Discrete Preamp

UPDATED July 2017

My discrete preamp, which was based on the information in this Zetex datasheet.
There is also a PCB layout for this available which can be downloaded below.
It would be quite trivial to construct this on veroboard (as I did with my prototypes) but the PCB layout provided makes for a neater job.
This little preamp has excellent performance and very low noise. I have compared this to several commercial designs including Cambridge C500, Rotel RC971, Adcom GFP345 and it compared very favourably.
You can see some pictures of the completed article on the gallery pages.


Please note: there are a couple of mods - one in particular "C7" needs to be soldered to the bottom of the board.
RL (22k) is just a test load for simulation and is not required.
R7 (collector of Q2) has also been omitted and a link must be fitted in it's place.
Q3 (output transistor) dissipates around 260mW (collector current is ~18mA) - I fitted a TO92 heat sink to mine to keep it cool, although a heat sink is probably not really necessary.
Discrete Preamp Schematic

Specifications as measured by RMAA

Discrete Preamp specifications


NEW! Download the entire discrete preamp project in DipTrace format here

DipTrace Project

DipTrace Discrete Preamp 3D rendered PCB DipTrace Discrete Preamp 3D rendered PCB (alternate view)

Old project

Discrete preamp PCB
Discrete preamp component overlay

PCB top silk (NOT actual size)

Discrete Preamp PCB silk screen

PCB bottom layer (NOT actual size)

Discrete Preamp PCB layout

Top layout with component designations.

Discrete Preamp top layout

Completed board mounted (this is an older version)

Discrete Preamp PCB