So I was considering building an eXstata, but I ran into a few stumbling blocks. Alex Cavelli doesn't seem particularly interested in maintaining the project, so much of the information on his web site is out of date, there is a lot of information that is just missing, and he hasn't expressed any interest in fixing either of these things himself. I'm still interested in pursuing the project, but if I'm going to go to the length of making part substitutions and designing a new board, I might as well share this information with the community. My hope right now is that if I share what I'm attempting to change, perhaps some of the more knowledgeable folks on here might be able to help me with the modified design so that I could then publish the finished product on a community driven website dedicated to the eXstata project. As of right now, here is what I plan to do:
Reduce the total number of resistors. The website for the eXstata indicates that several resistors were put in series because finding resistors of an appropriate tolerance, voltage, and power rating proved to be too difficult. I'm in the process of tracking down resistors which can be substituted for a few of the series of resistors in the original design. One resistor with a tolerance of 1% should be more reliable than three resistors in series with a tolerance of 1%, if I'm not mistaken. This should also clean up the board a little bit. On a similar note, I'm trying to make sure that as many of the resistors use the 2512 form factor as possible. The 2512 form factor seemed to offer the resistors with the best specs in a lot of cases, so I'd like to try and maintain a consistent form factor as I think this would look much more professional than a haphazard assortment of whatever resistors are cheapest. In general, I think I've got a pretty good handle on this side of things.
Get the spacing between holes right. The original design tombstoned a number of resistors and diodes. Granted there's not much of a reasonable explanation for it, but I'd feel like the build is more secure if it doesn't tombstone anything. Obviously the spacing between holes isn't the only thing that matters, given the high voltages in the eXstata amplifier, any PCB is going to need to be designed with appropriate space between traces. Does anyone know of a good guideline for space between traces when a lot of the lines are carrying 600V? Hopefully the reduction of the number of resistors might cut down on the number of traces on the board and free up some space.
Put all of the components on one board. This is going to depend on exactly how large the components are once the schematics are complete, but judging by pictures and the silk screen images, I don't think it's unrealistic to suggest that all of the components could possibly fit on a board that is less than 8" x 11". If I can fit everything onto one board, then hopefully I could do away with those blocks that the original design uses to connect the power supply to the amplifier. I'm hesitant about this though, because this might create some safety hazards while attempting to diagnose problems after the amplifier has already been plugged in and the capacitors have built up a charge. Do you think that putting everything on one board would be a safety concern, and if you do, do you think that substituting those blocks for wire and solder would be a viable solution?
Replace the old, hard to find transistors with transistors that would be readily available through mouser. This is where I'm going to need the most help. I don't know how to track down a suitable replacement transistor, and even if I find one, there is a lot of controversy over the transistors in the original design. I can't find a source for this, but I remember reading somewhere that a couple resistors could be swapped out with some sort of transistor to get better / louder sound, but I don't know which resistors were supposed to be replaced with which transistors...
Ideally, all of the parts required to get the amp up and running would be sourced from mouser (or another similar site). If all of the parts come from mouser, then I could create a project and share that so that other people who want to build an eXstata would be able to skip the process of searching for parts and adding them to their cart.
So what do you guys think? Are there any changes that I should be making that I'm not, or any changes that I do plan to make that I shouldn't?