Difference between revisions of "CGS Serge resonant equalizer (previous version)"

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(Created page with "thumb|center|600px| '''CGS202''' the '''CGS Serge resonant equalizer''' module is based on the Serge Resonant Equalizer. It will work on...")
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.
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 instumentinstrument sounds.<ref name="sc82">[http://www.carbon111.com/serge1982.pdf Serge Modular Music Systems catalog and data sheets, 1982]</ref>
There are three equalized outputs, two which mix the alternate filter bands, and one which is a mix of all filter bands. The upper (up arrow COMB) lets pass the outputs of frequency bands at 61&nbsp;Hz, 218&nbsp;Hz, 777&nbsp;Hz, 2.8&nbsp;kHz, and 11&nbsp;kHz. The lower (down arrow COMB) mixes the other bands (29&nbsp;Hz, 115&nbsp;Hz, 411&nbsp;Hz, 1.5&nbsp;kHz, 5.2&nbsp;kHz).<ref name="sc82"/>
This equalizer is different from other equalizers in that the bands can be set to be resonant. When the knobs are in the middle position, the response at the main EQ Output is flat. When the knobs are positioned between the 9 and 3 o'clock position, up to 12 dbdB of boost or cut is set at the band. If the knob is set beyond the 3 o'clock position, the band will become resonant, simulating the natural resonance of acoustic instrument formant structures. Below the 9 o'clock position, increased band rejection is achieved.<ref name="sc82"/>
== A little on how it works ==
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 ten 10n decoupling capacitors. These decoupling capacitors can be MKT, MKS, monolythingmonolithic 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.)
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