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 **

Stereo-Vibe 480+ // Copyright JC Maillet (c) 2005

Built June 27'th 2005


Light Source provided by ...

Radio Shack #272-1139 ... 1.5v/25mA Incadescent Bulbs



\\\ Background ///

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

www.formusiciansonly.com


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 ...

Patent #2988706

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 ...

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 ...

Fumio Mieda's Low Noise Frequency Shifter stages up close

Film cannisters shield the cells from the other channel's bulb when they operate in complimentary mode as well as outside light ...

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 ...



\\\ CLIPS ///

(c) 2006 JC Maillet

Wurlitzer 270 >> SV480 >> Korg D1600

Wurlitzer // stereo phasor

Wurlitzer // stereo vibrato


Wurlitzer 270 >> Nyquist Aliaser >> Yamaha DD-20MkII >> SV480 >> Korg D1600

nyquist SV480 wurly