Zesto Audio Leto 1.5 User manual

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Leto 1.5 Vacuum Tube Preamplifier
Owner’s Manual
Please read carefully before
installing and operating this equipment
Zesto Audio
3138 Calle Estepa
Thousand Oaks, California 91360
805-807-1840
www.zestoaudio.com
[e-mail]
Made in the USA
Using US and Imported Parts

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Dear Music Lover,
I wanted to personally thank you for your purchase of my Leto Preamp.
I have loved music all my life – as a musician, record producer and audio engineer. That makes me fussy about sound.
That’s a good thing.
Each unit is built by hand with precision and pride to produce the most enjoyable listening experience for you.
I am proud to put my name on it and honored to share this with you.
Wishing you many happy years of listening!
Sincerely,
-- George Counnas, President of Zesto Audio
FYI:
Zesto is Greek for hot
Leto is the mother of Apollo
Table of Contents
Thank You …………………………………….. Page 2
Table of Contents……………………………… Page 3
What’s in the box……………………………… Page 3
Warning and Caution…………………………. Page 3-5
Parts and Controls……………………………. Page 6
Specifications ……………………………..…. Page 7 & 8
Tube layout …………………………………… Page 8
Hookup, Settings and Adjustments……….. Page 9 & 10
Remote and Front Controls………………… Page 10
Tips and Tricks ………………………………. Page 11 & 12
Warranty Information……………………….. Page 12

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What’s in the box?
Leto 1.5 Preamp
Leto Remote Control
2 12AX7 Vacuum Tubes
2 12AU7 Vacuum Tubes
White glove for handling tubes
IEC power cable 6’
Not Included: Interconnect cables
Warning and Caution
WARNING: The triangle with the lightning flash symbol displayed on the unit advises the user of dangerous uninsulated
voltage inside the product’s enclosure.
CAUTION: To reduce the risk of electric shock, do not remove the cover. There are no user-serviceable parts inside; it is
recommended that only qualified personnel service this component.
1. OWNER’S MANUAL: Before powering up the equipment, read all safety and operating instructions and follow them as
instructed. Retain the safety and operating instructions for future reference.
2. ATTACHMENTS: Use only those attachments recommended by the unit manufacturer, as others may cause hazards.
3. ACCESSORIES: Do not place the unit on an unstable cart, stand, tripod, bracket, or table. The unit may fall, causing
injury to a person or damage to the unit. Mount the unit according to the manufacturer’s instructions with the
suggested mounting accessory.
4. WALL OR CEILING MOUNTING: Do not mount the unit on a wall or ceiling.
5. WATER AND MOISTURE: Do not use the unit near water (for example, near a swimming pool, bath tub, wash bowl,
kitchen sink, or laundry tub) or in a damp environment (like a basement or outside in the rain).
6. OBJECT AND LIQUID ENTRY: Do not push objects of any kind into the unit through openings as they could touch
dangerous voltage points and short-out parts, possibly resulting in a fire or electric shock. Do not spill liquid of any
kind on the unit. If water or any metal object (such as a paper clip, coin, or staple) accidentally falls inside the unit,
disconnect it from the AC power source immediately and contact Zesto Audio for further instructions.
7. HEAT: Position the unit away from heat sources such as radiators, heat registers, stoves, or other units (including
amplifiers) that produce heat.

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8. VENTILATION: Slots and openings in the enclosure create ventilation to protect the component from overheating. All of
these openings must remain unobstructed. Allow at least six inches of clearance above the unit, 0.5 inch below and
an opening behind the unit for airflow. Do not place the unit on a bed, sofa, rug, built-in bookcase, or rack without
adequate ventilation.
9. GROUNDING OR POLARIZATION: As a safety feature, the unit may be equipped with a polarized alternating current
line plug in which one blade is wider than the other and a has an additional grounding blade. This plug will fit into the
power outlet only one way. If you cannot insert the plug fully into the outlet, try reversing the plug. If the plug still will
not fit, contact a licensed electrician to update your outlet. Do not defeat the safety purpose of the polarized plug.
10. POWER SOURCES: Operate the unit only from the power source indicated on the marking label on the back of the
unit. If you are unsure of the type of power supplied to your home, consult your unit dealer or local power company.
11. POWER CORD PROTECTION: Arrange power supply cords so that they do not suffer from foot traffic or pinching by
items placed on or against them. Pay close attention to cords where plugs enter the AC outlet and where they exit
from the unit.
12. LIGHTNING: For added protection during a lightning storm or when the component is idle for long periods of time,
unplug the unit from the wall outlet. This will help protect the unit from lightning and power line surge damage.
13. POWER LINES: Do not locate an outside antenna system in the vicinity of overhead power lines or other electric light
or power circuits. When installing an outside antenna system, take extreme care to avoid touching the power lines or
circuits; contact with them could be fatal.
14. OVERLOADING: Do not overload wall outlets, extension cords, or integral convenience receptacles as this increases
the risk of fire or electric shock.
15. REPLACEMENT PARTS: When replacement parts are required, be sure the service technician has used
replacement parts specified by the manufacturer or those having the same characteristics as the original parts.
Unauthorized substitutions may result in fire, electric shock or other hazards.
16. SAFETY CHECK: Upon completion of any service or repairs to the unit, ask the service technician to perform safety
checks to ensure the unit is in proper operating condition.
17. IMPORTANT SAFETY NOTE:
• Before connecting a new product such as the Leto 1.5 Preamp to your audio or home theater system, turn off all
other equipment (preferably unplugging them from the AC power source). Many audio components feature
automatic turn-on circuits that may activate during an installation, potentially causing damage to electronic
components or speakers. This type of damage is not covered by product warranties, and Zesto Audio specifically
disclaims responsibility for any such damage.
• Power Cord: The removable IEC power cord provided with your unit was specifically designed for use with this
product, but other AC cords may be used. Consult your dealer for advice on AC power cords and high quality wire
in your system.
• AC Fuse: The fuse is located inside the IEC power entry connector and is not user serviceable. If the unit does not
power up, contact an authorized service representative.
• Wiring: Cables running inside walls should have the appropriate markings to indicate compliance and listing by the
UL, CSA or other standards required by the UL, CSA, NEC, or your local building code. Questions about cables
inside of walls should be directed to a qualified custom installer, licensed electrician, or low-voltage contractor.

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18. RECORDING COPYRIGHT: Recording of copyrighted material for other than personal use is illegal without
permission of the copyright holder.
19. FCC INFORMATION FOR USER:
• CAUTION: Any changes or modifications not expressly approved by Zesto Audio could void the user's authority to
operate the equipment.
• These limits are designed to provide reasonable protection against harmful interference in a residential installation.
This equipment generates and can radiate radio frequency energy, and if not installed and used in accordance
with the instructions it may cause harmful interference to radio communications. However, there is no guarantee
that interference will not occur in a particular installation. If this equipment does cause harmful interference to
radio or television reception, which can be determined by turning the equipment off and on, the user is
encouraged to try to correct the interference by one or more of the following measures:
• Reorient or relocate the equipment.
• Increase the separation between the equipment and receiver.
• Connect the equipment into an outlet on a circuit different from where the receiver is connected.

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Rear Panel Inputs and Controls
Power ON/OFF switch ……………………………………………. Turns the unit ON/OFF (located on side panel).
IEC Power entry connector …………………………………………… 110/120V AC power input.
(Optional factory installed 240V mains)
Remote bypass switch …………………………………………… Just in case remote is misplaced.
Turn switch up to override mute.
Cinema Bypass ……………………………………………………… Cinema out from Input 1
Inputs 1, 2 & 3 ……………………………………………………………. RCA single ended (SE)
High quality recessed gold pin connectors
Inputs 4 & 5 ……………………………………………………………… XLR True floating balanced transformer
Inputs. (BAL)
Outputs 4 sets……………………………………………………………… Two sets of RCA SE & 2 sets of XLR
transformer balanced outputs
Left and right Ground ON/OFF switch ………………………………… Connects or disconnects the ground to
the SE outputs

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Specifications
5 Inputs
 3 sets of Single Ended inputs with an impedance of 100K Ohms
 2 sets of true Balanced transformer inputs (pin 2 hot) with an impedance of 10K Ohms
 Maximum peak input level of 5 Volts RMS
4 Outputs + Headphone
 1/4 TRS inch stereo headphone jack
 4 Line outputs
 2 sets of true Balanced transformer outputs (pin 2 hot) with an impedance 150 Ohms
 2 sets of Single Ended outputs with an impedance 150 Ohms
 Maximum peak output level of 10Volts RMS +20dB
 Independent ground lift switches on the left and right Single Ended outputs
 1 set of Single Ended Cinema bypass outputs from input #1
Headphones
 Built in ~ 1 Watt class A-B headphone amp.
 2 Volts headphone output.
 Frequency response 20Hz to 50KHz
 Total Harmonic Distortion ~ .02%
Power
 Power consumption 27W, 0 drain when off
 Voltage 110/120V AC 60Hz
 Optional factory installed 220V or 230/240V AC 50/60Hz
 Standard 3 pin IEC power connector
 ON/OFF power switch conveniently located on the side panel
 Two internal high quality linear regulated power supplies, 250V and 12V
Other Features
 Each unit is hand made in the USA
 50 hour factory burn in on all circuits and vacuum tubes
 Dimensions 17” W X 12” D X 5” H
 Weight 23 lbs.
 16 gauge zinc plated steel enclosure

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Detailed Specifications
 Unity gain volume indicator for home theater surround sound integration.
 Frequency response 20Hz to 50Khz ~ 1dB
 Total Harmonic Distortion ~ 0.02% at 1V RMS input
 Gain 12dB
 Signal to noise ~ 100dB below operating level
 Non inverting output polarity
 Cross talk >90dB
 Remote control volume, mute and mono
 Remote bypass switch on rear panel (just in case the remote is misplaced)
 1% metal film resisters throughout
 Polypropylene capacitors throughout the audio path
Vacuum Tubes
 Two (2) Gold pin JJ ECC83S/12AX7
 Two (2) Gold pin JJ ECC82/12AU7
 High quality gold pin ceramic sockets

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Hookup, Settings and Adjustments
Before you start you will need:
RCA or XLR Interconnect cables to your system
Proper Care of your Leto Preamp
Very Important Read First
The simple rule to remember is to “turn on the preamp before turning on your power amp and turn off the power
amp before turning off the preamp.”
Not doing so may create a very loud noise that could damage your speakers or other equipment.
It is customary for vacuum tube equipment, when it is first turned on, while the unit is powering up, to have a brief initial
“hum” coming from the unit, not from the speakers.
It is very important that all of your audio equipment is turned off or unplugged from the main power before attempting to
install this unit.
Allow at least 30 minutes of warm up to get the best performance from the preamp.
Turn it on
Turn on the preamp using the ON/OFF switch located on the front left side. After a short time (about two minutes) the four
tubes should start glowing. The amber glow will be the only visible indication that the unit is turned on.
If they don’t, turn off the unit at the power switch and unplug the power cord. After waiting a few minutes unplug each
vacuum tube in turn (using the glove provided) and make sure that none of the pins are bent. If they are please contact
Zesto Audio for instructions.
Caution: Tube electronics should not be turned ON, then OFF, then ON again quickly. This could blow a fuse or create a
hum. Once the unit is ON, it is safe to wait a minute before switching OFF. If you do get a hum, leave the unit off for 15
minutes.
Power
carefully plug in the AC power cable to the preamp first then to your main power.
Burn-in
Like all high end audio equipment, this Vacuum Tube Preamp can take 200 hours to break in. For circuit testing and
quality assurance, Zesto Audio ships all the Leto Preamps with at least 50 hours of factory burn-in.
Vacuum Tubes
Important! First identify the two types of tubes as they are NOT INTERCHANGEBLE. Your input tubes are ECC83s
(12AX7) and your output tubes are ECC82 (12AU7). Please note that failure to follow this warning can cause considerable
damage.
Find the tube layout on page 8 in this manual in order to correctly plug in the right tube in the right socket. Using the glove
provided, unpack and carefully plug in the four vacuum tubes making sure they are firmly pushed in all the way in their
sockets. They can only go in one way.
Output
Using RCA or XLR interconnect cables; connect both the left and right outputs to your power amp.
Input
Using RCA or XLR interconnect cables; connect your sound sources to the inputs of the preamp.
Feet
Your unit is installed with four feet using #8-32 screws.

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Cinema Bypass
Input 1 RCA connector is tied directly to Cinema Bypass Out.
For example, you can plug your CD/DVD player into input 1 and take your Cinema Bypass output to your surround sound
processor for your home theater system.
This function works without the preamp turned on.
Remote
Remote has 3 functions: Volume, Mute, & Mono.
Mute:
Every time you turn on the Preamp it is set to default on Mute.
Located on the front panel, far right, the Mute function is on when the
Amber LED is illuminated.
Press the Mute button for on & off mute.
Mono:
On the far right front panel the Mono function is on when the
Green LED is illuminated.
This function adds Left plus Right. Press the Mono button for on & off Mono.
Volume:
The left knob on front panel controls the volume.
The volume is indicted by the black dot on the knob.
Remote Bypass Switch:
Located on the rear panel just in case the remote is misplaced.
Leave in down position.
Turn switch up to bypass Mute.
Front Controls
From left to right
(Left) ¼” Headphone Jack
(Center Knob) = Volume:
The volume goes from 0 to 10 and is indicted by the black dot on the knob. This is either manual or controlled thru your
remote.
Theater setting on Volume control:
Setting the volume control to "Theater" allows you to use your 2 channel system as part of your surround sound
eliminating the extra equipment. This sets the preamp to unity gain.
(Right Knob) = Selector Switch:
You have 5 inputs. #1 is for your cinema bypass. This is a manual control.
LED lights:
Amber = Mute. Green = Mono.
The amber glow of the vacuum tubes is the only visible indication the unit is ON.

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Tips and Tricks
Grounding
 Grounding switches apply to the outputs only.
 If you have RCA SE outputs, start with both ground switches up.
 If you have XLR outputs start, with both ground switches down.
 The ground switches work independently. You can adjust them for the least amount of noise.
Example;
 Right channel up, left channel down.
 Right channel down, left channel up.
 Right channel up, left channel up.
 Right channel down, left channel down
Volume control / internal gain adjustment
 Turning the volume control to “0” under certain circumstances may not necessary turn the volume all the way off.
Press the mute button on the remote to turn the volume off.
Internal gain switch
 The unit is designed to work with the volume control around the 12 o'clock position for normal operating volumes.
If the volume control is at 3 o’clock or 9 o’clock you may want to contact your authorized dealer or the factory to
adjust the internal gain of the unit.
 There are internal gain switches that switch between 12dB and 3dB of gain.
 At normal operating volume, the volume control should read around the 10 to 12 o’clock position.
 If the volume is less than the 9 o’clock position, the gain may need to be reset to 3dB.
 This usually happens with high gain power amps with 35dB and/or very high efficiency speakers.
 The factory default gain setting is 12dB.
 Units sold before January 2013, please contact the factory if a reset is needed.
 Due to high internal voltages there are no user adjustable switches, only authorized representatives can
make these adjustments.
Tube Rolling
Important! The wrong type and placement of the tubes can cause considerable damage. First identify the two types
of tubes, as input and output tubes are NOT INTERCHANGEBLE. You may use any ECC83s (12AX7) or equivalent only
for the input tubes and any ECC82 (12AU7) or equivalent only for the output tubes. See tube layout on page 8.
!!! Any damage caused by tube rolling is not covered by the manufacturer’s warranty.
Tube Rolling (The Sport of Audiophile Kings)
 The 12AX7 input tubes closest to the back/curve are the most sensitive and effective to tube roll.
 Only a 12AX7/ECC83s type will work and we recommend that it is high gain/ low noise.
 The unit is designed around the JJ’s because they are neutral, consistent and are high gain/low noise.
 If your tastes are warmer, you may want to try Mullard’s and if you like it brighter try GE.
 We cannot recommend any specific NOS tubes, as no 2 are the same. We prefer to encourage personal taste,
trusting your ears and enjoying the sport.
 Any damage caused by tube rolling is not covered by the manufacturer’s warranty.
Power cord
 For best performance, the Leto responds better to higher quality power cords.

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Mute
 When the mute is engaged it shorts out the output of the unit so there is no signal out. This can also be very
helpful for trouble shooting hum and noise issues.
Mono
 This is very useful to test for correct phase in your system. When switched to the mono mode your stereo image
should sound like it is in the center between your speakers. If the image goes all the way out or anywhere but
center it is an indication that there is an out of phase signal in your system.
Grounding
 Leto grounding switches only affect the Single Ended outputs, not the Balanced outputs and work independently.
Leaving the equipment on
 The filament on the tube will burn out quicker if switched on and off more often.
 The tube will wear out quicker if it’s left on all the time. There is no clear choice which is preferred.
Warranty
All Zesto Audio equipment is covered by a 2 year limited warranty for parts and labor to cover defects in materials and
workmanship and 6 month warranty on the original vacuum tubes from date of purchase.
To obtain this original owner warranty the completed warranty registration card should be emailed to the factory within 15
days from date of purchase. The warranty may be transferable during the 2 year period. Please contact factory to register
new owner.
This warranty is void if the product has not been used in accordance with the instructions found in this owner’s manual, or
if it has been misused, abused, damaged by accident or neglect, or in transport once in possession of purchaser. The
warranty is also void if the product has been tampered with or has been repaired or modified by anyone other than Zesto
Audio or its specifically authorized representatives. This limited warranty only applies to Zesto Audio equipment and
carries no responsibility for any other equipment attached to this unit.
Zesto Audio will not warranty any damage caused by “tube rolling”. The warranty only covers the use of12AX7’s and
12AU7’s in their proper positions.
To return the product it must be packed in its original packaging and returned to Zesto Audio or its authorized
representative via insured freight at the owner's expense. Returned products must be accompanied by written description
of the defect and a return authorization number that is available from Zesto Audio or the authorized representative. Upon
receipt of the defective product Zesto Audio or the authorized representative agrees to repair the product without charge
for parts and or labor if within the 2 year warranty period, except for vacuum tubes if the unit is more than 6 months old.
The product will then be returned via prepaid insured freight with a carrier at the sole determination of Zesto Audio or the
authorized representative.
Zesto Audio and its partners reserve the right to modify their products or change specifications at any time without
obligation or liability to previous purchasers.
Warranty will cover ownership outside the USA, but shipping is the sole responsibility of the owner. See your local dealer
for factory approved service in your area.
Factory service on non-warranty items will be billed at an hourly rate to be quoted before work is done.