The new "Cygnus X-2" amp modeling introduced a new parameter called "Plate Suppressor Diodes". Plate suppressor diodes, also known as "snubber" or "flyback" diodes are diodes connected between the power tube plates and ground.
The purpose of these diodes is to clamp the inductive "kick" caused by the reactive load seen by the plates. A speaker is a reactive load and has a positive reactive component at high frequencies. This means it looks inductive. Inductors resist change in current. When the plate voltage drops rapidly to zero the inductance of the load causes the voltage to undershoot.
A suppressor diode clamps the voltage and prevents undershoot. This does two things:
1. It prevents excessive voltage at the plates and transformer primary. This protects the transformer from damage due to dielectric breakdown.
2. It also reduces "fizz". The undershoot manifests as increased high frequency content in the range where the load is inductive, typically from 1kHz and up.
Most amps don't have flyback diodes but there are a handful of notable exceptions: Trainwreck Express, Fender Blues Jr., Peavey 5150, and several others.
Flyback diodes were originally added to amps to protect the output transformer but most, if not all, techs don't realize that they also change the clipping behavior.
Consider the graph below:
The blue trace is a plot of a tube power amp output with no flyback diodes. The green trace is the same power amp with flyback diodes. Those spikes in the voltage are what can damage a transformer and also what cause "fizz".
In a real tube amp these diodes are under intense stress and may fail. In our virtual world these diodes are indestructible.
So if you like your tones as fizz-free as possible experiment with the Plate Suppressor Diodes parameter. Note that turning them on will reduce the "chime" at edge-of-breakup and may not be suitable for vintage tones.
The purpose of these diodes is to clamp the inductive "kick" caused by the reactive load seen by the plates. A speaker is a reactive load and has a positive reactive component at high frequencies. This means it looks inductive. Inductors resist change in current. When the plate voltage drops rapidly to zero the inductance of the load causes the voltage to undershoot.
A suppressor diode clamps the voltage and prevents undershoot. This does two things:
1. It prevents excessive voltage at the plates and transformer primary. This protects the transformer from damage due to dielectric breakdown.
2. It also reduces "fizz". The undershoot manifests as increased high frequency content in the range where the load is inductive, typically from 1kHz and up.
Most amps don't have flyback diodes but there are a handful of notable exceptions: Trainwreck Express, Fender Blues Jr., Peavey 5150, and several others.
Flyback diodes were originally added to amps to protect the output transformer but most, if not all, techs don't realize that they also change the clipping behavior.
Consider the graph below:
The blue trace is a plot of a tube power amp output with no flyback diodes. The green trace is the same power amp with flyback diodes. Those spikes in the voltage are what can damage a transformer and also what cause "fizz".
In a real tube amp these diodes are under intense stress and may fail. In our virtual world these diodes are indestructible.
So if you like your tones as fizz-free as possible experiment with the Plate Suppressor Diodes parameter. Note that turning them on will reduce the "chime" at edge-of-breakup and may not be suitable for vintage tones.
. thanks for the detailed info!
