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Class D Illustrated (lots of pics)

#24
My previous post was my lame attempt at some techie humor. I really am in awe of BbyBld and guys like him who made this technology available to us bass players. Bobby Baldwin gets my thanks too for taking the time and effort to explain to us the basic principles involved.
Oh yeah, I currently use one of Bobby's babies; a Peavey VB-3. This thing really rocks.
 
#25
Great thread!

Perhaps it might be worthwhile to clarify some misconceptions about class D as a "digital" technology.

From what I understand, Class D is "digital" in a similar way to the old bucket brigade devices like the SAD1024A, which employ analog sampling using a digital clock to provide the sample rate; although clocking itself is digital, the audio path remains analog throughout.
 
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#26
^ That is true.

It is also worthwhile to acknowledge that PWM, and variations of PWM, is only one modulation technique out of many and there are also modulation schemes that accept conventional digital input like PDM.

Class-D basically just refers to scheme, any scheme, where output devices keep switching on and off. The drive setup can be fully analog or it can basically act as a DAC.
 
#29
Great thread, for the Class D folks. I'm using a PV IPR DSP 1600, with a PV6 as a pre. On the Psychoaccoustic low boost, I've simply assumed that the DSP would amplify every other peak of a sinewave, to simulate an octave lower waveform. Do you have a graph illustrating what is actually happening?...oh yes, if this a good time to set me straight...go for it.
 
#30
4-stringB said:
Great thread, for the Class D folks. I'm using a PV IPR DSP 1600, with a PV6 as a pre. On the Psychoaccoustic low boost, I've simply assumed that the DSP would amplify every other peak of a sinewave, to simulate an octave lower waveform. Do you have a graph illustrating what is actually happening?...oh yes, if this a good time to set me straight...go for it.
Click to expand...

That's not how Maxxbass works...

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http://www.soundonsound.com/sos/feb98/articles/waves.html
 
#31
Amazing thread!! Thanks for the explanation. As a electronics hobbyist who built his own class D amp from pre fabbed modules this really helps take some of the mystery out of how those things work. Next, I'll have to read up on how the switching mode power supplies work. Sub'd!
 
#32
BbyBid's OP takes me back to a time when I worked on SMPS, as a tech. The ones I worked on were used in the telecom industry, but the same principles he illustrated apply.
Click to expand...

That's a good point. A class D amp is basically a high quality voltage inverter, or in other words, a device that converts DC to AC.

As a electronics hobbyist who built his own class D amp from pre fabbed modules this really helps take some of the mystery out of how those things work. Next, I'll have to read up on how the switching mode power supplies work. Sub'd!
Click to expand...

I've thought about posting a similar thread about switching power supplies, but I'm not sure if TB is the right place for that. There are lots of types of switching supplies, and there's a lot of background information that needs to be understood first, so I think it would be too techie. Soft switching power supplies have been taking off over the past 10 years even though they were invented in the 80's. That type of technology is one of the reasons these amp modules are going down in price and physical size. Soft switching means less EMI noise, which allows for minimal product packaging (shielding). There are a few types of soft switching resonant power supply topologies that are popular for use in audio amplifiers. I highly recommend reading up on LLC resonant half-bridge converters, which are popular in audio amplifiers up to 800W, not to mention lighting, LCD televisions, computers, etc. To go along with that, you may be interested in some of the reference design module kits (specifically for powering audio amplifiers) that are available from some of the companies that make the power supply controller chips. The main thing to remember if you start experimenting with power supplies is that most of the information out there is for supplies designed to work under constant load, not inconsistent audio amp loads.
 
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#33
As Bobby implies in his post above, much ofthe most important information is contained in the details. SMPS design is a specialty unto itself, there are folks who make entire careers in that field.
 

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