Guitarists are a strange bunch. With all the digital techniques and additional ease of use, the analog delay is still the pinnacle of guitar effects for many guitar enthusiasts.
Not infrequently, there are even several on the pedal board and form analog delay the secret ingredient for their rousing guitar sound. There’s something magical about the warm repeats that are so characteristic of analog delay pedals. The silent force behind these pedals is the Bucket Brigade Device, about which more in this article. This is an article for pedal geeks and nerds who are interested in the technology behind the analog delay and of course also for those interested.
The first analog delay pedal
The first analog delay pedal dates back to the early 1970s. Introducing Bucket Brigade chips made it possible to create analog delay in a small size. The analog delay came at a time when only tape-based delay units were on the market. These devices were large, unstable and often broke. In 1969, Philips Research Laboratories developed the Bucket Brigade Device (also called BBD) that made it possible to send a stored analog signal through a successive series of capacitors. This development was the prelude to a series of delay pedals that are still very popular today. In addition to the analog delay, the digital delay was developed some time later. In this article I explain the differences between analog and digital delay pedals.
The best known analog delay pedals
The best known analog delay pedals are the Memory Man from Electro Harmonix, the MXR Carbon Copy Analog Delay and the Boss DM-1. One (or even several) BBD(s) forms the heart of these pedals. In a BBD, the guitar signal is passed through a number of phases much like a human chain passes buckets in a fire. The result is a warm and analog sounding delay effect. This BBD chip is the heart of the effect, but it’s not just responsible for this warm, analog-sounding effect. In addition to a BBD, there are several components in an analog delay that provide this warm effect.
How does a Bucket Brigade Device work?
A BBD is a so-called Integrated Circuit (IC), most people know this better under the name ‘chip’ or ‘microchip’. A chip contains several electronic circuits, with a BBD there is a series of capacitors on it. So a BBD is an analog circuit that causes an incoming signal to be delayed. This works as follows, capacitors in the chip carry the signal just like buckets carry water, one capacitor is empty and the other is filled. This process takes a while, causing a delay in the signal.
What else is involved?
However, an analog delay is more than just a BBD chip, much (and perhaps most) of the effect comes from the design of the overall circuitry. BBD chips only work well if the incoming signal has little noise and little dynamics. In addition, a BBD cannot properly process a signal with many high frequencies, which causes all kinds of ‘aliasing artefacts’ in the signal. Finally, the ‘clock’ that controls the BBD creates a kind of tick in your audio signal, which you would rather not have. This unwanted noise also has to be filtered out.
Electronic circuit of an analog delay
The circuitry of virtually every analog delay pedal is made up of the following components: input mixer, compressor, filter 1, bbd, clock, filter 2, expander, feedback, and an output mixer. The audio signal goes through these components with the exception of the clock, which drives the BBD, where the audio signal does not go through. How this works exactly is shown in the figure below, which shows the electronic circuit of an analog delay. You read this diagram from left to right.
Input mixer
First, the guitar signal is split into 2’s. One bit of signal goes directly to the output mixer and the other bit of signal goes through the compressor and first filter to the BBD. The signal going to the BBD must have low distortion, low noise, and narrow bandwidth for the BBD to work efficiently.
Compressor
There is often a lot of dynamics in a guitar signal. This means that the signal can be either soft or loud, depending on your playing style. The BBD doesn’t like this, so the signal has to be compressed for this. This makes the soft parts harder and the hard part of your signal softer. This helps to reduce distortion and noise.
Filter 1
BBDs do not like high-frequency audio because this creates so-called ‘aliasing artifacts’. To avoid these artifacts, the signal passes through a low pass filter. This filter ensures that high frequencies are not passed. The signal is now ready to go to the BBD.
BBD
In a BBD, the signal travels from one capacitor to another, causing a delay (see also the section above on how BBDs work).
Clock
The clock is the metronome that tells the BBD what speed to move the audio signal from one bucket to the next. This clock is set to virtually any analog delay with a rate knob. A high speed means a short delay, a low speed means a long delay.
Filter 2
The signal coming out of the BBD needs to be cleaned up. The clock produces a kind of ticking sound as soon as you turn on the pedal. By passing the audio signal through a second low-pass filter, this clock noise is removed.
Expander
The expander unpacks the delayed signal from the BBD, as it were, and returns the dynamic range. The signal now resembles the input signal again (in terms of dynamics). The signal has acquired a dark character due to the two low pass filters.
Feedback
Part of the delayed signal is split off and fed back to the compressor. The following applies: more signal return means more repetitions. You control these repetitions with the repeats or intensity button on your pedal. Feeding back too much signal leads to self-oscillation. This is a repeating delay that distorts a little more each time. Not every analog pedal produces this effect, with some analog pedals the signal dies out.
Output mixer
The original audio signal and the delayed signal are recombined, with the two signals controlled by the mix or echo knob on your pedal.
Modern analog delay pedals
Although the analog delay pedal dates from the 1970s, it is still being made. The BBD is often still the heart of these pedals. If you got excited and want to try one yourself, check out one of the modern analog delays below. The most important features are listed for each delay.
| Name | Max delay time | Tap tempo | Tap divide | Modulation | Presets | Self-oscillation | Midi | Price* (eur) |
|---|---|---|---|---|---|---|---|---|
| EHX Memory Toy | 550 ms | no | no | yes | no | no | no | 95 |
| EHX Memory Boy | 550 ms | no | no | yes | no | yes | no | 128 |
| EHX Memory Man 1100-TT | 1100 ms | yes | 5 | yes | no | yes | no | 293 |
| Foxgear Echoes | 680 ms | no | no | no | no | yes | no | 78 |
| JAM pedals Delay Llama | 600 ms | no | no | no | no | yes | no | 219 |
| JAM pedals Delay Llama Xtreme | 800 ms | yes | no | yes | 4 | yes | no | 329 |
| JHS Panther Cub V2 | 1000 ms | yes | 4 | yes | no | yes | no | 355 |
| Chase Bliss Tonal Recall Blue Knob | 550 ms | yes | 6 | yes | 122 | yes | yes | 469 |
| Chase Bliss Tonal Recall Red Knob | 1100 ms | yes | 6 | yes | 122 | yes | yes | 579 |
| MXR Carbon Copy | 600 ms | no | no | yes | no | yes | no | 155 |
| VS Audio Project Diana | 550 ms | yes | no | yes | 4 | yes | no | 279 |
In this article information from this article about Boss Pedals has been used, the book Pedal Crush: Stompbox Effects for Creative Music Making by Kim Bjorn and Scott Harper and Wikipedia.