viva Analog “6G VIBRATO” // jcm 2020

On my list for the last two years, a compactified redux of my precision emulation of the original late-50’s Fender “Harmonic” Vibrato effect.

The circuit is based around a Univibe style LFO oscillator which drives a pair of OTA’s in anti-phase fed from a cross-over network centered around 300hz. The scheme works so well that when the Vibrato intensity is set to null there is no perceptible sonic difference between bypass/engage modes (see video below).

The circuit features an on-off-on switch that mixes in and out of phase versions of the top-side signal – an idea I discussed with Roly Roper when I met him in Melbourne around 2014. In one position the circuit operates like the stock Fender summing circuit does, in the other a slight amount of phasing is present with the effect – quite lovely. The middle “off” position ends up producing a dark/choppy effect that is very interesting in itself.

a quick glimpse:

 

video caption:

“A balanced high-headroom OTA based mixer driven from a Univibe LFO produces an interesting emulation of the late 50’s 6G-series tube amp Harmonic Vibrato – yeah, I screwed up the graphics 🙂 …

in this case, I put a twist on things by making one side of the High-Pass/Low-Pass mixer invertible in phase, thus producing a small amount of “phasing” (what else!) in that mode … in the “stock/Fender” mode there is NO phasing …

in the middle position the High-Pass feed is cut out, leaving a choppy Low-Pass feeding through // a freebie that falls out when making use of an on-off-on SPDT selector switch … 

The demo was played thru a modded ’79 Fender Champ (“unleashed Champ” jcm2013) and recorded using a Zoom H1 pocket recorder running at 24bit/48k”



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