Inrush into 4.3mF capacitor bank

[marconi]

I knew the academic definition of crest factor but wanted something which applied it to music and provided some numbers which might aid the design team. Here is a piece I researched today:

https://www.mc2-audio.co.uk/wp-content/uploads/mc2_crest_factor_and_amp_power.pdf

In it it says:

When specifying a system -(DPG's earlier point) , it is important to not only know the dynamic performance and limits of the loudspeakers and the amplifiers, but also the expected signal type to be used. Please bear in mind that any signal source that has a lot of constant tones (CF between 3.0 and 1.5) will require twice as much available power than a typically ‘heavy’ dynamic music signal (CF between 3.0 and 5.0), and about ten times the power of a system mainly used for speech and ‘light’ music.

Thus it seems to me that one would need to determine the range of crest factor of the bass music to be amplified before designing the amplifier. This may require different selectable modes by the power supply for classical, pop, heavy metal, jazz.....

 

[Lucien Nunes]

And therein lies the difference between a professional-grade amplifier where you don't have to think about these parameters during use - you just use it - and a 'DJ-grade' amplifier that can survive and deliver power within a specified envelope but lets out the magic smoke when you make the slightest move outside of that envelope. With bipolar output transistors there was typically a headroom limitation imposed by the SOA of the output devices. With MOSFET it's more a PSU and overall thermal limit. Having become accustomed to MOSFET in the late 1980s, I recall our attempts to destroy Amcron Macro-Tech 2401s and 5000s (bipolar BTL output with flying rails) at university, with some very loug gigs. We failed, because the Amcron was a well-engineered, heavy duty amp.

 

[marconi]

So that Lucien and I educate - SOA - is safe operating area. Here is a graph for a transistor. So when you read a 'rating' for component there is more to say to fully describe it and even this diagram does not completely describe its rating. When selecting components one wants to be some margin away from the boundaries so that the device is in its comfort zone. I am old school that does not believe in operating things at their limits.

It is not wrong to minimise the margin but it has consequences to bear in mind eg reduced life but it produces a more economical product - perhaps.