Linear Tube Audio ZOTL10 User manual

ZOTL10
POWER AMPLIFIER
USER GUIDE
Linear Tube Audio
Takoma Park, MD USA
WARNING: For safety, the cover of this amplifier should be secured at all times. DC
voltages as high as 700V and peak AC voltages as high as 800V are present inside. The service
information contained in this manual is intended only for trained service personnel. Furthermore,
this amplifier generates radio-frequency energy that can interfere with communications
equipment.
Note: The circuitry is different in ZOTL amplifiers than any other tube amplifier. Do not
attempt to service this yourself even if you are familiar with tube amplifier circuitry.
Call or email Linear Tube Audio if you have any need to service this amplifier.
301-448-1534
[email protected]
Introduction
The ZOTL10 is a high quality Class AB tube Power amplifier utilizing ZOTL (Zero-hysteresis
Output Transformer-Less) technology. This is significantly different from traditional OTL
(Output Transformer-Less) technology.
Features
•ZOTL technology eliminates the need for output transformers,
•ZOTL technology enables the correct turns ratio coupling between amplifier and speakers
(which cannot be done using output transformers)
•ZOTL technology operates tubes operated in a manner to last as long as 10,000 hours
•Very little hum – not audible until volume is turned up more than 50%
•Uses 4 EL-84s, 2 12AU7s, and 2 12AT7 tubes. Supplied with current-production Genalex
Gold Lion tubes.
•3 Inputs – RCA without volume control, RCA with volume control, or unbalanced XLR/
phone jacks
•Sophisticated protection circuity monitors the output to shut the amplifier down if the
wrong signal is detected. Amplifier is not harmed if nothing is connected when turned
on, but the protection circuitry functions much better if speakers are connected.
•Auto-bias circuitry for automatic tube biasing.

•Universal voltage power supply – works in any country automatically
•Low impedance output easily matches wide range of speakers
•Designed by David Berning, one of world’s leading amplifier designers
•Same technology and tone as ZOTL amps that cost thousands more
•No heavy power or audio transformers – unit weighs only 14 lbs.
•Patented impedance conversion technology
Operation
Operation of the ZOTL10 amplifier is straightforward. It is not an integrated amplifier, but can
be used with a high-level source such as a preamp, CD player, DAC or electronic crossover. We
do recommend that it is paired with a preamp. The amplifier has one set of speaker binding posts
per channel. There is a volume control on the front panel that can be used or not depending on
which input the source is connected. There should be only one source connected to any of the
three inputs. Speakers from 2 ohms to 16 ohms can be connected to the speaker terminals. You
will not damage the amplifier if there is nothing connected to the speaker terminals, but we
advise that speakers are connected when the amp is in use, to optimize the function of the
protection circuit.
When the amplifier is powered up, the tube high voltage is delayed until the tubes are heated.
This takes about 45 seconds. A brief burst of electronic noise that sounds like static is normal.
The amplifier should quickly smooth out into its normal musical output. Be sure that the
amplifier is operating in a well ventilated environment to ensure the heat from the tubes
adequately dissipates.
Power Sources
The universal input automatically adapts to the input voltage almost anywhere in the world. The
voltage is rated to work with any voltage between 100VAC and 240VAC, and from 50Hz or 60
Hz.
Inputs
There are three different inputs. However, only one input can be used at one time. The three
are described below:
Direct Input: a stereo pair of RCA jacks go straight to the amplifier with nothing in the path.
XLR Inputs: a stereo pair of unbalanced, combo XLR and Phone plug jacks are also available.
Each 3 pin XLR contains one stereo channel. The XLR is standard Pin 2 hot.
Volume Control Inputs: There is another pair of RCA jacks that go through the volume control
located on the front panel when using the amplifier with a source device that does not have a
volume control. It is a Japanese ALPS Blue Velvet volume control.

Mono-Stereo Switch: On the back panel next to the RCA inputs there is a mono-stereo slide
switch. Normal operation with Right and Left inputs and Right and Left speaker outputs are
enabled with the switch in the Stereo position. The ZOTL10 can be operated as a mono
amplifier, with both channels bridged into one speaker to provide approximately 1.7 times the
singe channel output. To operate in the mono bridged mode:
1. Set the mono-stereo switch to Mono.
2. Use any of the Left inputs for one channel of input to be sent to both of the amplifier
channels.
3. Connect the two red speaker output terminals together to be the Mono+ speaker
output and connect the two black speaker output terminals together to be the Mono-
speaker output. DO NOT CONNECT the red and black speaker output terminals
together, as the SHORTS the amplifier output. The binding posts are spaced so that a
standard dual banana plug (.75” spacing) can be used to connect the two black
speaker terminals or the two red speaker terminals.
Speaker Outputs
The amplifier outputs 10 watts. One set of stereo 5-way binding posts are provided. Speakers
from 2 ohms to 16 ohms can be used with the binding posts. Not having speakers connected
when the amplifier is on will not damage the amplifier, but we recommend that speakers are
connected when turning the amplifier on, to optimize the function of the protection circuit.
Technology
In 1996 David Berning developed a new and technically advanced vacuum tube architecture
designated as ZH, for Zero-Hysteresis which has come to be called ZOTL. ZOTL stands for
Zero-Hysteresis Output-Transformer-Less amplifiers. The ZOTL architecture eliminated the
problematic sound quality issues that audio-output transformers caused.
As in all ZOTL amplifiers, the ZOTL10 Power Amplifier uses radio frequency to change the
voltage-current transfer characteristics of the output tube from its normal impedance plane to one
suitable for driving a dynamic loudspeaker. The radio-frequency remapping is implemented
using special high-frequency power-conversion techniques. The high-voltage, low-current tube
impedance plane is remapped to the high-current speaker impedance plane through special
transformers operating at a constant RF carrier frequency of 460kHz. Because the audio signal is
riding on a carrier, it is not subject to parasitic elements of the transformer that would distort the
audio signal. Unlike the conventional audio-output transformer, this impedance transformation
operates on both the ac and dc components of the signal.
The signal is amplified in a much more linear manner when amplified on the carrier. For this
reason, the bass response is flat down to 6Hz.
In the transformer-coupled amplifier, the turns ratio of the output transformer determines the
impedance matching between the output tube(s) and the speaker. There are practical limits to

how large this ratio can be made because of the parasitic elements of the windings, and it is
difficult to make an output transformer with more than a 25:1 ratio.
With the ZOTL technology, the impedance matching is determined by the effective turns
ratio of the RF converter transformers. Without the parasitics of an iron transformer core to affect
the audio, these RF transformers can have much higher effective ratios, and actually provide the
correct turns ratio to properly couple to the tube. This is more than twice the maximum turns
ratio that can be achieved with an output transformer.
The ZOTL technology results in very wide, linear frequency response along with an uncolored
and detailed presentation of the recording.
Amplifier Maintenance
The amplifier is self-biasing, and has no adjustments.
The amplifier operates the tubes in a manner that maximize tube life. The tubes are expected to
give 10 to 20 years of service based on several hours of use per day. See the section on Vacuum
Tube Replacement.
Fuses
The ZOTL10 has three fuses, two of the 5x20mm type 3.15A, in the AC power input assembly.
There is a 5A 5x20mm fuse on the audio board in the power supply in the lower section of the
amplifier enclosure.
Vacuum Tube Replacement
The amplifier comes with Genalex Gold Lion, which are high quality tubes currently in
production. Changing or “rolling” the tubes is at your own risk. If you choose to change the
tubes, be extremely careful to ensure the unit is off for at least 5 minutes to allow voltages to
dissipate. Avoid touching the board, as high voltages may still be present even if the unit is
off. Ensure the pins of the tubes are aligned with the tube socket. The amplifier is self-biasing, so
there are no adjustments necessary. Any damage caused by changing the tubes is not under
warranty.
Troubleshooting
If the amp is not turning on immediately after going into protection, turn it off and wait 30-45
minutes before trying again. Occasionally the circuit takes longer.

If you’re experiencing distortion immediately and cannot identify the source, look for
components in the source chain that may be leaking DC, such as power supplies. The ZOTL10
does not have a capacitor at the input to filter DC (in order to not compromise audio quality), so
is susceptible to such leaks. If you do identify something that is leaking DC (when taken out of
the chain, the distortion should disappear) and would prefer to keep it, we can install a capacitor
at the input of your ZOTL10.
Specifications (Typical Performance Values)
• Sensitivity: 1.2V RMS for 10 watts output
• Output impedance 1.2 ohms
• Input impedance: 50k
• 100V / 120V / 240V operation: Auto-switching
• Hum and noise: 94dB below full output (measured at 20Hz-20kHz)
• Carrier: -50dB (460kHz)
• Power output with 4-ohm load: 12W, 0.5% THD
• Power output with 8-ohm load: 10W, 0.5% THD
• Frequency response (8-ohm load): 6Hz to 60kHz, +0, -.5dB
• Amplifier class: Push-pull Class AB
• Voltage gain (8-ohm load): 18dB
• Size: 9 inches (23 cm) wide, 8 1/2 inches (22 cm) tall, 18 inches (46 cm) deep (including
connectors)
• Net weight: 14 lbs. or 6.4 kg
• Finish: Aluminum case
• Tube complement: two 12AT7s, two 12AU7s, and four EL-84s
Limited One-Year Warranty*
1. Your new product is covered by a limited one-year warranty against defects in material and
workmanship. Any repairs required will be made at no charge within the first year after purchase
as a new unit.
2. Any units returned for warranty repair must be shipped prepaid after receiving return
authorization. For safe handling, and if at all possible, the unit should be shipped in its original
carton. If such is not possible, the unit should be well packed with particular attention paid to
protection of all corners and avoidance of any looseness in the carton.
3. This warranty does not apply to damage resulting from physical abuse or unauthorized
alterations or repairs; or from tube rolling, or damage to exterior finish resulting from careless
use. The warranty is void if the serial number has been removed, altered, or defaced.
4. This warranty is void if improper voltage is applied to any input or output.
5. Linear Tube Audio reserves the right to improve or change its products without obligation to
modify previously manufactured units.
* Applicable for domestic sales only. There is a one year warranty for overseas customers.
Handling and shipping costs are the responsibility of the overseas customer