Class D is just Dandy!

Glad to have been helpful, Dan.  Enjoy!

Best regards,
-- Al
 

Thanks for the additional info, Dan. But if I understand correctly it still leaves open the possibility that the DVR or its remote may be the source of the noise, as it would seem conceivable that the class D amps may simply be more sensitive to pickup of electrical noise that is present in their environment than the SET amp. Perhaps as a result of wider bandwidth, or differences in gain (which is typically higher for class D amps than for SET amps), or any of the many other differences that may exist between the two designs.

Obviously what I was speculating is a somewhat wild guess, but it was prompted by your mention of the effects of the DVR’s remote.

Best regards,
-- Al

...when my home theater setup is on (Comcast DVR, Primare SP 31 HT processor, Sony HDL display), when making changes on the Comcast remote, the noise abates momentarily during the sequence of time the button is being pushed.

Hi Dan,

That’s certainly an interesting finding. Perhaps the DVR is the root cause of the noise, possibly even when it is turned off and most (but presumably not all) of its circuitry is unpowered. If you already haven’t, you might try disconnecting it and pulling the plug on it. Also, does the remote communicate with it optically, or via RF? If the latter, you might try removing its batteries.

Best regards,
-- Al

George is correct in categorizing the Technics SE-R1 as a class D amplifier. It uses a pulse-width modulated switching output stage, and it is therefore a class D amplifier by definition. Various architectural differences that it has with respect to most other class D amplifiers, including the ability to accept digital inputs from a mating Technics preamp and keep the signal in the digital domain until it is converted to the PWM signal that controls the output stage, do not change that fact. Statements such as the following, which appeared in this TAS review, are misleading and incorrect in drawing a distinction between class D and digital amplifiers:

Indeed, this is not a traditional Class A, Class AB, or even Class D amplifier. Rather, it is a rare breed known as a “digital” amplifier....

As with Class D amplifiers, digital amplifiers use a switching output stage; however, they accept digital rather than analog input signals. These “digital” amplifiers take in the pulse-code modulation (PCM) signal from a music server or other source and convert those audio data to a pulse-width modulated signal. This PWM signal then drives the output transistors, just as in a Class D amplifier. The difference between a Class D amplifier and a digital amplifier is that the digital amplifier accepts digital data rather than an analog signal.

What would be correct would be to say that a "digital amplifier" in this context is a form of a class D amplifier. And as such, like any other class D amplifier its design must address the issue of output stage switching speed.  And the sonic consequences, if any, of the low pass filter at the output of the amp for which the required bandwidth is a function of that switching speed.

Regards,
-- Al

Atmasphere 5-11-2017
... you might be interested in a book called ’Born To Run’ by Christopher McDougall. In it, we find out that we are the dominant species not just because of our brains but also because of our ability to run further than any other animal. Not as fast for sure- its well-known that a cheetah is only good for short bursts. Its a fascinating read.

Thanks, Ralph. I’ll check it out. Having run one marathon and a lot of middle distance races in my younger days it definitely sounds of interest.

My understanding is that at middle distances the fastest land animal is the pronghorn antelope, which is found in western North America. According to Wikipedia it can do 35 mph for 4 miles. Of course there are many humans who can go vastly further than that.

And of course +2 re the importance of putting amps and speakers into context with each other, and being cautious before making blanket statements.

Best regards,
-- Al

For that matter, Bolt can also "compete" against a cheetah.

https://www.youtube.com/watch?v=VZuRTNidtCM

:-)

But I think we all know what the others mean by "compete," whether we agree with them or not.

Best regards,
-- Al
 

Given that this is Erik’s thread, I presume Guido and the others posting above won’t deem it inappropriate if I comment on the disagreement between Erik and Ralph. Apologies if that is an incorrect presumption.

Ralph, it appears to me that what underlies much of the disagreement between you and Erik is that he is viewing the impedance of an output coupling capacitor, if present, as contributing to and being part of the component’s output impedance. While you are not, possibly because you are considering "output impedance" as corresponding to "specified output impedance," which as we all agree is often based on a mid-range frequency such as 1 kHz. The capacitor’s impedance of course being unlikely to be a major contributor to the 1 kHz output impedance in just about any reasonable design.

Regarding that terminological difference, I would have to agree with Erik, and consider "output impedance" to be whatever impedance is seen "looking back" into the output of a component, at a frequency that should be and hopefully is stated. Also, as he pointed out, measurements of **many** popular high quality components that have been presented over the years by John Atkinson in Stereophile, that have specified output impedances of perhaps a few hundred ohms, show impedance rises to the vicinity of 3 or 4K or even more at 20 Hz. Obviously the sonics of such a design would be compromised to some degree when driving a low impedance, such as 10K, or even 30K or more in some cases.

On the other hand, regarding this part of Erik’s statement that you quoted above:

I say high output impedance causes frequency response changes which vary based on the load. This is an irrefutable fact based on simple serial circuit analysis.

As I assume he would agree, high output impedance will not affect frequency response when driving a resistive load if the output impedance itself is resistive, and does not vary significantly at relevant frequencies. As I said in an earlier post, it is the **variation** in output impedance, as a function of frequency, that may be significant in that regard. Although of course under extreme circumstances high output impedance can in itself affect frequency response in the treble region, even if there is no variation as a function of frequency, due to its interaction with cable capacitance. Capacitance not being a resistive load, of course, by definition.

Hopefully this post will result in the divergent opinions expressed in the foregoing posts becoming less divergent.

Best regards,
-- Al

Good comments by Erik.

In the situation Autre described in his post dated 4-29-2017 it is very unlikely that impedance compatibility issues were present.  The Rogue Sphinx has a very high input impedance (more than 100K according to Stereophile's measurements).  And although I don't know what the input impedance of the Peachtree Nova 125 SE is, it is most likely much higher than the output impedance of the solid state Onix CD player which was driving it.

Impedance incompatibilities between line-level source components, such as CD players, and integrated amplifiers such as those, or between preamps and power amps, are likeliest to arise when a tube-based output stage is driving a solid state input stage.

Regarding the 10x rule of thumb guideline which Todd alluded to, I would state it as follows:

The input impedance of the amp (or other component that is receiving a line-level input signal) should be at least 10 times the output impedance of the preamp or line-level source component that is driving it, at the frequency within the audible range for which that output impedance is highest. Which in the case of preamps or source components having capacitively coupled outputs (such as the majority of tube preamps) will usually be at 20 Hz.  And the output impedance at that frequency will often be far higher than the specified output impedance (which is usually based on a mid-range frequency such as 1 kHz), because the impedance of a capacitor rises as frequency decreases.

That doesn’t mean that there will necessarily be a problem if the guideline is not met. It depends on how the output impedance **varies** as a function of frequency. What it means is that there **won’t** be an impedance compatibility problem if the guideline **is** met.

If Stereophile has reviewed the preamp or source component, the measurements section of the review will usually indicate the output impedance at 20 Hz as well as at other frequencies.  But if only a nominal impedance can be determined, such as a manufacturer's specification that is presumably at a mid-range frequency, to be safe I would suggest a ratio of 50x or preferably even 75x.

Regards,
-- Al
 

Toddverrone 5-1-2017
The gods must be crazy!

Great film! And as those who have seen it will realize, its mention was à propos.

Regards,
-- Al