I wish to thank Kev and Byron from Group DIY for test-piloting this project, and for their changes and comments on the original design. Without those guys this level of DIY-friendlyness would’nt have been even remotely possible.
Take a look at how Kev Ross builds this project Kev and Byron’s page on building the Gyraf G9.
The G9 contains two channels of real-tube, high-gain, transformer-balanced microphone preamplifiers with additional line and instrument inputs and transformer balanced output. It also features switchable phantom power, high-pass filter and phase reverse, as well as independent controls for input gain and output level – giving the user some creative options to work with.
The signal path contains only tubes, transformers and passive components, to preserve your signal integrety. VERY different from many “tubed” consumer products. But as we are not purists, we incorporate modern semiconductors in the powersupply sections – simply because this is way the easiest, cheapest and best solution available. For power amplifiers there’s quite an audible reason to use tubed power supplies, but for preamps I haven’t been able to spot any advantage so far.
I will try to update this page reguarly if anyone shows interest in its topics. Comments and corrections are extremely welcome, but I can’t promise to reply to all mail I receive. In “The Lab” – a forum on GroupDIY.org – there will surely be people that can and will answer most of your questions regarding the design, construction, and sourcing of parts. If you build this project and describe elements of the process, I’ll be more than happy to add it – or a link to it – here, so others can benefit from your experiences.
– NEVER work with live voltage switched on. Switch off, discharge, work, connect measuring equipment and power up. The G9 powersupply takes an average of 15 minutes to come down to non-dangerous voltages, providing that the tubes has had a chance to get hot. But if there’s something really wrong, the lethal HT can stay for weeks! TAKE CARE!! ALWAYS positively measure HT voltage on the PSU caps before touching ANYTHING. A good idea is to have a resistor, like 10K/2W, on a cable with two clips that you can attach to the caps for discharging. But please. Remember. Take care.
– Always keep your mains connector in plain sight when working, so you can assure yourself that it really is disconnected.
– Always tidy up your working area before connecting your project to the mains. This gives you some time for second thoughts about what you are doing.