Triton Audio FetHead by RebornOnline
Some microphones need a lot more gain than others. Think ribbon mics and broadcast dynamics such as the GearSlut's favourite SM7B and RE20.
Some of this mics need upwards of 60dB and for many pre-amps this is just outside of the quieter part of the gain stage.
The aim of the FetHead is to boost the signal cleanly by up to 20dB before hitting the mic-pre so you can use less gain and have a cleaner recording. It does this by using double jFET configured as a double class-A amplifier which is super clean and is conveniently powered by the phantom power from your pre. Phantom power is not passed through the FetHead and so you can use it safely with ribbon microphones (a phantom version is available if you want to use a FetHead with a condenser)
I've seen the question asked on GS forums "why not use two pre-amps in series". It's important to understand that although described as a pre-amp the FetHead keeps the signal at a microphone level suitable for the input of your mic pre. A mic preamp of course changes the signal from microphone level to a line level, these are two very different kinds of pre-amp. Simply putting two mic preamps in series would not have the same effect as using a FetHead and would introduce noise, hence why the FetHead is such a innovative and useful piece of kit.
Even if you don't need more signal, some users have even reported that just by using the FetHead they have noticed an improvement in the sound from the mics. So it can also be used to open up the sound a little for that perfect, airy vocal take.
It's hard to criticise the FetHead and it will work perfectly in almost every scenario. However I am one of the unlucky ones.
The FetHead requires the mic-pre amp to have an input impedance between 500 ohms and 1000 ohms to get toward the potential 20dB of gain. Below 500 ohms and the gain level drops off sharply. My JoeMeek VS3 v2 having an input impedance of 200 ohms only sees about 10dB of gain which for me was not enough to get a good, loud and clean signal from my RE20. Those with older preamps, or ones closely based on classic designs will have even lower input impedance. For example, the Black Lion Audio Dizengoff D173 based very closely on the Neve 1073, has a fixed impedance of 150ohms and in these scenarios the "Classic" FetHead may not give the best results.
Do not fear however, for TritonAudio have released the "Broadcast" FetHead which has a fixed gain, no matter what the input impedance. It's nearly double the price however, so those like myself hoping to save a much loved but underpowered preamp may feel the investment would be better spent toward a mic pre upgrade.
Overall the FetHead is a great bit if kit and a highly recommended addition to your studio.