THE CLAPHAM JUNCTION TYPE
This type of tone control, was proposed by John Linsley Hood to provide a more versatile type
of tonal adjustment than that offered by the conventional standard systems, for remedying specific
peaks or troughs in the frequency response, without the penalties associated with the graphic equaliser type of control.
The name “Clapham Junction tone control” was coined by John Linsley Hood (JLH) himself in the late 1960s.
🔹 Clapham Junction is a railway station in London, well known for the convergence and intersection of dozens of tracks and branches. It is one of the most tangled railway junctions in Europe.
🔹 Linsley Hood used this image as a metaphor:
• In a Baxandall tone control, the signal follows a clean and simple path, with just two boost/cut networks (bass and treble).
• In the design he called “Clapham Junction,” the signal encounters a veritable crossroads: multiple RC networks, lift/cut switches, several injection points, and summing.
• This tangle of signal crossings reminded him of the tangle of tracks at the London station.
That's why the term is somewhat ironic: the circuit is very versatile, but in return it becomes an electronic "railway node."
At the top left side, we find 4 switches that serve to “Lift” low frequencies, the values of these frequencies from left to right are: 50, 100, 200 and 400 Hz. Similarly, in the upper right side we find another 4 switches that serve to “Cut” the same low frequencies, now the values of these frequencies are read from left to right and are: 400, 200, 100 and 50 Hz. At the bottom, using the same logic as the left side, we find 4 switches that serve to “Lift” the high frequencies, the values for each switch from top to bottom are: 1.5k, 3k, 7k and 14 kHz, on the right side we see the same thing, only now the switches serve to “Cut” the high frequencies.
Ref: Audio Electronics-page 194
2nd Edition
John Linsley Hood
1999 Newnes. An imprint of Butterworth-Heinemann
Linacre House, Jordan Hill, Oxford OX2 8DP
