Buckeye Nc502mp Review (6 Channel Amplifer)

[rdenney]

Remember that a radio transmitter is modulating a carrier frequency with baseband audio, using the modulated RF as the transmission medium to be demodulated by the distant receiver. So, the RF is always harmonically coupled to the baseband signal at much higher frequency. The RF can therefore ring the baseband audio, creating RF feedback. That is hearable when the RF signal is demodulated by the receiver. Effort is therefore made to keep RF away from the audio input.

An audio amplifier is not modulating on a carrier, but is rather just increasing the amplitude of the baseband signal to send to speakers. So, frequencies are the same and one does not modulate the other with stray RF, at least in theory. Class D amps do have switching at RF frequencies, but the speakers attenuate that—there is no receiver trying to demodulate that radio frequency signal.

Rick “fun with the frequency domain” Denney

 

[jimk1963]

Remember that a radio transmitter is modulating a carrier frequency with baseband audio, using the modulated RF as the transmission medium to be demodulated by the distant receiver. So, the RF is always harmonically coupled to the baseband signal at much higher frequency. The RF can therefore ring the baseband audio, creating RF feedback. That is hearable when the RF signal is demodulated by the receiver. Effort is therefore made to keep RF away from the audio input.

An audio amplifier is not modulating on a carrier, but is rather just increasing the amplitude of the baseband signal to send to speakers. So, frequencies are the same and one does not modulate the other with stray RF, at least in theory. Class D amps do have switching at RF frequencies, but the speakers attenuate that—there is no receiver trying to demodulate that radio frequency signal.

Rick “fun with the frequency domain” Denney

Thanks Rick. With RF amps, our first concern is the carrier frequency feeding back to the input, because that’s where the max gain is. The same issue should apply to a Baseband amp. As an example, if I literally connected a 29 dB gain audio amp’s output back to its input, say through a voltage divider, I’m pretty sure one could make that amp sing like a bird, no?

 

[SIY]

Thanks Rick. With RF amps, our first concern is the carrier frequency feeding back to the input, because that’s where the max gain is. The same issue should apply to a Baseband amp. As an example, if I literally connected a 29 dB gain audio amp’s output back to its input, say through a voltage divider, I’m pretty sure one could make that amp sing like a bird, no?

Do a quick calculation of the capacitance between in and out.

 

[jimk1963]

Do a quick calculation of the capacitance between in and out.

Apologies, not following…

Just trying to understand a simple question - why does this Hypex amp module place input and output connectors so close together? Is this common practice in the audio world? Nothing to worry about here?

 

[SIY]

Apologies, not following…

Just trying to understand a simple question - why does this Hypex amp module place input and output connectors so close together? Is this common practice in the audio world? Nothing to worry about here?

The input to output coupling would be capacitive. So a quick calculation will show that it’s not terribly significant at these frequencies.

 

[antcollinet]

Apologies, not following…

Just trying to understand a simple question - why does this Hypex amp module place input and output connectors so close together? Is this common practice in the audio world? Nothing to worry about here?

Nothing to worry about.

We use RF carrier frequencies precisely because they can propagate as electromagnetic waves over long distances.

What SIY is saying is that at RF frequencies even tiny capacitances between output and input will be low impedance, and allow coupling.

At audio frequencies the the tiny capacitances will be high impedance. So no coupling.

 

[jimk1963]

The input to output coupling would be capacitive. So a quick calculation will show that it’s not terribly significant at these frequencies.

I see. Even accounting for inductive coupling (these wires run along side each other in the box), the capacitive and/or inductive coupling amounts are infinitesimal at Baseband. So if I draw out the closed loop system, the feedback path is so lossy, there just isn’t enough loop gain to support an oscillation. On the right track?

 

[jimk1963]

Nothing to worry about.

We use RF carrier frequencies precisely because they can propagate as electromagnetic waves over long distances.

What SIY is saying is that at RF frequencies even tiny capacitances between output and input will be low impedance, and allow coupling.

At audio frequencies the the tiny capacitances will be high impedance. So no coupling.

Got it, thanks!

 

[boXem]

Apologies, not following…

Just trying to understand a simple question - why does this Hypex amp module place input and output connectors so close together? Is this common practice in the audio world? Nothing to worry about here?

Grouping IOs is good practice for EMI by minimizing the loop area. There is actually a risk of coupling with these modules, but it is between the mains and one input.

 

[jimk1963]

Grouping IOs is good practice for EMI by minimizing the loop area. There is actually a risk of coupling with these modules, but it is between the mains and one input.

I see, thanks. Decades of RF design have made me a bit colorblind to audio band best practices. Gotta tweak my thinking. Appreciate the insights.

 

[Sal1950]

I see, thanks. Decades of RF design have made me a bit colorblind to audio band best practices. Gotta tweak my thinking. Appreciate the insights.

That's what I love about ASR, plenty of folks here with the knowledge to teach us all.