bombshell”. Class D amplifiers are NOT 90+% efficient as advertised by
pretty much all companies who tout their wares. A well designed class D amplifier will be
90+% efficient based on two conditions. First that the amplifier is driven into some
optimum impedance (typically greater than 2 ohms) and secondly that the amplifier be
driven with a sine wave at just below clipping (typically 1% THD). Mmmmmm well this
now opens a new can of worms, does it not?
Now for another “bombshell”. Class D amplifiers are NOT 90+% efficient as advertised by
pretty much all companies who tout their wares. A well designed class D amplifier will be
90+% efficient based on two conditions. First that the amplifier is driven into some
optimum impedance (typically greater than 2 ohms) and secondly that the amplifier be
driven with a sine wave at just below clipping (typically 1% THD). Mmmmmm well this
now opens a new can of worms, does it not?
Page 6

MYTHS, MAGIC AND FACTS
Output level all the time, in fact very rarely. So referring back to the fact that the average
level is about 10-15% of the maximum or peak power of the amplifier, the efficiency is
substantially lower than the 90+%. Typically with a class D amplifier this figure is around
75% or less which is an order of magnitude better than class B amplifiers. This ability of a
class D amplifier makes it a far more viable choice than class B amplifiers for producing
efficient or green (might I say?) amplifiers.
The impedance of the speaker also determines the point at which the efficiency is
optimized. Well as was said on a famous TV show “FOREGETABOUTIT”, this is a pipe
dream. Speaker’s impedance curves are all over the map and too many car audio buffs
love to drive their megawatt class D amplifiers into low impedances, like 1 and 2 ohms.
Well now that I mention “1 ohm”, I cannot resist getting into this subject. Scenario: Kid (or
middle aged person) buys gizzilion watt amplifier with manufacturer’s specifications of x
watts into 4 ohm, y watts into 2 ohm and z watts into 1 ohm. Well let’s take a wild guess
and I bet you all that the vast majority will drive the amplifier into 1 ohm. Why? Easy, he
feels that he is getting his “moneys worth” by doing this. OK let’s see what reality is. Said
amplifier is maybe rated at say 600w into 4 ohm, 1000w into 2 ohm and 1500w into 1
ohm. We will assume that the speaker impedance is resistive. The difference between the
4 and 2 ohm power is 2.2dB, the difference between the 2 and 1 ohm power is 1.76dB
and the difference between 4 and 1 ohm power is 3.9dB. So what do these numbers tell
us. First if the speaker is 4 ohms vs 2 ohms, no way you can hear any difference. Same
issue comparing 2 as to 1 ohm. I grant you that between 4 and 1 ohm there is almost 4dB
difference BUT at what price and this difference is just percebtible! Two issues. Low
impedance loads affect the amplifier’s sound quality adversely and this is quite easy to
prove. Load an amplifier with a 4 ohm woofer and listen. Add parallel resistors to the
speaker to make the amplifier “think” that it is driving a low impedance speaker and listen
to the difference in sound quality. You will be surprised. This test is not 100% valid in fact
as the resistive loads added, let the amplifier off the hook as the reactive components of
the load are confined to the 4 ohm part. The idea of this test is to keep the loudness about
constant but load down the amplifier.
The average person can just perceive a 3dB (doubling of power) difference and to actually
double the sound pressure on your eardrum, you require TEN TIMES the amplifier power.
Yes TEN TIMES!
The other consequence of driving amplifiers into these ridiculously low impedances is that
the amplifier is stressed substantially more as compared to when driven into more sane
impedances. Efficiency drops as the losses in the output stages increase dramatically
even with “super efficient” class D amplifiers.
It
serves ONLY to boost the ego of the owner of the car so he can quote numbers to his
buddies.
We at Zed are absolutely against these loads of less than 2 ohm.
Page 7

MYTHS, MAGIC AND FACTS
Our design philosophies have been influenced by both the professional and home audio
markets. Traditionally the professional market has been driven by reliability with sound
quality as second. The home market was the reverse. Today however both reliability and
sound quality carry equal weight in both sectors. Cosmetics for obvious reasons are
important in any sector. My experience in designing and building professional amplifiers
has helped me in taking a similar approach in the design of mobile audio amplifiers. No
matter how pretty or good sounding an amplifier may be, if it fails then it is a bad amplifier.
The lesson learned many years ago was “silicon”, and use lots of it. All things being
equal, if an amplifier drive circuit is stable, then adding an output stage (itself stable as
well) with enough power devices will make the amplifier reliable. This assumes of course
that mechanical issues are taken care of. Zed has always been a proponent of using a
generous amount of power transistors in the output stages of our amplifiers. In addition
we design at temperatures of 80 degrees Celsius. All semiconductors must be derated at
these elevated temperatures and we use enough power devices for safe operation into
the lowest load impedance the particular amplifier has been designed to drive.
Cables and others.
Our personal opinion about “fancy” cables and exotic passive components may shock
some of you. I have never been able to hear the difference between a cheap or an
expensive RCA patch cord. My listening has been done using double blind A-B
comparisons. Electrons are not very clever things and they have no knowledge of the type
of material through which they are flowing at the speed of light (312,000 Km/second). The
ONLY reason we recommend high quality double shielded RCA patch cords in mobile
installations is to reject noise. My opinion about speaker cables is the same. As long as
the wire is thick enough, it’s construction makes no difference. As long as the amplifier is
stable into reactive loads with phase angles of up to 60 degrees, the amplifier is none the
wiser what type of speaker cable is used.
The use of teflon, polypropylene, tantalum or other capacitors does not make a good
sounding amplifier. There are too many other variables in the audio chain that one
capacitor can make a difference. The use of metal film resistors is only of use in low noise
circuits and where tolerance is of an issue. Never forget what the music signal had to go
through to get onto your CD or vinyl. The signal began as a micro volt specimen at the
microphone, sent through a high gain pre-amplifier, passed through equalization circuits,
possible compressors, limiters or other processing gear and then mixed with all the other
tracks. In analog days and today still, this signal was sent to a 24 track tape recorder
again through a multitude of transformers, pre-amplifiers, equalizers and yikes the tape
heads themselves. Then the signals were passed back through the tape deck’s playback
circuits including the equalizer for playback, then back into the mixing console for mix-
down to two track and then this was repeated again onto a two track tape recorder, then
sent to the cutting head amplifier where the masters were then cut. A torturous journey
one could say for this fragile audio signal.
Page 8

Page 9
MYTHS, MAGIC AND FACTS
Oh I forgot some facts about cables I would like to mention.
This applies really to home stereo. The typical RCA patchcord cable length from CD
player/Tuner to the pre amplifier is maybe 1.5 metres (4.8’). Even if the capacitance
between the inner conductor and shield is 350pF (Pico Farads) the CD player or tuner
has absolutely ZERO knowledge of this amount of capacitance. The same argument
applies to mobile systems where yes the RCA cables are maybe 5 metres (16’) in length
and typically we use a stronger construction type of cable in the vehicle, the inter-
conductor capacitance is again meaningless.
I measured a 6.5’ length of really cheap RCA-RCA cable and the capacitance was 500pF.
Example: The output impedance of the Head unit is say 1K ohm (On the high side in my
opinion) and together with the cable capacitance of 500pF forms a low pass filter with an
Fo (-3dB) of 318.471KHz! With a more typical output impedance of say 50 ohms this Fo
moves to 636.942KHz. So using a 5m (16’) decent quality well shielded RCA-RCA cable
from the Head to the amplifiers should not cause any high frequency roll off that you can
hear - unless you are a bat of course.
Here are two interesting takes on this issue.
Http://www.mmxpress.com/technical/interconnect_myths.htm
Http://www.audioholics.com/education/cables/skin-effect-relevance-in-speaker-cables
I read an interesting article from a guy “down under”. He makes some interesting claims
concerning cables one of them being that skin effect is audible. It is well known that skin
effect (the tendency of current to flow only on the outside surface of the cable) only occurs
at frequencies above about 100KHz. Now we are not bats (no I do not have a bat as a
pet) and no music gets to 100KHz so the cable companies push this %#@&* to sell to
unsuspecting consumers.
Semiconductors have more tolerance in their specifications than any capacitor or
resistor.
A well known fact is that different types of capacitors work better at certain jobs than
others.
Example, disc ceramic capacitors are better in high frequency compensation circuits
than film types. Film types work better in audio frequency selective circuits than ceramics.
So we at Zed choose our components to suit the application.
Finally this “fetish” that has been thrown around about low ESR 105C capacitors. If you
are looking for long lasting electrolytic capacitors then choose the hideously expensive
10,000 to 15,000 hour types. I have not seen a rational manufacturer using these in a
consumer product. To obtain low ESR (Equivalent Series Resistance) you can use a
single low ESR capacitor OR use a few “regular ESR” types in parallel, the result is the
same. Space restrictions force us to use low ESR types in many places but I have no
aversion to those regular old 85C electrolytic capacitors.

MYTHS, MAGIC AND FACTS
Zed does not recommend the use of power distribution blocks for the purpose of
distributing the +12volt voltage to several amplifiers. The reason is that the vehicle’s
battery is the lowest AC impedance point in the power grid of the vehicle. We want each
amplifier to draw it’s current from this low impedance point. Thus any modulation on any
+12v power cable (which is inevitable) is then shunted to ground by the massive
capacitance of the battery. This is the reason that “star” grounding is used in grounding
circuits/equipment so that ground current is drawn from a common point and thus no
ground loop can occur. Fortunately for us, the body of a vehicle made of steel is so large,
and is thus a very low impedance path for ground currents, that it is not necessary to
ground all equipment at one point. In fact we do not advocate it at all as this would then
necessitate the head unit’s ground running all the way to the battery location and the
amplifier’s ground(s) also running all the way to the battery.
If multiple amplifiers are being used we highly recommend the use of separate ground
points at the amplifiers’ location. This spreads out the amount of current being drawn
through one bolt connection.
However we do recognize the impractical issues of running separate +12v wires to the
battery and so of course accept that distribution blocks will be used.
Stiffening capacitors. These are of NO use with our amplifiers due to the fact that
We utilize fully regulated power supplies. The power supplies will compensate
for small volt drops which exist on the +12v power cable. The amount of current drawn by
a particular amplifier would drain a fully charged 1 Farad capacitor almost instantly.
Consider the theory:
Energy(Joules) = Power(Watts) x Time(Seconds). The energy in a 1 Farad capacitor =
0.5CV.V= 0.5x1x12x12= 72 Joules. Let us assume an amplifier such as MINOTAUR. Let
us assume that we are playing it such that the amplifier(into a 4 ohm load) is just clipping
on the loudest musical peaks. This means that we are delivering 500 watts on peaks. The
amplifier’s average efficiency is about 75%. The peak to average power ratio is about
10% so average power is 10% of 500 = 50 watts. The input power is therefore 66 watts. If
the 1 Farad capacitor was charged to 12 volt and we remove the main source of power --
the battery, the amp would remain playing for 1.075 seconds! (Put the numbers in the
formula (E=PxT above and solve for time T). Now compare this to the battery. The
amplifier will play for some hours (depends on actual battery of course) as compared to
1.075 seconds! So what good is a 1 Farad capacitor?
Power cables - Owing to the high efficiency of our amplifiers, #8 wire is sufficient for a 5
metre run from the battery to the amplifier. If a distribution block is used with multiple
amplifiers, then #4 wire from the battery to the block is required. From the distribution
block to each amplifier again #8 is all that is required.
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MYTHS, MAGIC AND FACTS
Damping Factor - This amplifier specification has been blown out of all proportion. What
it means is the ability of the amplifier to resist a change in it’s output voltage. The formula
is DF= Speaker Z / Amplifier output Z (where Z is impedance). So many manufacturers
have claimed ridiculous, and often false damping factors. A damping factor of 1000
implies that the output impedance of the amplifier is 0.004 ohms (4 ohm load). The only
way to attain this figure is to apply masses of negative feedback (or use positive
feedback) and too much feedback makes amplifiers sound harsh and clinical. Also
damping factor changes with frequency. The lower the frequency the higher the DF
number. Typically the DF can be ten times larger at higher frequencies.
Let us take this amplifier whose output impedance is 0.004 ohms (Zout). The speaker
circuit is a series circuit and the following impedances(resistances) are in series with this
0.004 ohms. Let us assume that this DF measurement was made at the amplifier’s
speaker terminal. The first extra contact resistance is the speaker wire to the speaker
terminal (WT ohms). Then there is that of the wire itself for two conductors (W). Next is
the contact resistance of the wire to the speaker terminal (WS). Next there is the contact
resistance of the wire from the speaker terminal to the voice coil (WV) and lastly there is
the DC resistance of the voice coil itself (DCR). So what we have is a series circuit with
the following resistances in series and adding up. WT+W+WS+WV+DCR+Zout.
WT,W,WS,WV and Zout are very small indeed. Certainly less than 0.1 ohms. Whoa, look
what has happened the EFFECTIVE DAMPING FACTOR has been reduced from 1000 to
40 by just taking into account those pesky unavoidable contact resistances. Now for the
cruncher, remember that the DCR is also in series and is typically 3.2 ohms for a nominal
4 ohm speaker. So we must add 0.1+3.2 = 3.3 ohms and now EFFECTIVE DAMPING
FACTOR is now a magnificent 1.212! (4 divided by 3.3)This is the real world. We see that
the DCR of the speaker swamps all other resistances in the speaker circuit and the 0.004
ohms amplifier output impedance is almost meaningless. It has been found that a DF of
about 20 is quite sufficient to dampen the voltage spikes from the speaker. An eye opener
this one is it not? Good tube amps sound marvelous - low damping factors!!
Output Power of Amplifiers - This spec has been so badly abused it is not even funny.
Peak power, Maximum power, Transient power, RMS power these are titles that have
been given to the power spec of amplifiers. The above all mean nothing. Peak power
needs to be associated with a time period, Maximum power is just nonsense, Transient
power is even more nonsense and . The ONLY
meaningful way to specify an amplifier’s output power in watts is CONTINUOUS POWER.
The formula for power is: (RMS volts x RMS amps) or (RMS volts x RMS
volts/Impedance) or (RMS amps x RMS amps x Impedance). In each of these formulae
there is an RMS number multiplied by another RMS number (or by itself) and RMS x RMS
cannot = RMS. RMS means
root mean square and it is the same as saying 4 x 4 = 4 Which we know is not true.
The answer is just 4 with no root sign attached.
RMS power is just not a specification
So THERE IS SIMPLY NO SUCH THING AS RMS POWER.
Page 11

MYTHS, MAGIC AND FACTS
Bridging two channels of an amplifier is not a magical thing. Most are mystified by the
power figures quoted under the “bridge” column. It is actually very simple. When two
channels are driving a common load, one channel is out of phase with the other by 180
degrees. So when one channel swings positive the other swings negative. There is a
catch however. Each channel “sees” fifty percent of the common load and that means that
each channel of the bridged pair must be capable of delivering current to this lower load
impedance. Thus a 4 ohm bridged load presents a 2 ohm load to each of the bridged
channels. The power into a 4 ohm load in bridged mode is twice the rated 2 ohm power
per channel, the reason is that the power supply voltage is effectively doubled when two
channels are bridged.
Harmonic Distortion - This specification has for years been a benchmark with which to
compare one amplifier to another. This is all fine on the test bench where pure resistive
loads are used and sinewaves are amplified. Unfortunately it tells us very little about the
audible performance of an amplifier. Today it is relatively easy to build an amplifier with
THD figures in the “triple oh” region, but what do they sound like. Normally not very good.
To obtain these low THD numbers all we do is design an amplifier with high open loop
gain. That is before negative feedback is applied. Once we apply a lot of global feedback,
we improve all measured parameters such as THD, Noise, Frequency response and
Damping factor. Our class B amplifiers are designed a little differently. We use very little
global feedback but rather optimize each stage with local feedback. This allows us to
design an amplifier with lower open loop gain and thus we only have to apply about 8dB of
global feedback. Ultra low THD was not our goal but rather an amplifier which sounds the
way we want it to. Other factors affect THD such as PCB layout, grounding and power
distribution to the amplifier channels. Our class B amplifiers do however achieve very low
distortion due to the fact that we follow the “rules” and their circuit design is conducive to
low distortion. Class D amplifiers operate somewhat differently to Class B types.
Headroom
This term does not refer to how much room there is above your head! Rather it is a
specification that signifies how good or bad the power supply is. Zed Audio has NEVER
quoted a headroom specification. Why you may ask? Simple our amplifiers have no
headroom, zero dB, zip dB, nada dB however you say it. A regulated power supply does
not allow the amplifier to have any headroom. A quote from a well respected designer who
said that amplifiers with many dB of headroom simply have poorly designed power
supplies, either through ignorance or to save costs. When one sees a specification of an
amplifier quoting a headroom figure of 3dB this means that the droop of the power supply
is such that when unloaded it is capable of twice the power as compared to it’s loaded
condition.
Page 12

MYTHS, MAGIC AND FACTS
Headroom - continued.
So a 100w/ch amplifier running into 4 ohms must develop 20 volts across the speaker
terminal. This requires a net (under load) rail voltage of about +/- 33 volts. Now for it to
have 3dB of headroom it must be capable of delivering 28.28 volts across the speaker
terminal. This requires a rail voltage of +/- 43 volts. So the above power supply will droop
a total of +/- 10 volts (a 23% droop!). This puts additional stress on the output devices
(Mosfets or Bipolars) because they still have to deal with this higher rail voltage . To us
this kind of power supply sounds like the amplifier is “breathing” and not the kind of
amplifier we want to listen to. Regulated power supplies are more expensive to
manufacture, are less efficient but we feel those are tradeoffs we can live with!
If one examines the specifications of an amplifier, it is relatively easy to tell apart those
With well regulated power supplies and those with sloppy unregulated power supplies.
The ratio of 4 ohm as to 2 ohm power will readily inform us of the quality of that power
supply. Typically if the amplifier can double or almost double it’s continuous power rating
from 4 ohm to 2 ohm at ALL battery voltages this is indicative of a well regulated power
supply. There are a few manufacturers who manipulate the rail voltages at lower speaker
impedances so that the 4,2 and 1 ohm power specs are the same. We believe that this is
a cop out to save putting in a beefy power supply which is capable of the higher currents
needed for these low impedance loads.
Fusing of amplifiers. Of all the amplifiers which we see at Zed, less than “5%” have
correctly rated fuses installed. These are non Zed manufactured amplifiers. The result of
this over fusing practice is that the power devices and printed circuit card burn up and
save the fuse (Ever heard of Murphy’s Law)?
During the past year we have done quite a bit of testing with regards to how large a fuse is
required. The rating of the fuse is dependent on two things, the impedance of the
speakers and how long and how loud the music is to be played. The average power is
about 10-15% of the maximum peaks. So add up all the channels and multiply by the
power per channel. Divide this by 0.3 for an average efficiency of 30%. Let’s divide this by
say 5 (20% average to peak ratio for some fudge factor) and this number divide by 12.
Example: A 100 watt x 4 at 4 ohms amplifier. We will assume that we will be playing it so
musical peaks reach 100w/ch. Okay so 100 x 4 = 400. Divide by 0.3 = 1333 Divide by 5 =
266 and divide this by 12 = 22 amps. Use a 25 or 30 amp fuse.
Putting a 100 or 150 amp fuse * on an amplifier is useless. That guy Murphy says the
amplifier will burn up to protect the fuse..... And it will.
* Of course very powerful amplifiers >2Kw require large fuses.
Page 13

MYTHS, MAGIC AND FACTS
Subsonic filters and CLIPPING. The former are simply steep slope high pass filters with a
frequency range between 10 to 50Hz. Their only function is to filter out those frequencies
which lie below audibility. The woofer’s cone will not “flop” around as it does without the
use of the filter and because all the low frequency energy that we cannot hear is filtered
out, the amplifier runs more efficiently since it does not have to amplify all those inaudible
low frequencies. Remember one fact, ALL amplifiers are pretty dumb. They will amplify
anything you put into them (assuming the amplifier’s frequency response is wide enough)
and whether we can hear a particular frequency range is not the amplifier’s concern. Put
in an inaudible frequency and the amplifier dutifully does it’s thing. It does not care about
the load. This is why tweeters are easily burnt when amplifiers are clipping. The amplifier
generates high frequency harmonics and this energy is thrown to the unsuspecting
tweeter. When an amplifier is driven into clipping it basically generates a square wave.
This contains a large amount of energy but also due to the fact that the square wave sits
at a positive (or negative) state for a “long” period of time, the natural cooling effect of a
continuously moving cone/voice coil is inhibited and can lead to failure of a speaker.
Typically woofers are more tolerant of clipped power than mids and tweeters due to the
fact that they are more robust and that they do not respond to those high frequency
harmonics very well (but do not be fooled, woofers can be hurt by these harmonics even if
we cannot hear them). The inductive reactance is (2 x 3.14 x freq x inductance) and so
the higher the frequency the higher the inductive reactance of the speaker becomes.
However it’s DCR does not change with frequency.
A quick point about the term DCR (resistance at DC). I believe that this term was coined
because we all use a meter which operates with batteries and we measure the simple
resistance of a resistor or piece of wire with this meter. We take this measurement at a
frequency which is low enough so that if we increased the measurement time the result
would be the same. So using an ohm meter which works at say 50Hz would yield the
same result as long as the measured part has no AC reactive component.
Page 14

The following pages show some interesting facts
about sound, hearing issues, power and most of all
dispel many of the ill gained facts in the car audio
industry.
DECIBELS (dB) POWER RATIO VOLTAGE RATIO
0.5 1.12 1.06
0.7 1.17 1.08
4.0 2.5 1.58
5.0 3.16 1.78
6.0 4.0 2.0
Perceptions of Increase in Decibel level
5dB Quite Noticeable change
PLEASE LISTEN TO YOUR MUSIC RESPONSIBLY - ONLY 1 SET
OF EARS IS GIVEN TO US.
1.0 1.26 1.12
1dB Imperceptible change
So as we can see a 1dB change in power results in a power increase of 26%which is
absolutely inaudible. The 100w amplifier as compared to 125w - NO difference, or a 500w
as compared to 625w, again NO difference.
2.0 1.58 1.26
2dB Imperceptible change
2dB power increase a similar result where the power increase is 58%! The 100w as
compared to the 158w amplifier again nothing.
3.0 2.0 1.414
3dB Barely Perceptible change
At a 3dB power increase (doubling the power) we have a barely perceptible change. So
upgrading that 100w to a 200w amplifier is just barely audible in terms of loudness.
10.0 10.0 3.16
10dB Twice as loud
Now a 10dB power increase (10 times the power) results in a doubling of sound pressure
on your ear drum.
20.0 100 10.0
20dB Approximately four times as loud
Page 15

Page 16

Setting the controls on amplifiers
evel control - This control is the most misunderstood control on any amplifier. It’s sole
Lpurpose in life is to level match the head unit’s output voltage to the gain structure of
the amplifier so that the user can use the head unit’s volume control in the “best
physiological position”. To best understand this let us look at a simple example. Assume
that the head unit is rated at 1 volt output. Now what this means is rather ambiguous.
Does the head deliver 1volt with the volume control at maximum, at 75% or where?
Unfortunately no head manufacturers supply this information. Also it depends on the
modulation level of the program material. Be it a CD/Mini Disc or FM we have no control
of this specification. Most consumers never want the volume control to be turned past 3
o’clock (We use a traditional rotary control for reference since all digital controls do not
have the same amount of digits or “little blocks” on their LCD displays to show relative
volume level). On head units which we have tested the results are all over the page so we
shall assume the 3 o’clock position as the maximum we want the control to be turned to.
So far you can see that the need for level matching is critical indeed as there are no
standards from head manufacturers. So we now have this 1 volt level. What this means is
that the output voltage from the head will approach 1 volt on musical peaks. Let assume
we have an amplifier of 100 watts. This implies that we can deliver 20 volts across a 4
ohm load. Let us assume that the amplifier needs 1 volt in for the 20 volt out - a gain
structure of 20x. So in this case with the head delivering 1 volt on peaks, the amplifier will
deliver 100 watts into 4 ohms on the same musical peaks. Well this sounds all well and
good but we have a small problem and it is that all heads are not rated at 1 volt, and all
amplifiers have variable level controls. This actually means we can change the gain
structure of the amplifiers from “x” to “y”. With no standard levels we have to set the level
control on the amplifier to “match” to that of the head. We have tested no head units
whose output level corresponds with that of the printed specifications. Typically the output
level is substantially lower than the specification. Here is our recommendation. With your
favorite music playing set the amplifier’s level control to minimum (CCW) and set the
head unit’s volume control to 3 o’clock. Assuming all crossover controls have been set,
advance the level control on the amplifier until the music is as loud as desired. This is the
only way to do this without the use of an oscilloscope. In multi way systems begin with the
low frequency amplifier, set its level to a point where the bass is as loud as you want it,
turn back the Hu’s volume to a sane level, then repeat the level adjusting process on the
midrange and tweeter amplifiers. You will have to tweak these level controls again several
times to attain a good balance between the various amplifiers.
rossover and equalizer controls - The crossover controls must be set to suit the
Cspeakers being used.
The equalizer controls can be set by ear or with instruments. This is a personal
preference. Most users only have ears (duh) and not instruments so ears must suffice!
Page 17

Quality control (QC) is a process which begins from the first designs entered into a
computer and then never ends.
Zed is continually striving to improve the products which we design and manufacture.
All our semiconductors are purchased from either the manufacturer direct or through
reputable distributors. Electrolytic capacitors which have the highest long term failure rate
of any component are chosen for their durability and sonic qualities.
Each and every product manufactured at Zed is tested using Audio Precision test
equipment. Software is written for each type of amplifier and then on final test the
amplifier must pass these rigorous tests.
If not it is rejected and returned to the production line
for repair. Samples are pulled from the line for further testing.
Mechanical inspection is done throughout the manufacturing process. Before each
amplifier is packed it is fully inspected again for any cosmetic flaws. Any damaged or
any part which is out of specification is replaced.
Zed takes pride in what we design and manufacture and we trust that this shows in the
final product.
Stephen Mantz
Page 18