Of EQ, the HM-2, and single-ganged gyrators

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11/2/1999 2:12 PM

Mark Hammer

Of EQ, the HM-2, and single-ganged gyrators Last night, I got an updated schematic of the BOSS Heavy Metal pedal from one of the Scandinavian sites (Stellan's or Robin's, I forget which). Gazing over it on the bus ride home, I saw the familiar op-amp gyrator-based EQ section that RG informed us about on GEOFEX (www.geofex.com). What grabbed my attention was the fact that the "treble" pot was ganged to *two* gyrator circuits, such that turning up the one pot (and it IS one pot not two ganged together) adjusted two bands simultaneously.     Two issues emerge:     1) Is this correct? Can it be done, and what are the design constraints if it can?     2) It should technically be possible to select desired gyrator-based bands and use single pots to introduce specific voicings. E.g., lovers of scooped-mid death-metal sound should be able to add a single-pot-based control on a favoured fuzz, and just turn it up. The filter-panning tone section on the Big Muff and related pedals (including Jack's and Aron's homebrew designs) lets one pick either full bass, OR full treble, but doesn't have any true mids-only setting. Conceivably, the single-ganged design should be able to let one have the pedal equivalent of a loudness control on a stereo; in other words, simultaneous single-control tone compensation for playing volume or cabinet/speaker complement.     There are some interesting possibilities here. What makes them more interesting is the notion that much can be accomplished in a small-footprint chassis box using easily obtainable parts.

 

11/2/1999 10:54 PM
marrk	"What grabbed my attention was the fact that the "treble" pot was ganged to *two* gyrator circuits, such that turning up the one pot (and it IS one pot not two ganged together) adjusted two bands simultaneously."     I was looking at the schematic for the Boss Blues Driver from Aron's site the other day. It appears to be a similar situation. Or, is this a dual ganged pot? Mark

 

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