Tube sound without the tube! (almost)

[Pano]

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)

[OneyedK]

It's a very good day to review circuits like these

[rknize]

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?

[jrenkin]

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 ;-(

[Ty_Bower]

Didn't Butler already do this with the Monad?

Butler Audio

[rknize]

Maybe the heater needs to be biased.

[Soonerorlater]

Anyone tried it in push-pull

[Magura]

This has SY written all over it!


Magura

[Obe1]

Fascinating!

How strong was your input signal?

Thanks for sharing this.

[dosilegecko]

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...