a Trademark of High Fidelity Engineering Co. Zen Designed Single Ended Triodes



If you've been looking for a great sounding tube preamp for your system and are considering resurrecting an old Dynaco or constructing something from scratch, don't waste your time. We've done our research by purchasing all of the available preamp kits in this price point, and frankly it's not a contest. Based on the superior sounding 6N1P dual triodes and 6DJ8 / 6922 family of tubes this preamp has the speed, air and space, inner detail and slam the 12AX7 family of tubes just can't achieve.

The cathode followers give this unit such a low output impedance that besides being able to drive almost anything, the frequency balance is preserved on everything you drive with it. This as opposed to having a preamp that sounds particularly good with certain amplifiers and less than wonderful on others. Cable selection will also become easier because the cathodes can drive a small capacitance without effecting the frequency balance. This pure class A single ended triode preamp accomplishes all this without any negative feedback loop. With only two resistors and two capacitors in the signal path, it remains transparent at all times.

The attractive aluminum plate is easy to work on and looks great when set into our aluminum chassis and really impressive with our hardwood base.  See bottom of page.

Something this simple has to sound good!  And it does!  Take a look, this is the circuit. Think you can build it?  Notice except for a 2 inch piece of wire from the input jack to the pot, this entire signal path is parts-lead to parts-lead with no wire and no extra solder joints.


The Zen Plate comes with an assembly manual.  Here are some excerpts from it:


    Congratulations on the purchase of your new Zen Plate Kit !  You have the model ZSP-1. This kit when assembled should bring you a lifetime of hi-fidelity with the added satisfaction of knowing your built it yourself!  This preamp was designed by Decware's owner, Steve Deckert.  It was done with the same care and style found in all of his tube gear.  

    The actual circuit and parts used are no different than what go into our finished products. That means the performance and rather special signature of Decware’s Zen Triodes is here in spades!  This particular preamp was designed and laid out as a purist line stage with a single pair of inputs and a single pair of outputs.  There is a volume control, on/off switch and that’s it.  This somewhat hard core approach is for serious audiophiles who recognize that less is actually more!  It is ideally suited to drive tube power amps but will work with anything.

    Your kit comes with a 040 aluminum plate (easy to drill) and a suggested layout template. Obviously you may come up with your own layout if you wish and even add features such as more inputs.  The suggested layout and included parts and components have been selected to achieve a specific signature found in all of Steve’s designs.  You may of course wish to use different components such as your favorite flavor of capacitor but we recommend that you build it to original specs and listen to it first.  This way you’ll have a solid reference before making any changes.

    Please check you package for damage before you start.  Check the parts list against the contents of your kit to be sure you have everything on the list before you begin.

    Handy tools to have for this project include the following:  

    Drill, 1/2 inch stepped drill bit, 1 inch stepped drill bit, 5/64 & 1/8 inch drill bits, a 4-40 tap, 40 watt soldering iron or station, Dremel tool, solder, screwdrivers,  pliers, heat shrink tubing, possibly some hook-up wire.


    These kits require a basic knowledge of electronics with the ability to read a schematic and the mechanical aptitude to layout and drill the plate. You will also need to make a wood base for the flat plate to rest in. (We have these pre-made for those without wood working skills)  
    WARNING: There is 500 volts of DC involved with this circuit.  Assembling it without basic electronics knowledge could get you killed. This kit is not recommended for beginners.


    The model ZSP-1 has some solid features that make it attractive.  It is built around a top quality USA made power transformer that is seriously larger than required.  Many people don’t realize that a power supply is the heart of any audio component and is more responsible for the overall sound and performance than the audio circuit itself.  Never skimp on a power supply.  Other goodies include tube rectification, a point-to-point layout with no hook-up wire, minimal solder joints, precision resistors, poly coupling caps, an alps volume control, gold/Teflon input and output jacks, an IEC connector with integrated fuse holder,  removable power cord and top grade ceramic tube sockets with gold pins for all the signal tubes.  

    The circuit is based on the 6DJ8 family of tubes which includes the 6922 and the 6N1P. Any of these tubes may be used without modification.

    This circuit is a form of cathode follower offering a low impedance output combined with high voltage capable of driving long lengths of cable without problems. It uses 4 tubes in total, one pair per channel. The input stage consists of a paralleled 6N1P per channel driving a paralleled 6N1P per channel, the later wired as a cathode follower to the first stage. This offers a high current drive which adds polish and performance to its amazing sound. 

    The hum and noise on the model ZSP-1 is below 2 millivolts making it dead quiet in any application. There is no need for fancy regulation, hum balance circuits or special biasing to maintain this level of “quiet”. Once completed there is no reason why the quality US made parts of this unit shouldn’t last a lifetime.

    The ZSP-1 has tons of gain. With 2 volts on the input you can expect to get 18 volts on the output with ultra low distortion. 

    As with all the different Zen Plates, the model ZSP-1 caused the inevitable argument between myself and Dr. Dave about it sounding too good to sell as an affordable kit.  His concern that it would compete with our other finished products and hamper sales.  He probably has a point, but around here the spirit of sincere audio ecstasy greatly outweighs the prudence of big business.

    The application of the model ZSP-1 is simple; You may place it anywhere in a line level signal path. This includes recording applications in home studios.


Picture of ZSP-1 installed on optional aluminum chassis

Picture of ZSP1 installed in our aluminum chassis and setting inside our hardwood base. Notice the rear of the hardwood base has been designed so you can optionally run your jacks and or power cord out the back.


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Preamp kit 120/240 volt


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