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is it a dedicated response to the question at hand ?
There were a bunch of words; my computer ate them.
Much of it had to do with putting the Solution ("without input trafo... with ef 86") before the Problem. GSB has a wish-list of parts he does or does-not want. He does not define the problem, and nobody here has really dug into that aspect beyond Paul's quite-right general observation that dynamic mike, transformerless, and tube are rarely the happy solution to the general recording problem.
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Can i put volume control instead of R4
Do whatever you want. Anything sounds better with a EL84 in it.
When you get weak distorted signal to laptop, don't blame me.
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Doesn't seem like that is much gain for a mic - looks like it's around 35dB or less?
Good gain-guess. (I simmed 38db but it is VERY sensitive to supply.)
But how much gain do you want? Remember this is a
notebook input. Anything over 2V will clip madly. Anything much higher is going to smoke 2-cent parts on a $600 motherboard.
I say the output of an SM58 on acoustic performances is 5mV-20mV. Times gain of 100, we get 0.5V-2V. For gain of ~~60, a bit less.
What we really need to do is get the mike and preamp self-noise above the ~~40uV noise of the notebook ADC. If we had a super-quiet studio and a super low noise preamp, that's actually tough. But in almost all practical recording, we don't have to get absolutely lowest noise.
There is
nothing wrong with pushing 0.5V at a notebook input. Capture the signal,
then normalize it in the Audio Edit program.
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begs for using at convenient +48V
What convenient? He has a dynamic mike, a notebook, no Phantom in sight. Yes, you can buy a 48V wall-wart, but they are rare, and I thought some Euro safety agency was discouraging stuff over 24V? I really wanted 12V so he could use heater power for B+; can't get enough ooomph out of any reasonable tube. I settled for maybe stacking a 12V and a 24V to get 12V heater and 36V B+. Or 4-D cells and 4-9V batteries; D-cells are cheap and will run all day, the 9Vs will last months at a couple hours a day.
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or do you want to keep the plate-voltage deliberately low as is it now ?
Safety to humans, safety to notebook, dirtiness. It is easy to design a 400V tube preamp so clean it sounds like transistors and at 60V output level. I don't think that's the right answer for a notebook recordist focused on specific solutions to a vague problem.
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I thought the CW was you get a less "tube"-ey sound if you just use a triode as a cathode follower.
So who is conventional or wise? 10K soundcard input is a
heavy load on a triode, moreover a triode starved for supply voltage. The thing bends the sound for-sure as it gets near 2V output.
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Triode driving the BJT-follower?
Noise of BJT working like this will be under 1uV, maybe under 0.5uV (I hope). Noise of a starved tube will be over 3uV. Try it. We made money with it. But any time we could, we used lo/hi-Z transformers between 200R mikes and tube grids. It really is audible. Getting a "nice" Noise Figure with 635A or SM58 into a tube grid requires a heroic tube working at huge current. Do that, and your voltage gain goes away. So you need another stage.
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417a single tube preamp by CJ. Works great and is cheap to build.
Brilliant use of a fabulous tube. Really wants transformer in and out (hmmmm....). Able to pound about 10 times more power into the notebook line input than it needs or can stand. At lesser levels it won't have much "tube sound".
Frankly: go to Guitar World, there are $49 tube preamps with both guitar and XLR-mike inputs, and knobs to adjust gain and tube-strain/sound. They are differential input so you could run longer mike-cable than my unbalanced input above (though I routinely ran 50 feet unbalanced low-Z mikes with little trouble; and the notebook IS portable). They have Phantom for the day you want to try a condenser mike. Much better known-good plan, with warranty. Maybe less "fun", but are you making music or just want to splash solder?
__
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