Yet another BBD question...

[Haible Juergen]

	>But the minimum delay time is limited, too. It takes time for the 
	>electrons to flow from one cap to another. Clock it too fast and
the 
	>dynamic range starts to suffer. And every stage adds a little more 
	>error and a little more noise--the more stages the crummier the 
	>signal will be at the output.
	>
	>Even so you can get some large time ratios with analog delays. The 
	>shorter Panasonic delays are spec'ed at 20:1, which is only a 
	>ballpark figure and depends on the application--and what you can
put 
	>up with. The old Reticon delays could be clocked even faster, 
	>although they were noisier.

The MN3004 is spec'ed for 10kHz - 100kHz. But in the Polysix they are
clocked as high as 600kHz.

	>Another trick is to have one delay fixed to a short delay time
while 
	>varying the other. This makes it possible to flange (comb filter)
all 
	>the way out of the AF range (as the variable delay time approaches 
	>the fixed time), sidestepping the minimum delay time problem 
	>completely--at the expense of introducing a short, fixed time delay

	>into your "straight" signal, as well as making it noisier. I'd like

	>to try this myself.

That's exactly what I did last night.
I did some hacks on a Polysic FX board (another one ...), modified the
clock and signal path that all BBDs can be swept from 8kHz to 600kHz
with the trimmers on the board, and the outputs of two lines being
added rather than one line + the direct signal.
I haven't done in depth tests yet - it was early in the morning - but
I'll go on later that week. BTW, where would one apply the feedback loop
for resonance in such a flanger ? Around one BBD line only ? From
the output of one to the input of both ? From the added outputs to both
inputs ? Or feed back the difference while using the sum for the output ?
Lot of things to try.

JH.


> >Are there other ways to do analog delays?
> 
> Reverb springs are analog delays, albeit with a lot of resonance.
> 
> Harry once suggested two tin cans and a piece of string. I have to 
> give credit where it's due.
> 
> Terry Bowman, KA4HJH
> "The Mac Doctor"
> 
> ICQ: 45652354