Heathkit XO-1 Guide

Assembling
and Using Your...
Heathkit
ELECTRONIC
CROSSOVER
MODEL XO-1
595-130

STANDARD COLOR CODE —RESISTORS AND CAPACITORS
AXIAl LEAD RESISTOR
lr*wn —Insulated
Hack— Nan*ins«lated
Taltrnnce
Multiplier
ist and 2nd Significont Figures
Wire weund resisters have
1st digit band deuble width
INSULATED FIRST BING SECOND BING THIRD RING
UNINSUIATED BODY COLOR END COLOR DOT COLOR
Color First Figure Second Figure Multiplier
BIACK 00None
BROWN 110
RKD 2200
ORANGE 33,000
YELLOW 440,000
GREEN 5500,000
BLUE 66000,000
VIOLET 770,000,000
GRAY 8800,000,000
whut: 99000,000,000
DISC CERAMIC RMA CODE
S-Dot 3-Dot
Capacity
MultipKer ~
^Telerance
Temp. Ceeff.
RADIAL LEAD DOT RESISTOR
Multiplier
Ist Figure
’2nd Figure
5-DOT RADIAL LEAD CERAMIC CAPACITOR
-Capacity
Multiplier Tolerance
EXTENDED RANGE TC CERAMIC HICAP
Temp-Ceell. nvCopacity
TC Multiplier Multiplier t<«'^nce
RADIAL LEAD (BAND) RESISTOR
•Multiplier
i-2nd Figure
BY-PASS COUPLING CERAMIC CAPACITOR
Capacity
f-f
AXIAl LEAD CERAMIC lAPAaTOR
Temp. Ceeff. —i•—iCopecity
Multiplier Tolerance c..1)
Telerance
Tolerance 1st Figure
The standard color code provides all necessary information re-
quired to properly identify color coded resistors and capacitors.
Refer to the color code for numerical values and the zeroes or
multipliers assi^^ned to the colors used. Afourth color band on
resistors determines* tolerance rating as follows: Gold =5%,
silver =10%. Absence of the fourth band indicates a20%
tolerance rating. MOLDED MICA TYPE CAPACITORS
The physical size of carbon resistors is determined by their
wattage rating. Carbon resistors most commonly us(‘d in Heath-
kits are 3^ watt. Higher wattage rated resistors when specified
are progressively larger in physical size. Small wire wound
resistors }/2 watt, 1or 2 watt may be color coded but the fi^’s!
band will be double width. ^
White (RMA)
Hock (JAN)
CURRENT STANDARD CODE
2iid [
Figure
Class
-Multiplier
Telei
JAN C
1948
RMA
CODE
RMA 3-DOT (OBSOLETE)
RATED 500 W.V.D.C. ±20% TOL.
Multiplier
Figure
BUTTON SILVER MICA
CAPACITOR
class
Toleronce
Multiplier
3rd digit
RMA (5-DOT OBSOLETE CODE)
7n6 [
Figure Voltage
Multiplier
Front
-Working Voltage
sRear
—Telerance
Ist 2nd
Working
Voltage
Telerance
Multiplier
Significant Figure
—Multiplier
Toleronce
'flank
RMA 6-DOT (OBSOLETE)
‘1st
I
-2nd ^Significant Figures
-3rdj
Multiplier
Tderance
Working Voltage
RMA 4-DOT (OBSOLETE)
-Working Voltage
-Multiplier
h
I
Significant Figure
MOLDED PAPER TYPE CAPACITORS
TUBULAR CAPACITOR 1Significant Figure
Multiplier
-1st}
-2ndC
1
1
Telerance
Normolly
stomped for
value
Significont
Veltoge Figure
MOLDED FLAT CAPACITOR
Commercial Cede
Hack
ledy
JAN. CODE CAPACITOR
1st /Significant
A2digit voltage rating indicates mere than 900 V.
Add 2zeros to end of 2digit number.
The tolerance rating of capacitors is determined by the color
code. For example: red =2%. green =5%, etc. The voltage
rating of capacitors is obtained by multiplying the color value
by 100. For example: orange =3X100 or 300 volts. Blue =
6X100 or 600 volts.
IWerking Veits
Multiplier
I"
^I
Significont Figure
S2nd CFigure
-Multiplier
Tolerance
In the design of Heathkits, the temperature coefficient of ceramic
or mica capacitors is not giuierally acritical factor and there-
fore Heathkit manuals avoid reference to temperature coeffi-
cient specifications.
Courtosy of Centrolob

HEATHKIT ELECTRONIC CROSSOVER
MODEL XO-1
SPECIFICATIONS
Input: ITigh impedance.
Outputs: (1). Low-frequency.
(2)
.High-frequency.
(3)
.By-pass. (Input signal may be transferred
•to this output jack by means of switch pro-
vided. )
(Low and high-frequency outputs are low im-
pedance from cathode-followers.
)
Cutoff Frequencies: 100, 200, 400, 700, 1200, 2000 and 3500 cycles.
The high and the low-frequency channels can be
individually adjusted to any of these frequencies
by means of two rotary switches.
Total Hum and Noise, Each Channel: 70 db below« 1.5 volts out.
Tubes: Two 12AX7.
One 6X4 rectifier.
9*’ wide, 53/4” high, 43/4” deep.
105 -125 volts, 50-60 cycles AC. 5watts.
6lbs.
Dimensions:
Power Requirements:
Kit Shipping Weight: .

HEATHKIT ELECTRONIC CROSSOVER
MODEL XO-1
Page 2

Maximum Gain of Each Channel:
Normal Operating Level:
Maximum Recommended Operating Level: ..
Frequency Response:
Low-Frequency Channel:
High-Frequency Channel:
Unity.
2.0 volts rms or less.
5.0 volts rms.
±1.2 db from 10 cycles to cutoff frequency.
±1.2 db from cutoff frequency to 20,000 cycles.
FREQUENCY- C.P.S.
Figure 1
FREQUENCY- C.P.S.
Figure 2
Distortion: Distortion introduced bytheXO-1 is extremely low, and can be considered negligi-
ble. It was not possible to measure intermodulation distortion with laboratory equipment ordin-
arily available, owing to the frequency characteristics of the XO-1; distortion figures so obtained
would not be valid. For this reason, harmonic distortion tests were relied upon to furnish in-
formation as to linearity of the XO-1 circuits.
Page 3

Harmonic Distortion:
Low-Frequency Channel: Less than .1 of 1% at2 volts out at anyfrequency
up to approximately one-half the cutoff frequen-
cy. See curve (Figure 3) for further data on dis-
tortion vs. frequency.
High-Frequency Channel: Less than .25 of 1% when measured at the cut-
off frequency; drops rapidly at higher frequen-
cies, to less than .1 of 1% (see curve of Figure 4).
FREQUENCY
LOW FREQ. CHANNEL
HARMONIC DISTORTION VS. FREO.
Figure 3
100 FREQUENCY 1000
OB
HI. FREO. CHANNEL
HARMONIC DISTORTION VS. FREO.
Figure 4
NOTE: The proper interpretation of these harmonic distortion vs. frequency curves is com-
plicated by the fact that the response is far from flat. In other words, the relative levels of the
fundamental frequency and the total harmonic content are upset by the inherent sloping response
which is an essential characteristic of the XO-1. Thus, the harmonic content measured is not
atrue ’’percentage distortion” under the normal interpretation.
Nevertheless the curves indicate the relationship between harmonic content and the fundamen-
tal at various frequencies in the region of cutoff, which would hold under actual operating con-
ditions; it is NOT aTRUE measure of distortion introduced by non-linearity of the XO-1 itself.
Since the measurements were made by the method which shows ’’total harmonic content”, it is
difficult to accurately correct the curves in order to gain atrue distortion figure for the XO-1.
However, if this were done, it would be found that the distortion would not rise appreciably with
decreasing frequency as appears to be the case in Figure 4. In Figure 3the corrected distortion
figure would be somewhat higher at frequencies close to Fc and would tend to level off above Fc
instead of dropping. However, these corrected distortion figures are of little value anyway in
the case of Figure 3since harmonic products of frequencies approaching Fc are rapidly atten-
uated. From this it can be concluded that distortion introduced by the XO-1, at normal oper-
ating levels, can be considered negligible.
Page 4

NOTE; The performance specifications given are based on careful measurements made on a
typical unit, and kits constructed in exact accordance with the instructions can be expected to
conform to these specifications to areasonable degree. We cannot guarantee, however, that
measurements made on completed kits will be in exact agreement with the specifications, owing
to factors beyond our reasonable control. Such factors include placement of critical leads, nor-
mal variation of components and tube characteristics.
INTRODUCTION
It is generally appreciated that to satisfactorily reproduce the spectrum of audio frequencies
from approximately 30 cycles to 15,000 cycles requires arelatively large speaker or "woofer"
to reproduce the low frequencies, say from 30 to 1000 cycles and acomparitively small speaker
or "tweeter" to reproduce the higher range, in this example, from 1000 to 15,000 cycles. Such
asystem requires anelectrical dividing network or "crossover" to divide the total audio spect-
rum into the proper ranges, in order that only the high frequencies will be fed to the tweeter
and only the low frequencies to the woofer. (Many 2-way speakers built as an integral unit with
separate cones for the high and the low frequencies have abuilt-in or "mechanical" crossover
and are not considered here. Best results and greatest flexibility are generally achieved by the
use of aseparate woofer and tweeter and an electrical, rather than amechanical crossover.
Figure 5shows, in block diagram form, the connection of aconventional electrical crossover
unit of the type which has come into general use. Note that the crossover unit is connected be-
tween the output of the power amplifier and the speakers.
TO PROGRAM
SOURCE
;
(TUNER, PREAMPLIFIER.
ETC. )
TWEETER
WOOFER
Figure 5
The Heathkit XO-1 Electronic Crossover is designed to operate in conjunction with atwo-way
speaker system where separate power amplifiers are used for the high and the low frequencies
as shown in the block diagram of Figure 6. This has several important advantages over the
conventional method of Figure 5.
Figure 6
(1) Since the crossover unit operates at the input of the power amplifiers rather than at the out-
put, no output power is dissipated and therefore wasted in the crossover unit itself. In con-
trast, it is to be noted that aconventional type crossover with an insertion loss of only 1
db would reduce the power capability of a20 watt amplifier to 16 watts and a50 watt ampli-
fier to 40 watts.
Page 5

(2) In an electronic crossover device, it is practical to vary the crossover frequency over a
wide range to accommodate almost countless woofer-tweeter combinations and acoustic en-
vironments. Changing speakers in your hi-fi system will not obsolete the XO-1. Also,
there are no complex impedance matching problems in assembling your own speaker cross-
over system.
(3) It is possible to achieve anear ideal crossover characteristic by means of electronic cir-
cuitry, without significant peaks or valleys in the overall response. Also, the response and
crossover characteristics are unaffected by differences in speakers and enclosures.
(4) Amplifier damping factor is not altered by the crossover device.
(5) The possibility of intermodulation distortion (modulation of the high frequencies by high-
amplitude low frequencies) in the amplifiers is reduced, particularly at high power levels.
(6) No reactive-load conditions, sometimes caused by conventional crossover units, are im-
posed on the power amplifier. Such load conditions can result in instability (oscillation)
in amplifiers with heavy feedback.
It should be noted that while the above discussion is confined to two-way speaker systems, the
XO-1 may be used to good advantage in three or four- way systems. Anumber of suggested
arrangements are given in the section entitled ’’Installation and Operation”.
CIRCUIT DESCRIPTION
The circuitry of the XO-1 is quite simple and straightforward. Refer to the Schematic. It con-
sists basically of ahigh-frequency channel and alow-frequency channel. A12AX7 dual triode is
used in each channel. A6X4 rectifier tube is used in aconventional full wave power supply with
atwo-section RC filter.
The high-frequency channel is actually ahigh- pass filter; it passes only those frequencies above
the cutoff frequency, as shown in the curves of Figure 1. It will be noted that the cutoff fre-
quency may be adjusted to 100, 200, 400, 700, 1200, 2000 or 3500 cycles by means of arotary
switch. Similarly, the low-frequency channel is alow-pass filter which will pass only frequen-
cies below the cutoff frequency, as shown in Figure 2. The cutoff frequency of this channel is
adjustable over the same range by means of another switch. The input signal is applied through
the high and low-frequency LEVEL controls, through suitable isolating resistors to the input of
both channels. The 12AX7 dual triode in each channel is utilized so that one section functions
as again stage and the other as an output cathode follower. Each channel employs two RC net-
works in order to achieve acutoff slope of 12 db per octave since each network contributes 6db
per octave. In each channel the 12AX7 gain stage serves to separate the two RC networks. Ap-
proximately 14 db negative feedback is applied around each channel from the cathode-follower
output back to the grid of the gain stage. The function of this negative feedback is three-fold:
(1) It modifies the shape of the response curves in the region near the cutoff frequency, so that
amuch sharper ’’knee” is imparted to the curve than if feedback were not used. This makes it
possible to maintain essentially flat response up to and including the cutoff frequency, with as
much as 12 db attenuation at twice and one-half this frequency for the low and high-frequency
channel, respectively. (2) Any harmonic distortion developed is reduced by feedback, at fre-
quencies within the passband of either channel. (3) The amount of feedback used reduces the
overall gain to unity since gain is not required in the unit.
The cutoff frequency is varied by switching different values of capacity in both RC networks of
each channel. Although this could be accomplished by switching resistors instead, the level in
the ’’flat” region would vary appreciably with the cutoff frequency due to the finite values of resis-
tance already in the circuit. Aunique method of switching capacitors has been devised whereby
each capacitor (with exceptions) serves for two successive cutoff frequencies. This greatly re-
duces the number of components required and is made possible by ’’staggering” the turnover
frequencies of the two RC networks in each channel.
Page 6

NOTES ON ASSEMBLY AND WIRING
Agreat deal of enginnering has gone into the design of your Heathkit Electronic Crossover to
ensure highest performance and the components have been carefully selected for quality and
long life. We urge you to proceed with the utmost care in construction, follow the instructions
exactly and perform each step in the most workmanlike manner possible. By so doing you will
protect your investment in time and money and be rewarded with the fine performance of which
your Electronic Crossover is capable as well as the deep feeling of satisfaction that comes from
ajob well done.
This manual is supplied to assist you in everyway to complete the instrument with the least pos-
sible chance for error. The detailed instructions are specifically written to allow either the
experienced or inexperienced constructor to construct the unit with aminimum of difficulty.
Only avery small percentage of Heathkit assemblers encounter any difficulty whatsoever in com-
pleting kits of this kind. The large fold-in pictorial diagrams included in this manual are in-
tended to be attached to the wall above your work space, for convenient reference. The dia-
grams are repeated in smaller form within the manual proper.
UNPACK THE KIT CAREFULLY AND CHECK EACH PART AGAINST THE PARTS LIST. DO
NOT DISCARD ANY PACKING MATERIAL UNTIL THIS HAS BEEN DONE. In so doing you will
become acquainted with each part. Full size sketches of the various type parts will be found on
Page 28 to help you identify any questionable components. If aparts shortage is found, please
notify us promptly and return the inspection slip to us with your letter. Hardware items are
counted by weight and if afew are missing, we suggest that to save time, you obtain them locally
if at all possible.
Resistors and controls generally have atolerance rating of ±20% unless otherwise stated in the
parts list. Thus a100 KQ resistor may test anywhere from 80 KQ to 120 KQ and still be ac-
ceptable. Tolerances on electrolytic condensers may be even wider and commonly run from
±100% to -50%. The parts furnished with your Heathkit have been specified so as to meet the
performance specifications given. Refer to the color code information given on the inside front
cover of this manual when in doubt as to the value or tolerance of aresistor or capacitor.
In order to expedite delivery to you, we are occasionally forced to make minor substitutions of
parts. Such substitutions are very carefully checked before they are approved and the parts sup-
plied will work satisfactorily in your kit. For example, if your kit is short a15 K12 resistor
and an 18 K^2 resistor is furnished which is not on the parts list, you will understand that such
asubstitution has been made. This fact is mentioned here only to prevent any confusion in check-
ing the contents of your kit.
CAUTION* We strongly urge that you follow exactly the wiring and parts layout shown in this
manual. The position of certain leads and components in this instrument is quite critical and
changes may seriously affect the characteristics of the circuit.
STEP-BY-STEP ASSEMBLY INSTRUCTIONS
First attach the large fold- in pictorials to the wall above your work space. Then we suggest
that you carefully read through the entire assembly and wiring instructions. This will famili-
arize you with the construction procedure and will tend to prevent errors before they occur.
WE URGE YOU TO FOLLOW THE STEP-BY-STEP INSTRUCTIONS IN THE EXACT ORDER
GIVEN. Read through each step carefully then perform the operation indicated. Place acheck
mark in the space provided ( ) as each step is completed.
In assembling the kit, use lockwashers under all nuts unless otherwise specified. Tube sockets
are mounted inside the chassis; the filter condenser mounting wafer is mounted on top of the
chassis. Other details of construction are included where pertinent in the instructions.
Page 7

Page 8
PICTORIAL
1