Little Dot MK III User manual

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Little Dot MK III
Little Dot MK III Headphone Amplifier/Pre-Amplifier
Reference Guide
Version 1.2
Last Updated 10.17.2014
The latest version of this Reference Guide can always be found here

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Safety Notice
1．Risk of electric shock - do not open chassis during operation.
2．Do not use inside poorly ventilated areas with restricted airflow (such as within cabinet).
3．Do not use near heat sources, or any other apparatus that produces heat.
4．Clean only with a dry cloth, and do not use near water or moisture.
5．Unplug during lightening storms or when unused for long periods.
6．For best protection from power spikes/brown outs, use with a battery backup and/or surge protector.
7．Amplifier may be hot during operation. Do not touch vacuum tubes or chassis during operation or
immediately after operation.
8．Keep away from small children and/or pets.
9．In case of damage or malfunction, suspend usage immediately, unplug the power source, and refer
all servicing to qualified personnel. Please contact Little Dot for assistance.

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Basic Troubleshooting
Ground Loops: In systems where the components have multiple paths to ground, you may notice a 60
Hz hum on the Little Dot output. Please only use a cheater plug power-cord as the last resort, as this
can be a safety hazard. To resolve ground loop issues, the better method would be to use a ground
loop isolator. The ideal method would be to solve the ground loop at its source by connecting all
components to common ground and/or have your electrical wiring checked by a professional electrician.
Swapping Tubes and other changes: To minimize chances of damaging your Little Dot, make sure to
power off, disconnect the power cable, and wait at least 5-10 minutes before attempting swapping tubes,
changing gain settings, or capping/uncapping the jumper switches. This allows the capacitors to fully
discharge.
Plugging/Unplugging Headphones: It is recommended to only plug/unplug your headphones while
your Little Dot is powered off.
Channel Imbalance: Try swapping the left and right side tubes to see if the channel imbalance moves.
If so, continue swapping the tubes as needed to isolate the particular tube that’s causing the issue.
Also verify the gain settings are set the same way for both channels.
Static/Noise in one or both channels: Try cleaning the tube pins to free them of oxidation. Also check
for sources of interference nearby such as wireless routers, telephone base stations, and other RF
emitting devices. Check the fuse and re-seat it so that it makes good electrical contact. Move all
switches back and forth several times to “loosen” them, and then set them securely into position. Both
the switches and fuse can shift during transit. Lastly, try a different power cord than the one included.
Loudness is constant, and volume control does not work for one or both channels: You likely
have your source hooked up to Little Dot pre-amp outputs instead of the inputs. Verify your RCA cables
are connected to the INPUT and try again.
Little Dot does not power on: If you are using the stock power cord, try another. Check the condition
of the fuse located beside the power cord plug and replace if necessary.
General: For general strange behavior (noise, non-functioning channels, etc) please check and re-seat
the fuse. The fact that the amplifier powers on does not necessarily mean the fuse is making
optimal contact. When new, the gain switches can be tight. Move each switch back and forth several
times and then securely set them into position. Swapping the power cord is also a recommended
troubleshooting step

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Vacuum Tube Troubleshooting
Noisy Tubes: Since the tubes used in Little Dot amplifiers can be very old, there is a distinct possibility
the pins have oxidized and therefore can cause hissing, crackling, buzzing, and various other noises
during operation. This is common with vacuum tubes and is nothing to worry about, as there is an easy
remedy. There exists de-oxidizing electronics cleaner (for example Caig deoxIT) which will remove all
hissing and noises in 95% of such cases. It is also good tube practice to regularly clean tube pins with
such de-oxidizing cleaners.
Interference: Interference can be picked up by the tubes and cause odd noises. To minimize
interference, keep your Little Dot isolated from wireless routers, cell phones, telephone base stations,
and other common sources of RF or EMI noise. Generally speaking, the M8161 and other mil-spec
tubes will reject much more interference than the 5654/M8100s.
Isolating Tube Noise: To isolate tube noise, first note which channel the noise appears in, and then
power off the amplifier and wait 5-10 minutes before swapping the front driver tubes. Listen again to
check if the noise has traveled to the other channel. If so, you have isolated the problematic tube. If
not, repeat for the rear power tubes. Problematic tubes may need cleaning/de-oxidizing or replacement.
Signs of Failing Vacuum Tubes:
oWhooshing noise (likely a faulty driver tube)
oGlow changes to purple (not blue) color
oTube once had a mirrored or silver tip, but now is white or clear (lost vacuum)
oScratching/high frequency distortion
oGain has decreased significantly

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First Time Use
Before powering on your Little Dot for the first time, please make sure the tubes are all securely inserted into
their sockets as they can become loose during transit. It is also recommend to first clean the tube pins with
electronics or de-oxidizing cleaner to remove any grime or oxidation that may have occurred. While the
tubes are cleaned in the factory with isopropyl alcohol, a de-oxidizing agent is not used since we do not
have access to such compounds in China at the current time.
“Burn-In”
While it’s OK to burn-in your Little Dot amplifier, it is not recommended to leave your Little Dot running 24
hours a day. We suggest for every 6-8 hours of burn-in, you allow your Little Dot to cool-down for 30
minutes to an hour. Please also refrain from burning-in your Little Dot in an area with little to no airflow, and
can easily build up heat. Any music, sine sweeps, or pink noise is acceptable, and the volume should be
just slightly higher than listening volume. Headphones should be plugged in during burn-in.

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Little Dot MK III Introduction
Thank you for purchasing the Little Dot MK III vacuum tube headphone amplifier! Hope this manual can help
you easily enjoy your Little Dot MK III’s sonic capabilities.
Before you use Little Dot MK III, please read this manual carefully. If you have some other problem, please
contact us or visit our website www.littledot.net, and we will answer all your questions as soon as possible.
The All-New Little Dot MK III succeeds our Little Dot II++ by improving upon it in every possible
way. Boasting the highest stability and sound quality yet, the sound-stage realism and imaging precision
have improved dramatically over our previous amplifiers, and even at high volumes the Little Dot MKIII
delivers a smooth, non-fatiguing sound with no hint of dynamic compression or imaging fuzz. Of course the
liquid warm midrange tube lovers expect is here in spades, balancing right in with a dynamic low-end and a
sweet, airy treble. Tracking precision with low distortion is provided by an ALPS-16 potentiometer, and
Rubycon, German WIMA and ERO capacitors ensure the internal circuitry is built with quality in mind.
The Little Dot MK III also adds in user-tweaking options such as two gain switches to delivery maximum
compatibility with all your headphones, regardless of impedance or sensitivity. Also available for the very
first time in a Little Dot amplifier, is an internal jumper to allow use with a wider range of driver tube-rolling,
including the EF92, EF91, CV138, CV131, WE403A/B, GE5654, M8100, CV4010, EF95, 6JI as well as all
equivalents to these vacuum tubes!

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Little Dot MK III Technical Specifications
Frequency response: 12 hz~100 Khz (-1dB)
THD+N: 0.15% (80 mW @300 ohm)
Power Output:
350 mW @ 300/600 ohm
300 mW @ 120 oh
100 mW @ 32 ohm
Variable Gain: 3,4,5, or 10x
Recommended Load Impedance: 32 ohm~600 ohm
Input Impedance: 50K ohms
Pre-Amplifier Output Impedance: 600 ohms
Pre-Amplifier Gain: 3-10x (also controlled via gain switches)
Pre-Amplifier Voltage: 10V RMS
Power Consumption: 30W (228V * 0.130A)
Pre-Amplification circuit includes both driver and power tubes
Driver Tubes: 2x GE5654
Power Tubes: 2x Soviet 6H6PI
High quality aluminum chassis
Dimensions (Metric): 270mm deep by 175mm wide by 123mm high
Dimensions (English): 10.6 inches deep by 6.9 inches wide by 4.8 inches
Weight: 3 Kg or 6.6 lbs

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Little Dot MK III Gain Control
The Little Dot MK III has two internal, red DIP gain switch boxes, which controls the gain of the amplifier.
You can access the gain switches through the center oblong hole on the bottom of the amplifier. Please
power off the amplifier, and unplug it for at least 10 minutes before attempting to change the gain settings (to
ensure capacitors have fully discharged).
Each red box (that has two switches on it) controls the gain for its particular channel. Under most normal
circumstances, you would want the same gain in both channels so please remember to configure the
switches on each red box identically with respect to the other:
Switch 1 Position
Switch 2 Position
Gain
Recommendation
OFF
OFF
10
Low impedance and/or low
sensitivity headphones
ON
OFF
5
Medium impedance/sensitivity
OFF
ON
4
Medium impedance/sensitivity
ON
ON
3
High impedance and/or high
sensitivity
Note: The gain settings also affect the pre-amplifier output.
These gain settings are recommendations only and there is no “correct” gain for any particular headphone.
You are encouraged to test each setting out with your headphone(s) to determine which setting sounds best
for you.

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Little Dot MK III Pre-Amplifier Use
The Little Dot MK III is not to be used with a DC or direct coupled power amplifier. Doing so may
result in damage to your Little Dot and/or downstream components!
The pre-amplification signal in the Little Dot MK III includes both the driver and power tubes for better
compatibility with power amplifiers with low input impedance (for example, transistor-based power amps).
Always power on your Little Dot MK III pre-amplifier before you power on your connected power amplifier as
this is good practice for any pre-power combination (i.e. power on components from upstream to
downstream). It is also highly recommended to wait at least a minute after powering on your Little Dot
before turning on your power amplifier so that the Little Dot’s tubes have time to stabilize.
When powering your system off, always switch everything off from downstream to upstream, i.e. first turn off
your power amplifier, then your pre-amp, and finally your source.
For best sound quality and lowest noise, first maximize your source’s output level without introducing gain
(i.e. to 0 dB), and then set your Little Dot MK III’s volume to a relatively high level. Amplification done at the
pre-amp stage will result in less noise than amplification done at the power amplifier stage (if the amplifier
you are using as a power amp has volume control at all).
One last thing to remember is keep all your components connected to the same ground, as introducing
another amplifier in a pre-power setup increases the likelihood of introducing a ground loop.

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Little Dot MK III Jumpers for Driver Tube-Rolling
The Little Dot MK III has three jumper pins (JI) that allow two different types of driver tubes (earlier circuit
versions may have switches or 2 pins). You can access the jumper pins through the amplifier’s bottom panel,
and they are located to the sides of the pair of capacitors closest to the front of the amplifier. Please power
off the amplifier when you are doing this.
If the jumper caps are covering pins 1 and 2 (OFF), the following EF95 type driver tubes may be used:
WE403A
5654, CK5654, GL5654, 5591, CV4010, CV5216, CV8246, 6069, CV10442
EF95, M8100, 6AK5W, CV10100, CV8159, CV8225, CV850
6J1
If jumpers are covering pins 2 and 3 (ON) the following EF92 type driver tubes may be used:
EF92, 6CQ6, CV2023, V884, VP6, M8161
EF91, 6AM6, CV10327, CV138, CV1955, CV2195, Z77
CV131, 9D6, W77
Any other equivalents or drop-in replacements for the above-mentioned tubes (both sets) may also be used.
IMPORTANT: Please be careful when setting switches and jumper caps as these are circuit elements and
will be fairly delicate. Using too much force may result in damage!