|True passive preamps contain no active components, which is to say that if you have to apply power, it is not passive.
I have come across some commercial passive preamps costing several hundred dollars. The circuit I've presented here will perform identically at a fraction of that cost. This passive preamp presented here has been successfully built and is in use by many audiophiles. It will get you closer to the elusive "perfect preamp" because is does not amplify, condition or impedance transfer. It is the perfect preamp for systems with power amplifiers having input impedance greater than 50 K ohms (this includes nearly all tube amplifiers). It is ideal for systems with tuner, tape, and CD (especially our own CD12V) as the primary sources.
However, be very careful with using it to drive active crossovers since many depend upon low source impedance (and this unit does not comply).
Our passive preamp incorporates some useful functions (e.g. Mute, Mono, Channel Rev) which will have little if any effect on its audible signature. However if you wish to build a true minimalist preamp you need only include the volume control and I/O connectors. Of course you give up source selection and other features. So examine the schematic, and include those functions that have value to you in your system.
The enclosure shown was provided by Spire Audio, Unfortunately, after tempting the DIY community with a fine selection of standard and custom enclosures at very reasonable process, Fred at Spire has decided to close his business. We are in the process of trying to find another supplier willing to cater to the DIY community- in the meantime please consult our recommended source of suppliers list where several generic enclosure suppliers are included.
We welcome your comments.