3 Diffenerent THD Ratings!

[malvado78]

Look at this play on specifications for this receiver being auctioned at ubid.

Kenwood VB-S610DV/ VRS-6100 Home Theater Receiver, New !

Scroll doen to specifications they list 3 different THD's .7%, 10%, and.05%. This is not a questionI understand how they get each of these. I am just saying its ridiculous.

Sort of reminds me of governement defense contractor propsals. If you've ever worked on one you'll know what I mean.

 

[j_garcia]

The way I read that is that at 80w, it has .7% THD. To produce 100W, it jumps to 10%THD, which is not unusual for a digital amp.

This one sounds the most correct:

Rated Power (Stereo): 65 watts per channel minimum RMS, both channels driven at 8 ohms from 20Hz to 20kHz with no more thanActual 0.7% total harmonic distortion (FTC).

 

[malvado78]

I understand what they are doing and I know that digital amps have higher THD. I was just merely saying it is ridiculous to show three metrics rather than one. With that kind of process they should graph the THD vs power for us it look like it is almost exponential.

 

[mtrycrafts]

The way I read that is that at 80w, it has .7% THD. To produce 100W, it jumps to 10%THD, which is not unusual for a digital amp.

This one sounds the most correct:

Why does this only apply to class D amps? By the way, it is not a digital amp, but a switching amp.

Any amp that is driven beyond its RMS rating will start to increase its distortion and also reasch 10% at some power point.

This amp is a 65 watt amp.

 

[mtrycrafts]

I understand what they are doing and I know that digital amps have higher THD. I was just merely saying it is ridiculous to show three metrics rather than one. With that kind of process they should graph the THD vs power for us it look like it is almost exponential.

Firstly, it is a class D switching amp, not a digital amp.

How is it that class D amps have more THD? Please explain

It so happens that this is not a very powerful amp, 65 watts with .7% THD. They could have just as well tested it at a lower THD level and get a lower wattage. This also applies to other amps as well. You increase the power beyond their design point and it will increase THD as well and pretty soon, it too will have 10% at some point beyond its rated RMS power. Simple.

this is a low power amp.

 

[j_garcia]

Sorry, I thought I saw digital in there somewhere. I didn't read it close, just looked at the THD noted.

 

[MacManNM]

Why does this only apply to class D amps? By the way, it is not a digital amp, but a switching amp.

Any amp that is driven beyond its RMS rating will start to increase its distortion and also reasch 10% at some power point.

This amp is a 65 watt amp.

It is digital. The output is either on or off. PWM is digital. Oh, it's junk too.

 

[annunaki]

Devil's Advocate:

If it were truly digital, would, or does it have an analog to digital converter for the analog input sections?

If so, essentially, the amplifer would then be a large digital to analog converter.

I am also under the understanding that PWM (Pulse Width Modulation) were just switching amplifiers, and nothing more. They are very efficent, and very close to being digital, but they are completely digital. If an amplifier (ignoring the fact that this unit is a receiver) were digital, it would require an analog to digital converter for any analog input. Otherwise it would simply require a digital tos-link or coaxial connection.

I have only seen one amplifier like this. it comes from Alpine in the car audio world. It actually had an analog to digital converter on the input stage of the amplifier.

 

[Tomorrow]

It is digital. The output is either on or off. PWM is digital. Oh, it's junk too.

What do you expect for a hundred bucks? Macs?

 

[j_garcia]

Devil's Advocate:

If it were truly digital, would, or does it have an analog to digital converter for the analog input sections?

If so, essentially, the amplifer would then be a large digital to analog converter.

I am also under the understanding that PWM (Pulse Width Modulation) were just switching amplifiers, and nothing more. They are very efficent, and very close to being digital, but they are completely digital. If an amplifier (ignoring the fact that this unit is a receiver) were digital, it would require an analog to digital converter for any analog input. Otherwise it would simply require a digital tos-link or coaxial connection.

I have only seen one amplifier like this. it comes from Alpine in the car audio world. It actually had an analog to digital converter on the input stage of the amplifier.

I was under the impression that Class-D amps were basically digital, unlike PWM amps, but looking back at the ad for that receiver, it doesn't mention digital (though it is also not a manufacturer's ad). In fact, class D amps are not digital. Never really thought about what some of these companies meant by "digital amp" when it comes to receivers. Are they talking about BASH hybrids, which use digital switching but AB output like many subwoofers use?

In terms of digital receivers, the Sony digital amps DO say they convert every incoming analog signal to digital and keep it that way until it is output as analog signal to the speakers.

 

[mtrycrafts]

Sorry, I thought I saw digital in there somewhere. I didn't read it close, just looked at the THD noted.

No problema I rather this 'digital' amp not be part of the urban legend.

 

[mtrycrafts]

It is digital. The output is either on or off. PWM is digital. Oh, it's junk too.

We went over this. Gave you a link. You don't like it. Tough. It is a switching amp, period.

 

[Buckeyefan 1]

Google explanation

Class D Amplifiers – Not 'Just Audio'
by Steve Somers, Vice President of Engineering
Extron Electronics

D Does NOT Equal Digital
Class D amplifiers are not digital in the true sense. They are not driven directly by coherent binary data. They do act digitally in that the output drivers operate either in the fully ON-region or fully OFF-region. Think of Class D amps as being similar to a switch-mode power supply, but with audio signals modulating the switching action.

A switch-mode power supply uses pulse-width modulation (PWM) to control the on/off duty cycle of the power switching transistor(s) providing power to a load. The efficiency is high because there is little voltage drop across the switch transistor during conduction. This means very low power dissipation in the switch while virtually all the power is transferred to the load. During the OFF period, there is essentially zero current flow. The quality and speed of MOSFET (metal oxide semiconductor field effect transistor) devices has led to compact, efficient, high frequency power supplies. Switch-mode power supplies are more efficient at high frequencies. At higher operating frequencies, components may become smaller and the power supply becomes very compact for the power delivered. In addition, the output filter components may be much smaller. Today, switching frequencies over 1 MHz are not uncommon. But, as you probably know, switch-mode supplies generate considerable noise.

[Edit - abbreviated with link to avoid copyright issues - Admin]

Here's the full article which includes graphs.
http://www.extron.com/technology/archive.asp?id=ts122001

 

[mtrycrafts]

Class D Amplifiers – Not 'Just Audio'
by Steve Somers, Vice President of Engineering
Extron Electronics

D Does NOT Equal Digital

Here's the full article if anyone needs graphs.
http://www.extron.com/technology/archive.asp?id=ts122001

That is what I have said. It is a switching amp, period.
Same or similar to the link I posted.