Intubator

Device type	Tube distortion unit
Purchased when	03-Aug-2007
Purchased where	DIY project
Price including S&H	TBD
Condition when purchased	DIY
Current condition	working
Status	in use

TBD


This is my first tube amp experiment, it works without any semiconductors, the circuit just consists of an ECC83, 7 resistors and 3 capacitors. It is intentionally build a bit unclean, but it works very linear with an input of 1Vpp, the wonderful tube distortion starts above this level. The circuit works fine even at 3 volts, but as the level goes down then, SNR is decreased. So the more voltage you have, the better the output is. But i did most of my tests with just 30 volts, so it really is possible to build valve circuits with low voltages. A 12 volts wall wart might be enough for a valve circuit not intended to be used as a noise free HiFi amplifier but more as the beloved tube amp effect. Technically, this amp consists of 2 inverting amplification stages, which aren't really used as amplifiers, as the input signal to those stages is attenuated to get an allover gain of exactly 1:1 when powered with 30 volts. The 2 stages are built with the 2 triodes in the ECC83 (aka 12AX7).

Here, here and here are small sound demos - left channel is original signal, right channel is after the circuit. The most interesting results come out from sine and triangle inputs, and for obvious reasons, a square input is nearly unchanged. The second demo is from a Technics SX-K700, just to demonstrate the effect on several input sounds known to everyone. The third demo is a sound from a PRophet 10 provided by MFox as a base for comparing several tube-equipped devices in sound behaviour.
More sound demos coming - i think i have to clean up this little test page somewhen. The next two sounds use the same format - left channel is original sound, right channel is the breadboard output. The circuit now has a transistor preamp to pump up the signal to nearly 20Vpp (currently, the circuit is powered by 20V), which leads up to 10Vpp at the tube gate. So the range of distortion is quite large now. As nothing good is for free, this has to be paid by a remarkable noise level. So the circuit is no longer really usable as a good preamp, but only as a tube effects device giving this fine warm tube overdrive sound we all love so much. The demos are here and here. The first is the Prophet 10 sound again, this time with much more distortion, the second is the classic example of tube overdrive sound - an electric guitar.

Also have a look at the images and the movie:

photo 1
photo 2
movie 1 (oscilloscope view, not from the final version)

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News... after spreading development in several directions and meanwhile getting a lot of tubes to experiment with, i tried out several more design. Here are some impressions:

photo 3 is a new concept of controlling the tube. Have fun rebuilding it, my new camera is quite usable :)
movie 2 shows the "boot process" of the circuit at the output. Quite funny what happens when the tube warms up.

As this was quite a bit from perfection - too many semiconductors in the signal path, and besides i really love DC coupled circuits - it was not practical here, i redesigned it a bit. Not the final circuit consists of heater voltage/current regulation, automatic bias adjustment, opamp preamp for low level inputs (guitar), so the tube can concentrate on what it's inside for - destroying the audio signal in a funny way :). This circuit can be called release candidate...
I just tested it in the studio, which looks this way with the breadboard in it. Checked it with this good old analog organ, followed by the Elektor Formant, and finally, there is an electric guitar inside. Just listen to it here

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News...
okay. not really new :) A photo collection of the final intubator can be seen here

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