Hello All,
So my BBD project
is not working quite yet. There are many factors at play here, not
least of which is the quality (or lack thereof) with regards to the
bread boards. Here is a listing of the issues encountered so far:
Bread Board
Issues
Bread boards can be notorious for having to get the parts seated
right. This just means that as more parts are added to the circuit,
you need to check and re-check every part to make sure it sits
properly in the bread board.
BBD driver
issues
I
unfortunately, have not been able to get my BBD chip to work yet.
Part of the problem here is the biasing needed for driving these
chips. Whereas opamps, transistors and many other components have to
be biased simple ratios like ½, BBD chips need a 14/15 ratio. In
the older model chips, like the MN3005, MN3007 and so on, which ran
on +15V, the newer chips like the MN3205, MN3207 and the one I am
using, the BL3208, all run on +9V. I have still not isolated the
proper voltage divider with simple resistors and in looking at
schematics for most of these circuits, they utilize a carefully tuned
trimpot resistor to bias the chip. Hopefully I will have this
figured out by the end of the next class period.
Circuit
Integration
Beyond
these issues, most of the schematics available online for analog
delay pedals are not correct or missing certain components. I have
been able to find limited resources in regards to setting up the
clock source within a circuit that is leveled beyond the simple
schematic in the Stompbox cookbook. Datasheets for the clock driver
are also very vague in regards to the test circuit, ie one is not
provided, and I have been having to use the Stompbox cookbook as a
reference.
I
am at this point attempting to simply build the basic sections for
the pedal such as preamp buffer, BBD section and then the pre and
post filters. I have a working preamp buffer and I am currently
working on the BBD section. I have attached photos of each section
as well as the schematics of each section as built so far in a subsequent post. If I
cannot successfully get the BBD to work by the end of class week 7, I
will probably have to switch over to building my Alice microphone for
time purposes and I so I have a completed project at the end of this
class. The knowledge gained on this project has been very helpful
but it is definitely not an easy project at all. There is reason why
you pay high prices for analog BBD delays.
Edward