Hello;
I am looking for tube preamp stage for my class d amplifier.
I am looking for low voltage simple cheap and tuby sound.
Nutube is good but expensive.
I am glad if anyone know and share the circuit which have same design goals.
Thanks in advance
I am looking for tube preamp stage for my class d amplifier.
I am looking for low voltage simple cheap and tuby sound.
Nutube is good but expensive.
I am glad if anyone know and share the circuit which have same design goals.
Thanks in advance
You might want to check out this mega-thread over at AK:
FX Audio 6j1 tube preamp - a $31 wonder | Audiokarma Home Audio Stereo Discussion Forums
FX Audio 6j1 tube preamp - a $31 wonder | Audiokarma Home Audio Stereo Discussion Forums
I just want to add some tuby colour into the sound. I can add volume control between pre and power amplifier.
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thanks, 6j1 tube is fine but i am looking for proven design rather than commercial product.
Tubey color to the sound = intentional distortion of the audio signal.
Are you looking to add some 2nd harmonic distortion of the audio signal before your class D amp, and that is all?
What is your amp's input resistance? (That's an important consideration for a tube line stage.)
The TPA3116 based class D amp I have has a 10k ohm volume control at its input, which defines its input resistance. 10k ohms is a somewhat heavy load for a vacuum tube line stage to drive.
Remember that tube amps typically have input resistance of 100k ohms or greater, and most class AB solid state amps I've seen have input R of 47k ohms or so, although this does vary.
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Are you looking to add some 2nd harmonic distortion of the audio signal before your class D amp, and that is all?
What is your amp's input resistance? (That's an important consideration for a tube line stage.)
The TPA3116 based class D amp I have has a 10k ohm volume control at its input, which defines its input resistance. 10k ohms is a somewhat heavy load for a vacuum tube line stage to drive.
Remember that tube amps typically have input resistance of 100k ohms or greater, and most class AB solid state amps I've seen have input R of 47k ohms or so, although this does vary.
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10 Kohms is difficult, but it happens to be the IHF "standard". Fortunately, the plate resistance (RP) of the 12B4 is low enough to deal with that 10 K.
The provided design, with minimal tweaking, should do what the OP wants. Well filtered "150" VDC for the B+ is good enough. Bridge rectifying (perhaps hybrid) the O/P of a Triad N-68X will get that, world wide.
The OP wants some 2nd order HD, for "warmth". So, bypass the 500 Ω cathode bias resistor with a 150 μF. 'lytic. The 100 μF. part shown grounds the heater's CT and is associated with biasing the heater off B+, for noise control. Use a 10M45S as the constant current source (CCS) plate load. In this particular application, a CCS whose performance is not "super/duper" is advantageous.
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Well, considering that they've sold huge numbers of these I would consider it to be a proven, if not optimal, design.
I was in the process of breadboarding simple preamp designs with various tubes so, out of curiosity, I breadboarded it based on information contained in the thread I posted earlier. My comments about my experiments with it are from page 69 to page 90 of that thread. There are schematics of the stock unit as well as ones with the operating points I tried later.
As for impedance matching, I was using a tube amp but most everyone who has posted about it on AK is using Class D amps.
So when you say "low voltage" how low are you wanting it to be?
I tried it at the voltage which the commercial pre uses, which was a B+ of under 70v but I liked it better with a higher B+. I was also using a conventional PS, not the design used in the commercial preamp.
I meant to try it wired as a buffer (no gain) but I never got around to it and I'm just now starting to build something but with a different tube.
Again, check out the link I posted.
The commercial units, like the FX, are powered by a 12v wall wart but many users seem to replace it with a linear supply that puts out a bit more, maybe ~13.2v. The preamps then use some type of multiplier circuitry to boost the voltage to what the tube itself uses.
Again, there is a schematic in that thread.
There are different brands and some may use different PS designs - which is also a subject discussed in that thread - but they all end up sending about the same voltage to the plate of the tube.
I breadboarded it out of curiosity because I wanted to hear the tube without having to buy the preamp and I already had the breadboard set up. I used an adjustable bench PS and a traditional, tube rectified CLC circuit in order to produce the same plate voltage that the stock FX uses. But, again, I had that set up already as I was using it to test a variety of tubes. I then experimented with higher plate voltages.
There may be kits available that are similar to the Class D amp kits. Although, from what I've seen, those aren't really kits they're just pre-built boards that people hook up and mount in a box.
I can't imagine why you would want to build something like this truly from scratch considering how cheap they are and how difficult it must be to work with SMD parts. I suppose it's possible if you have a good microscope.
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The 6GM8/ECC86 works at that voltage, but its RP = 5385 Ω. Asking that triode to drive a 10 Kohm load will (IMO) end badly.
The complete set of desired specifications may be placing you in a "can't get there from here" situation.
12AU7 are often used in guitar effects at 9V on plate. It "works", not clean.
10k is "heavy" for clean, but that's not the point here?
Also: is gain needed? Or just "color"? A heavily loaded cathode follower at low supply voltage will distort near hi-fi line level.
10k is "heavy" for clean, but that's not the point here?
Also: is gain needed? Or just "color"? A heavily loaded cathode follower at low supply voltage will distort near hi-fi line level.
Look into building a Bottlehead Quickie clone. It is a battery powered preamp using two 3S4 tubes. Easy and fun to build. You can contact Bottlehead and purchase the assembly instructions.
kodabmx said:
Yup, that looks good. Takes a 48VDC psu, which is easy enough to find these days. Something like this one.
PRR said:
I was playing around with simulations of a 6N6P cathode follower, using 48VDC for the supply voltage.
The 6N6P is readily available, and it's not expensive. You could use 5687 if you prefer.
6N6 heater draws 650mA.
Each cathode follower would draw maybe 3mA or so.
656mA load on a 1A capable PSU should be fine.
Just make a standard cathode follower but use an LM317 wired up as a 3mA current sink for the cathode load. Use fixed bias via a voltage divider to put the grid of the cathode follower at about 6V (3M B+ to grid, with 430k grid to ground). The cathode would then stabilize at about 7V above ground. That would leave about 41V plate to cathode, which is lower than optimal for clean operation, but not that bad.
It wouldn't be the cleanest cathode follower but it could be done for cheap, so why not?
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