Nowadays, if you want to delay an audio signal for, say, an echo or a reverb, you’d probably just do it digitally. But it wasn’t long ago that wasn’t a realistic option. Some devices used mechanical means, but there were also ICs like the TCA350 “bucket brigade” device that [10maurycy10] shows us in a recent post.
In this case, bucket brigade is a euphemism calling to mind how firemen would pass buckets down the line to put out a fire. It’s a bit of an analog analogy. The “bucket” is a MOSFET and capacitor. The “water” is electrical charge stored in the cap. All those charges are tiny snippets of an analog signal.
In practice, the chip has two clock signals that do not overlap. The first one gates the signal to a small capacitor which follows the input signal voltage. Then, when that gate clock closes, the second clock gates that output to another identical capacitor. The second capacitor discharges the first one and the whole process repeats, sometimes for hundreds of times.
In addition to a test circuit and some signals going in and out, the post also shows photomicrographs of the chip’s insides. As you might expect, all those identical gates make for a very regular layout on the die.
You might think these devices are obsolete, and that’s true. However, the basic idea is still in use for CCD camera sensors.
Sometimes, those old delay lines were actually columns of mercury or coiled-up transmission lines. You could even use a garden hose or build your own delay line memory.
Bucket brigade chips are still popular in guitar delay effect pedals, due to the specific way they color the sound.
A YouTuber named Moritz Klein recently released a decent video which goes into how they work, and also how to use them in audio applications. Like the linked post, he also constructs a couple of stages using discrete components: https://www.youtube.com/watch?v=4LjP5Y1yxXs
Ahh, memories of playing with the SAD1024, sold by Radio Shack. Circa 1978 or so. Fun chip. Could be split into two 512-element lines for stereo. Looping back its output made some neat effects.
All more easily done with any audio plug-in now, of course, but a lot of fun for a young nerd to play with back then.
Yep. I built a delay/phase-shifter/chorus/flanger in the late 70s using some PC boards and schematics from Electronics Today International – an electronics magazine once available in Canada. I still have it somewhere. The actual BBD ic was a MM something. The unit was great for phattening up things like acoustic guitar.
I used a SAD1024 to make a pseudo surround sound system. I set the delay when watching a baseball game to make it sound like I was in the stands and a little echo to make it sound like I was in a movie theater. They were pretty expensive back then. Nevertheless, after a month or so, I got tired of it and relegated it to the junk drawer. I’m sure I still have it around somewhere.
This article reminds me of my Tek TDS1012. The 1GS/s was possible by the CCD analog shift register. I’ve heard it somewhere over EEVblog.
I thought about that, and tried it. I don’t know about that TCA350, but the SAD1024 really pooped out past 1 MHz clock rate: it couldn’t ‘sample’ more than a 250 kHz signal. Really just an audio device.
Delay via mechanical means…. In the ’50’s a spring was used to delay (echo) the signal. Periodically, it would generate its own sproing independently.
I pulled one of those out of an electric organ. It was two long springs stretched in a metal box with a transducer of some sort, if I recall correctly.
Like the reverb on a Hammond organ?
“Sometimes, those old delay lines were actually columns of mercury or coiled-up transmission lines.”
They still are! Low-frequency delay lines can be done via any number of methods pretty trivially: but if you’re talking about wideband RF signals, your options drop to nearly zero. Coiled transmission delay lines are definitely an option for a fixed delay. Nowadays PCB production is cheap enough they’ll typically do it as something like stripline, but I’ve still seen coiled coax if it gets wideband enough.
But for variable delays they get more interesting – I’ve got one which actually uses transistor-switched delay lines (I don’t know if they’re coiled, I don’t want to take it apart!) to give you 10 ps overall resolution with pretty flat bandwidth up to 3 GHz (its 3 dB point), but the super-wideband ones actually use transmission lines in a trombone configuration: the waveguide is physically moved by a stepper, elongating it.
Reminds me of the 38 miles of fiber optic cable on a spool that was used to slow down stock trades , but hackaday already covered it here
https://hackaday.com/2019/02/26/putting-the-brakes-on-high-frequency-trading-with-physics/
I helped some guys set up a relay of Canon laser beam transceivers from lower Manhattan to New Jersey back in the 90s
By help, it was more like “hey you know you don’t need an FCC license for laser beam and here’s the page out of the canon sales catalog, I think they are for broadcast television signals, but you know data is data”
I never really heard how that turned out, but they were pretty excited about not having their data go up to the George Washington Bridge and back.
So now someone needs to repurpose a surplus ccd to make an audio delay!
I love my SWTPC Ambiance Synthesizer dual double chip delay.They also made one of the first computer kits, so I was familiar with them and saw an ad for this delay device back then, lust! In the 90’s at a hamfest I instantly grabbed it up for $20. Without inputs I can make the sonic landscape of Forbidden Planet live, with ten knobs. The circuits are a little wonky, pots that electrically go from 8oclock to 4oclock leaving the bottom and top ends with dead zones. There were no bypass caps at each op-amp. Also got one or two RS kits with a new unopened SAD1024.
Hamfests are great for unique vintage scores.
Interesting. So how do you get a capacitor to pass all it’s charge to another capacitor? Every step would halve the voltage.
I’m assuming there is some active electronics between them that voltage-follows the first capacitor, and that is what gets imprinted onto the second…
Like how you siphon all the water from one cup to the next: you place the second cup lower than the first.
The inventor (G .E. Smith of Bell Labs) gave a talk on the Bucket Brigade at Stevens Tech. It is fascinating to see how this invention developed into the CCD camera and more.
The Pioneer SR-303 Stereo Reverberation Amplifier (1980-1982)
uses MN3008 Bucket Brigade Devices to delay the audio signal.
https://www.hifiengine.com/manual_library/pioneer/sr-303.shtml