This PreAmp module is designed to amplify low level phono signals in stereo. By changing the gain resistors it can be used as an universal low level amplifier, such as a magnetic head amplifier. The needed frequency curve should be implemented in the DSP of a connected soundcard. So it is possible to match or equalize every possible input source frequency curve. Features are medium impedance input, low impedance output, low noise and low power consumption (< 6mA). It is possible to use the device, powered by a 9V 6F22 Battery, more than 60 hours continously. To build the PreAmp you need the following layouts. Please download the Target application from electronics main site before, to view and print the layouts.
Linear PhonoAmp - Layout
Linear PhonoAmp - Component positioning layout
Print the layouts mirrored to a high-res inkjet-paper (80g /m2) in photo mode (> 720dpi). Set the process time for PCB much longer than for transparencies, so that enough UV radiation will pass through the paper.
Soldering of the components is relatively easy - solder first the passive resistors, then capacitors and diodes (watch for correct polarity). Finally solder the OpAmp IC. Soldering temperature should be around 270 deg. Celsius.
At last connect some shielded wires on input and output and connect there some plugs of your choice. Put the whole device with the battery (or accu ;-)) and on/off-switch (or external power plug) inside of a shielded box (connect shield with ground). Test the device with your turntable on the line in of your soundcard. Watch the level of the incoming signal. If itīs much lower than 0 db, increase the resistors R9 and R10 up to 1.2 MOhms. If the level is constantly above 0db or distortion occurs, then decrease R9 and R10 down to 560 kOhms,
The device will work in a supply voltage range of 6V to 16 V - if used with external supply, be sure that you use a well stabilized power source. The module has a reverse polarity protection. It has also an ESD input protection and short circuit protection on output; you can hot-plug your turntable on input without damaging it.
Comments and suggestions are welcome!