High Speed MN3005 Chorus – Analog Bucket-Brigade Chorus Design

RE-DEFINING BBD CHORUS DESIGN PARAMETERS

The Problem with Traditional BBD Chorus

Analog chorus pedals based on BBD delay IC’s have a distinctive metallic edge that many players – including myself – find fatiguing. The root of the issue lies in how those circuits handle sampling. In many cases the clock frequency can drop quite low – even to around 10kHz – which tends to violate the Nyquist requirement and introduces audible aliasing. To try counteracting this interaction the signal is often heavily filtered at the top end where the design then tends to exhibit a characteristic dark and lo-fi response.

It’s easy to see there’s a trade-off at play in the general “BBD-chorus” concept … and since much of the “chime” comes from the signal’s high-frequency content – this strategy can ultimately be seen as somewhat self-defeating.

A Modern Solution: The Super Chorus

To address this, the viva Analog “SUPER CHORUS” concept multiplies both the delay memory and the clock speed by a factor of at least four. A MN3005 running at the four times the speed of an N3007 yields the same delay time, but with the lowest clock frequency pushed up to at least 40kHz. With the audio bandwidth set slightly beyond 12kHz – essentially full range for guitar – this expanded headroom dramatically reduces aliasing and produces a smoother, warmer chorus or vibrato tone. It also reduces the need for aggressive filtering.

INNOVATION

A major part of this re-designed chorus topology is a synchronous high-speed sampling system placed after the BBD. It can operate reliably well above 4MHz and relies on CD40xx CMOS chips pushed beyond their typical speed range, all running from a 9-volt supply. The details here are complex and not easily explained informally.

The measured BBD input headroom comes in at 1400mVpp once the bias adjustment is properly centred, and to which a clipping indicator circuit is set. Controlling pre-gain allows near-saturating the input of the BBD – with gtr, bass, or keys – yielding best signal-to-noise without relying on a fidelity-robbing COMPANDER chip-set. With two independent WET/DRY return paths in the output mixer a proper “makeup-mix” can be achieved between Vibrato and Straight signals and overall matched accordingly to effect-bypass levels. This manual approach is not only capable of yielding best signal-to-noise ratios but also allows experiencing the full “tape-like” dynamic fidelity analog BBD systems are capable of delivering … which is even more evident here on account of the increased sampling rates.

Another unusual choice is the modulation source. Instead of the standard triangle-wave LFO found in most chorus pedals, this circuit uses an extended-range Univibe-style LFO. The result is a more natural and expressive modulation character – far more interesting, in my view, than modern digital LFO implementations.

A short audio example was recorded on October 4. 2025, during the first power-up of the prototype.