This article deals with the field of surveillance. In this article the author performs a product review of the various General Purpose Amplifiers, whos purpose will be discussed below. The intent of this article is to make you aware of the various models of such units from different manufacturers as well as the prices of such units. In addition, each unit will be reviewd for quality and usefullness.
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Revision 2 Product Review and
1 January 1996 Technical Analysis of
General Purpose Amplifiers
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Written by: Alan Hoffman
(a.k.a. -Q-)
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FOREWORD:
This article deals with the field of surveillance. In this article
I will be doing a product review of the various General Purpose
Amplifiers, whos purpose will be discussed below. The intent of this
article is to make you aware of the various models of such units
from different manufacturers as well as the prices of such units.
In addition, each unit will be reviewd for quality and usefullness.
The author writes a variety product reviews on a quarterly basis.
In my reviews, I cover all types of products used in the field of
surveillance and countermeasures. Prodct reviews include: audio
surveillance, video surveillance, countermeasures (TSCM), data
interception surveillance, and occasionally I review Quick-Entry
tools for locksmithing. All articles are updated on a quarterly
basis. Read end of this document for instructions on getting on
the authors mailing list.
-------------------------------------------------------
GENERAL PURPOSE AMPLIFIERS:
A General Purpose Amplifier, often abbreviated as a G.P. Amp
in surveillance lingo,is designed to amplify sound for audio
intercept purposes. GP-Amps are of course not limited to use
by surveillance and countermeasures technicians, but for the
purposes of this article we shall try to stick to that topic.
GP-Amps are not much different than any other type of amplifier
which you can purchase at various electronics outlets, insofar
as their main function it to amplify audio. However, GP-Amps
very often are specifically tailor made for surveillance appli-
cations.Many of the better units have various adjustable notch-
filters to eliminate low-frequency sounds such as vibrations.
In addition, some of the better GP-Amps have impedence switches
on their imput and output jacks so you can interface the ampli-
fier with various other types of surveillance tools including
contact, spike, tube, strap or clip microphones, as well as
recordering systems or transmitters.
What Is The Purpose Of A GP-Amp?
As mention before, its main purpose is to amplify sound for purposes
of audio interception during surveillance applications. However, by
no means is that its only purpose. So lets just take a brief look at
some various uses of General Purpose Amplifiers.
Surveillance Applications:
(1) Listening to conversations through walls, floors, ceilings, glass.
(2) Listening to conversations in adjacent rooms in a structure via
picking up sound vibrations in the plumbing.
(3) Listening to conversations in adjacent rooms in a structure in which
the sound waves travel through metal air ducts.
(4) GP-Amps have ceartain uses in TSCM (Technical Surveillance Counter
Measures) (often referred to as "bug sweeping"). Also usefull for
ensuring COMSEC (COMmunications SECurity). While performing a COMSEC
survey the technician determines if a room is vulnerable to
eavesdropping by measuring audio leakage.
Other Miscellaneous Applications:
(1) Counter-Terrorism squads have used GP-Amps to listen-in on airplane
hijackers for the purposes of intelligence collection to aid
the entry team in its task of eliminating the terrorists during
a tactical penetration.
(2) Bomb Squads or EOD (Explosive Ordinance Disposal) often uses GP-Amps
to examine suspicious packages (potential bombs) for mechanical
or electrical timing or detonation mechanisms.
(3) Plumbers could use a GP-Amps to hear potential water leaks very easily
in pipes or in hot water heating or furnace units wheras the pipe
itself is not readily accessible for physical inspection.
(4) A naturalist could use a GP-Amp to hear rhodents, even insects possibly
burrowing underground when attached to a spike microphone.
(5) Exterminators often use GP-Amps to listen to termites burrowing in
the wood in your walls of your house or building.
(6) Farmers may find it usefull to detect various insects located in grain
storage bins, etc..
(7) Rescue workers, police, firemen can utilize this unit to help locate
people buried under collapsed structures.
(8) Geologists could use a GP-Amp for geological surveys by listening to
various sounds underground occuring through natural anomolies.
So as you can see, GP-Amps have many legitimate purposes, and arent
necessarily just tools for eavesdropping. Before I begin my review
of GP-Amps, I would like to quickly introduce a few more terms as
well as briefly discussing how a GP-Amp works.
Through Wall Listening Device- This is a term which is somewhat symoymous
with a GP-Amp. The difference mainly, is
that when you refer to the device in this
manner it usually implies that you want to
use the GP-Amp specifically for eavesdropping
through walls, floors, ceilings, etc..
Mic- Pronounced "Mike". This is a generic electronic industry term for the
word microphone. It can also be abbreviated as "mike" or "mik", etc..
How Do GP-Amps Work?
A General Purpose Amplifier (or through wall listening device)
usually consists of 2 or 3 seperate units.
(1) Microphone Unit: The microphone is the device which collects the sound
in the form of vibrations or pressure waves which resonate
either through the air or through a solid mass. These
vibrations are then converted by the microphone into
audio modulated electric impulses. Their are dozens
of different types of microphones (discussed earlier
in this chapter) which may be used with through-wall
listening units. Each microphone has a specific purpose
for a particular task. The following are the most common.
A. Contact Microphones- A contact mike is a sensitive microphone
utilizing a unique principal that receives
for vibrations rather than sound pressure
waves. It usually consists of a piece of
piezoelectric material that produces an
electric current that is modulated by
vibrations caused by audio. The contact
microphone is coupled to a powerfull
handheld amplifier either as an integral or
seperate unit. Contact microphones can
clearly pick up a voice through up to 12
inches of concrete or 3 inches of solid wood.
[a] Contact mics- Presses up against the wall, or attaches to
glass and is held in place by light double
sides adhesive tape. Also can be placed in
air ducts, etc..
[b] Clip mics- Clip mics are basically the same as contact
mics, only they literally can be clipped onto
a surface. They are not all that usefull, but
in rare cases they could be handy.
[c] Stud mics- A stud microphone is the cheapest and poorest
quality of all the various models. It simply
consists of a small plastic 'stud' which is
similar to a very tiny nail. The stud mic is
often built into very poor quality through
wall listening devices. You push the GP-Amp
against the wall, and the build in 'stud-mic'
makes contact with the wall picking up sound
vibrations.
[d] Strap mics- Strap mics are velcro type bands which can be
wrapped around a small plumbing pipe and can
intercept audio from adjoining rooms by sensing
the vibrations in the water/radiator pipe.
B. Spike Microphones-A spike microphone consist of a supersensitive
crystal or electret microphone, and is coupled
to a 2 to 12 inch metal spike. This metal spike
is driven into the wall or the ground and picks
up resonations from the wall very clearly. The
audio signal from the microphone is then fed
into a powerfull handheld amplifier.
C. Tube Microphones- A tube microphone consists of a small 2 to 12
inch hollow metal tube approximately 1/8th to
1/4 inch of an inch in diameter. The tube
microphone is placed into a hole in the wall
or through an air duct etc. and picks up
sounds coming from directly in front of it.
The sound resonates inside the small diameter
tube and is amplified by resonation. The audio
then reaches a sensitive microphone on one end
of the tube. The electric signal from the
microphone is then amplified by a powerfull
handheld amplifier.
(2) General Purpose Amplifier: This is the actual amplifier unit.
GP-Amps vary in quality. Some have a very high amplification
power, yet a very poor sound quality, others have great
sound clarity but poor sound aplification. Yet others have
many features, and some have very few features. The key is
to pick a general purpose amplifier with the features
that you want. In my article I will attempt to review the
quality of each unit and briefly discuss its features.
Some GP-Amps have a built in contact microphone, others
require a seperate microphone. It is always best to
purchase a unit which requires a seperate microphone, as
the microphone is probably the most important part of
the device, more important even perhaps than the GP-Amp
itself.. Usually the cheap (read: low-quality) units
will have a built in 'contact' or 'stud' microphone.
(3) Filters, Equalizers, Audio Enhancement Units: This is an optional
category. You really do not need equalizers or notch filters
or sound enhancement utilities. These options can be attached
to the GP-Amp itself through the output jack, or usually
you will record an intercepted conversation onto a high
quality audio tape (DAT or 1 inch tape), then you can run
the audiotape through the laboratory later and 'clean'
it up using audio filters and enhancement devices to make
the sound more clear. This is really only usefull for
law enforcement purposes wheras you need an audiotape
which is as 'clean' as possible so that a judge or jury may
readily identify somebodies voice. Such devices may also
be necessary if you have a particularly large amount of
extemoraneous background noise on the recording which may
be caused by vibrations in the building.
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PRODUCT TESTING:
Please Note: I have reviewed most of these items myself, however I
have not personally review each and every one of them. In several
instances I relied upon 2nd hand accounts from people that I know
own such units, and they have reported to me their opinions on
the device, and I base some of my findings on their opinions.
The reason I did not personally test all of the units on the list
is quite clear... MONEY... These units cost in excess of $200 to
$500 each, and obviously for all 18 seperate units which I have
done a review of, that would cost me at least $6,000 to purcahse
each and every unit. On occasion, the manufacturer will allow me
to 'borrow' the unit for testing purposes, since I have a working
relation with several of these companies. However that is not always
the case.
You might also notice that on some of the products I did not list the
name of the manufacturer. This is because I simply do not know who
manufactures the unit. Finding the manufacturer is not the easy task
that it appears to be. Many companies take the manufacturers unit and
stick their label on it so you never really know who the real manufacturer
of the product is.. This is true for many of the products including the
SM-11 and SM-33 which really are Lorraine Electronics units which some
other unscrupulous company slapped their label on it. In addition, many
catalogs from small mail order "spy shops" do not readily list the manuf-
acturer. I find this to be a reprehensible and slightly sleazy business
practice. These small mail order catalog companies seem to be afraid that
if they list the manufacturer, that the customer will go right to the
source instead of buying from them (which may be true).
Please Note: That up to this point, I have not yet done a THOROUGH
technical review of these units. To do so is extremely
complicated, and involves oscilliscopes, and well, all
kinds of other fancy equipment. In this review I have
based all my findings on my personal opinion and that
of others. In other words, I did my review quite lite-
rally "by ear". I observed which units "sounded" the
loudest and clearest. Starting in Revision 3, I will
do an actual technical review giving more precise
measurements such as clarity and path loss, and dBgain.
-------------------------------------------------------
Ratings Measurements
'Star'
Rating Amplification Sound Clarity
------ ------------- -------------
**** Extremely Powerfull Very Good Clarity
*** High Power Good Clarity
** Medium Power Fair Clarity
* Low Power Very Poor Clarity
Technical Note- In order to perform the test uniformly, I used the
Illiads S-2203G Square Contact Microphone. I have
found this contact mic to be the best all around
mic for a reasonable price. It has a very high
audio gain, and produces very clear audio.
(NOTE: Some units I had to use an impedance matching
device on the input because some amps were
made for a specific impedence mic. Beware of
this fact before purchasing any specifi unit.)
I performed this test under a variety of conditions
including through walls, and through an air duct.
To do the testing, I placed a Tone Generator in an
adjacent room. The tone generator was hooked to a
small amplifier, which produced an audio level
equivelant to about the decibal level of human talking.
I then observed the clarity and made my second set of
measurements. In my second test, I simply played an
audio cassette with music, again it was set at around
the level of human speech, and I then measured the
clarity of the intercepted conversation with each and
every model (excluding the ones which were tested by
other individuals).
The wall which I made my measurements from consisted of
2 layers of 3/4 inch drywall (sheetrock).. 3/4 Inches is
the 2nd thickest sheetrock available for your reference.
(I think 5/8th's is the thickest, but the difference
between the two is negligible). Many of these units are
even potentially capable of listening through concrete
cinder blocks (6 inches), or 4 inches of solid concrete.
NOTE: You can take note that many spy shops and mail-order
catalogs quite often claim that their unit can intercept
sound through up to 30 centimetes (12 inches) of concrete.
I will have to tell you right now, that those figures are
GREATLY exxagerated. It isnt so much how thick the barrier
is, but how well the barrier conducts or absorbs sound.
In ceartain cases you can hear through up to over 30
centimeters of barrier, and with other substances, you
may only have the ability to listen through 8 centimeters.
If you wanted to listen through a really thick wall,then
you would have to utilize another type of microphone
system such as a spike microphone. Using a spike mic
entails boring a tiny (1/16th) inch wide hole into the
wall using a high speed silent drill or a reamer. The
hole should come very close to the adjacent wall, but
care should not be taken not to let the hole penetrate
through the other side. The spike mic is then inserted
into the hole in the wall.
-------------------------------------------------------
PRODUCT REVIEW:
Model : Ear-200 (Electro Acoustic Receiver-200)
Manufacturer : Research Electronics Inc. (R.E.I.) (Made in the U.S.A.)
Approx Price : $120 - $300 (price fluctuates dependant on reseller).
Size (englsh) : 2.4" x 3.8" x 1.2" (120 grams)
Amplification : *** High Power
Sound Clarity : * Very Poor Clarity (with built-in 'stud' mic)
Input Jack : Yes
Output Jack : Yes
Addtl Comments: Most popular 'through-wall' listening device currently sold
in the United States. Manufactured by a very reputable
company. Although the unit does not have the greatest
amplification power or clarity, it nevertheless should be
considered a top choice if your are looking to buy one of
these amplifier units. The unit has 2 seperate output jacks.
The only area which I find it seriously lacking is that it
does not have a seperate 'input' jack so that the user can
plug in a microphone of his choice.
Model : WCA (Wall Contact Amplifier) / SM-33
Manufacturer : Lorraine Electronics / Ruby Electronics Ltd. (British)
Approx Price : $185 - $200
Size (metric) : 82 x 50 x 21mm
Amplification : *** High Power
Sound Clarity : *** Good Clarity
Input Jack : Yes
Output Jack : Yes
Addtl Comments: High quality unit in all respects packaged into a small
compact durable metal case. The one area this unit lacks
is in its availability in the United States. However. the
unit is often resold in the USA as the "SM-33 Concrete
Microphone". I do not believe that their is any difference
whatsoever between the actual Lorraine WCA and the SM-33
but I could of course be wrong.
Model : Ruby Suction / SM-11
Manufacturer : Lorraine Electronics / Ruby Electronics Ltd. (British)
Approx Price : $150 - $200
Size (metric) : Unknown
Amplification : ** Medium Power
Sound Clarity : * Very Poor Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: Despite the fact that this unit is manufactured by Ruby
Electronics, it is nevertheless one of the worst units
on the market. The developers of this unit probably had
good intentions when designing the unit, however what looks
good on the drawing board does not always work well in the
real world, which is obviously the case with this unit.
This unit consists of a large suction cup with the contact
microphone built into the aforemention that sticks to the
wall. The problem is obvious.. It never sticks to the wall!
Even on a smooth surface such as glass, the unit seems to
lose its suction and detach itself after a few minutes time.
Thusly, the unit is useless for real world applications.
NOTE: A bit of advice.. Whenever trying to adhere a suction
cup to the wall, adding a bit of water always seems to help
create a 'seal' and to increase the vacume and thus the
suction. However, that trick did not do much for this
unit as it fell off anyway even with the water added.
Model : CM-8 (Concrete Microphone)
Manufacturer : CONY Manufacturing Company (Japan)
Approx Price : $100
Size (metric) : 67 x 50 x 20mm
Amplification : ** Medium Power
Sound Clarity : *** Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: This unit gets my vote for one of the best quality units
for a reasonable price currently on the market. The device
is manufactured by CONY MANUFACTURING company, which is
Japans premiere supplier of low grade 'bugs' which are often
resold in american 'spy shops'. The only problem with this
particular unit is the fact that it is not available on the
american market through any companies to the authors
knowledge. If you want it. You have to get it directly
through CONY. (They do accept US funds).
Model : T-1201
Manufacturer : Illiadis Corporation (Made in the U.S.A.)
Approx Price : $100
Size (metric) : Unknown
Amplification : ** Medium Power
Sound Clarity : *** Good Clairity
Input Jack : Yes
Output Jack : Yes
Extra Features: The author has not personally used this unit, however I
have relied upon the results of somebody who has used
this unit, and it seems he holds this unit in high
ragards. The tester of this unit, claimed that the T-1201
worked slightly better than CONYs' CM-8 gp-amp, and sells
for the same exact price of around $100 (US funds). I cannot
verify the quality for myself since I have not tested the
unit at this time. I will check it out and if it is true,
I will add this unit to my list of best units to buy while
on a budget [see below for that list].
Model : USI
Manufacturer : USI Corporation (Made in the U.S.A.)
Approx Price : $150
Size (metric) : (Unknown) approx. size of cigarette pack.
Amplification : * Low Power
Sound Clarity : ** Fair Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: I havent tested this unit myself, however I have relied
upon the results of somebody who has. The tester claimed
that the unit does not produce the results consistant
with its price. It has very low amplification power, and
the clarity of the sound is also somewhat poor. The
tester had this to say about the unit:
"If this unit were priced at $60 - $80, then it might be worth purchasing"
Model : TARS (Tactical Audio Recovery System)
Manufacturer : Unknown.... Distributed by Sherwood Communications
Approx Price : $400
Size (metric) : Unknown
Amplification : *** High Power
Sound Clarity : *** Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: What makes the TARS such a nice unit, is the fact that it
comes with a variety of different microphones (at least
the authors unit did, I did not however get my unit
directly from the manufacturer and am not even sure
who the real manufacturer is). The unit I received came
with 2 different sized spike mics, a small tube mic,
and a decent quality contact microphone. This accounts
for the somewhat expensive cost of the unit.
Model : 4020 Mini-Stetho
Manufacturer : Martin L. Keiser
Approx Price : $265 - $550 (dependant upon reseller and options)
Size (metric) : approx. 92 x 50 x 18mm
Amplification : *** High Power
Sound Clarity : **** Very Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: This is one of the premiere units in production. Many persons
within the industry including myself give the 4020 very
high ratings not only for the quality of the amplifier
itself, but for the selection of accessories that come
with the unit. The contact microphone that comes with
4020 is one of the best that I have ever used, and is
highly sensitive, picking up even the minutest sounds.
The only problem with this unit however, is that it is
an import model which is extremely hard to find in the
United States. Their are a few mail-order spy equipment
suppliers that carry this unit, but it is usually re-sold
at outrageous prices between $600 to $900.
Model : Mic-23
Manufacturer : Unknown.... Distributed by Electronic Securities Ltd.
Approx Price : $125
Size (metric) : Unknown
Amplification : * Low Power
Sound Clarity : * Very Poor Clarity
Input Jack : No
Output Jack : Yes
Extra Features: This is a low budget unit which my company used to resell.
It sells for $125 and quite frankly isnt worth its price.
The unit has very low amplification power, very poor clarity,
and worst of all does not have a seperate input jack so you
can add your own contact microphone. If you needed to, you
could always cut the wire of the built-in contact mic and
splice in your own cable for the microphone of your choice.
Model : Atomic Ear
Manufacturer : Original Unit Modified by PROTECTOR ENTERPRISES
Approx Price : $325
Size (metric) : 82 x 50 x 21mm
Amplification : *** High Power
Sound Clarity : **** Very Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: The author has not personally tested this unit, but I
hear that it is tops as far as clarity goes. The tester has
told me that the unit uses a unique "stethoscope" type
system, such as they had in the 'old days' and which are
still present on some of the very advanced listening devices.
A hollow tube is used to transmit the sound rather than
wires, supposedly this allows for a much higher degree of
sound quality. Although I have not had the pleasure of
testing this unit myself, I trust the judgement of others
who have told me this unit is great.
Model : Amp-1
Manufacturer : Resold by Viking International (Made in the U.S.A.)
Approx Price : $65
Size (metric) : Unknown
Amplification : ** Medium Power
Sound Clarity : *** Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: The Amp-1 gets my vote for the best general purpose amp
for somebody on a very tight budget. This unit only costs
$65 and actually is well worth it. It compares favorably
to similar units costing $100 - $150. The only problem
however, is that this unit is simply an amplifier and
nothing more. In other words it does not come with a
contact microphone (or any microphone for that matter).
So if you want to use this as a 'listening device' you
will need to purchanse a contact, tube, spike, strap mic,
etc.. which will cost an additional $30 - $70. As usual,
if your going to use a contact microphone, I recommend
anything made by ILLIADIS CORP.
Model : Model 12-B (Super Compression Amp)
Manufacturer : Resold by Viking International (Made in the U.S.A.)
Approx Price : $100
Size (metric) : Unknown
Amplification : ** Medium Power
Sound Clarity : *** Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: The model 12-B is a very unique amplifier, it has special
circuitry within, that automatically tapers sound volume
so that it is at an even decibal level. This is usefull
for hardwiring purposes when 'wiring' a room for audio
for covert surveillance purposes. (of course their are
dozens of other usefull purposes for such a unit).
To be more specific, what I mean is that, this unit will
amplify weak sounds perhaps that are far across a room
at a distance from the microphone, and it will raise the
volume of those distant sounds to the same volume level as
the sounds which are right next to the microphone.
Quite honestly, I dont know how this unit works as far
as a 'through-wall' listening device goes since my testing
was fairly limited. This unit would require 'special testing'
to check out its unique capabilities. I can say however,
that if you have a need to 'hardwire' a room, this unit
works wonders, and will increase the quality of the
intercepted audio and your subsequent recordings by several
factors of magnitude. All at a very low price! As with the
Amp-1, this GP-Amp does not come with any type of microphone,
you need to buy one seperate.
Model : MAS (Microphone Amplification System)
Manufacturer : Lorraine Electronics / Ruby Electronics Ltd. (British)
Approx Price : $300
Size (metric) : 80 x 50 x 20mm
Amplification : *** High Power
Sound Clarity : *** Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: This is another fabulous product of Lorraine/Ruby Electronics
This unit is very similar, to the WCA (SM-33) unit. In fact
it is so similar in performance, that the author does not
even think that their is any real difference between the two.
This unit is supposedly designed for 'hardwiring' a room.
Hardwiring, means that you run a microphone inside of a
'target' room, the microphone gets connected to an amplifier
unit some distance away usually in another room called the
'listening post'. The unit comes with a quality microphone
for hardwiring. The unit does not come with a 'contact'
microphone, so you have to buy one seperate if you choose
to use this as a 'through-wall' listening device.
Model : Model 1059
Manufacturer : Martin L. Keiser (Made in the U.S.A.)
Approx Price : $265
Size (englsh) : 3 x 5 x .75 Inches
Amplification : *** High Power (100db Gain)
Sound Clarity : ***/* Good Clarity to Very Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: Has a wide variety of input and output jacks as well as
a large selection of accessory switches for hi/low pass
filters, tone generators, accessory controllers, impedance
selection switches, etc.. Very sophisticated unit in a
small package. This unit is more suitable as general purpose
amplifier as opposed to a dedicated through-wall listening
device. To use this unit soely as a listening device would
be considered 'overkill' because of its complexity.
The unit happens to be a favorite of the authors, however
I feel it lacks in only 1 respect. That being in clarity.
Although the unit does have a high degree of clarity
(ie: it is a low-noise amplifier), it nevertheless is
not consistent with either its price range or moreover with
the way it is "hyped up" to be a "low noise amplifier"
according to the advertised specifications.
Model : Model 1079
Manufacturer : Martin L. Keiser (Made in the U.S.A.)
Approx Price : $150
Size (englsh) : 2 x 4 x 4 Inches
Amplification : **** Extremely Powerfull (1 Watt Output)
Sound Clarity : *** Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: This model has a 1 watt output power which outputs to a
small speaker. The small speaker however is a possible
disadvantage as it loses a bit of the clarity, but you
may find it usefull for ceartain projects.
Model : Model 1019
Manufacturer : Martin L. Keiser (Made in the U.S.A.)
Approx Price : $335
Size (englsh) : 2 x 3 x 5 Inches
Amplification : *** High Power (1/2 Watt Output)
Sound Clarity : **** Very Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: This is a 1/2 Watt pre-amp packaged with an in-built
loudspeaker. The unit has a low 8 Ohm output jack,
and a medium impedance 1K output jack, both driven
at 1/2 watt of power. The author has not personally
tested this unit himself, but relies upon the judgement
of a friend of mine who just loves this unit. However,
he states that this is more of a general purpose
amplifier. It is too big, bulky, and complex for use
as a 'through-wall' listening amplifier.
Model : Model 7059
Manufacturer : Martin L. Keiser (Made in the U.S.A.)
Approx Price : $200 - $300 (approx)
Size (englsh) : .75" x 3" x 4"
Amplification : ** Medium Power (10X with 12dB per octave roll-off)
Sound Clarity : **** Very Good Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: This is a combination amplifier and filter. This unit is
not suitable for either 'hardwiring' or for use as a
'through-wall' amplifier because of the weak amplification
of this unit. This unit is designed as an "accessory" which
can be added onto other amplifiers. This unit is most
usefull for its 'filtering' capabilities. Recommended use
with the Keiser model 1059 pre-amplifier.
Model : VA-95
Manufacturer : Unknown
Approx Price : $450
Size (metric) : not available at this time
Amplification : ** Medium Power
Sound Clarity : ** Fair Clarity
Input Jack : Yes
Output Jack : Yes
Extra Features: This is another unit meant for 'hardwiring' a room. This
unit comes with a variety of probes mics (4), as well as
a tube mic. You will need to buy yourself a good contact
microphone as well a 100 foot 'electret' or super-sensitive
'FET' (field effect rransistor) microphone for a complete
hardwired listening post unit. The amplification and
clarity of the unit is not the best, but it suffices
considering its purpose. With a hardwiring amplifier, the
design requirements for the amplifier are a bit different
from those of the 'through-wall' amplifiers. In fact I'd
say that with a 'hardwiring' amplifier, the quality of the
sound is not so much a factor as is the amplification power,
which is the exact opposite of the requirements for a
'through-wall' amplifier. This unit has other features such
as a 6 position VOX (voice activated) control, on/off switch
for the headphones, six position gain control for the amp,
and the tape recorder output jack has 2 modes: VOX & direct.
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Quick Reference Chart
Model Manuf Apprx Price Amplfcation Clarity In-Jack Out-Jack
--------------------------------------------------------------------------
Ear-200 R.E.I. $150-300 *** * No Yes (2)
WCA Ruby $185-200 *** *** Yes Yes
SM-11 Ruby $150-200 ** * Yes Yes
CM-8 Cony Mfg $100 ** *** Yes Yes
T-1201 Illiadis $100 ** *** Yes Yes
USI USI Corp $150 * ** Yes Yes
TARS Unknown $400 *** *** Yes Yes
4020 Keiser $265 *** **** No Yes
Mic-23 Unknown $125 * * Yes Yes
Atomic Ear Protctor $325 *** **** Yes Yes
Amp-1 Vyking $65 ** *** Yes Yes
Model 12-B Vyking $100 ** *** Yes Yes
MAS Ruby $300 *** *** Yes Yes
1059 Keiser $265 *** **** Yes Yes (2)
1079 Keiser $150 **** *** Yes No
1019 Keiser $335 *** **** Yes (2) Yes (2)
7059 Keiser $200-300 ** **** Yes Yes
VA-95 Unknown $450 ** ** Yes (1) Yes (3)
MW-303A Kant Inc 9,500 Yen ----------- NOT TESTED -----------
M-66A Kant Inc 18,000 Yen ----------- NOT TESTED -----------
==========================================================================
Authors Afternote
As a businessman who sells such equipment it would be semi-unethical for
me to choose one specific unit over any other unit, or to recommend any
specific manufacturer. All units have their advantages. When purchasing
a unit, keep in mind the old saying; "you get what you pay for". Each
model has its advantages and drawbacks and every user has a different
set of requirements. The higher-end units provide greater clarity and
greater amplification, while the lower price units represent an affordable
alternative to those individuals who are on a budget or dont have any
strict requirements for the unit.
However, as an independant and unbiased reviewer of such equipment, it is
is only natural that I have my personal preferences of which units I would
recommend to others. The following are my choices:
Highest Performance for Quality Model:
4020 Mini-Stetho: My evaluation of this unit were based on my own testing
of the unit and on the general consensus in the industry
as this particular unit is quite possibly the best unit
on the market for generic eavesdropping purposes.
The unit comes with one of the best contact microphones
on the market that is amazingly sensitive considering
its relatively modest cost. In addition, the ampli-
fication power of the 4020 is quite powerfull and
the sound clarity is quite good. The 4020 comes with
1 contact microphone (if you buy it indirectly from
a reseller, sometimes they throw in extra goodies)
as well as a set of 2k Ohm headphones.
My one big gripe is the 2k headphones which come
with the unit. These headphones have very bad audio
quality and the 2k Ohm impedance output makes it
difficult to interface the device with other ancillary
equipment (recorders, additional amps, etc..)
The unit is manufactured by MLK (Martin L. Keiser)
and that means quality! (and likewise greatly
overpriced products which make it a toss up as
to whether the product is even worth the money.)
This unit sells for between $350 and $600 depending
on where one purchases it (it is best to buy it
directly through MLK, Inc.) Although this unit
walks a fine-line between being an overepriced
rip-off, practicallity and reason must prevail.
The unit is among the best, and if you need the
best, then you must be willing to cough up an
extra few bucks and not think twice about if
its really worth it.
WCA (SM-33) : The WCA (Wall Contact Amplifier) is manufactured by
Ruby Electronics and is distributed by the very popular
british company Lorraine Electronics. In the United
States, the WCA is often sold under a different name
known as the SM-33 (that is to the authors knoweledge).
It seems one of the problems is that small companies
are always taking another manufacturers product and
slapping their label on it to deceive buyers. To my
understanding, this is the case with the SM-33
wall cointact amplifier. It is really a Ruby Electronics
WCA with the SM-33 label slapped on it.. Irregardless,
this is a very high quality unit manufactured by a
well known reputable company. I find the unit to have
a large degree of amplification with very little audio
distortion. The unit comes with a 'decent' (but not
great) contact micriophone, and the amplifier unit
itself has a volume control, and input jack so you
can use the microphone of your choice and it has
an output jack which you can interface to a tape
recorder, a transmitter, or audio enhancement eqpt.
Atomic Ear : The 'Atomic Ear' is a very high quality through-wall
listening device. This base unit is actually
manufacturered by another company, but PROTECTOR
ENTERPRISES has modified this unit quite a bit to
enhance the quality of it. They have done this by
replacing the standard wiring system, with a sort
of "stethoscope" system which uses hollow rubber
tubes to transmit the sound rather than wires. This
technique has been used extensively in very high-end
professional listening systems. The author has not
personally tested this unit. I have relied upon the
testing of a customer of mine who purchased one of
the units and then sent me an evaluation of its
quality.. It was claimed that the sound clarity
from this unit was absolutely superbe, but I cannot
personally verify that because the evaluator really
did not have many other units to make a comparison
against.
Highest Performance for Budget Model:
CM-8 : This unit is manufactured by a Japanese company known as
CONY Manufacturing which is a well known manufacturer of
low-grade transmitters ('bugs'). I find that the circuitry
of the CM-8 to provide very high quality audio with a fair
amount of amplification power usefull for casually listening
through walls for security purposes. At a price of only
$100 (US funds) this unit cant be beat. The only problem
however, is that CONY Manufacturing only takes bulk orders
of $300 or more (US funds), so if your planning to buy this
unit you will most likely have to buy an extra $200 worth of
CONY equipment to meet the $300 minimum order limit. As far
as the author knows, their are absolutely no resellers of
this particualr unit in the United States with the exception
of the authors company. The reason is simply because the
EAR-200 manufactured by Research Electronics has become more
popular in the states. [see below for info on EAR-200].
Ear-200: Although the author does not particularly care for the quality
and performance of the EAR-200, I nevertheless will admit that
it does provide fair quality for a reasonable price. The cost
of the EAR-200 fluctuates greatly depending upon where you buy
it from. I have seen the EAR-200 being sold for as little as
$120 (USA cost) to as much as $300 (USA cost) from various retail
mail order companies. In addition, the EAR-200 does also enjoy
a few other luxuries. The first being that this is the most
widely sold and used 'through-wall listening device' sold in the
United States, possibly in the world. Virtually every mail-order
surveillance & security company carries the EAR-200 in stock,
so if you are looking for a good deal it is best to shop around.
Secondly, and most importantly, the EAR-200 unit is manufactured
by a very reputable company known as "RESEARCH ELECTRONICS" which
is well known in the security industry for providing quality
products.
Most Usefull General Purpose Model:
Model 1059: The model 1059 from Martin L. Keiser is a personal favorite
of this author. I give the unit nothing but high regards
and I find it to be the most usefull tool in my toolbox.
Not only is it usefull for general surveillance or counter-
measures or comsec purposes, it also makes a handy general
purpose amplifier for simple home projects. What makes this
unit so amazingly unique aside from its great clarity (the
unit has very little audio distortion), is the fact that
the unit has several output and input jacks, as well as
a plethora of selector knobs, switches and gizmos for
selecting input and output impedance.. This is very usefull
for working with various audio equipment where you need
the ability to match impedances. The unit also has other
functions such as a hi/low pass filter, tone generator,
and an output jack for powering accessories such as Infrared
Probes. The unit has a gain of over 100dB according to the
specifications although I cannot confirm that.
My one big gripe is the 2k headphones which come
with the unit. These headphones have very bad audio
quality and the 2k Ohm impedance output makes it
difficult to interface the device with other ancillary
equipment (recorders, additional amps, etc..)
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The author also gladly welcomes any questions you may have about the
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or snail mail me with any technical questions, and I will gladly send
you a reply when I can, assuming I can answer your question. And if
I cant, then I shall refer you to somebody who can. If you mail me a
question via 'snail-mail' (postal mail), please include a SASE (Self
Addressed Stamped Envelope) or just enclose a stamp with your letter.
The author maintains a security consultation company and sells a
wide variety of surveillance equipment. To receive a 150 page
catalog of products, send a 'snail-mail' request ONLY (no e-mail
requests accepted) to the address listed below. To guarentee a
catalog, send a $5 Postal Money Order (ONLY) to defray the postage
and printing costs.. Those that want a free catalog, will be added
to my mailing list, but to be honest you'll get last priority..
(Sorry,wish I could mail everyone free catalogs, but I'm not a rich
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Author : Alan Hoffman
E-Mail : sahoffman@dockmaster.ncsc.mil
Snail-Mail: Electronic Securities Ltd.
PO BOX 519
Shoreham, NY 11786
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