Usually I don't encounter much problems simulating amplifier schematics, except when attempting to simulate (older) amps with a single power-supply.
Problem is that THD figures in most cases do not match the specs provided by the manufacturer (off by a factor 10 sometimes). This also might lead to the conclusion that the specs are wrong, but since I'm not a LTspice specialist, I assume that there is a "bug" in my knowledge of LTspice to simulate these schematics in a proper way.
Frequency response seems ok, BTW.
Currently I am not able to attach a schematic (I'll do so when I have the opportunity) so I'll give you a description of the layout.
The input circuit consists of a single PNP transistor. The (resistor loaded) VAS is build around one NPN. The power-stage uses a complementary driver and two NPN power transistors, also feeding a bootstrap. The LS is connected through a decoupling capacitor.
Anyone suggestions? Please enlighten me 😎
Problem is that THD figures in most cases do not match the specs provided by the manufacturer (off by a factor 10 sometimes). This also might lead to the conclusion that the specs are wrong, but since I'm not a LTspice specialist, I assume that there is a "bug" in my knowledge of LTspice to simulate these schematics in a proper way.
Frequency response seems ok, BTW.
Currently I am not able to attach a schematic (I'll do so when I have the opportunity) so I'll give you a description of the layout.
The input circuit consists of a single PNP transistor. The (resistor loaded) VAS is build around one NPN. The power-stage uses a complementary driver and two NPN power transistors, also feeding a bootstrap. The LS is connected through a decoupling capacitor.
Anyone suggestions? Please enlighten me 😎
Post a .asc example file, that will be the quickest way to solve the problem, if indeed there is one
I suspect you need to take the time constants out of the circuit by either making caps big, I often use 800,000uf, and also by letting the sim run for say 400ms and looking at the last 40ms.
This is the offender:
It ought to give max 1% @30W in 4Ohms and Max 0.1% @20W in 4 Ohms, yet it does 0.8% @ about 2W in 4Ohms and higher when pushed harder.. (quiescent current is correct)
It ought to give max 1% @30W in 4Ohms and Max 0.1% @20W in 4 Ohms, yet it does 0.8% @ about 2W in 4Ohms and higher when pushed harder.. (quiescent current is correct)
Two things: you didn't specify the timestep for the sim, and LTspice has chosen what it thinks is adequate, but isn't in this case, because it is audio, and you left the waveform compression active: for audio, it has to be turned off by including the directive .options plotwinsize=0.
With these mods, the sim gives more realistic results, maybe leaning a bit too much on the optimistic side this time.
With these mods, the sim gives more realistic results, maybe leaning a bit too much on the optimistic side this time.
Attachments
Thanks for helping out, that looks much, much better.... I already suspected my LTspice-abilities 
So I've always got to include the :
.options plotwinsize=0
and the max. timestep ...
So I've always got to include the :
.options plotwinsize=0
and the max. timestep ...
Post #19 here explains how to calculate the timestep,
http://www.diyaudio.com/forums/soft...ng-ltspice-beginner-advanced.html#post4031841
http://www.diyaudio.com/forums/soft...ng-ltspice-beginner-advanced.html#post4031841
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