Can this 4QD circuit be improved?

[keantoken]

I have been looking over the 4QD circuit archives and I have been wondering if this amp could be improved with modern transistors an such:
http://www.4qdtec.com/pwramp.html
I like this design, it has current limiting and uses complimentary symmetry (cool to me ). I am not necessarily looking for high wattage, I just want a good low-distortion amp for my room. feel free to branch out and create your own modifications. Some features that I would like but aren't necessary are phono and video inputs, tone controls (better than the one proposed on the link), of course-volume, line-in and microphone ports, headphone jack, phono and video outputs. I know that all this may seem like I'm going commercial, but these are just suggestions. I would try this on my own but as was shown in my thread, Feedback on my design (in this forum), I am not quite the competent designer yet! . Any replies are appreciated!

[anatech]

Hi keantoken,
There are a couple others. For a low power (50W) look at the Symasym. Do a search.

-Chris

[keantoken]

I know about symasm4, but I was wondering what could be done with this one. It seemed that the guy that published it hadn't really messed with it and I was wondering if maybe you (or someone) could get lower distortion out of it with new transistors. It seemed like a pretty good design to me, the way it handles a large range of supply voltages and has current limiting. I at least want a few more comments! Anything is appreciated!

[anatech]

Hi keantoken,
But ..... there are so many things I don't like about it. I vote for starting with a basically good amplifier. I see too many bad ones in the course of my work. Honest!

New parts will not help an unsound design. Any improvement will be a change the schematic so you may as well start with a good design and improve it further. The results are more worthwhile.

-Chris

[keantoken]

oh, well. What about focasm? how good of a design is that?
I tried simulating symasm but my simulator (LTSpice/SWCADIII) came up with an error "singular matrix. check node xxxx" and I can't figure out why. I am wondering about a bad transistor model. Know of any better simulators? I need one.

[Tim__x]

Generally (but not always) that means you made a mistake in drawing the circuit, find the node it mentioned and take a look.

As I said in the other thread LTSpice is one of the best simulators around.

Post the .asc file (change the extension to .txt and then attach it) so we can see what needs to be changed.

[keantoken]

thanks. Here is the circuit:

[Tim__x]

I swapped all the transistors out for the standard models, since I don't have whatever models you're using, feel free to switch them back if your models are working. I got rid of "1K POT", that name was causing an error*. I tidied up the layout a little. Since you're simulating with ideal components paralleled capacitors arn't necassary, nor are caps on the zero-impedance supply lines. Your input was still floating so I grounded one side of V3. R1 (4 Ohm) is the speaker, the output is taken between ground and L1, the 8 Ohm resistor you'd labeled speaker was in the wrong place.

I also changed the simulation command (no need to simulate for 50 cycles) and changed the input voltage so the output's around 1v rms, but that's not really important.

*LTSpice decides what model to use for a component by it's name, "Cx" and it simulates as a cap, "Rx" and it's a resistor, etcetera.

[keantoken]

Thanks, I was assuming that output was between the battery's and the ground (it's hard for me to know from lack of experience when they don't show it on the schematic). I had looked at the node and it didn't seem suspicious.