Mosfet

[Tomorrow]

The recent thread that questioned whether my receiver was digital or analog still has me scratching my pate. We were forced to assume the questioner was asking whether the amplifier section was d or a. There was no help for an answer to that question from either the manual or the mandatory-customer-service-dummies (at Panasonic..but they're the same everywhere, generally).

I noticed that the amp is a MOSFET type. One... does that indicate a digital amp? And two...while I know that MOSFET amps are more efficient than nonFETs, can anyone tell me in plain Eengleesh, why? (Chris, this must be up your alley.)

T'anx.

 

[3db]

Won't touch the effciency part

need more info about your Panny to see if its classified as a digital amp. The output stage of your amp, the stage that drives your speakers is purely analog. Passive speakers are all analog devices and thus require analog signals. If you tried driving a speaker with a digitial signal with the equivalent power of an analog signal, you would be burning out the coils of your speakers.

As far as effiency goes (trying to remember way back into my Electronics Theorey): mosfets require far less current on the input to control the output compared to that of regular transistors NPN and PNP types. Mosfets are similar to tubes in that respect as they are considered more a voltage device then a current device. And efficiency on amp stage is approximately,

(output - input) / output *100% . I may have this wrong...Its been so long

 

[MacManNM]

The output stage of your amp, the stage that drives your speakers is purely analog. Passive speakers are all analog devices and thus require analog signals. If you tried driving a speaker with a digitial signal with the equivalent power of an analog signal, you would be burning out the coils of your speakers.

This is not necessarily true. Class D amps are PWM (pulse width modulated) which uses a full output and varies the pulse width to control the amount of movement of the driver. Technically it is a pure digital signal, and the drivers are the D/A converters.

Most likely your amp is analog though. Mosfets are current devices. They may be a bit more efficient due to their internal resistance being a bit lower than standard transistors, and the design characteristics of the circuit.
(3db, you had it flopped)

 

[3db]

This is not necessarily true. Class D amps are PWM (pulse width modulated) which uses a full output and varies the pulse width to control the amount of movement of the driver. Technically it is a pure digital signal, and the drivers are the D/A converters.

Most likely your amp is analog though. Mosfets are current devices. They may be a bit more efficient due to their internal resistance being a bit lower than standard transistors, and the design characteristics of the circuit.
(3db, you had it flopped)

Which amps/receivers do you know of that use class D other than those in subwoofers ?

Unless mosfet is different than fet.. I don't have it flopped.

 

[Votrax]

Which amps/receivers do you know of that use class D other than those in subwoofers ?

Unless mosfet is different than fet.. I don't have it flopped.

3db is correct about a MOSFET being a voltage controlled device and bi-polar transistors being a current controlled device. All transistors deliver current on the output which might be where the confusion is.

 

[MacManNM]

3db is correct about a MOSFET being a voltage controlled device and bi-polar transistors being a current controlled device. All transistors deliver current on the output which might be where the confusion is.

Yes, I'd say.

Traditionaly, Mosfets handle more current. I thought that was the question.

 

[MacManNM]

Which amps/receivers do you know of that use class D other than those in subwoofers ?

Unless mosfet is different than fet.. I don't have it flopped.

None that I can think of at the moment.

Right, I was trying to explain that Mosfets in general, output more current, I wasn't talking about the input characteristics.

 

[Votrax]

Which amps/receivers do you know of that use class D other than those in subwoofers ?

I don't think your Panasonic receiver has a class D output. The Sony ES line and Harman Kardon DPR series are class D. There are some others I can't think of off the top of my head.

 

[3db]

You mean??

I don't think your Panasonic receiver has a class D output. The Sony ES line and Harman Kardon DPR series are class D. There are some others I can't think of off the top of my head.

That the output stage is effectively a DAC?

 

[Votrax]

That the output stage is effectively a DAC?

Sort of. In a class D amplifier the digital signal is actually converted to a pulse width modulated signal then amplified and filtered before going to your speakers.

 

[mtrycrafts]

This is not necessarily true. Class D amps are PWM (pulse width modulated) which uses a full output and varies the pulse width to control the amount of movement of the driver. Technically it is a pure digital signal, and the drivers are the D/A converters.

Most likely your amp is analog though. Mosfets are current devices. They may be a bit more efficient due to their internal resistance being a bit lower than standard transistors, and the design characteristics of the circuit.
(3db, you had it flopped)

http://users.ece.gatech.edu/~mleach/ece4435/f01/ClassD2.pdf

It is a switching amplifier. Specifically states it is not digital.

 

[mtrycrafts]

Sort of. In a class D amplifier the digital signal is actually converted to a pulse width modulated signal then amplified and filtered before going to your speakers.

You too need to read:

http://users.ece.gatech.edu/~mleach/ece4435/f01/ClassD2.pdf

 

[MacManNM]

http://users.ece.gatech.edu/~mleach/ece4435/f01/ClassD2.pdf

It is a switching amplifier. Specifically states it is not digital.

The output is either on or off. That is digital. I don't care how you try to hide it.

 

[3db]

Thanks Mytr...been a long time but I actually understood the article

http://users.ece.gatech.edu/~mleach/ece4435/f01/ClassD2.pdf

It is a switching amplifier. Specifically states it is not digital.

I guess its really crucial then to have a good filter and to carefully match the filter with the impedance of the speakers being driven. I cant help but wonder though that relying on simple RCL networks to clean up the waveform introduces even more noise. I know they are passive components but my mind keeps drifting back to both the capaictive and inductive charging cycles. I can see where this kind of amp is used in active subwoofers where the wavelength of bass is so long compared to that of the charging/discharhing cycles of the filter. But in the higher end of the audio spectrum..where the wavelengths get shorter with respect tocharge/discharge cycles of the filter....I dunno..Guess another read is needed.

Thanks for the article..

 

[Votrax]

You too need to read:

http://users.ece.gatech.edu/~mleach/ece4435/f01/ClassD2.pdf

I know what I'm talking about. Your link says the same thing I previously stated. The signal is an amplified PWM signal. The only difference in the link is it's taking an analog signal and converting it to PWM before amplification. I was talking about a signal straight from a DSP.

 

[mtrycrafts]

I guess its really crucial then to have a good filter and to carefully match the filter with the impedance of the speakers being driven. I cant help but wonder though that relying on simple RCL networks to clean up the waveform introduces even more noise. I know they are passive components but my mind keeps drifting back to both the capaictive and inductive charging cycles. I can see where this kind of amp is used in active subwoofers where the wavelength of bass is so long compared to that of the charging/discharhing cycles of the filter. But in the higher end of the audio spectrum..where the wavelengths get shorter with respect tocharge/discharge cycles of the filter....I dunno..Guess another read is needed.

Thanks for the article..

Sure

If it has more noise, it will show up in the specs, no? If it is unacceptable, buy a different amp

 

[mtrycrafts]

The output is either on or off. That is digital. I don't care how you try to hide it.

Tell that to the author. Maybe he will listen to you. In the meantime, it is not.

 

[Votrax]

The output is either on or off. That is digital. I don't care how you try to hide it.

Digital signals don't have a varying pulse width.