IMPORTANT NOTICE:
If you own an older Eagle product, more than 10 years
old, we STRONGLY recommend having all the electrolytic capacitors replaced.
For Eagle 2 series amplifiers, we have a flat fee service with two year warranty.
Please contact Eagle concerning other products. This is true no matter what
brand of amplifier is involved. Failure to replace worn out electrolytic capacitors
in any amplifier can result in catastrophic failure, possibly damaging the amplifier
and loud speakers.
WHAT AMPLIFIER DO I HAVE?
There are only three different amplifier series service by EKSC Eagle.
First is the Eagle 2 series which include the Eagle 2, 2a, 2b, 2c, 3, 4, 10, 11, 400, & HC. All these
amplifiers look the same from the outside with a 5 1/4 inch tall chassis and heat sink fins on the back.
Stereo and mono amplifiers were manufactured on this chassis with the latest being the Eagle 2c prime rack
mount stereo, Eagle 4 no rack mount stereo, and the Eagle 11 mono amplifier. There are two main types of Eagle 2 series amplifiers. The early type Eagle 2, 2a, 2b, 3 and early Eagle 400 have some different circuitry than the late type Eagle 2c, 4, 10, 11, and late Eagle 400. Late 400 types have serial numbers greater than 20,000 or less than 2,000. Stereo units may be converted to mono units and mono may be converted to stereo. Specification wise there is little difference in the numbers except in time delay through the amplifier, the latest versions, Eagle 2c prime, Eagle 4, and Eagle 11 being the shortest delay time.
There are several other limited production Eagle 2 series amplifiers. Several dozens of the Eagle 400i and Eagle 3 mono block amplifiers were made which are designed to drive loads down to 1 ohm for the Eagle 3 and 0.5 ohm for the Eagle 400i. A few pair of Eagle 400hc mono block were made with dual power supplies and are 250 watts into 8 ohms and work down to 1.5 ohms.
Second is the Eagle 7 series which include the Eagle 7, 7a, and 7b. The 7 and 7a are almost the same and
are very large heavy amplifiers being 10 1/2 inches tall with weight about 90 pounds. The 7b is limited
production with only 22 being made.
Third is the Electro-Research A75 which was produced in the 1970's and has a stainless steel face and
handles.
RECAPPED EAGLE 2 SERIES-
The two options are factory service or a kit for the owner technician to install. Recapping replaces all the parts which wear out with time any Eagle amplifier. Because the amplifiers tend to last for a very long time, it is wise and economically feasible to rebuild the amplifiers every 5 to 15 years. Two processes are done to the amplifier. The first step is to make all the upgrades including circuit changes, wiring changes, and resetting feedback loop time constants to bring the amplifier circuitry up to the latest version for its type, either early or late. Second is replace all the electrolytic capacitors with the much better and larger capacitors available today. A new switch is included. For all practical purposes, a recapped amplifier is better than new because all known issues and circuitry have been updated to the most reliable and sonically pleasing version of the amplifier.
REFURBISHED EAGLE 2 SERIES INCLUDING 2, 2a, 2b, 2c, 3, 4, 10, 11, 400, & HC-
Factory service only. This includes all upgrades to the amplifier meeting the latest EKSC Eagle standards with a complete 2 year
warranty. During the refurbish process about 105 parts on older amps and about 65 on newer amps are
changed, replaced, or added. Each and every electrolytic capacitor is replaced with new components
including the two original 80,000 microFarad main filters replaced by two new 120,000 microFarad units.
This increases the main filter capacitance 50% to once again be some of the largest capacitors found in
audio, improving bass and amplifier control. High frequency bypass capacitors are added to output
transistors. An obsolete protection circuit is removed providing greater stability and cleaner high frequency.
All feedback loop time constants are "retuned" to the latest EKSC values greatly improving all aspects of
dynamic performance and stability. A higher current, higher gain drive circuit is installed lowering output
impedance and "speeding up" the amplifier. This is done by converting the output stage amplifier from
resistance coupled to direct coupled operation. Internal wiring is rerouted and reconnected for much lower
ground noise. A shield is added to the transformer and then mounted using mechanical isolation "feet" on
transformer legs. This reduces unwanted magnetic fields and eliminates the mechanical effects of
magnetostriction vibrating the amplifier chassis. A new switch is installed and the amplifier goes into a 96
hour burn in before final calibration and testing. If all else is good, the finished amplifier is given a listening
test to verify sound quality before cleaning and packaging to be shipped UPS to the purchaser. Class A
operation to 1 watt.
Because all parts which wear out have been replaced and the amplifier is brought to the latest standards,
EKSC Eagle provides a two year transferable warranty on every unit. The Eagle 2 series historically
provides at least five years of trouble free service.
EAGLE 7 SERIES-
The two options are factory service or a kit for the owner technician to install.
There are two main points to the Eagle 7 upgrade. The first fixes a recurrent problem with the power supply
and the second adds time domain filters to the amplifier circuitry. This repair increases power output from
300 to 430 watts per channel. The power supply is fixed by removing the voltage regulator for the main
power supply. Then, the two main 58,000 microFarad 80 volt electrolytic filter capacitors are replaced by
two new 68,000 microFarad 100 volt filter capacitors. The “Double Cap” upgrade units receive four of
these main filter capacitors for a total of 272,000 microFarads or over 1/4 Farad of total capacitance. A 3
microFarad high frequency bypass capacitor is added to each channel. Other components are replaced as
needed depending on what version of Eagle 7 is being upgraded. “Double Cap” upgrade units also receive
all new electrolytic capacitors.
Time domain filters are added to the Eagle 7 for enhanced sonic performance and stability. Time domain
filters reject ultrasonic signals from being amplified by the Eagle 7 making its job much easier. Two choices
of time domain filter settings are available. One setting, NORMAL, is for listening to music and moves the
time domain limit near the upper end of the audio band. This setting gives the best sound and greatest
stability. The other setting is for laboratory use. The LABORATORY setting places the time domain filter
well above the audio band for wider time bandwidth. Sonics are not quite as pure but the Eagle 7 will then
produce full power at ultrasonic frequencies. For all music applications, EKSC suggests the NORMAL
selection. Class A operation to 8 watts.
After the upgrade is performed the Eagle 7 is calibrated and goes into 96 hours of burn in. During burn in,
calibration is checked several times to ensure stability of set points. At final calibration the amplifier is
precision set for low distortion (typical 0.0025% THD) and then given a listening test to verify amplifier
performance.
Because all parts which wear out have been replaced and the amplifier is brought to the latest standards,
EKSC Eagle provides a two year transferable warranty on every “Double Cap” unit. The Eagle 7 series
historically gives at least 5 years of trouble free service after the power supply upgrade. Warranty on
other Eagle 7 services is 90 days.
Electro-Research Class A-75 Amplifier-
This historic amplifier is rebuilt with all new electrolytic capacitors. Replacement of the four old, tired
original 15,000 microFarad electrolytic capacitors with four new 47,000 microFarad capacitors over triples
the capacitance in the A-75 giving it a total near 200,000 microFarads. Bigger caps really improve the
sonics of this amp. Several smaller capacitors are added elsewhere for bypass purposes enhancing
performance. In addition, there are four capacitors added changing circuit configuration for improved
sonics and stable operation.
Very important is the installation of a brand new custom bias module for each channel. This module
accurately controls bias current and thermal set point for precision Class A amplifier operation. Normally,
bias is set for Class A to 32 watts and Class AB to 90 watts. This is the setup when EKSC gives a One
Year warranty. Bias set for Class A to 75 watts is special and warranty is 30 days. Sonics of these two
settings are VERY, VERY similar. Amplifier reliability is greatly enhanced by the slightly lower bias current
do to reduced operating temperature.
Normally, EKSC disconnects the Hobbs type hour meter on the front panel. All this work is then topped off
by the replacement of the relay with a heavy duty definite purpose contactor. This part then never fails.
There are many mechanical items checked and tightened on this amp before it is powered up the first time.
After the burn in and final calibration, the amp is brought to the listening room and given a sonic evaluation.
When all is well, the A-75 classic is shipped back to you and you receive an amplifier which will give many
years of trouble free service and fantastic sound Class A sound.
Transistor replacement is done on certain early version of the Class A-75 amplifier. These units use a
small, old style flat pack power transistor which may not be reliable. In certain cases we have traced
amplifier failure to these components. These old, low power transistors are replaced with twenty new, high
power, high current, high voltage devices. This fixes the transistor problem. Class A-75 amplifiers with old
style transistors will not be warranted. These components must be replaced to receive any warrantee.
Interconnects-
EKSC uses Belden 9259 cable exclusively. This oxygen free coaxial cable is bare copper stranded center
conductor with bare copper braided shield over a polyethylene foam dielectric. EKSC has real use tested
this cable over a ten year period and found it to be very consistent from batch to batch and stable over long
periods of time. Designed as a video studio cable, it is mechanically tough and electrically consistent.
Because this cable is 100% sweep tested for quality and has superior mechanical design, we feel this is
one of the best cable values available. EKSC offers chrome or gold RCA style ends as standard. Any
customer supplied connectors may be used for this cable. Additional charges apply to lengths greater than
four meters and certain customer supplied connectors.
EKSC offers a variety of other services. One of these is maintenance and calibration of the
Electro-Research EK-1 strain gauge preamp. Another is service on Eagle 2000 preamps. EKSC offers
engineering design, development, and research.
Please contact EKSC for details.