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IRF510 sucks for distortion as amplifier


 
8/14/2000 8:14 AM
aron
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IRF510 sucks for distortion as amplifier
I cascaded 2 IRF 510 power mosfets hoping to hear _something_. I did manage to make it distort and bias ok, but it doesn't sound very good even when distorting.  
 
Kind of a rough distortion with not much sustain. I was hoping to get something good going.  
 
I used Gus' MOSFET overdrive as a starting point but added a tone control as well as biasing trimmers.  
 
If anyone has gotten it to sound good, let me know.
 
8/14/2000 10:58 AM
Doug H
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I've tried them in a 2 stage cascode arrangement, similar to the booster2 or something. They don't seem to develop enough gain on their own to be used like that.  
 
However, if you drive them with an opamp or a JFET circuit, they can sound pretty good. Try subbing them in the output stage of your Shaka circuit and see how that works. I did that with the Shaka 4 circuit and was pretty pleased. It saturated real fast, so it's kind of a one trick pony-but it's a nice trick.  
 
I just thought of another tip: make sure you run a 1M feedback resistor from drain to gate. That tames harshness and kill noise, and was real key for me.  
 
Doug
 
8/14/2000 11:57 AM
Gus
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Aron I should have given you a write up. The two mosfet overdrive is very mosfet sensitive. I used power mosfets. It does not have a alot of gain however it will smooth out a Transistor amp IMO. The input cap of the devices is high so the lowpass action can be heard and "tuned" with the source R. Using an fuzz/dist before is a fun thing to do. For you I would use it as a building block. Try some very low RDS resistance Drain to source power devices under 1ohm.
 
8/14/2000 12:17 PM
Doug H
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quote:
"the input cap of the devices is high so the lowpass action can be heard and "tuned" with the source R. "
 
 
"Lowpass" is the operative word here. The mosfets really roll the highs off. That's part of the uniqueness/coolness of the sound but it can get overbearing at times too. Like Gus said, the source resistor can tune that (the lower the better, if I remember), but I am also wondering if putting a low pf cap in parallel with the feedback resistor would help? Then, trade off rejecting noise/harshness with allowing more highs. I will have to try...  
 
Doug
 
8/14/2000 7:43 PM
aron
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I used the IRF510 which are power mosfets as well (I think).  
 
>lowpass action can be heard and "tuned" with the source R  
 
OK, I will fool around with this.  
 
I used sockets so I can pretty much put anything in.  
 
Thanks,  
 
Aron
 
8/14/2000 1:52 PM
Eric H
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quote:
"I've tried them in a 2 stage cascode arrangement, similar to the booster2 or something. They don't seem to develop enough gain on their own to be used like that.  
"
 
Doug, I was under the impression that mosfets had higher potential gain than jfets, I'm thinking maybe you aren't biasing them correctly.  
 
-Eric
 
8/14/2000 7:38 PM
aron
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>I've tried them in a 2 stage cascode arrangement, similar to the booster2 or something.  
 
I've tried this about a year ago with BS170s but that didn't sound too good either. Oh well....  
 
>They don't seem to develop enough gain on their own to be used like that.  
 
I managed to get it to distort alright - actually a lot - just not "good" distortion or good sustain/compression.  
 
>Try subbing them in the output stage of your Shaka circuit and see how that works.  
 
I will try this as well.  
 
>I just thought of another tip: make sure you run a 1M feedback resistor from drain to gate.  
 
Hmmm, I can try this.  
 
Thanks,  
 
Aron
 
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