Xvive Audio manufactures replicas of the Matsushita MN3005 chip found in original Electro-Harmonix Deluxe Memory Man pedals—as well as in its own W3 Memory Analog Delay.
But don’t blame the Matsushita BBDs too much. They were limited by their companion clock generators: the MN3101 (for MN30xx chips) and MN3102 (for low-voltage chips). These provided an inexpensive, simple, compact solution for directly driving Matsushita’s BBDs, but they couldn’t adequately overcome that clock-pin capacitance. They were great for chorus or medium-delay echo, but you couldn’t get them to clock fast enough for great flanging, and they couldn’t handle the total capacitance of more than 8,192 stages (i.e., from a pair of 4,096-stage chips) needed for longer delay times. However, when properly buffered to overcome that capacitance, Matsushita BBDs can be pushed much higher—just like a buffered guitar signal can travel long cable distances and still retain treble. I’ve witnessed MN3207s pushed to 1.5 MHz clock rates without difficulty.
Can it work the opposite way? That is, can you buffer a clock chip to drive, say, four MN3005s (for a total of 16,384 stages, and 11,200 pF of clock capacitance)? It’s a bit like our earlier example of a 100-watt, EL84-powered amp: In theory, it could be done—but why not simply go digital?
Cut out That Racket!
BBD-based designs are susceptible to noise. The chips themselves differ in their individual noisiness, but the necessary inclusion of a clock only makes matters worse. There are two basic sources of noise to contend with in normal use. One is the sometimes-audible whine of the high-frequency clock that’s always running. If a 10 kHz clock pulse is required to achieve the desired delay time, there’s a chance you might hear that clock leaking through to other parts of the circuit, and eventually coming out your speakers.
Now let’s talk about the second kind of noise. We may think of BBDs as providing a seamless, continuous representation of the input signal, but in actuality there are teensy-weensy steps between each successive sample, and those can create the illusion of high-frequency content riding on top of the actual signal. This is referred to as aliasing noise.
Historically, these two noise sources have been addressed using some combination of the following five strategies:
- Low-pass filtering. A low-pass filter is placed before and after the BBD in an effort to eliminate everything above the highest frequency that’s intended to be audible. This approach is used in virtually all BBD-based effect devices.
- Gating. A noise gate is applied at the BBD output, so that any remaining BBD noise is killed when you stop playing. This approach is used in the Boss CE-1 Chorus Ensemble and A/DA Flanger.
- Treble manipulation. Treble is emphasized at the input and then de-emphasized in complementary fashion at the output. This restores normal tone to the dry signal, but cuts any hiss or clock whine added by the BBD to the delayed signal. This approach is used in the Boss CE-2 Chorus and BF-2 Flanger.
- Companding. Companding—compressing and expanding—keeps the audio input to the BBD at an optimal level, well above the noise floor, and restores dynamics after the delay is created. This approach is used in the Electro-Harmonix Deluxe Memory Man and Boss DM-2
- Output balancing. As noted earlier, a trimpot is used to balance BBD levels in an effort to cancel out clock noise.
Ironically, a great deal of the “warmth” that players are referring to when discussing analog delays is actually a result of the low-pass-filtering strategy for eliminating clock noise. The thing is, if you use the same sort of filtering in a digital delay circuit, it can sound remarkably similar to analog!
Grading BBD Chips
For the longest time, there were effectively three manufacturers of BBDs: Reticon, Panasonic/Matsushita, and Philips. I’m not sure about Philips, but Reticon stopped making BBDs in the early ’80s, so anyone trying to repair or clone a Reticon-based pedal has to pay astronomical prices for NOS replacements. Panasonic (formerly Matsushita) stopped production in the late ’90s, but since there was demand for them, several companies resurrected clones of the old Matsushita chips. In the late 1990s, Belling began reissuing copies of Matsushita’s MN3208 and MN3207 with the designation BL3208 and BL3207, and more recently Coolaudio started producing clones of the MN3207, MN3208, and MN3205. Even more recently, China-based Xvive Audio (which, not so coincidentally, has its own line of very affordable stompboxes) began making replicas of Matsushita’s venerable MN3005. The chip is available for sale separately, but is also used in the company’s higher-end W3 Memory pedal—which was designed by Howard Davis, manager of analog circuit design at Electro-Harmonix from 1976–1981. The chip itself isn’t cheap, but it’s not prohibitively priced, either. Sadly, new Reticon chip clones don’t seem to be on the horizon.
As with seemingly everything else in guitar gear, there are many legends attached to different BBD chips. One is that there’s a difference between generations of Matsushita chips—particularly between the MN30xx series and the lower-voltage MN32xx series. Certainly the earliest Matsushita chips (like the MN3001 and MN3002 used in the Boss CE-1, and the MN3010 used in the A/DA Flanger) were quieter and could be clocked faster (because they had a lower clock-pin capacitance). But the quality of the signal in any of the various issues is still very much a matter for debate. I’m not so sure specs and data sheets capture the differences people think they hear.
With regard to the difference between the MN30xx and 32xx generations, recall that BBDs can’t pass an audio signal unless it’s sitting atop a DC bias voltage (derived from the power supply). In the 1980s, the power supply for the bias voltage would’ve usually been a battery. As the battery aged and the voltage dropped, dividing down that voltage could result in the “wrong” bias voltage, and sound quality would suffer. It seems a silly consideration now, in an era of plentiful power supplies, but back then there were no pedalboard power bricks, and you couldn’t expect musicians to keep changing the battery or opening up a pedal to twiddle the bias trimmer. So Matsushita designed the MN32xx series to operate off of 5 volts, and the bias would be derived from that 5 volts. The pedal’s 9-volt battery would then be down-regulated to provide a stable 5 volts for the BBD and its bias until the battery dropped below around 7 volts—at which point it wouldn’t have enough juice to power the pedal anyway. The redesign allowed the MN32xx series to work flawlessly without any drift in the bias as the battery aged. But with contemporary powered pedalboards, concerns about supply-voltage drift are history.
Tying It All Together
Happily, in comparison to modern production of vacuum tubes, the quality of BBDs currently in production is generally no different from those made in bygone days. A new MN3205 is the equal of a NOS version from 1981. Further, many of today’s effect designers have mined the rich vein of tricks and strategies for extracting the best out of this technology. That said, there were a lot more BBD types and configurations available 30 years ago, and I do wish someone would reissue certain models—like the Reticon SAD-1024 used in great old flangers from Boss, A/DA, EHX, and MXR (as well as in the ADR S24 Scamp), and the multitap Matsushita MN3011, which powered the legendary A/DA STD-1 Stereo Tapped Delay exploited to such great effect by Allan Holdsworth. But that hasn’t stopped current designers from coming up with feature-rich pedals yielding remarkable sounds and options that nobody dreamed of in 1979—including things like tap tempo and digital control.
Although many stompbox companies are migrating to the digital domain, I find it both interesting and heartening that new BBD pedals are unveiled quite often these days. Which prompts the question, is there anything about using BBDs that’s somehow inherently better than state-of-the-art digital circuitry? Probably not. And certainly, back in the day when all effects were analog, there were both stellar and ho-hum products. But the reason many BBDs have been reissued in recent years is not simply due to romanticized notions about the good ol’ days. When all is said and done, it’s because both the established old-school BBD know-how and newly discovered circuit-engineering tricks—and yes, even the things that have to be done to keep noise down—simply sound great when done well.
Special thanks to Joel Korte at Chase Bliss Audio, Steve Daniels at Small Bear Electronics, and Mike Irwin.