Hi all, I'm a complete newbie here. I have a fair bit of digital experience, some analog experience, a tiny bit of Spice experience, but I'm a total newbie when it comes to vacuum tubes.
I am trying to figure out how the Poddwatt circuitry works before I attempt to build one. I found the post earlier in this thread showing the 5 different variants of the Poddwatt circuitry as it has evolved. To make it easier for anyone reading this to find all those circuit diagrams, here is a link to the exact page:
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=1232&start=670I started off by trying to make a Spice model of the Poddwatt type "E" (the most modern version). It went surprisingly well (aside from Spice being Spice), and I now have what appears to be a working Spice model of the Type E circuit.
While looking around at the signals during operation, the first thing that came up was that I don't see how the subwoofer output signal works. It was introduced in Type C, where the A/C coupled input signal gets divided down by the subwoofer divider resistors to create the output signal. The subwoofer output signal is referenced to GND due to the .33 uF AC signal coupling cap and the subwoofer voltage divider, and everything looks fine. In the type D and E circuitry, a positive bias voltage got added to the grid inputs, apparently to make the LM317 perform better. However, the new bias voltage will also bias the subwoofer voltage divider, and that seems like a potentially bad thing for whatever subwoofer amp might be downstream. A spice run clearly shows that the subwoofer output gets shifted entirely into the positive voltage domain. I tried to attach a screenshot of the Spice run showing that the subwoofer output for this particular test exists entirely in the positive voltage range, but the system is throwing an error when I try to attach the JPG.
In any case, please let me know if I am not thinking about this correctly.