The current version can be found here.
This module is based on the Serge Resonant Equalizer.
To quote the 1982 catalog:
The RESONANT EQUALIZER (EQ) is a unique ten-band filter designed specifically for electronic sound synthesis and processing. Except for the top and bottom frequency bands, all other bands are spaced at an interval of a major seventh. This non-standard spacing avoids the very common effect of an accentuated resonance in one key, as will be the effect from graphic equalizers with octave or third-octave spacing between bands. Spacing by octaves will reinforce a regular overtone structure for one musical key, thereby producing regularly spaced formants accenting a particular tonality. The Resonant Equalizer's band spacing are much more interesting, producing formant peaks and valleys that are similar to those in acoustic instument sounds.
It will work on either +/- 12 volts or +/-15 volts without modification, though in the case of the latter, all input voltage sensitivities, and output voltages are proportionally increased.
A little on how it works:
Click here to view an enlarged copy of the schematic. Note the change of one value of resistor in the 218Hz filter. A 910k has been substituted for the original 470k.
Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.
When you are happy with the printed circuit board, construction can proceed as normal, starting with the resistors first, followed by the IC sockets if used, then moving onto the taller components.
Take particular care with the orientation of the polarized components, such as electrolytics, diodes, transistors and ICs.
When inserting the ICs in their sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.
Traditionally, polystyrene capacitors are used for all of the smaller value capacitors in this module. I have not tried using other types an cannot say whether using the polystyrene capacitors makes any audible difference. From 10n, up greencaps were used. In modern terms these would be MKT or MKS. Note that there are also 10 x 10n decoupling capacitors. These decoupling capacitors can be MKT, MKS, monolything ceramic, or anything else that will physically fit.
Note: Apparently some time in ancient history, an incorrect value has crept into the Resonant Equalizer in the 218Hz filter network. I have not seen enough examples of the module to make a general statement, but the info I have hints that this network may have been wrong for a long time. To get this filter back to how is should be, replace the 470k in the 218h filter with a 910k resistor. This will correct center frequency and gain. (Thanks Michael for spotting the problem.)
There is no setup required.
This is a guide only. Parts needed will vary with individual constructor's needs. Alternative part numbers are provided in brackets ().
If anyone is interested in buying these boards, please check the PCBs for Sale page to see if I have any in stock.
Article, art & design copyright 2010 by Ken Stone