PVA Passive Pre-Amplifier is very easy to build. There are very few parts and it can easily be upgraded. Both copper or silver Electra-Print PVA transformers are available. Silver transformers are particularly good with very low power, high efficiency systems. This design works particularly will when driven from op-amps, such as found in CD players. Output impedance stays constant at any position of the attenuator. The gain will drive any amplifier. If you want to read the article from AudioXpress, contact Electra-Print Audio and we'll email you the whole story. All designs are the sole property of Electra-Print Audio Company with all rights reserved worldwide. Licensing is available for commercial use.