Studio Pre Rehash

Written by Super User Print Email

First to be tested using the "ampsim" tool is the Redeye Studio Pre.

Based on the famous Alembic F2-B circuit ( which is basically a Fender preamp circuit ) this preamp is used throughout the world in studios, particularly favoured for bass guitar.

I have several real tube amplifiers at home built using this circuit so it is perfect for me to compare results with the real thing ( Recordings to follow ! ).

Some experiment is need when breaking down the circuit into blocks that keep the resulting filters simple enough to not cause problems in the dsp implementation.


I Finally decided to break into 3 stages

stage1 12AX7 -> tone stack -> stage2 12AX7


Stage 1


 This is a basic 12ax7 preamp section as seen in a lot of "Fender" amplifier circuits. R5 has been added to give it a load so that simulation was a little more accurate. Ideally I should look at the real load presented by the tone stack.


Tone Stack


The basic tone stack, again a standard "Fender" design.


Tone Stack with Bright Switch


Same circuit with the bright capacitor bypassing the volume. This is not an ideal simulation as the software calculates its filters assuming the volume is at half way ( I believe ) so there will always be a bright boost, in reality the bright boost is greatest at minimum volume and switched off at maximum volume. I may look at a better way of simulating a bright circuit. 

Stage 2


The output circuit is almost identical to the input stage. I have added a Master volume as this makes the plugin more usable.