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In Reply to: RE: Audio Research EC21 crossover on tympani speakers posted by lefty707@hotmail.com on March 19, 2016 at 05:06:17
There was not much of a manual for he EC-21 basically just a chart showing crossover points and required cap values to achieve the crossover.
The EC-21 is a two-way crossover, active vacuum tube circuit for the low pass, 6dB or 18dB/octave selectable. The high pass is a passive 6dB only. 3 tubes for the low pass filter all 12AX7.
If you don't have the crossover/cap chart you will need to get one from ARC. This will give the crossover values for the low pass filter. If using it as 6dB there will only be one cap to deal with. For the 18dB there will be 3 caps. All low pass caps are soldered to the bottom of the PCB.
The high pass filter is a single cap. You will need to know the input impedance of the high-pass amplifier to calculate the required capacitance. The cap solders between the input and high-pass out.
These units are quite old most over 40 years. If all the power supply caps are original probably a good idea to replace them.
Follow Ups:
I should add that the target crossover is 1khz and the Tympani 1D is intended for a 6db high pass and 6db low pass. .
http://www.audioresearch.com/ContentsFiles/EC-21%20Schem%20%20PList.pdf
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