Eros Owners manual-3
EROS 300
Class A Monaural Power Amplifier
Owner’s Manual
Please read carefully before
installing and operating this equipment
Power ON/OFF switch
………………………………………………………………. Turns the unit
ON/OFF (located on front panel).
Front panel LED lights ……………………………………………………………………..
high voltage, Amber indicates low voltage (Both lights
will remain on when unit is in use)
IEC Power entry connector ………………………………………………………………
power input with 6.3 Amp slow blow fuse.
Red indicates
110/120V AC
Fuse installed in
mains inlet connector.
Optional factory installed 220V, 230V/240V main with
3.15 Amp slow
Input …………………………………………………………………..………..……………
Ended high quality recessed gold pin connectors and
XLR true floating balanced transformer input.
RCA Single
Input Ground ON/OFF switch …………………………………………….…...………….
disconnects the ground (pin 1) to the Balanced input
Connects or
Speaker outputs……………………………………………………………..……………… 5 way binding
posts with 4 and 8 Ohm taps with Black common.
connecter (see manual for wiring)
Outputs fuses………………………………..………………………………………………
5 Amp slow blow fuses for each output tap
Proper Care of your EROS 300 Power Amp
Very Important Read First
Individual 8 and
The simple rule to remember is to “turn on your preamp first 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.
The unit is ready to listen to within a few minutes after powering up, however for best performance
allow at least 30 minutes of warm up.
It is not recommended to drive the EROS 300 directly from a DAC or to use a passive volume control. The
EROS is designed to be driven by a powered preamp.
Like all high end audio equipment, this Vacuum Tube Amplifier can take 200 or more hours to break in. For
circuit testing and quality assurance, Zesto Audio ships all the EROS 300 Amps with at least 50 hours of
factory burn-in.
Installing Tubes
This EROS 300 ships with a matched sextet of KT88’s so they can go in any socket V1 thru V6. KT88’s
have a key and can only go in one way. Tip: The logo and the key on the tube faces forward.
Caution! Do not ROCK the tube, install straight up and down holding the metal collar. If you look at the
bottom of the tube there is a black plastic cylinder in the center of the pins with a key. This plastic is fragile
and can easily break if you rock the tube. Broken key’s are not covered under warranty. However a broken
key does not effect the performance of the tube or the amplifier.
WARNING! If the tube is not installed in the correct orientation it is likely that you will do permanent
damage to the amplifier with a considerable amount of drama.
ECC82/12AU7 tubes only go in one way in any socket V7 thru V8
Hookup, Settings and Adjustments
Before you start you will need:
RCA or XLR Interconnect, power and speaker cables to your system.
Using speaker cables connect the speakers to the common and either 4 or 8 Ohm output binding posts. You
can also connect the speaker cable using a 4 pin SpeakOn connector.
Using RCA or XLR interconnect cables; connect your preamp to the input of the power amp. you have a
choice, balanced cables are preferred for sonic reasons as well as it will allow you to use the ground lift
switches if you encounter any ground loop problems.
Important! Power amps need good clean power.
For best results it is recommended to plug the EROS 300 directly into an AC wall outlet with a proper ground
and not through any power conditioner, extension cord or power outlet strip. Carefully plug in the AC power
cable to the power amp first then into the wall outlet.
Turn it on
Turn on the power amp using the ON/OFF switch located on the front logo plate. The amber LED indicates
low voltage and the red LED indicates high voltage. Both lights will go on together and will remain
illuminated while the unit is on. The eight tubes should start glowing.
If they don’t glow, 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.
Zesto Audio
3138 Calle Estepa
Thousand Oaks, California 91360
Made in the USA
Using US and Imported Parts
Front and Rear Panel Inputs, Outputs and Controls
Zesto Audio 2015
Page 3
Zesto Audio 2015
Page 3
Custom Toroidal power transformer with global mains
Choke based power supply design
120 Volts AC mains
Optional factory installed 220V, 230V/240V 50/60Hz
Power consumption at rated output 360 Watts
Power consumption at idol 348 Watts
On/Off switch conveniently located on front panel
3 pin IEC power inlet connector with built in fuse
Active Components
Matched sextet set of six (6) KT88’s vacuum tubes
Two (2) Gold pin ECC82 (12AU7) vacuum tubes
High quality gold plated ceramic sockets
Other Features
Each unit is made by hand
50 hour factory burn in on all circuits and vacuum tubes
Dimensions 17" W X 20" D X 10" H
Weight 59 lbs. (26.8 Kg)
16 and 14 gauge Zinc plated steel enclosure
Two year limited warranty
Six months warranty on Vacuum Tubes
Pure Class A
150 Watts per amp
4 and 8 Ohm output taps
8 and 5 Amp Slow-blow fuses for outputs
Three 5 way binding posts
One SpeakOn connector
Non inverting output polarity
Push-Pull Ultra-Linear design
Transformer floating balanced XLR input
Balanced inputs with pin 2 hot, impedance 12K Ohms
Single Ended input, impedance of 100K Ohms
XLR ground lift switch on balanced input
1.5 Volts RMS input to reach rated output
Detailed Specs
Auto bias
No negative feedback
Frequency response 20Hz to 50Khz ~ 2dB
Total Harmonic Distortion ~ 0.8% at 1W into 8 Ohms
Gain of 29dB
Noise level > 5 mV RMS into 8 Ohms with input shorted
1% metal film resisters throughout
Polypropylene capacitors throughout the signal path
Enjoy the music!
• 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
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.
• Before connecting a new product such as the EROS 300 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 user replaceable. Only
replace fuse with the exact same type that was removed. Only use slow blow fuse. 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.
18. RECORDING COPYRIGHT: Recording of copyrighted material for other than personal use is illegal
without permission of the copyright holder.
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 12 inches of clearance
above the unit, 1 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.
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
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.
.Table of Contents
Thank You ……………………………………..
Page 2
Table of Contents………………………………
What’s in the box………………………………
Warning and Caution………………………….
Parts and Controls…………………………….
Specifications ……………………………..….
10 - 11
Hookup, Settings and Adjustments………..
12 - 13
Tips and Tricks ……………………………….
Warranty Information………………………..
What’s in the box
EROS 300 Monaural Power Amp
6 KT88 Vacuum Tubes
2 ECC82 (12AU7) Vacuum Tubes
White glove for handling tubes
IEC power cable 6’
Not Included: Interconnect or speaker cables
Dear Music Lover,
I wanted to personally thank you for your purchase of my EROS 300 Monaural Power Amp.
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
I am proud to put my name on it and honored to share this with you.
Wishing you many happy years of listening!
-- George Counnas, President of Zesto Audio
Zesto is Greek for hot
EROS is the God of Love and Desire in Greek mythology
Tips and Tricks
Safety Tips
Power amps get hot when operating properly. It’s important to provide adequate ventilation of at least 12”
above the unit and on all sides.
Turn unit OFF when changing cables.
If you break a tube, turn unit off immediately. Wait at least 1 hour for the high voltage to discharge
completely to replace it.
If you spill any liquids on the unit , turn off immediately and call the factory.
The grounding switch applies to the XLR Balanced input only.
The grounding switch does not affect the RCA Single Ended input.
If you are using the XLR input, start with ground switch up and adjust it for the least amount of noise.
Tube Rolling
Important! The wrong type of the tubes can cause considerable damage.
Your unit is designed to work safely with any KT88. It will also work with KT120’s, but with auto bias it will
not provide more power, just sound different. Class A design provides plenty of power.
Warning! 6550, KT90’s, KT100’s tubes will NOT work in this unit. Because they have a lower power rating,
they will cause DAMAGE to the power amp and the tubes.
Any damage caused by tube rolling is not covered by the manufacturer’s 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 must be received at the
factory within 15 days from date of purchase. The warranty is not transferable.
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.
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
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.
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