Hi stewin,
tell me about your amp sound. I`ve simulate with LTspice and its weird regarding the sound at output, distort at high volume ? did it produce noise? I`m asking this because the value resistor R6, R11 and R35, R28, R19 and R12. If this resistor that i mention is not have proper value, than this amp ucd will produce noise alot, maybe less but will have noise and will follow with your volume control, because this system work like RF.
And the heart of this amp is R1 on your schema is R10, you can use trimpot for this, if u wanna try, first take 1k trimpot and tune it at maximum 1k resistance. turn on the amp and start lower the 1k resistor until u get the sound at output. Dont make it lower than that, because u just got proper value for the R10 when the amp start osc and u get sound at output, and u will found mosfet will cool even u play hard. i`ll post here with your setup but i`ll not include op-amp yet okay, i`ll do put op-amp later and simulate will post result also.
here is mine first. Input 2vrms freq 100Hz, power rails +/- 48vdc , 100Hz freq output +/- 24 vac at 6 ampere at 4 ohm load, 470n filter cap, 30uH inductance.
Starting source stepping with srcstepmethod=0
Source Step = 3.0303%
Source Step = 33.3333%
Source Step = 63.6364%
Source Step = 93.9394%
Source stepping succeeded in finding the operating point.
Fourier components of V(out)
DC component:0.0000834
Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+02 2.262e+01 1.000e+00 -124.68° 0.00°
2 2.000e+02 9.930e-04 4.391e-05 -35.90° 88.78°
3 3.000e+02 2.565e-02 1.134e-03 -168.04° -43.36°
4 4.000e+02 5.921e-03 2.618e-04 142.70° 267.38°
5 5.000e+02 8.691e-03 3.843e-04 -62.36° 62.32°
6 6.000e+02 1.849e-03 8.177e-05 -120.58° 4.09°
7 7.000e+02 4.359e-03 1.927e-04 46.69° 171.36°
8 8.000e+02 1.655e-03 7.318e-05 -17.55° 107.12°
9 9.000e+02 2.364e-03 1.045e-04 157.75° 282.43°
Total Harmonic Distortion: 0.025101%
Fourier components of V(in)
DC component:6.85373e-012
Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+02 2.000e+00 1.000e+00 0.00° 0.00°
2 2.000e+02 7.652e-11 3.826e-11 -41.81° -41.81°
3 3.000e+02 7.637e-11 3.819e-11 150.80° 150.80°
4 4.000e+02 5.838e-11 2.919e-11 -148.85° -148.85°
5 5.000e+02 1.304e-10 6.519e-11 -34.88° -34.88°
6 6.000e+02 6.466e-11 3.233e-11 121.59° 121.59°
7 7.000e+02 9.702e-11 4.851e-11 -171.13° -171.13°
8 8.000e+02 1.236e-10 6.180e-11 23.47° 23.47°
9 9.000e+02 1.144e-10 5.720e-11 65.58° 65.58°
Total Harmonic Distortion: 0.000000%
Date: Sun Feb 26 09:16:53 2012
Total elapsed time: 896.354 seconds.
tnom = 27
temp = 27
method = modified trap
totiter = 13922616
traniter = 13919918
tranpoints = 3697359
accept = 2594680
rejected = 1102679
matrix size = 95
fillins = 206
solver = Normal
Matrix Compiler1: 23.5 KB object code size 8.8/5.9/[2.5]
Matrix Compiler2: off [2.7]/3.2/17.0