Don Bonham's Magnatone 480
Stereo Vibrato Circuit
emulation/re-design using
Univibe Bulb-and-Photocell Phase Shifters
** all class-A control and signal path **
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Stereo-Vibe 480+ // Copyright JC Maillet (c) 2005
Built June 27'th 2005
Light Source provided by ...
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Radio Shack #272-1139 ... 1.5v/25mA Incadescent Bulbs
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Excerpts from Analog Man's Guide To Vintage Effects ©2004
(with permission from the author)
An awesome player and friend in CT sent me a few scans out of Analog Tom's recently published pedal reference bible Analog Man's Guide To Vintage Effects because he knows I like to read on the subject of the Univibe - I found this quite stimulating to say the least. With permission from Tom, I'm reproducing two paragraphs from that text which stimulated the creation of this design - thanks Tom !!
Analog Man's Guide To Vintage Effects
can be ordered directly from the publisher by visiting
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Univibing Don Bonham's Magnatone 480 Circuit
Some googling led me to Don Bonham's 1961 Patent on stereo Vibrato - thanks to Zack's Vibroworld !! ... this Patent was originally written in the context of electronic organs but later the idea was applied to guitar in the Estey/Magnatone line of amplifiers ... [ Note: some of these amplifier models had either an exact replica of the Patented circuit or a simpler version ] ... after analyzing this circuit I realised Mr. Mieda and Co. could very possibly have based their monophonic Leslie simulators on Don's shifter concept ... a conjecture on my part no less ...
From an electrical point of view it became apparent that Mr. Mieda's light-and-photocell circuit is functionally equivalent to Mr. Bonham's in terms of phase-shifting signals ... the translated text suggested to me it could be possible Don's Patent is exactly where ideas for the Vibra-Chorus, Resly Tone and Univibe originated ... so in reverse I started to wonder about exploring Don Bonham's full stereo topology in its original configuration by using the quieter bulb-based Mieda stages, while at the same time preserving the Vibe LFO feel in the LFO stereo-izing process ... this scheme also opened the possibility of having each side operate either in Vibrato or Phaser Mode - same as the Univibe ... resulting on a Stereo circuit that also provided Phasing on top of pitch-shifting Vibrato ...
This 24vdc build includes the same variable-Gain and tunable Presence low-noise FET preamp as in my Univibe+ ... it gives good FET warmth with a boost factor of up to x5 ... a tweaked Univibe phase-shift oscillator drives the whole works and comes with a waveform inverter for driving the two bulb circuits in synch or in anti/phase - giving Mono and Stereo modes ...
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Both shifter channels have a six position Frequency Pair selector switch for altering the location of the shift frequency centers across the audio band - this sets the feel of the filtering ... three position sets give even ratio values, similar to the Magnatone, while the other three as set in 10:1 ratios, similar to the Univibe sets like I use in my Small-Stone and Phase-45 mods ... aside from their Vibe/Maggie qualities these settings are chosen to allow different frequency matching between instrument, filters, and amplification equipment ...
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Fumio Mieda's Low Noise Frequency Shifter stages up close
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Film cannisters shield the cells from the other channel's bulb when they operate in complimentary mode as well as outside light ...
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The Stereo-Vibe 480+ does stereo bi-mode phasing as well as true bi-mode pitch shifting Vibrato a la Maggie 480 ... the Univibe based LFO circuit provides a wider speed range than stock and preserves the Univibe feel, even in stereo modulation mode ... the circuit is single-ended (class A) all the way, including the control circuitry ...
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(c) 2006 JC Maillet
Wurlitzer 270 >> SV480 >> Korg D1600
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Wurlitzer 270 >> Nyquist Aliaser >> Yamaha DD-20MkII >> SV480 >> Korg D1600
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