Actually I sort of feel I'm getting ahead of myself on this. I'm going to build this amp first and see what I can tweak. I also happened to find a board house that allows multiple designs on the same pcb as long as they're separated by only silkscreen. So I guess I'll fit a simple LM3886 amp next to the preamp of P27. Honestly, I think they should sound pretty much the same as far as clean tones go, but I'm rather excited to hear the difference in distorted sound. Is the pa of P27 one of those "simple" and well behaving ss amps? I guess we'll figure it out. This may take a long time, both 'cause of I'm busy and it takes ages to ship stuff here inexpensively. I also couldn't find any sound tests of this particular amp and I'm planning recording one, as soon as I get my hands on those boards.

Phil, that was a very detailed answer, thanks. To be honest I would use tubes rather than going into so much trouble of emulating them, especially if I'm going to need an output transformer (which are hard to find and expensive here) anyways.

As for the light bulb trick, I believe any resistor with appropriate power rating should cause voltage sag and limit the current. Does dependence of bulb resistance to temperature play a big role in your application?

Thank you, as I said, I am currently reading the book, but identifying everything is not trivial to me. Also, Rod Elliott modified this circuit so that it uses current feedback. I know it's common in guitar amplifiers and I think it has to to with emulating valve amplifier output impedance. But hopefully someone can clarify the issue and lay out the exact decision making process.

Sorry I wasn't clear about what I was looking for. Though, your reply helped, I can already identify long tailed pair. What do Q5 and Q6 do for ex? At first I thought they were current mirror but it doesn't really resemble a current mirror, it's wired differently and its on the emmitter side of the LTP.

Also I observed a huge difference in the behavior of the amp when I connect R8 to ground or leave it floating (same thing just changes R7s value), both of which common practices it seems, from what I've seen. Also, R27s value affects the output drastically. Ex. if I wire R8 directly to ground and not to spk- net, the output voltage stays more or less constant with the variable load impedence. I guess this is one of the changes Mr. Elliott made from early version of his amp, but I've yet to understand why and how this improves the circuit. Can you clarify whats going on with the spk- net please?

Edit: I was suspecting that P3A and P27B, both would output contant voltage, much like when I disconnected the R8 from SPK- net, now that I built P3A in LTSpicee I can confirm that (Good thing is my simulation matches real measurements perfectly). So maybe this load dependence thing is just a way to simulate valve amplifiers? Even if so, if I recall correctly those should be constant current drives, which again our circuit doesn't behave like. Does this circuit use some kind of Mixed Mode Feedback? as decribed here: http://sound.whsites.net/project56.htm

Thanks

Hi,

I've been trying to get into discrete amplifiers. I know the electronics and I can derive the output as function of inputs etc. But it's only doable on smaller sections of amplifiers so, I suppose working on an amplifier requires a perspective, being able to see all the blocks at first sight. Right know I'm looking into somewhat complex designs and try to separate them into smaller building blocks in my mind. Here's Mr. Elliotts P27 power amp, I built it in LTSpice and played with simulation. Can someone help me understand this circuit? I have a couple of guesses but would like to hear from you instead.

Thanks in advance

Edit: I currently am reading the book published here, teemuk's, but working on something real is always more rewarding in my experience.