The circuit itself isn't too complicated for me at all, also i've made quite a lot of self designed and etched pcb's, including even some smd stuff. But i'll look around in this nice forum i just discovered. For now i have to finish new cabinets for my speakers and tweak the xovers a bit. After that i'll be concetrating on the amp, it's a long and dark indoorsy winter period, so i have time to work on this stuff, in summer i fly rc aircraft.. 😀
Btw, how long does the moderator preview my posts before they're actually posted here? Is it linked to the number of posts?
Btw, how long does the moderator preview my posts before they're actually posted here? Is it linked to the number of posts?
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So heres a preliminary board layout for this amp thing:
An externally hosted image should be here but it was not working when we last tested it.
I upped the voltage on the godzilla amp to 2x50V, had to remove the BD139/140 to get it to work without oscillating though.
Heres the result:
YouTube - 214 watt amplifier
Heres the result:
YouTube - 214 watt amplifier
so, since photobucket has made it impossible to look at the rest of this thread, could you re-post the schematics?
Heres the schematic for the high power amp:
Schematic for the low power amp:
And again, the pics of the stereo amp:
Schematic for the low power amp:
And again, the pics of the stereo amp:
Heres one channel made on a piece of chinese copperclad using chinese rtesistors from one of those cheap 2500pcs resistor kits from ebay, using small signal transistors bought on ebay.
A video:
YouTube - Own design mosfet amp
A video:
YouTube - Own design mosfet amp
This design has this problem (current mirror in the input leg) if you stimulate with a square wave at input with high dv/dt ie: 1usec or less the amp will enter in oscillation (ringing). Remedy: put some resistance at the emitters of Q8 Q9 and add more neutralization (capacitance) for Q2. The drawbacks are less bandwith and more distortion, less slew rate
Cheers
Arturo
Cheers
Arturo
Maybe 100pf could be enough, but I recommend you to do a ac simulation from 1hz to 100MHz to verify a clean and smooth BW plot (no peaks), remenber that the signal transistors have gain well above 100MHz, and the feedback loop has several frecuencies where the phase is out 180°, that mean positive feedback = oscillation
Cheers
Arturo
Cheers
Arturo
nice... it's basically a big op amp.... don't know that the VAS has enough oomph to drive 12 mosfets though. you need to drive a lot of gate capacitance... 1700pf per device.... that's about .02uf (20nf)
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The 12 mosfet model was strictly intended as a subwoofer amp.
This is the simulated frequency response:
For this circuit:
This is the simulated frequency response:
For this circuit:
I see C7 in the schematics in post #27, it's between the bases of the current source (or technically, current sink) transistors and ground. This should instead go directly across the top and bottom of the three-diode string, otherwise it will amplify any voltage variation between ground and the negative rail, and it could also contribute to instability/oscillation problems.
I'm not sure exactly what it's for to begin with, presumably to stop any noise generated by the three forward biased diodes. It looks like a rather low impedance node, so I'm guessing it should have a larger value to go down to 20Hz.
I'm not sure exactly what it's for to begin with, presumably to stop any noise generated by the three forward biased diodes. It looks like a rather low impedance node, so I'm guessing it should have a larger value to go down to 20Hz.
I'm not actually using the C7, its not actually needed, but those who are allergic to any kids of noise may want to use it anyways.
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