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Content:

• Analogue Delay
• BBD

Analogue Delay

Analogue delays are very interesting from a technical point of view. They are somehow in-between analogue and digital. On one hand the signal is split into frames and the Shannon Theorem applies, on the other hand the information is stored in real values and not in a binary manner.
The principal of analogue delay is that a signal is transformed into charge packets which are transferred by a time fix sequence from one storage unit to the next. The components used for analogue delay are thus called bucket-brigade device (BBD).

BBD

Simplified spoken a BBD is just a chain of semiconductor switches and capacitors. Every odd switch is connected to the clock signal and every even switch is connected to the inverted clock signal. The number of capactors is called number of stages and defines the delay time. Most common are 512 and 1024 stages.

This schematic diagram shows a BBD with four stages:

BBDs had been invented by F. Sangster and K. Teer at Philips in 1968. Reticon took up the idea and developed the first dedicated audio BBD, the SAD1024. SAD stands for "serial analog delay". If was introduced to the marked around 1975.

There had been only a few manufacturers for BBS, mainly Philips, Reticon, Valvo and Panasonic who all stopped production of BBDs. Thats why the prices of these are nowadays astronomic compared to other integrated circuits. On the other hand in 1977 a new SAD1024 costed 40 US$ which equals 150 US$ by 2010 inflation-adjusted.

Only some of the Panasonic BBDs (e.g. MN3207) are reissued and still widly available.

Comparison of popular BBDs:

Normally the delay time of a BBD is calculated: delay [ms] = stages / (2 * f_clock [kHz])

Although the SAD1024 has 1024 stages these are run as 2 time 512 in parallal in the Electric Mistress which will give the same delay as a single 512 stage BBD but will imporve performance.

The delay time of the RD5106A is calculated: delay [ms] = stages / (0.5 * f_clock [kHz])