Bucket Brigade Delay

[Harry]

I've been scouring the web looking for info on this method of delay, but can't find much good info.

Anyone can tell me how they work?

[d95err]

It's a sequence of "bucket" stages. Every stage consist of a transistor and a capacitor (and probably some more junk). The signal enters into the first stage capacitor. A clock pulse will then alternately turns on every other transistor. This causes the caps of the "open" stages to unload to the next stage. When the clock turns off the transistor, the charge (i.e. signal level) is stored in the capacitor. Thus the signal is passed from stage to stage.
The output is taken from the last capacitor.

Functionally, it's the same as digital sampling - the signal is divided into sections with a certain frequency and stored in a buffer. The main difference would be that the amplitude of each section is analog (stored in a cap) rather than digital (stored as a binary value). The practical difference is mainly that the clock frequency of a BBD is a lot lower than a digital delay.

Thus, the sound quality is a lot worse. According to the Nyquist theorem, a sampled signal can only correctly represent frequencies of 1/2 the sampling rate or lower. To compensate for this, BBDs need a lowpass filter that removes all the junk that appear in the treble. By sheer coincidence, this happens to sound really good for guitar; thus the analog delay mojo.

[TELEFUNKON]

http://www.elixant.com/~stompbox/smfforum/index.php?topic=30655.0

[Mark Hammer]

Here's a nice read: http://www.web-ee.com/Electronic-Projects/data/mn3004.pdf

You'll also find a lot of pertinent documents here: http://www.synthdiy.com/view/filecat.asp?type=4

[Harry]

Thanks for all the great info guys. I'll let you know if I have any other questions after I finish reading all that.