Xkitz XAMP-M2 User manual

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Audio Bi-Amplifier, 40W, Mono, 2-Way Active Crossover
Model XAMP-M2
Assembly and perator’s Manual
Rev 5.1.2
Xkitz.com
Features
•2-way active cross-over drives dual amplifiers for driving separate woofer and tweeter
•Linkwitz-Riley crossover, 4
th
order, 24dB/ ctave roll-off
•Uses the highly respected LM4766 Chip Amp to produce 40W peak on both woofer and tweeter
•Crossover frequency configuration components are on a single socketed module - quick and easy to change
the X frequency by simply snapping in a new module.
•Wide range of standard X frequency modules are offered by Xkitz, any frequency available on request
•Baffle Step Compensation, optional, adjustable and configurable to support various baffle sizes
•Supports unbalanced signal inputs by default, balanced audio signaling is available as an add-on option.
Unbalanced signals are connected via standard RCA jacks
Balanced signals are connected via optional 3.5mm TRS jack. The TRS jack is wired to be directly
compatible with the new hi-def audio players such as the Pono
•Specifications:
THD: 0.044%
THD+N: 0.046%
Frequency Response Linear from 20Hz – 80KHz
CMRR (balanced input): > 55dB
Input Impedance 20K ohms unbalanced, 40K balanced
Input verload: 3.8V peak-to-peak
Voltage Gain: Adjustable, Max 26dB
Power utput Per Channel: 12W RMS into 8 hms, 21W RMS into 4 hms
Filter Topology: Linkwitz-Riley, Constant Voltage, 4
th
rder, 24dB/octave
Amplifier Type: Class AB
Power supply: Single positive DC rail (no negative supply required) 22V–50V DC
•Applications:
•Active Monitors
•Speaker Bi-Amp conversions
•Bi-Amp’ed Active Speaker System
•Portable boom-box
•Portable guitar amplifier
•Custom speaker systems
•Channels are phase aligned to within a fraction of a degree to minimize distortion around the X frequency
•Separate bass and treble output level adjustments via on-board multi-turn trim-pots
•Low power consumption and no negative supply needed - perfect for portable battery powered speakers
•Quiet power N / power FF
•This is a mono device, two units are needed for stereo operation
•PCB Dimensions: 3.4” x 3” x 2” high (86mm x 76mm x 51mm)
•This is an intermediate electronic kit containing 85 components, and can be assembled in about 1-2 hours

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Unpacking Your Kit
Carefully unpack and take stock of the components in your kit. The electronic components are packed in 2 bags
labeled ‘Bag A’ and ‘Bag B’. See Table 1 for a complete listing of your components.
Assembly Instructions
It is very important that you read and understand all of the following instructions before you start your
assembly so that you don’t make any mistakes that might be difficult to recover from. The assembly should be
done in the order listed in Table 1 or you may have difficulty physically accessing components for soldering.
What you’ll need
 Soldering iron with small or medium tip
 Damp sponge for tip cleaning
 Solder
 Solder wick or solder sucker in case of solder bridging (stranded wire could substitute)
 Small needle nose pliers.
 Small wire cutters
 Small straight screwdriver
 Sharp knife
 Magnifying glass to read the markings on the tiny components
General Assembly Guidelines
 Take your time!! Most mistakes are made when rushing through the assembly. Taking the time to
double check every step will pay off with a first-time functional device.
 In cases where it is necessary to re-form the leads on components (such as resistors and diodes),
be very careful not to put stress where the lead enters the component itself. The physical
attachment of the lead to the component can sometimes be very fragile and the lead may break off
if too much force is applied. Reforming the leads can be done by gripping the lead with small
needle-nose pliers at the base of the component while bending the lead on the other side of the
pliers.
 Use as little heat and solder as necessary to affix the components to the PCB (printed circuit
board). Many of the parts in this kit are temperature sensitive. verheating may damage them.
 Always clean the soldering iron tip on the damp sponge prior to every solder joint. Re-tin whenever
the tip gets a little dull. (tinning is the application of fresh solder to the tip of the iron until its
shiny, wipe excess on a damp sponge).
 Inspect the solder joints. They should be shiny and smoothly connect the pad to the lead. A dull
looking joint may indicate it is ‘cold’, meaning that either the pad or the lead weren’t heated enough
to allow reliable connection. This could lead to erratic operation of the device. Re-flow the joint
again with the soldering iron, apply equal heat to both the pad and the lead, apply a little more
solder if needed to get a good shiny connection.
 When clipping the excess leads of the through-hole parts, don’t try to clip too close to the PCB. Clip
just above the solder joint to avoid fracturing the solder joint, which could lead to device failure
sometime in the future.
 Carefully inspect each solder joint to make sure you didn’t accidentally form a ‘solder bridge’, or
connect two adjacent pads together. Remove solder bridges by using solder wick or a solder sucker.
If the bridge is small you may be able to remove it by just reheating the joint and sliding the
soldering iron across the bridge. If not, see the next step.
 If you need to remove solder from a hole (or a solder bridge) and you don’t have solder wick or a
solder sucker, you can use stripped stranded wire in place of solder wick. Place the stranded wire
across the hole and touch the soldering iron to the wire, above the hole. As the wire heats it will
melt the solder in the hole, and the melted solder will tend to wick up into the stranded wire. When
the wire fills up with solder, move a clean part of the wire over the hole and repeat until the hole is
clear of solder.

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ircuit Board Assembly
You're ready to begin assembling your XAMP-M2 circuit board. Assemble the board in the order listed in Table
1. The components for the standard kit (in bags marked ‘Bag A’ and ‘Bag B’) support the default configuration:
UNBALANCED signal mode. If you purchased the BALANCED signal mode upgrade, you will have an additional
bag labeled ‘Balanced Mode Upgrade’, which contains the components required to configure the XAMP-M2 to
support balanced input. Table 1 below lists the parts and assembly steps for the standard board. Table 2 has
the parts lists and specific instructions for the Balanced mode option. Use the install check boxes on the right
side to track your progress. The 'Install Notes' column will alert you to any special instructions (listed below) for
each of the components. We recommend reading and understanding all the design notes before you start your
assembly. The PCB has large, heavy metal planes, which makes de-soldering components extremely difficult.
Soldering a component in the wrong location may be a difficult mistake to recover from.
Table 1. ircuit Board Parts List – Parts Used for All onfiguration Options
Pack
√ Device Value Marking Qty Reference Designators
Bag Install
Notes
Install
√
CIRCUIT B ARD (PCB) REV 5.1 XAMP-M2 1
RESIST R 1K,1% BRN-BLK-BLK-BRN-BRN 10
R1,R14,R15,
R16,R19,R25,
R27,R45,R50,
R62
A
RESIST R 10K,1% BRN-BLK-BLK-RED-BRN 6 R4,R7,R10,
R12,R49,R51
A 1
RESIST R 20K,1% RED-BLK-BLK-RED-BRN 3 R2,R11,R17 A 1
RESIST R 10K,1% BRN-BLK-BLK-RED-BRN 3 R21,R22,R23 A 2
RESIST R 20K,1% RED-BLK-BLK-RED-BRN 2 R20 ,R24 A 2
RESIST R 4.7,1% YEL-VI -BLK-SLV-BRN 2 R3,R18 A
RESIST R 10 BRN-BLK-BLK 1 R26 A
RESIST R 15K,1% BRN-GRN-BLK-RED-BRN 1 R28 A
RESIST R 82.5K,1% GRY-RED-GRN- RA-BRN 1 R6 A
RESIST R 100K,1% BRN-BLK-BLK- RA-BRN 1 R9 A
RESIST R 200K,1% RED-BLK-BLK- RA-BRN 2 R5,R8 A
DI DE 1N5240 1N5240 1 D1 A 3
CAPACIT R 10pF 100 2 C11,C14 A 4
CAPACIT R 100pF 101 1 C59 A 4
CAPACIT R .1uF 104 9
C2,C7,C9,
C10,C26,C27,
C28,C29,C32
A
4
CAPACIT R .47uF 474 2 C30,C31 A 4
CAPACIT R 10uF 106 4 C12,C13,C18,
C21
A 4
CAPACIT R .015uF, 5% 153 (Blue colored ones) 10
C49,C50,C51,
C52,C53,C54,
C55,C56,C57,
C58
A
4
CAPACIT R
BSC Configuration Cap:
ne of: (See Table 3)
.022uF 223
.033uF 333
.047uF 473
1 C42
A
5
S CKET – 8 PIN 1 U2 A 6
S CKET – 14 PIN 2 U1,U3 A 6
P AMP IC TL072 TL072 (or PA2227) 1 U2 A 7
P AMP IC TL074 TL074 (or PA4227) 2 U1,U3 A 7
S CKET – 20 PIN 1 X M DULE A 8
C MP NENT CARRIER – 20
PIN 1 X M DULE 8
SPADE TERMINAL 6 SP1,SP2,SP3,
SP4,SP5, SP6
A
TRANSIST R 2N3904 2N3904 2 Q1,Q3 A 9
V LTAGE REGULAT R LM317TG LM317TG 1 U4 9
TRIMP T 10K R10K 3 VR1,
VR2,VR3
A 10
ELECTR LYTIC CAPACIT R 10uF 10uF 1 C5 A 11
ELECTR LYTIC CAPACIT R 22uF 22uF 3 C1,C6,C8 A 11
ELECTR LYTIC CAPACIT R 100uF 100uF 2 C25,C39 A 11
ELECTR LYTIC CAPACIT R 1000uF 1000uF 1 C3 B 11
ELECTR LYTIC CAPACIT R 3300uF 3300uF 2 C4,C24 B 11

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RCA JACK 1 J2 B 12
AMPLIFIER CHIP LM4766 1 U5 B 13
HEAT SINK 1 B 13
4-40 SCREW 1 B 13
4-40 L CK NUT 1 B 13
N C MP NENTS G HERE J3 14
Table 2. Balanced Signal Input Upgrade Parts List
Pack
√ Device Value Marking Qty Reference Designators
Bag Install
Notes
Install
√
RESIST R 10K, 0.1% BRN-BLK-BLK-RED-VI 3 R21,R22,R23 2
RESIST R 20K, 0.1% RED-BLK-BLK-RED-VI 2 R20,R24 2
3.5MM TRS JACK 1 J1 12
ircuit Board omponent Installation Notes:
1. You will have extra 10K and 20K resistors after this step. These extras will be used in the next step.
2. Install the 1% tolerance 10K and 20K resistors included in the standard kit NLY if you’re running in
UN-BALANCED input signal mode. If you purchased the optional BALANCED mode upgrade, then
discard these 1% 10K and 20K resistors, and install the 0.1% tolerance 10K and 20K resistors
included in your BALANCED Mode Upgrade packet instead.
3. Diodes are polarized devices; which means they won’t work if installed the wrong way around. A solid
bar on one end of the diode marks the cathode. The cathode goes in the square pad hole on the
PCB.
4. Be sure to install these caps as close to the PCB as possible, especially C26 and C27, as they must fit
underneath the U5 LM4766 amplifier chip.
5. To configure the Baffle Step Compensation circuit, install the appropriate cap value in C42. There are
3 possible cap values to install for C42, depending on your baffle size. See Table 3 below.
6. Solder the 8 pin and 14 pin sockets into the PCB to hold the op amps. Align the notches on one end of
the sockets to the notches shown on the PCB silkscreen.
7. Install the TL072 and TL074 op amp chips (or the PA2227/ PA4227 chips if you’ve purchased this
upgrade) into the sockets. The op amp chips are polarized devices, installing them backward will
permanently damage the devices. Align the notch on one end of the op amp chips to the notches
shown on the PCB silkscreen. Be careful not to bend the leads on the op-amp chips when inserting
into the sockets.
8. Install the 20 pin socket in the location on the board marked ‘X M DULE’ (the row of resistors from
R57 at the top through R56 at the bottom). Install with the pin 1 notch toward ‘R57’ at the top of the
M DULE. Carefully insert the 20-pin component carrier into the 20-pin socket marked ‘X M DULE’
with the chamfered corner matching that of the PCB pattern. Solder the 10 resistors included in the
X component pack to the component carrier to configure your crossover frequency. Use the parts
placement diagram below and the instruction slip in your X component pack to assemble the
Module. The 10 resistors are simply inserted across the component carrier and slipped into the two
horizontally adjacent, fork shaped pins. When you’ve double checked they’re all in the correct
locations, solder them in place. Cut the excess leads.
9. Install the transistors and voltage regulator with their shapes matching the shapes on the PCB
silkscreen.
10. Install the multi-turn trim-pots in the orientation shown on the PCB pattern.
11. The electrolytic capacitors are polarized devices, be sure to install them the right way around. The
positive lead is longer than the negative lead. The positive lead goes in the square pad hole on the PCB.
Note that the polarity is also marked on the outer casing of the caps.
12. Install the RCA jack in locations J2 NLY if running in the stock UN-BALANCED mode. If you
purchased the optional BALANCED mode upgrade, then discard the RCA jack and install the 3.5mm
jack included in your upgrade packet in location J1 instead. Note that the PCB hole patterns for the
RCA jack and the 3.5mm jack overlap on the PCB. This is not a problem, since the RCA and 3.5mm
are used mutually exclusively.
13. Install the amplifier chip. Attach the LM4766 to the heat sink loosely with the screw and nut. Insert
the assembly and solder the chip pins and the heat sink tabs. Tighten the screw to secure the chip to
the heat sink.
14. Leave these locations empty. They are not required for this kit.

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Figure 1. P B Parts Placement and Dimensions
0.12"
3.4"
0.12"
3.0"
Board Height: 2.0"

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Input Signal onfiguration – Balanced or Unbalanced (Optional)
There are two basic systems used to connect the audio signal on consumer and pro audio equipment;
unbalanced lines and balanced lines. Unbalanced lines use one wire for signal and the other for ground.
Balanced lines, on the other hand, have two signal wires and a shield ground wire.
Unbalanced lines are most common in consumer grade audio, and are generally much more susceptible to
audio noise like 50/60Hz hum. Unbalanced lines will also pick up any electro-magnetic noise in the nearby
environment (such as computers, cell phones, microwaves, etc.) and adds it to your audio signal, making it
audible in your speakers. Unbalanced lines can also lead to ground loops, which are the major source of
50/60Hz hum in your sound system. Ground loops arise whenever there is more than one path from any piece
of audio equipment to earth ground. Your equipment will always be grounded through your AC line. Adding
another path to ground through your unbalanced audio cable adds a second path to ground, and this can
cause audible 50/60Hz hum.
Balanced lines are more common in high end consumer and professional audio systems and are much less
susceptible to noise. Balanced lines allow you to run very long audio cables without allowing electro-magnetic
noise to couple into your signal. They’re also not susceptible to 50/60Hz hum; there is no connection to ground
in the audio signal cable, so they can’t create ground loops in your sound system.
For unbalanced signal input, you’ll install the RCA jack in location J2, and leave the J1 location empty.
For balanced signal input, you’ll install the 3.5mm TRS jack in location J1, and leave the J2 location empty.
Figure 2. Balanced Mode signal Input TRS Jack Wiring
Heat Sinking
The XAMP-M2 includes a heat sink to remove heat from the LM4766 amplifier chip. This heat sink is sufficient
for lower power applications. For applications that are expected to run at high power for long periods of time,
you may want to attach an additional heat sink to augment the existing one.
The stock heat sink is conveniently mounted on one edge of the board, allowing easy attachment of an
additional heat sink, or to the interior wall of a metal chassis.

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ustomizing Your Active rossover Frequency
The crossover (X ) frequency is determined by the value of the ten resistors mounted to a 20-pin socketed
component carrier called the ‘X Module’. All 10 resistors are set to the same value.
Xkitz offers a wide range of standard X Module frequencies at this location:
https://www.xkitz.com/collections/active-crossovers-and-bi-amplifiers-1/products/xo-module-for-use-with-
xover-2-and-xamps
r you can select your own custom X frequency resistor values with our filter calculator tool at:
http://www.xkitzconnect.com/files/Linkwitz-Riley-2Way-Calculator.htm
Just enter your desired crossover frequency. Then hit the ‘Calc’ button. It will give you the suggested resistor
value for your crossover, and it will show a schematic diagram of the crossover. You may have to round the
suggested values to standard available resistor values. High precision (1% or better) resistors are recommended
to minimize distortion.
Selecting Your Ideal rossover Frequency
Consult the specifications of your loudspeakers to select your ideal X frequency. Every loudspeaker has its
own ideal operating frequency range. Woofers, of course, work well in the low frequency range, but as frequency
increases their performance deteriorates. Same for tweeters; they operate well at upper frequency ranges and
deteriorate as the frequency comes down. Your crossover frequency should be somewhere near the mid-point
between points where both the woofer and the tweeter are still solidly within their ideal operating frequency
range.
Baffle Step ompensation
The Baffle Step Compensation circuit, or BSC, if you choose to use it, allows you to apply a low pass filter
function to the audio signal to compensate for a phenomenon where sounds above a certain frequency
(determined by the size of the baffle, or the front of your speaker box) are actually reflected by the front of the
speaker enclosure. Sounds that fall below that frequency do not get reflected, but instead wrap around the back
of the speaker enclosure. This has the effect of reducing the magnitude of the lower frequencies. Your ear hears
the primary waves plus the reflected waves on the highs, but only the primary waves of the lows. The BSC
circuit, by applying a low pass filter, will roll off some of the highs to restore the overall sound to a more natural,
linear state. Check the web for more detailed description of BSC.
The VR3 precision 20-turn trim-pot allows the BSC magnitude to be adjusted. Turning the pot 20 full
revolutions counter-clockwise reduces the BSC magnitude to the point of being entirely disabled. Turning it
clockwise increases the BSC magnitude to a maximum of 6dB. In other words, it increases the amount of
attenuation of the higher frequencies to 6dB below the lower frequencies. This compensates for the theoretical
6dB attenuation of the low frequencies due to the baffle step.
Table 3. Baffle Step Compensation – Recommended C42 Value
Baffle Width (in Inches) Baffle Step Freq. C42 Value
Less than 10" 507Hz 0.022uF
10" - 16" 351Hz 0.033uF
Greater than 16" 240Hz 0.047uF

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Initial Power-up and alibration
Before applying power for the first time, it’s a good idea to make sure the bass, treble and BSC are fully
disabled. The trim-pots are high precision, 20 turn pots, so in order to ensure the bass, treble and BSC are fully
FF you need to turn all three trim-pots 20 full revolutions counter-clockwise.
There are a number of different methods to calibrate a 2-way active crossover. Below is the method we generally
prefer. We like to first set the bass level using a voltmeter or an oscilloscope, then gradually raise the level of the
high channel and set the ideal level exclusively by ear or with a spectrum analyzer.
In a stereo system, you’ll want to try and calibrate both L and R at the same time to maintain a close balance of
the L and R volume levels.
For steps 1-4, you should disconnect your speakers from the amplifiers because it’ll be very loud.
1. Use a signal generator of some kind to inject a sine wave into the XAMP. Free signal generator apps are
widely available for any smart phone or on the PC.
2. Set the level of the signal generator to 0.5V RMS. n a voltmeter set to AC, it will read 0.5V. n an
oscilloscope you’ll see a signal with a swing of 1.41V peak-to-peak.
3. Set the frequency of the signal generator to around 50Hz.
4. Set your voltmeter to AC and connect it to the Woofer speaker outputs. Raise the Bass level pot until
the output voltage is equal the ‘Volts RMS’ listed in Table 4 below for your power supply voltage and
woofer impedance. The table also shows the max RMS watts per channel power you can expect for each
setting.
5. Now that you have your bass level set, it’s time to set the crossover Treble levels. Connect your
speakers to the amplifier and your normal audio signal source to the input and set the volumes to a
comfortable listening level. Either use a spectrum analyzer (free smart phone or PC apps are available)
or just use your ears to monitor the audio from your speakers. Since the Treble levels are set to zero,
the sound will start out dull and lacking in any high frequencies. Slowly raise the Treble level control
pot until your treble levels are flat on the spectrum analyzer, or until they sound natural by ear. You
may want to adjust the L and R in isolation so that you can make sure both are dialed in perfectly,
without the other channel interfering.
6. Now slowly raise the BSC pot(s) until your bass response sounds natural, or the lows below the baffle
step frequency look flat on the spectrum analyzer (see table 3).
Table 4. Max Woofer Output Voltage vs. Power Supply Voltage and Driver Impedance
4 hm Speaker 8 hm Speaker Power Supply
Volts DC Volts RMS RMS Watts Volts RMS RMS Watts
22V 5.9V 9W 6.2V 5W
24V 6.4V 10W 6.8V 6W
26V 6.9V 12W 7.5V 7W
28V 7.5V 14W 8.3V 9W
30V 8.1V 16W 9.0V 10W
32V 8.6V 19W 9.4V 11W
>34 9.2V 21W 10.0 12W

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Power Supply
The XAMP-M2 requires only a single positive DC voltage from 22V up to about 50V. The LM4766 will only
operate properly in this voltage range. The higher the voltage, the more audio power it will produce. Higher
supply voltage will also put out cleaner audio, even if you’re not running it loud, but it will consume more
power.
n the XAMP-M2 there is no real advantage to using a supply voltage greater than 34V, as this won’t lead to
any higher power output, and will only cause more unnecessary heat for you heat sink to dissipate.
Batteries are a good choice for powering the XAMP-M2, they will provide very clean DC voltage. A good selection
would be two small 12V lead acid batteries in series. This has the advantage of being rechargeable, and they’re
reasonably priced.
If you plan to run the amplifier from AC mains voltage, either 110 or 220VAC, consider our Audio Grade 200W
DC power supply: the XAPS-200W. It takes in AC from a power transformer and creates very clean, well
regulated DC voltage for your amplifier.
Troubleshooting
If you’re having trouble with your device, check Table 5 below for possible cause and solution.
Table 5. Troubleshooting Guide
Problem Possible Cause Solution
Power supply not
working, no input
signal
•Verify DC voltage input is applied and connected K
•Check line level signal wiring
No activity - circuit
doesn't seem to do
anything
Power supply
voltage out of the
range of 22V-50V
•The LM4766 amplifier chip will not operate outside of this
voltage range
Sounds bad, muffled Woofer/Tweeter
swapped
If the woofer and tweeter driver wires get swapped, it will sound
very bad, check your wiring.
60Hz audible hum Grounding
problems, noise
on the DC supply
•Make sure all you’re audio source and amplifier and any
other components are solidly grounded to earth ground
•Try driving the amp with a 9V battery, if the hum goes
away then there’s noise on your DC power supply.
•Change line-in configuration: balanced or unbalanced

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Figure 3. Woofer, 2.83V into 8 Ohms (1W) THD=0.038% THD+N=0.041%
Figure 4. Woofer Full Output, THD=0.054% THD+N=0.049%

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Figure 5. Tweeter, 2.83V into 8 Ohms (1W) THD=0.044% THD+N=0.046%
Figure 6. Tweeter Full Output, THD=0.12% THD+N=0.11%

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Figure 7. XAMP-M2 Schematic