24 August 2009

6418 Sub-miniature Tube Preamp / Headphone Amp

We often get questions asking about suitable vacuum tube (valve) kits for beginners or first time DIYers. Aside from the fact that vacuum tube audio kits are generally expensive, there is also the safety concern that most tube circuits operate with potentially lethal voltages. Mark in Australia found the following 6418 tube preamplifier and headphone amp kit which is an exception - it is inexpensive and can operate from single 9V battery.

6418 sub-mini Tube Preamp / Head Amp Kit
The tube preamp / headamp kit is from Oatley Electronics in New South Wales Australia and based around the Raytheon JAN6418 sub-miniature valve (tube) and an IC. The K272 Stereo Tube Preamplifier – Headphone Driver kit cost $27AU (~$23US – August 2009). The kit is complete including a printed circuit board (PCB) which makes for easy assembly but you will need to provide your own enclosure. The kit only consumes about 12mA at 9V and can be powered with a single 9V battery making this a safe and ideal kit for those who are new to vacuum tube electronics.

6418 Tube Preamp / Headphone Amp Kit

The photo above is a build of the kit using the supplied parts. Since the 6418 tube are extremely microphonic and will "ring" if they are subjected to vibrations rubber grommets are used to help damp the tubes. Mark has built a number of these kits now including a few with upgraded parts (metal film resistors, polypropylene film inter-stage capacitors and a Burr-Brown OPA2134 op-amp). The photo below is a tube preamp in a plastic ABS enclosure using the kit and upgraded components.

6418 Tube Preamplifier Kit
Mark reports that the kit performs well and sounds good. The bandwidth is very wide, the -3dB points are 10Hz and 50kHz. As a preamp there is good depth, wide breadth and sharp detail revealing fine recorded detail with no hard edges. The photo below shows the kit in a plastic enclosure being used as a portable headphone amplifier.

6418 Tube Headphone Amplifier Kit

The tube preamp / headamp kit from Oatley Electronics is well worth the $27AU price tag. For complete project details and more variations see the project page for the 6418 Tube (valve) Preamplifier / Headphone Amp Kit.

Additional Tube Headphone Amplifier Projects:


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3 comments:

  1. i dig it, i was thinking about getting one to boost the power from my desktop sound card to my headphones, I got a pair of studio monitors that seem to need a bit more power than most, is that what you are using them for as well?

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  2. Is it possible to reconfigure this as a guitar headphone amp? For example, take the output of the right channel, filter it through a Fender-style tone stack, and then feed it back into the left channel which would operate as the sole driver?

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    Replies
    1. Oatley actually offers another kit (the K270) that is intended to be used as a guitar (or any other source) preamp. It makes an excellent clean boost pedal. If you're fine with mono, then you just need the appropriate output transformer to match your headphones.

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