Spica SERVO User manual

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INTRODUCTION
Your new SPICA SERVO subwoofer is designed to extend the low frequency
performance of the SPICA TC-50 speaker system. Its computer-optimized crossover
network, servo error correction circuit, specially designed S" woofer, and
internal 70 watt power amplifier all contribute to give a dramatic improvement
in your system's clarity and definition, while allowing higher sound pressure
levels to be obtained. And it does all of this without degrading the superior
stereo imaging that the TC-50 is famous for. We are confident that you will be
more
than pleased with this addition to your system.
An important consideration in the design of the SERVO was to make it
flexible enough to be used with whatever rec.iver or power amplifier you might
be using for your TC-50s, while retaining the sonic purity that your system
already has. To accomplish this, a simple passive filter is used in the portion
of the crossover network that feeds the TC-50s. This part of the setup procedure
represents aminor inconvenience for you, the end user. Although the procedure
is asomewhat technical one, we have made every effort to present it as simply
as possible. Please read and follow the instructions carefully.
Some of the 'tools' you
> CASSETTE PLAYER
> MEASURING TAPE
> SOLDERING IRON
will need are:
(for setting levels)
(for physical placement)
(for capacitor installation)
For setting the relative level of the subwoofer with greater accuracy, a
method
is provided that requires the use of an AC VOLTMETER. If you do not have
a soldering iron, your SPICA dealer will be able to assist you in installing the
capacitors into the passive box.
We mentioned above that the SERVO does not degrade the stereo imaging
abilities of the TC-50. Another way of saying this is that the SERVO is a phase-
coherent addition to the TC-50. This is quite a distinction from all of the
'generic' subwoofers available which, by their very nature, can only give
'generic' results. If by chance you are using the SERVO with satellite speakers
other than the TC-50, we have no way of predicting how sucessfully the SERVO
will match up with them, and the setup procedures given in this manual may not
be applicable to your system.
We would like to acknowledge the fine folks at PS AUDIO for the design of
the internal 70 watt power amplifier and the servo circuit.
CHECKING SYSTEM POLARITY
Suppose you were standing in front of a mirror that turned everything
reflected in it upside down. All the features of the image would be there, but
they would be inverted. This is a visual analogy of what is called POLARITY. The
audio industry has not established any polarity standards, so some pieces of
equipment
invert the signal as it passes through them, and others do not. In
order to determine the polarity of your system, you must find out which pieces
in your system invert the signal, and which ones do not. This information is
often given in the owner's manual of each piece. If it is not, contact your
dealer or the manufacturer to find this out now.
2

FIGURE 1
SYSTEM POLRRITY
;..-
(+ )
(-)
(+ )
(+ )
Phono
-----
Head
'-----
Pre
f-----
Powe r
Cartridge
-----
Rmp 1; f ; e r ,...---- Rmp 1 if i e r
f-----
Rmpl ifier
To assist in the polarity-hunt, a sketch of your system in the form of a
'block diagram' will help immensely. FIGURE 1shows such adiagram of a typical
system. Draw up a similar diagram for your system, including everything from the
source device (phono cartridge, tape player, etc.) to the speaker outputs of
your
receiver or power amplifier. If you have a receiver, the "AIN OUT jacks on
the back panel are functionally the same as the 'Pre Amplifier' in FIGURE I,
The (-) or (+) above each block refers to the inverting or noninverting
status of each piece, where (-) signifies the inverting condition. Do the same
on your diagram, noting the polarity of each piece above it. Now give each (+) a
value of 0and each (-) a value of 1. Add up all the values from the SOURCE
device to the PREAMPLIFIER(MAIN OUT). If the number you get is an EVEN number or
ZERO, no change in the SERVO is requi red. If it adds up to an ODD number I you
must follow the procedure given below to change the polarity of the SERVOs
woofer.
Now, check the polarity of the amplifier being used with the TC-50. Add its
value (0 or I) to the previous total. If this new total is EVEN or ZERO, the (t)
terminal of the amplifier powering the TC-50s should be connected to the red
input of the TC-50s, as is normal. If it is ODD, you should reverse the
connections to each TC-50 at its input terminals.
CHANGING THE SERVOs POLARITY
WARNING I UNDER NO CONDITIONS SHOULD THE SERVOs POWER CORD BE PLUGGED INTO
AN AC OUTLET WHILE THIS OPERATION IS BEING PERFOR"ED. The damagl
that results is not covered under warranty, and plrsonal injury Is
poui bIt.
If you have determined above that the SERVO's polarity needs to be
reversed, you will need a SOLDERING IRON and aPHILLIPS SCREWDRIVER to change
it. Place the SERVO on a table or bench, and proceed as follows:
1> MAKE SURE the SERVO's power cord is DISCONNECTED.
2> Remove the.grill frame from the front of the enclosure by tugging firmly on
it at the bottom of the enclosure.
3> Using aPHILLIPS SCREWDRIVER, remove all eight of the screws that secure
the woofer onto the enclosure.
4> Free the woofer, and set it face-down in front of its mounting hole.
5> Make note of which color wire is connected to which terminal on the woofer.
From the factory, the GREEN wire is connected to the woofer terminal marked
with a RED DOT near it.
6> Unsolder both wires and resolder each of them to the terminal that was
previously connected to the other color.
7> Replace the woofer into its mounting hole, lining up the screw holes in its
frame with the holes in the enclosure.

= Capacitor value lin microfarads}
~
8) Screw each screw in part way, making sure the woofer is seated evenly all
around, then tighten them up in a cross-wise fashion. DO NOT overtighten
them, or the holes will strip. They should be firmly snug.
9) Replace the grill frame onto the enclosure, pushing around the perimeter to
engage the Velcro fasteners.
10) VOILA '!
PASSIVE INTERFACE SETUP
To interface properly with the SERVO, the signal sent to the amplifier that
is driving the TC-50s must be 'high pass filtered' at the correct frequency,
This is accomplished by installing the proper value of capacitor into the
PASSIVE INTERFACE box. The value of this capacitor is determined by the input
impedance of the power amp you are using. If you are using a receiver to power
the TC-50s, it must have Preamp Out! Main Amp In jacks on the rear panel. If
yours does not, you should contact your dealer to make the appropriate modifica-
tions to your unit.
Find out the input impedance of your amplifier unit, This information is
normally given in the owner's manual; if it is not, your dealer can find it out
for you.
Locate the impedance value on the vertical axis of the chart in FIGURE 2 on
the next page. Using a straight edge placed parallel to the bottom of the chart
at the point located, mark the point where it crosses the curved plotted line.
Now drop this point straight down to the bottom of the chart and mark it. Find
the value of the nearest major division (the ones that are labelled), and count
the number of small tick marks between this major division and your mark. If
your mark is to the left of this division, ADD .001 to the number at the major
division for each tick mark you counted; if is to the right, SU8TRACT .001 for
each tick mark. The total you get is the capacitance in microfarads you will
need to install into the PASSIVE INTERFACE box.
If your unit has an input impedance outside the range of the chart, you
will have to calculate the value or ask your dealer to do it for you. The
formula is: 1808.92
Input Impedance
CAPACITOR SELECTION
Some of the values necessary are not 'standard values', so they must be
obtained by combinations of parts. We have provided a selection of capacitors
with the PASSIVE INTERFACE that will satisfy the required values.
Open up the PASSIVE INTERFACE box and take a look at the parts in it. There
are three sets of larger value capacitors (yellow color), and four values of
smaller ones (silver colorl. The large parts have values of .018, .039, and
.056 . If the value you need is within ~ .001 of one of these, just grab a pair
of them and proceed on to the 'Capacitor Installation' section.
Everyone else gets a little lesson on the inconsistent ways in which the
values of the smaller parts are marked on them. Some manufacturers mark these
parts in microfarads, and others in picofarads. ".01" microfarads is "10000'
picofarads. Likewise, ".005" microfarads is "5000" picofarads. So, while we are
discussing values in microfarads, be aware of this difference in the way these
parts may be marked. To convert picas to micros, place a couple of zeroes in
front of the picofarad value, and then place a decimal point six digits to the
left, starting at the right end of the number, and there you have it.
4

PASSIVE INTERFACE CRPRCITOR CHART
.018 .025
.076 .068 .061 .054 .047 .040 .032
CAPACITOR VALUE (Microfarads)
.083
40k
50k
30k
90k
70k
60k
80k
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Okay' A calculator will come in handy now. From the three larger parts,
select the value that is less than the value you need. Subtract it from the
total. Then find the nearest value that is less than or equal to this remainder.
Do this until you are within .002 of the value you need. The nearer the better,
but this accuracy is sufficient. If your amp's input iapedance is 60K Ohms or
greate" get within .001 of the target value.
CAPACITOR INSTALLATION
Its time to fire up your soldering iron. You will find a length of solder
in the PASSIVE INTERFACE box; it's good stuff, so use it. If you needed more
than one capacitor to get your target value, hold the smaller parts length-wise
along the larger part, and BENTLY wrap the lead of each smaller part a couple of
turns around that of the I arger at each end. The leads of the small si I ver parts
are a little fragile, so don·t tug on thea too hard. You will do this twice,
once for each channel. Do yourself a favor, and double check your work before
you solder. You should have two capacitor clusters with identical parts in each.
5

Solder the capacitors together, working as swiftly as possible so as not to
damage the parts. Cut the leads of the smaller parts off I leaving the leads of
the larger part extending on either end.
Before installing the parts into the PASSIVE INTERFACE box, take alook at
FIGURE 3, which shows the correct orientation of the parts and their connection
inside the box. The installation procedure will be described for one capacitor,
and should be repeated for the other as well •
.......................................................................................
......................................................................................
....... .
............................................ .. .••.....................................
......................... /'". ,.,.,.,..,.,.,.,..,.
.. -.
..
...........
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......................................................................... .
......................................................................... .
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............................
FIGURE 3
CAPACITOR INSTALLATION
Place the box so that the insides aro exposed. Cut the leads of the capaci-
tor so that the total length from end to end is just shy of the long dimension
of tho box. Bend one end of the leads to form a small hook. Hook the load
through the small hole in the CENTER POST of one of the phono jacks at the long
end of
the box, and the other end through the center post of the phono jack
directly opposite it. Do not cross the leads of the two parts; if they touch
each other, you will convert your wonderful stereo into amonaural system,
although it is not likely to do any damage.
Crimp
the leads loosely onto the posts, and solder them. Now put the top
onto the box, securing it with the screws provided, and you're done!
MAKING THE CONNECTION
Place the completed PASSIVE INTERFACE behind your other components. Turn
all of the components in your system OFF. With patchcords, connect the output of
your
preamplifier to the jackS marked "IN" on the PASSIVE INTERFACE, making
sure, as always, to keep your 'lefts' and 'rights' consistent (if you don't know
your left from your right, your SPICA dealer is qualifiod to help you). Connect
the jacks marked "SATELLITE OUT' to the input of the power amplifier that is
driving the TC-50s. Connect a long set of patchcords to the jacks marked ·SERVO
OUT", and let them be for the moment.
6

PLACEMENT
In phase-coherent systems (as in life in general), TIMIN6 IS OF THE
ESSENCE. In order that the timing relationships of the SERVO and the TC-50s be
correct, it is necessary that the distance from the SERVO to your listening
position be greater than the distance from the TC-50s to your listening position
by a certain amount. If this is not done, all of the other system parameters
will be thrown out of whack. Also, where you place the SERVO(s) depends on
whether you are using one or two of them in your system. Fortunately, this is a
very simple procedure. All you need is a MEASURIN6 TAPE, and possibly a helper.
FOR SIN6LE SERVO SYSTEMS:
As shown in FI6URE 4, the SERVO should be placed in between the TC-50s.
Placing it anywhere else in your room will result in reduced accuracy, because
the SERVO must be placed at a fixed distance offset from each TC-50. And since
one SERVO is serving this function for two TC-50s, placing it in between the
TC-50s is the only way this condition can be satisfied •
,
,
FIGURE 4
,
,
SINGLE
•I
I
I
I
I
I
I
•
SERVO PLRCEMENT
7

FOR DUAL SERVO SYSTEMS:
As shown in FIGURE 5, the SERVOs should be placed as closely as possible to
each TC-50. Having them on the outside is slightly preferable, but the inside is
fine. For optimum performance, you may want to consider using the stands which
have been
specifically designed for the TC-50 when used with dual SERVOs. They
are made by Chicago Speaker Stand. These stands mount on top of the SERVO
enclosure, placing the TC-50 at the correct distance offset, and can accomodate
a
range of listening heights through their tilt adjustment. Ask your dealer for
more information.
/
/
.
.
/
I
I
/
/
I
"'-. '',- \/ ,/ /
"'-.'\\ //
~:
\\\\
\
,,,
,.,
,,
FIGURE 5
DURL SERVO PLRCEMENT
ALL SYSTEMS:
1> Put a small piece of masking tape on the couch or chair you listen in, at a
point near where your head is located when you are seated.
2> Use your measuring tape to find the distance from this point to the BOTTOM
FRONT EDGE of one of the TC-50s, and write it down.
3> Now measure the distance to the other TC-50 from the same point, and move
it backward or forward until the two distances are identical.
4> Place the SERVO(s) in the location described above, at a distance that is
4.5 inches GREATER than the TC-50s, as measured from the same point to the
BOTTOM FRONT EDGE of the SERVO(s).
8

5> Plug the patch cords from the PASSIVE INTERFACE into the SERVO Is). If you
are using one SERVO, it makes no difference which cord is plugged into
which jack. If you are using two, check to make sure your lefts and rights
are consistent with the rest of the system, but don't use the furnished
shorting plug until we find out later whether you need to or not.
6> Plug the pDwer cord Df the SERVO(s) into an AC Dutlet. OON'T turn it on
just yet.
SETTING LEVELS
It is nDt uncommDn these days for people leven non-hobbyist types) to have
an AC Voltmeter around the hDuse. or at least tD have a friend that does. If YDU
do, here's an DppDrtunity to put it tD gDDd use.
On the back panel Df the SERVO is a level contrDl. It is used to set the
lDudness Df the SERVO to the prDper level. There is sufficient gain (12 dB) in
this cDntrDl tD match the sensitivity Df almost any amplifier you may be using
tD drive the TC-50s. There is alsD enough gain here SD that if the cDntrDl has
inadvertantly been 'cranked up', SDme damage could be dDne tD the amplifier Dr
wDofer in the SERVO. Turn the control tD its fullv counter-clDckwise positiDn.
We are prDviding two methods Df setting levels; one is strictly subjective,
the Dther is empirical. If YDU have access to a vDltmeter, we strDngly suggest
YDU use the empirical methDd; why guess if you dDn't have to? Both methods
require the use of a CASSETTE PLAYER; the quality of the unit is not important.
The level setting procedure takes advantage Df the following fact, AT ONE
FREQUENCY, THE ACOUSTIC OUTPUT OF THE SERVO AND THE TC-50 ARE THE SAME. We have
furnished a cassette that has five minutes of this frequency recorded on each
side of it. If you are going to follow the SUBJECTIVE METHOO, a friendly
assistant would be helpful.
BOTH METHODS,
1> Connect a cassette player tD the apprDpriate inputs of your system.
2> Turn the level contrDl on your preamp or receiver all the way down.
3> Set your Bass and Treble controls to their center (off) positions. They
should remain off for the entire setup procedure.
4> Turn all of the cDmponents in your system ON, except the SERVOls).
5> Place the SERVO SETUP cassette into your player.
SUBJECTIVE METHOD,
This method requires a little bit of explanation before we jump right into
it. You will be listening to the tone recorded on the SERVO SETUP tape, first
played through the TC-50s alone, then through the SERVO Is) alone. You therefore
need SDme way of disabling the output to the TC-50s when listening to the tone
through the SERVO. To accomplish this;
> If YDU have a separate power amplifier for the TC-50s, all you have to do
is turn that unit off.
> If you have a receiver or integrated amplifier that has speaker switching,
all you have to do is switch the speaker selector to off or to the other
DUtpUt.
> If you have none of these, you must turn the receiver off lwithout changing
the level control on it), disconnect the patch cords from the Passive
Interface Box to the receiver main input, then turn the unit back on.
Whichever
is appropriate for your case, it is referred to in the instruc-
tions that follow as "disabling the TC-50s".
If you are using a DUAL SERVO setup, the instructions given should be
repeated for each side. Use your balance control to get the tone output from the
side that the setup is being done for. During the setup, if you should find that
9

the SERVO level control is turned all the way down and is still too loud, then
insert a shorting plug into the unused input, and start the level procedure
again. This will give an additional b dB of attenuation.
If you are using a SINGLE SERVO setup, place your balance control in the
center position. Do not change it during the setup procedure.
5) Start the cassette running. and set the level to a comfortable one, using
your preamp/receiver's level control. Do not change the setting of this
control during the setup procedure.
b> Disable the SERVO by turning its power switch to OFF.
7) From your listening location. listen to the loudness of the tone that
comes through the TC-50s alone.
8> Disable the TC-50s, and turn the SERVO power switch to ON.
9> Listen to the loudness of the tone from the SERVO alone. and adjust the
SERVO level control until it is the same as it was from the TC-50s. If
there is any doubt. set the SERVO level on the low side.
10> Repeat steps b through 9 until you are satisfied that the levels from the
TC-50s and the SERVO are the same.
11) For dual
SERVO setups, turn your balance control to the opposite side.
and start at step b again.
12> Skip to the section on 'Some Fine Points'.
EMPIRICAL METHOD:
This is the easiest and most accurate method. Making sure not to move the
SERVO from its optimum location. remove the grill frame from the SERVO. Above
the woofer. to the left, flush with the face of the enclosure. are two exposed
Test Points. Before we proceed, a word of caution is in order. These Test Points
are connected DIRECTLY to the power amplifier, and are also part of the SERVO's
'comparator', If they are accidentally shorted together. connected to an AC
ground. or if any voltages are applied to these test points, you stand a good
chance of 'blowing up' the power amplifier in the SERVO. Before measuring the
voltages at these Test Points:
) YOUR VOLTMETER MUST BE SET TO MEASURE AC VOLTS. If it is set on the Resis-
tance mode. it will insert a reference voltage into the SERVO circuit, and
most
assuredly will cause some damage.
>
YOUR VOLTMETER MUST NOT BE CONNECTED TO AN AC OUTLET. but should be
operating on its internal batteries. If EITHER test point is connected to
an AC GROUND. the SERVO will go up in smoke before your very eyes.
If you have a SINGLE SERVO system. turn your balance control all the way to
one side or the other, and start at step b.
5> Set the balance control on your preamp/receiver to its center position.
b> Turn the SERVO(s) power switch on.
7) Start the cassette running. and set the level to a comfortable one, using
your preamp/receiver's level control. Do not change the setting of this
control during the setup procedure.
8> Measure the voltage at the input terminals of the TC-50, and write it down.
9> MULTIPLY this figure times ~ .
10) Hook the voltmeter to the Test Points on the SERVO.
11> Adjust the SERVO level control until the voltage measures the same as the
figure obtained in Step 9.
12> For DUAL SERVO systems. repeat Steps B through 11 for the other channel.
13) Replace the grill frame onto the enclosure, pushing around the perimeter of
it to engage the Velcro.
14> Th-th-that's all, folks'
10

SOME FINE POINTS
Before going on further with this, take some time now and listen to some
music through your new system. Listen to a variety of material, and notice how
different the character of the low frequency part of the music is as you go from
one
recording to another. Then come back, and we'll go through some fine points
regarding the setup.
If you're pleased as punch with your system, and can't imagine that it
could be any better, then you're all done and you need not concern yourself with
this section on fine tuning your system. If you'd like to extract the last ounce
of
accuracy out of it, and you don't mind a little 'tech talk', then read on.
There
are two factors that can affect the absolute accuracy of the setup
procedure you've just completed. The first factor is a combination of al the
distances from the SERVO and your listening position to the various surfaces in
your room, and bl the 'liveness' or 'deadness' of the floor immediately in front
of the SERVO, which can be 'tuned' by fine changes in the placement of the
SERVO. The second factor is variations in the sensitivities of the drivers in
both the TC-50 and the SERVO, which can be 'tuned' by adjustments to the SERVO
level control. This is what we call OPTIMIZING, a procedure that is avery
meaningful one
for us here at SPICA. It is distinguished from IDEALIZING in that
it takes into consideration the immutable 'undesirable' conditions as well as
the desirable ones in any circumstance.
The very walls in your room are one such undesirable condition, in that
they restrict the free expansion of the sound pressure wave, and create
resonances and cancellations at frequencies that are related to the distances
between these surfaces. This is actually a very complex subject, but the long
and short of it is that your listening position may be placed in a location
where there is a strong 'buildup' or cancellation of acoustical energy. and this
may be happening right in the frequency range where the SERVO and the TC-50s are
trying to combine their contributions to the overall sound. If the distance from
the SERVO to the wall behind it is identical to the distance from your listening
position to the wall behind it, you are most likely listening in one such
problem
area. The solution is to make these distances unequal by relocating your
listening position or the TC-50s and the SERVO together. After making any
changes to the position, remember to go through the procedures on placement
again, to ensure that the relative distances are correct.
Now lets take alook at the effects of the reflective character of the
floor in your room. The SERVO is specifically intended to be placed on the
floor, or 'floor coupled', as we call it. At low frequenties, this placement
effectively eliminates the floor from being one of the early reflective sources
that we mentioned above. At higher frequencies, this becomes increasingly less
true, so that the absorbtive character of the floor immediately in front of the
SERVO effects the smoothness of the SERVO's output at higher frequencies, which
in turn has a subtle (or not-sa-subtle, depending on your attentiveness) effect
on the audible result. We recommend that a rug be placed under or immediately in
front of the SERVO.
Hark the current position of the front of the SERVO on your floor with a
small piece of masking tape. From your collection, choose some recorded material
that has either very coherent depth in it, or very percussive low frequency
information. Choose a30 second long passage that 'grabs you', and listen to it
with the system set up the way it is now. Listen in particular to the quality of
the impact of low frequency transients, to the 'focus' of the instruments that
seem to come from further back in the soundstage, and to the general sense of
warmth of
the overall sound. Now experiment with moving the SERVO back a little
bit from the original position, listening to the same passage after every move.
11

There ~ill be a place ~here the three above qualities ~ill come together
dramatically. If you have gone more than an inch or so away from the original
position, you have gone too far, and you might want to choose a different
selection of program material.
To correct for the variations in the sensitivities of the various drivers
in the system, you can make minute adjustments to the SERVO level control, using
the same criteria as given above. Be sure to mark your original position before
you start, so that you can return to it for comparisons.
Some words of caution are in order here. If you do make adjustments to the
SERVO level control, keep the following in mind:
> We Americans, as a culture, tend to be 'bass freaks' ~ith our sound
systems, so there is going to be a tendency to want to keep 'cranking it
up' in order to achieve that indistinct· 'sameness' in bass quality that we
have all grown up ~ith.
> You will find that continually increasing the SERVOs loudness above the
proper level actually lessens the perceived bass' Things start to cancel
each other rather than working together.
> DO NOT use the SERVO level control as a bass tone control. Use your preamps
bass control to compensate for bass-deficient recordings.
> The SERVO has a built in 'rumble filter', We have purposely set it at the
extremely low frequency of 4 Hertz. If you are:
a) playing a record that is badly warped,
b) playing your system VERY loud,
c) boosting the bass with your bass tone control,
then you should consider engaging the rumble filter on your preamp I
receiver if it has one. Otherwise, you should leave it off.
>Avoid the use of the LOUDNESS button on your receiver.
TECHNICAL SPECIFICATIONS
System type
Woofer Enclosure Volume
System Resonance IQ
Low Frequency Extension
Woofer
Hipass Crossover
Lopass Crossover
Input Impedance
Polarity
Level Control
Power Amplifier
Size in inches(cm)
Weight in Ibs(kg)
Sealed box
1.25 cu. ft.
31 Hz, Total Q .5
-3dB @ 25 Hz
B" diameter with I" peak-to-peak excursion
Passive 1st Order, -3dB @ BB Hz
Electronic with computer-derived slope
110k Ohms open, 20k Ohms one input shorted
Inverting, for use with non-inverting TC-50s
Continuously variable within a 12dB range
Solid state 70 watts RMS minimum
17.5(44.5)W X 14.5(3b.B)H X 15.B75(40.3)D
:40(IB.251
WARRANTY
To the original purchaser, SPICA warranties the SERVO to be free from
mechanical defects for five(5} years and electronic defects for one(ll year from
the date of purchase, when purchased from an authorized SPICA dealer. Your sales
receipt is your proof of purchase. This warranty excludes damage caused by user
abuse, carelessness, and modifications other than those covered in the owners
manual.
SPICA reserves the right to make final determination of warranty
coverage. SPICA makes no other warranties, either expressed or implied.
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