Chumps Big Brother

Category: Audio DSP Blog Published: Saturday, 13 April 2013 Written by steve

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.

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The Experiment resumes .....

Category: Audio DSP Blog Published: Friday, 21 June 2019 Written by Steve Poskitt

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 ! ).

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Studio Pre Rehash

Category: Audio DSP Blog Published: Monday, 01 July 2019 Written by Super User

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.