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Old 6th February 2012, 04:14 AM   #11
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ok I am beginning to see the light. I would rather stay away from the FET. That would defeat the idea of the project. Not saying it is wrong but just wanting a tubes only circuit for ampification. If I need to beef up the power supply to add another 12ax7a I can. I have looked at other diagrams of guitar amps and about the cathode bias resistors; Instead of switches why not just say a 1k ohm resistor in series with a 5 k pot adjustable from the front panel? Or not. The 1 k to keep it from reaching zero at the low end of the pot. maybe a switch to switch caps in and out of circuit.
So I do need a clean circuit first and low noise?. Maybe that is all I need? Then let the computer simulate the other needs, such as overdrive etc. thanks for the ideas
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Old 26th January 2013, 05:47 PM   #12
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Printer2, I would love to see a rough sketch of a schematic of your FET idea.
As much as I consider myself a "tube nut" I can clearly see the benifits of running an FET in the first stage. Good clean stage with no requiered heater current, also microphonics would be less of a concern.
I don't see a down side to that idea. Might be a cool way to add gain to a typical fender schematic with out drilling the chassis for a tube socket and worrying about heater supply issues.
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Old 27th January 2013, 08:26 AM   #13
JMFahey is offline JMFahey  Argentina
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Quote:
If I cant overdrive the second half of the tube I will most likely be able to simulate it with computer program. I recall there is an overdrive simulator.
So you frown on a FET because
Quote:
I consider myself a "tube nut"
but you will simulate distortion (the main point of using a tube in a Guitar amp) with a computer?
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Old 27th January 2013, 02:41 PM   #14
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I'm confused? why am I being quoted?
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Old 27th January 2013, 03:23 PM   #15
JMFahey is offline JMFahey  Argentina
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Sorry I wasn't clear, I was referring to the OP seemingly opposite goals.
Picked the FET/tube reference while reading your post, understood you were backing his idea too, that's why I mentioned it.
Personally, I'm very happy with mixing FETs and tubes, if used properly.
Hey!, even using, say, an Op Amp driving a tube, as long as the Op Amp does not clip.
Not prejudiced against using "sand" at all , just recognizing (and respecting) the differences.

What I find strange is adding a clean tube (which is quite "transparent") to the mix, and then simulating distortion digitally.
I think (may be wrong, not really my area of expertise at all) , that if you can simulate a complex, "dynamic", "organic" , you-name-it heavy distortion, which presumably "reacts to pick pressure", is "warm, not buzzy", etc. , all of which I find a difficult goal to achieve, by comparison to add a mild , say, 1% to 5% square law distortion in the algorithm (what usually a "clean" triode stage provides) should be a piece of cake.
And would save on chassis real estate, filament and +V requirements, etc.
Hope this long winded explanation shows my doubts about this "mixed" approach.
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Old 27th January 2013, 11:54 PM   #16
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use the 250volts and yes you can overdrive the second triode in a 12ax7 with the output of the first triode.I use this same setup in my harmonica amps.
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Old 28th January 2013, 01:43 PM   #17
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sounds good to me, now I need to find the time to finish this. 250 volts it is.
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Old 29th January 2013, 02:42 AM   #18
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Started reading this and came to a post with the same ideas I would use, then realized it was my own post from a year ago. I found that funny.

So back to the circuit. Doesn't have to be a FET. The whole idea is to hit the first tube a little harder to get some distortion in that stage and then continue on with the next stage. It can be a transistor, opamp, does not really matter, just so the guitar does not get loaded down and you get a hotter signal to the tube. If you got real hot humbuckers it may not be nedded, just depends on where you say enough is enough.

Distortion sounds better when it is caused by multiple stages not all the distortion coming from one stage. You can use the first triode and hit the second with a big signal but sonically it is not the best way to go. A pot in the cathode circuit would work but you do not need the fine control.
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Old 29th January 2013, 03:35 AM   #19
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It has been over a year since I started on the project. Funny how that works. get started on something and never get back to it. I need to get a life so I can work on projects, now that is the life. I do hope I can get to this and some other projects of interest. I cant talk much more and give lip service as I must build and show the results. One day a week is not much time and then the day is already shot because of other events I have no control over. Have to go out of town for family birthday events, or always something. Oh I have been sick with the flu bug for almost a month. Burned up some of my vacation time being sick and sitting in a chair in front of the TV. You know the story, I am sure I am not alone. frustrating to say the least. I might be selfish I dont know, but I sure am looking forward to working on some projects. I might have to take some time off from work and home and head for the hills with my camper, soldering iron and a bag of parts. I will report back with the results or failure. Actually I think I started on this last November before this one. so 14 months ago. makes me wonder how that can be That I couldn't find even enough time in the smallest degree for this. Oh well have to keep pressing forward.
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Old 30th January 2013, 03:41 AM   #20
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I have an amp on the bench that I have not touched in over three months. About as long as it took to make my first guitar.
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