Decibel Dungeon Preamp for a Gainclone Amplifier
	Introduction: The BrianGT non-inverting Gainclone I built was a yawner. It was so easy and produced such fine results that I was determined to challenge myself, while at the same time adding some regulation for the signal I was putting through to the amplifier. The above link goes to the gainclone preamp page on the Decibel Dungeon website. Behind the website is a fellow who held my hand--from across the pond, no less--until I had every detail in the appropriate place. The decibel dungeon preamp was, indeed, a challenge, and stands as my first real project that involves mains AC. After I learned to keep the signal ground separated from the power ground, it has proven to be a great success. Here is the play-by-play of construction. Click on any thumbnail picture for a more detailed picture.   Power Supply: The power supply takes roughly 18VAC from the Avel Lindberg 50VAC transformer, pulling it through a rectifier bridge through a series of smoothing capacitors until it is regulated by the LM317/337 circuits for +/-21 VDC. Good stuff, if you hook the diodes in the right direction. I had a little smoking from overheating power resistors. That was an easy problem to fix.   PS Underside: I learned--for the next time--that a little more time may be needed for laying out the circuit. I think I went blind trying to trace the power rails.   The Preamp: It is a very compact little preamp, isn't it? When I discovered that it was so small, I decided to wire it directly to the BrianGT amp in the same chassis. And considering the pretty blue heatsink, I decided that it should bear the corny name: Nuuklear ReaGTor.   Buffer Closeup: More transistors! Precision resistors really make everything happy, especially past that final smoothing cap. There is, for all practical purposes, ZERO mVDC at the outputs. That helps keep down the DC offset at the amplifier output.   The Layout: I also learned--for the next time--that a little more time may be needed for laying out the chassis arrangement. Things were irrevocably wired. For the next time, this will be much different, but this works.   Just Before It Came Online: I did not yet know that power and signal grounds should be kept separated. A loud hum, some fire, and blown transistors taught me well. In truth, one of my regulating transistors in the second stage of regulation (C558) was damaged when a joint at the signal input of one of the buffers broke during installation of the preamp into the chassis. A new transistor, and rewiring the grounds made it all better.   Online: The Nuuklear ReaGTor is online, and sounds fabulous hooked up to the Hohl Flutes.   Home Hohlflutes Preamp BrianGT Amp Wallin Jig II