The Audio Research EC‑4A is a rare breed: a fully analog, tube-powered, three-way crossover that does its heavy lifting behind the scenes with grace and precision. Sporting six 12AX7 tubes and fixed crossover points—switchable via capacitor banks—it offers surgical clean division of your signal path without ever leaning on op‑amps or digital tricks. It sounds smooth and musically coherent, with that unmistakable warm vibe ARC is known for—though some users note the power supply could use an upgrade for extra finesse. In short, the EC‑4A isn’t just a component—it’s an audiophile’s secret weapon for building active, tube‑rich speaker systems that breathe just like live music.
Condition
9/10
Serial No.
475060-1
Orig. MSRP
$350
Restoration
- All tubes test good
- All are 1st order filters
- Bass is -6dB at 150Hz, -20dB at 600Hz
- Midrange is -6dB at 50Hz and 1kHz, -20dB at 10Hz and 6kHz
- Treble is -6dB at 250Hz, -20dB at 50Hz
- Midrange and especially treble would need to be changed if used with "normal" 3-way speaker or many a tweeter might meet a sad end
Factory Specs
Frequency response
+1 dB 5 Hz to 50 kHz, into 10k ohm load, maximum gain
Distortion
Harmonic Distortion: Less than .005% @ 2 V RMS output, IHF load, midband. IM Distortion: Less than .01% @ 2 V RMS output, IHF load, SMPTE method.
Noise & hum
Less than 100 µV RMS per channel, inputs shorted, maxiumum gain (more than 90 dB, ref. 5 V)
Gain
Adjustable from 0 (off) to +0.5 dB
Crossover points
Fixed with internal components. Standard factory values available are: 50 Hz, 100 Hz, 150 Hz, 200 Hz, 250 Hz, 400 Hz, 500 Hz, 800 Hz, 1 kHz, 1.5 kHz, 2 kHz, 2.5 kHz, 3.5kHz, 5 kHz, 7.5 kHz, 10 kHz (non-standard frequencies available at additional cost)
Crossover slopes
6 dB per octave on all channels, optional 12 dB on Bass channel only (recommended below 200 Hz only)
Input impedance
150k ohm @ 20 Hz to 30k ohm @ 20 kHz (typical for midband crossover frequencies)
Output impedance
Less than 600 ohm from 20 Hz to 50 kHz
Maximum inputs
Tube complement
(6) 12AX7
Power requirements
120/240 VAC 50/60 Hz, 30 watts
Other
Phase Response: Inverting output (-180°), +2° @ 20 Hz, to -7° @ 20 kHz, into 10k ohm load. Maximum Output: 5 V RMS, recommended maximum for minimum distortion from 20 Hz to 20 kHz into a 10k ohm (or greater) load
Dimensions
15¼"W x 5¼" H x 6¾" D (chassis only - 19"W x 5¼"H natural rack panel available)
Weight
7 lbs. net, 10 lbs. shipping
The History of Audio Research
Audio Research Corporation, affectionately known to fans as ARC, was founded by William Z. Johnson, who began designing custom audio electronics in the early 1950’s and who also operated a specialty audio retail store until the mid-1960’s. Johnson’s efforts almost single-handedly revived vacuum-tube designs at a time...
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Liner Notes
Bi- (and tri-) amplification has been popular with knowledgeable audiophiles for many years. Increased dynamic range, lower distortion, and higher definition are some of the advantages available through bi-amplification. Unfortunately, some music lovers view bi-amplification as "overkill" or needless technical "wizardry". To these music lovers we would like to suggest that you CAN hear a difference with bi-amplification, even on modest speakers. Of course, high quality speakers perform even better with bi-amplification. Many manufacturers of quality speakers recognize this fact, and supply bi-amplification connections for their speakers. If your audio system has quality components throughout, a logical area of improvement is through bi-amplification.
If you are a music lover with little interest in the technical aspects of a music system, we would like to assure you that bi-amplification is not as complicated as it might seem. Your Audio Research dealer can assist you in selecting the proper crossover frequency and components to bi-amplify your speakers. Once this has been done, it is simply a matter of attaching a few more wires and adjusting the balance of the system to your satisfaction.
If you own a high quality audio system, ask your Audio Research dealer to assist you in trying bi-amplification with your speaker system.
In simplified form, these are some of the benefits that bi (or tri)-amplification can offer:
(1) Increased dynamic range - Obviously two equal amplifiers can provide more power than one, but under certain musical conditions, there is an additional power bonus through bi-amplification - two amplifiers can provide more than the sum of the two amplifier's power. Yes, "2 + 2 can equal 5" through bi-amplification. (Your Audio Research dealer can supply you with the technical articles which have been written about this phenomenon).
(2) Reduced distortion - Complex musical information is difficult to amplify without audible distortion. By dividing the musical spectrum each amplifier has fewer demands placed on it, resulting in lower distortion under the dynamic conditions of music. Additionally, if one amplifier should be momentarily overdriven in a bi-amplified system, the other amplifier is unaffected. In this manner, brief periods of overload can be tolerated with less audible distortion.
(3) Elimination of the internal speaker crossover - Internal speaker crossovers divide the audio spectrum at "high power levels" where inefficiency and distortion can occur. In addition, speaker designers are often forced to use a less than ideal internal speaker crossover design because it can be too costly or impractical to manufacture an optimum internal crossover.
The Audio Research EC-2A and EC-4A divide the audio spectrum without adding to or subtracting from the complex musical waveforms. Although other electronic crossovers may offer some convenient features, the Audio Research EC-2A and EC-4A were designed to excel in dividing the audio spectrum without destroying the musical signal. Then and only then can the full potential of bi- (and tri-) amplification be appreciated.
Stock No.
9074070028509
