Very cool project! Nicely done. I especially appreciate that you simulated and measured with a complex load. Do you have any sense of whether the LF distortion comes from the load or from the amp?
I see you used the ModuShop 400 mm deep Dissipante chassis. One thing with them is that the heat sink is split into two 200 mm wide chunks. I realize I'm a bit late with my suggestion, but with two pairs of output devices, I would put one pair on each heat sink. That will make life a bit easier for the thermal system. That said, there's a fair amount of thermal connection between the two heat sinks, so it's probably not a huge deal to have them on the same heat sink.
Tom
Are you going to use it as your main amplifier for a while?
Fair enough. Thanks for confirming.The LF distortion comes from highly nonlinear ferrite choke 18mH. This is intentional and simulates the real speaker LF nonlinearity.
Fantastic! That's all that matters.To your second point, I am very well aware of the issue of the divided heatsinks in the 4U Modushop case. [...] This amp passes 1 hour test at both maximum power and 1/3 power and stays just warm, not hot to touch.
Fair enough. Thanks for confirming.
Fantastic! That's all that matters.
I realize now that I made a mistake when I made the comment about the heat sink. I was thinking 250 W into 8 Ω, which would have been 400+ W into 4 Ω. You built to 250 W into 4 Ω (so probably 130-135ish W into 8 Ω). That makes a big difference in the thermal math and neatly explains why you can run the amp at 1/3 the rated power for hours without it overheating. My bad... Carry on.
Tom
Actually, it's P = I_peak^2*R/2, so 80 mW in your case.
Tom
Ah. You're right. I can tell I haven't designed an output stage for a while.
P = (2Iq)^2*R/2 = 4Iq^2*R/2 = Iq^2*2R
Tom
True that. That might change, though.It's fine . You use too many chips instead of discretes
How about a low power sweep or a spot set of frequencies at 250mW?