Vigen BBD project Week 6

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