Has anyone built a homemade class A amp? I'm looking for schematics but it seems like there's no real consensus on the pros and cons of the designs. I do want to use transistors instead of tubes simply because they're easier to find.
I don't need a lot of power, but I would like more than a headphone amp. My current stereo delivers 30W/channel into 8 ohms and it is more than enough for me.
30W/channel of class A is going to be quite hot, regardless of whether it's idling or running flat out. Any particular reason why you think Class A is what you want?
It really is the wrong way to build audio amps, unless you're working under some quite peculiar constraints.
If you're doing it for fun, then knock yourself out, there's no great difficulty to it - they're simple enough, especially as I imagine you'll also be eschewing feedback.
Note that most modern MOSFETs are crap at being analogue transistors, they're designed to be switches, not to dither around at half-on, when they'll develop hot spots internally and fail orders of magnitude before you'd expect them to.
I just want to listen to a class A amp for a while and see if it sounds any better. I've used tube amps before and I do think they sound better with certain kinds of music, but not enough that I would use one all the time.
I don't care if the output transistors burn out faster because I can just order some more from Digikey or whatever.
A book on amp design would also be nice so I have some idea of what I'm doing. But I'm perfectly happy to just blindly follow a schematic.
Something like https://www.electroschematics.com/3537/2n3055-24-watt-class-a-amplifier/ ?
The wrong MOSFETs used in linear mode - you won't be replacing them every few weeks, more like 50ms after power-on. Linear ones do exist, they just cost a bit more and are very different architecturally.
That linked design uses classic old bipolar 2N3055s for the power stage - as long as you buy legit ones, they're quite robust, but there are a vast number of knockoffs with implausibly small die, thin heat spreader cases and generally smoke fodder.
Can't really help you, then. Good hunting!
Having just completed my first Silicon Carbide FET job - if you're looking to make your life even harder, and want to waste time and money, they'd make ideal class A power devices. Otherwise, probably best stick to good old silicon or vacuum.
