audioguru2
- Apr 6, 2004
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Your OP37A opamp has a voltage gain of 19k/10k= 1.9 with a low impedance source, and a voltage gain of 19k/(4.7k + 10k)= 1.3 without an input. But the OP37A opamp is de-compensated and is unstable with a voltage gain of less than 5. It will oscillate.
I don't think the 150pF capacitor at the input to ground of the opamp is a good idea. it might make the opamp oscillate.
The Mosfet has a high gate capacitance that an opamp might not be able to drive.
I don't think the 150pF capacitor at the input to ground of the opamp is a good idea. it might make the opamp oscillate.
The Mosfet has a high gate capacitance that an opamp might not be able to drive.
"Your OP37A opamp has a voltage gain of 19k/10k= 1.9 with a low impedance source, and a voltage gain of 19k/(4.7k + 10k)= 1.3 without an input. But the OP37A opamp is de-compensated and is unstable with a voltage gain of less than 5. It will oscillate."
does it matter since i'm not using a split supply?
does it matter since i'm not using a split supply?
audioguru2
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Don't use an OP37 opamp because it is unstable when it has low gain. Use an "ordinary" opamp that is stable at any amount of gain. Your opamp has a "gain" much less than a piece of wire. Its gain is only 0.033.
A single or a split supply has nothing to do with it. The OP37 is made for high gain at high frequencies.
The Mosfet has nothing to control its bias voltage so either it is saturated or it is cutoff.
A single or a split supply has nothing to do with it. The OP37 is made for high gain at high frequencies.
The Mosfet has nothing to control its bias voltage so either it is saturated or it is cutoff.
here are the node voltages, i have a vom hooked up to the bottom of r8 and the voltage is hardly moving but something is giving me crazy bass from this regge song, sounds great! 6 ohm load, r1 is 4 ohms, have on a small lead acid battery. i had it as shown and worked great. clean sine waves to 5Mhz, no artifacts to 15Mhz which is the max i can test to.
the more current i have the less voltage swing i need?
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audioguru2
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The Mosfet is saturated and the output swing measures in micro-volts.
The current regulator is not working because it is connected wrong. Here is the current regulator from the LM317 datasheet:
The current regulator is not working because it is connected wrong. Here is the current regulator from the LM317 datasheet:
your right, i have it hooked up right on the board but wrong in the schematic, funny thing it works fine in the sim then when i put it right i got a jagged wave!!! so i got rid of the 317 and put a more flexable current regulator in, tell me what you think.
still have to build this one but i must go to bed.
still have to build this one but i must go to bed.
audioguru2
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hi Elix,
Your new current regulator looks like it will pull the drain of the Mosfet to ground. I have fixed it and show another one.
Please start again:
1) Your opamp is the wrong one (it oscillates at low gain). Its circuit has a high signal loss.
The opamp does nothing good in your circuit and can be removed.
2) The Mosfet does not have automatic bias voltage control.
3) The Mosfet has a very high output impedance. Amplifiers usually have a very low output impedance to damp resonances in speakers.
Your new current regulator looks like it will pull the drain of the Mosfet to ground. I have fixed it and show another one.
Please start again:
1) Your opamp is the wrong one (it oscillates at low gain). Its circuit has a high signal loss.
The opamp does nothing good in your circuit and can be removed.
2) The Mosfet does not have automatic bias voltage control.
3) The Mosfet has a very high output impedance. Amplifiers usually have a very low output impedance to damp resonances in speakers.
audioguru2
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Your new output stage looks good. But:
1) It has a very high output impedance. It should have a low output impedance.
2) It doesn't have a method to automatically adjust the gate voltage for the Mosfet.
3) It wastes 3W as heat.
1) It has a very high output impedance. It should have a low output impedance.
2) It doesn't have a method to automatically adjust the gate voltage for the Mosfet.
3) It wastes 3W as heat.
i'll try and figure out a way to lower the impendance. some heat wasted is ok, i only need 1 watt from each channel and the mosfet bias will come from the op-amp.
question:
to lower the impendance don't i have to raise the current or can it be done a simple circuit, i'm trying to keep a class a single ended mosfet. (gotta learn
)
question:
to lower the impendance don't i have to raise the current or can it be done a simple circuit, i'm trying to keep a class a single ended mosfet. (gotta learn
)
audioguru2
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I connected the Mosfet as a source-follower that has a low output impedance.
I used AC negative feedback to reduce distortion, to control the gain and to make the output impedance even lower.
I used DC negative feedback to control the biasing of the Mosfet. The BIAS pot should be adjusted for symmetrical clipping at the output but the negative feedback will automatically adjust the bias to match the Mosfet.
I used AC negative feedback to reduce distortion, to control the gain and to make the output impedance even lower.
I used DC negative feedback to control the biasing of the Mosfet. The BIAS pot should be adjusted for symmetrical clipping at the output but the negative feedback will automatically adjust the bias to match the Mosfet.
even though it works perfectly in the sim i have to make something of my own creation, else i'm not learning so i'm going to try it now with a active current sink since i can use the gate voltage swing to my advantage.you've won this round *shakes fist*
;D
