EKSC Amplifier Upgrades
Components and Services

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Description of Services

If you own an older Eagle product, more than 12 years old, we STRONGLY recommend having all the electrolytic capacitors replaced. For Eagle 2 and Eagle 7 series amplifiers we have a flat fee service with two year warranty. Please contact Eagle concerning other products. This type of service should be performed 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 and of course very old electrolytic capacitors sound bad.

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 and polished aluminum face and handles.

The extremely poplular recapping replaces all the parts which wear out with time inside 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 including a two year warranty. The other option is a kit for the owner technician to install.

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 100,000 microFarad units. This increases the main filter capacitance to once again become 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. 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.

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 four new larger 100 volt filter capacitors. 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 to address all known issues and updates including all new much larger 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. This setting gives the best sound and greatest stability. 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). 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 7 series historically gives at least 10 years of trouble free service after the power supply upgrade. The two options are factory service or a kit for the owner technician to install.

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 100,000 microFarad capacitors increases capacitance almost 7 times in the A-75 giving it a total of 400,000 microFarads. Bigger caps really improve the sonics of this amp. Dozens of 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, 1.5 amps at idle, 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 with the lower bias generally sounding better in every way. Amplifier reliability is greatly enhanced by the slightly lower bias current do to reduced operating temperature. Some transistors are always replaced and dependant on specific amplifier configuration. 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. 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.

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