XD1 preamplifier with steroids
A stereo High-End preamplifier with many options.
I'm working as Sound Engineer from more than 30 year, always builded my own stuff and very experienced with analog circuits but in the last 10 years I've discovered microcontrollers that help me to better design analog gear because I can program critical things, save parameters and eliminate almost all cables inside cases by shorten connections. This is the final version of many prototypes I maded in the past. It's a fantastic sounding preamplifier, totally analog that works at high voltage by using 2 stage hybrid transistor/mosfet modules as active amplification, high end Lundahln transformers in each in/out and a controllable saturation double triode stage that works in series/parallel for adding harmonics. All signal path it's fully analog, really very low noise but it's all controlled by a microprocessor so I add the best of analog and digital worlds. The digital section it's totally separated by analog side, even grounds are separated, all connections are maded by Hi-Speed optocouplers. Power supply uses many stages with different transformers, 3 stage lowpass filters (that uses a lot of capacitors), ultra fast scottky diodes and super LDO's by Linear Technology and a 3 stage main supply filter and are designed for the most possible low impedance possible for maximum ripple rejection. As circuit topology I'm using a double stage amp with high-speed DC analog servo but I'm using a 32bit micro that samples DC and add a correction in case DC analog correction fails, it also help a lot to find the right level. Because of the microprocessor the preamp dinamically uses the 2 stage preamp as it needs so the overall noise and distortion it's always keeped as low as possible, but since the distortion it's a necessary color I've added a dual triode stage valve saturation (with a real valve) that can works in serial/parallel for maximum possibilities. Microphone inputs have variable impedance to adapt every type of mike and has a separate instrument input for guitar and a line input all with transformers. It's really heavy because it's full of heavy stuff so I used an heavy box maded by using 1cm to 5mm navy alluminium.
Features
- Very low noise discrete dual stage DC servo topology.
- Digital control with galvanic separated path.
- Variable impedance inputs.
- Fully programmable.
- Intelligent autogain and DC servo supervisor with a dedicated 32bit microprocessor.
- High impedance inputs for guitar/bass.
- All in/Out use Lundahlm transformers.
- Dual triode serial/parallel saturation programmable stage.
- Remote controllable in various way.