Now here is a very nifty circuit that I came up with by accident, just trying things out. It gives any signal that great "tube sound" super easy. OK, you do have to use a tube, but no power supply! It's passive line level.
Just about any tube will do, triode, pentode, tetrode. I've used this with various tubes including the 12AX7, EL34, 6SN7 and some Russian EL84 types. They all work and give the signal that rich harmonic warmth of tube sound, but without the heat or high voltage. Who knew?
You'll see a basic schematic below. Super easy. And you'll see the "trick" right away. The signal goes thru the heater. Yep, right thru the heater. That must be what gives it the tube signature. You do need to connect the cathode to the input side of the heater and the anode to the output side (see diagram) to get the full effect. It's works OK without this, but much better with, tho I'll be darned if I know why. Also note that the grid is tied to ground via a 100K resistor. Changing the value of the resistor will change the harmonics and the sound. So you could put a 100K pot in there and tune it to your taste. The tuning effect is rather subtle, but it works. 100K worked for me.
So there you have it. It's super easy to add tube sound to any line level signal. And easy to experiment with different tubes for different effects. On the pentodes and tetrodes I tied the screens to the grid resistor, this seems to work best. Leaving them open gave too much hum. Signal loss is about 2-3dB, so no big deal.
So grab a tube or 2 from the junk box and have at it! Let me know what you think. It's a very surprising circuit. And it does not even need a power supply. (Just be sure the heater is not burned out)
Just about any tube will do, triode, pentode, tetrode. I've used this with various tubes including the 12AX7, EL34, 6SN7 and some Russian EL84 types. They all work and give the signal that rich harmonic warmth of tube sound, but without the heat or high voltage. Who knew?
You'll see a basic schematic below. Super easy. And you'll see the "trick" right away. The signal goes thru the heater. Yep, right thru the heater. That must be what gives it the tube signature. You do need to connect the cathode to the input side of the heater and the anode to the output side (see diagram) to get the full effect. It's works OK without this, but much better with, tho I'll be darned if I know why. Also note that the grid is tied to ground via a 100K resistor. Changing the value of the resistor will change the harmonics and the sound. So you could put a 100K pot in there and tune it to your taste. The tuning effect is rather subtle, but it works. 100K worked for me.
So there you have it. It's super easy to add tube sound to any line level signal. And easy to experiment with different tubes for different effects. On the pentodes and tetrodes I tied the screens to the grid resistor, this seems to work best. Leaving them open gave too much hum. Signal loss is about 2-3dB, so no big deal.
So grab a tube or 2 from the junk box and have at it! Let me know what you think. It's a very surprising circuit. And it does not even need a power supply. (Just be sure the heater is not burned out)
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Finally, a used for those completely worn-out, useless tubes! Have you tried gassy tubes or tubes that have been taken apart to have the getter cleaned out and put back together?
No power means no glow and no glow means I won't feel that it is doing anything so I won't hear the warm tube sound ;-(
I'm kind of new to tubes, but could you just pass the signal through the heater and ignore the anode and cathode? Aren't they just hanging resistances since no current is flowing through the tube? Or maybe I'm too tired to think clearly right now... 
Oh god damnit! I should have known, I get punked easily I guess. O.T. but I did not sleep well last night, my poor dog has surgery today. Blah. F 4/1!
Best to build it today. EZ to do, you can whip it up with a few clip leads before the day is over.
If you need the glow, a nice yellow/orange LED under the tube will help.
But then it's not a "no power supply" circuit.
If you need the glow, a nice yellow/orange LED under the tube will help.
But then it's not a "no power supply" circuit.
Interesting thought! Will have to try it. You would need a DC blocker cap in the output, of course, but it's worth a try. Kinda kills the simplicity of the circuit, but the results might be worth it.
You forgot a switch, to flip cathode between left and right sides of the heater. The purpose of the switch is to flip polarities of even harmonics, to change focus of soundstage from widened to narrowed. If to use a pot you may fine-tune stereo focus.
Brilliant! We have some real sharp thinkers here on the forum. I knew that if I posted this circuit, someone here would improve on it. Bravo!
Thats clever, clearly you have borrowed that idea from optical 3D theory only in this audio application your exploiting the least known fact that one ear ( I can never remember which ) hears higher frequency sounds a fraction of a second later than the other thus this effect can be exploited by heater polarity to produce pseudo stereo signals that can be decoded by the switched on brain.
I am in awe😛
Has been recommended that filling up your speaker enclosures with all your old worn out tubes makes nice tube sounds.
And i heard that if you freeze some in the ice box, they make cool ice cubes for drinks. (Don't bite them though.)
And old tubes can be re-newed by putting the smoke back in them. Just crack them a little and blow smoke on them to fill them back up.
And i heard that if you freeze some in the ice box, they make cool ice cubes for drinks. (Don't bite them though.)
And old tubes can be re-newed by putting the smoke back in them. Just crack them a little and blow smoke on them to fill them back up.
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