Very cool bottle of ale.
After several weeks and a couple discussions with Jason Stoddard, I have a working coaster amp. I really did not want to say a lot till I got one going but suddenly one works, and works surprisingly well. I need to do more listening before i offer more of an opinion but for now, at least one is going! This is not easy soldering by the way but the parts are not very expensive and build time is not bad.
If any of you wish to attempt the build, PM me and I will tell you some things to avoid, I spent the last three hours troubleshooting and probably know more about this circuitry now than was my original intent.
I now have it hooked to a quality DAC with some Sennheisers and with the proper input I cannot think of a $40 amp (approximate) that could top this. Jason has been incredible throughout this and I hope to return this favor with one of my own.
Congrats!
And yes, soldering SMD parts takes some getting used to. The first SMD product I put together (the first Magni prototype) felt completely unnatural, weird, and wrong. Now, I can do SMD prototypes faster than thru-hole, and more accurately. Well, at least until the parts get too small. I draw the line at 402, and at anything with 0.5mm pitch or below. Believe it or not, we have a couple of people who can do those by hand. Everybody gives up when faced with parts that have pads hidden underneath, like the little 3x3mm regulators we use that have 16 pins and a thermal pad. At that point, if you want to do SMD in small quantities, it's time to get solder paste and an IR oven.
As far as performance goes, I hear you. I personally think the Vali Mini sounds pretty darn good. It's just not the highest-performance thing on the planet--it won't win any awards for low distortion, low noise, or high output. Ironically, after looking at some measurements of similar amps, or amps using NuTubes, Vali Mini's performance seems to be just fine for the genre. So, hopefully this week, I'll finalize the docs, write a chapter, and start selling coasters.
A couple of notes:
1. If you want to help minimize ringing with the small tubes, try using small strips of Sorbothane 30 durometer under the tubes. This is what we used in production. The prototypes I've made use the sorbothane. Small foam pads also work reasonably well.
2. To maximize power output, you're looking to hit about 9V DC before the output coupling capacitor. Tweaking the value of the plate loads can help you hit this number; the plate loads provided get near that for the tube types specified, but is not an absolute recommendation. You should use the same plate load for both tubes, however, since the plate load sets the overall gain of the system.
3. These small tubes vary pretty significantly in terms of gain. You may need to match them. Check each channel's gain and swap tubes if necessary.
Thanks again for taking the effort to build these, and to prove out the schematic and BOM!
Here is a great example of the power of the internet. If you search for coaster amp through Google images, among the roller coasters, normal drink coasters, etc. is now an early image of the Schiit product as I mounted one in a magic 8 ball. Do the same thing with Schiit Coaster Amp and Jason's photo appears.
Ah the power of Google.
