link about class d amp

MMmmmhhh i did get some samples from TI on the subject class D.

I do not like the "lowpas filter" in the output. A digital amplifier will not compensate for the LC-filter frequency response into different loads. At this point the Linear amplifier is superiorer. When you talk about settling time the linear amplifier is ~ min. 10 times faster than a class D amplifier with feedback... again you can blame it on the LC-filter.

Thats theory... another thing is real world sound.... I will only say TacT... I have not listning to one yet.

I get somewhat irritated when I hear of digital amps. The so called digital amps are just glorified switchers. Yes, PWM is 2 state but duty cycle isnt. Digital amps are still analog in nature. THey work on all of the same prinicples of analog electronics.

I work for a company that developes amplifiers to drive wierd piezo and mangeto-strictive actuators. We use class D solutions because of the the power levels we must meet and the size constraints. We have a design called PolyDrive that Gets rid of alot of the switching noise (at all inputs, not just zero!) with minimal filter. ALot of feedback and noise shaping is used. Our standard model can deliver 500W (Continuous Sine Wave into load). WE just recently did an audio test and it sounded as good as most linears I have encountered. But the real problem in implementation is cost. The amp requires alot of expensive (6 layer) PC boards and fast components. No one would buy it for audio use because you could buy an equivilent linear for .25 of the cost. The only advantage would be is small size. The main power FETS are attached to old Pentuim I style heat sinks. THe amp stays very cool. We also run the unit in current mode. Feedback is set up such that an input voltage commands a current into your load. This is neccessary for some types of actuators and works very well with audio.

Even though I think Class D's can be neat, There is no such thing as a digital amplifier. When those really come we will need digital power from the wall too!

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
The legendary Bob Widlar of National said that when
new circuit was created, they sent it over to the
digital guys. If they couldn't build it, then it was analog.

It's true that the "digital" amps are all analog, but the
marketing guys just can't help themselves when it comes
to putting "digital" on the faceplate. :)