Studio Pre Rehash
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.
Â
I Finally decided to break into 3 stages
stage1 12AX7 -> tone stack -> stage2 12AX7
Â
Stage 1
Â
 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.
Â
Tone Stack
Â
The basic tone stack, again a standard "Fender" design.
Â
Tone Stack with Bright Switch
Â
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.Â
Stage 2
Â
The output circuit is almost identical to the input stage. I have added a Master volume as this makes the plugin more usable.
Â
Â
Â
Â
Â
Â
Â
Â
The Experiment resumes .....
After a long time with no input finally decided to revisit the blog and continue with the quest!
Thanks to the Guitarix team there has been a major update to some of the tools used to simulate circuits using the DK method.
What were once experimental tools and used to generate filters to simulate the linear parts of a circuit have been expanded by brummer to enable simulation of the non-linear elements in a circuit ( by far the most important in guitar amplifiers and effects ! ).
Chumps Big Brother
So far so good with the simple valve amplifiers.
All the models so far are single ended designs, in which one single valve powers the output transformer, but most guitar amplifiers are push-pull designs, where a pair of valves ( or more ) drive the transformer.
This type of design is more complex and involves splitting the signal into positive and negative halves of the wave form ( phase-splitter ), amplifying both halves separately and then recombining by using them to drive an output transformer with 2 equal windings. This comes with a new set of problems and possible distortions.
VibroChump
As The Chump sounded so good decided to insert the tremelo circuit into the amp to clone Fenders later VibroChamp model, and again seems to work pretty well.
Â
Birth of a Chump
Having been pleased with the results so far it was time to try and build a complete guitar amplifier. To keep it as simple as possible the design is again loosely based on the Fender Champ, very simple in design, 2 stages of preamp valves and one power valve.
12AX7 --> Volume --> 12AX7 --> 6V6 --> 1x 8 speaker
Studio Preamp
Next a preamp based on the legendary F2-B studio preamp from Alembic. is used in many studios for direct injected bass in particular.
The circuit is almost exactly same as that used in many tweed Fender amplifiers.