Began parts-hunting for the project. Despite the amount of parts and miscellaneous hardware I have in my garage, I am missing a fair share of components. I have the heavy stuff - that counts for quite a bit actually.

I created a spreadsheet in Open Office's "CALC" program - an open source version of a well-known corporate company's EXCELlent program. Then, while uploading the file to google, it dawned on me - why not just have the spreadsheet online? I remember seeing some time ago that google docs can do just that - I uploaded my Open Office file and google converted it to it's online version. Now I can make changes from any computer and not worry about which PC at home had the most recently modified spreadsheet. Pretty cool.

Here's the link:

https://docs.google.com/leaf?id=0AkSr64f9Rb3DdFpQMHFCa2JlVE1zTVhfclNiSkxCVHc&sort=name&layout=list&num=50 

And an embedded html view of the spreadsheet:

I am going to wait on some parts and hope I can make a trade-able donation to SCC's Electronic Student Association for some small passive components

10:00AM-2:00PM (4HRS)

Today I finished drawing up the circuit sections for the tube amplifier that I intend to build. From this, a part list shall be made, and parts acquired. I ran some quick simulations of the preamp...

I successfully modeled a simple center tapped output transformer as well as the reverb driver transformer; based on the LTSpice manual, and examples on the web. The modeling created represents a simple, ideal transformer model. There are many parameters (beyond the scope of this class, i.e. engineering degree work) that should be considered if a true representation of a transformer is desired/required.

I also reinforced some electronics theory while working today:

Impedance ratio vs. Voltage/Turns ratio

Ratio(Z) = [Ratio(turns)] * [Ratio(turns)]

The output transformer I intend to use is rated (not verified) for 7.5k:8 OHMS.

The voltage/turns ratio is calculated as such:

That is, the turns ratio is 30.619 : 1

I don't know if I will have time to spec out the output transformer, but it would be interesting to document the parameters of the transformer, and compare actual performance versus simulated performance. I should at least make sure the transformer is "good" and splice longer leads to the main connections inside the bell housing.

Next step: spreadsheet list of components and finding/ordering parts.

1PM-3:45PM, 8PM-11:30PM (6.25HRS)

LT Spice Fender Preamp Section Simulation

Today/tonight I drew up the preamp section for the Fender tone control in LT Spice. I added the appropriate models as SPICE directives (.inc) and pointed to them in LT Spice. I also took the opportunity to try out the potentiometer models. At the moment I have not plotted multiple variations of potentiometer values for the tone controls, however I plan to do so soon.

As the schematics show, I decided to go with the Super Reverb schematic for the preamp stage, "Vibrato" channel, with "Mid" tone control. This was a matter of taste, as I have always liked the overall voicing of the Blackface era Fender amplifiers.

I have also included a link to a free PC program that plots frequency response simulations for various tone control types. It is called Tone Stack Calculator. The program allows the user to substitute different values of components and get a visual representation of the overall frequency changes.

I plotted a graph for the component values used in my planned tube preamp stage. It looks quite close to the LT Spice simulation results.

Next steps: Plot multiple frequency responses for changes in potentiometer variation. Draw up the rest of the tube amp schematic, with component designators, and make a list of parts needed so I can begin the physical build.

4-7PM, 11PM-12AM (4HRS)