Class D is just Dandy!

@atmasphere

Wrote:

As we can see, if one is to point at a tube preamp and blame it for a change in frequency response,

I don’t "blame" preamps for changes in frequency response. 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. Anyone with a basic understanding of AC circuit analysis would conclude the same.

It is also irrefutable that in general, tube preamps have higher output impedance than solid state. That is different than saying preamp X sucks, which is what you seem to have read.

the factor is not the output impedance (which is often only stated at 1KHz), its the coupling cap at the output. That is a bit different from ’output impedance’ and that is why I placed the correction.

A - I never limited myself to 1 kHz
B - It makes no sense to talk about changes in frequency response if i was talking about a single point
C - The coupling cap is a major if not THE major contributor to output impedance. However it is not the only issue. I never said it was. The factors that go into any devices output impedance is more complicated, but includes the coupling cap if any.

There is no logical way to make both of these statements true at the same time:

• Tube preamps don't have a problem with output impedance
• The problem with tube preamps is the impedance of the coupling cap
  

Since the first includes the second, you can't have both of these be true at the same time.

Best,

E

I was taking a look at the NAD C390DD integrated. I like the concept of being able to change out the boards as upgrades become available. Anyone have experience with the sound quality of that model?

Hi @autre

I got to hear the NAD Master series DAC two years ago. Cold, it was a painful screech.

I never heard it well warmed up, so I would strongly caution  you to get a good listen yourself.

I also heard Arcam, MUCH MUCH nicer. Like an inexpensive Ayre.

Best,

E

I don’t "blame" preamps for changes in frequency response. 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. Anyone with a basic understanding of AC circuit analysis would conclude the same.

And I showed the math for why that is not so: the first half of your quote here is false, the second half being based on the first is thus also false.

                                             **Do the math**.

Its the coupling cap at the output, not the output impedance that governs the frequency response.

Example: I've seen ARC preamps with 20uf output coupling caps. If you put them on a 10K load, they will be as flat as they are on a 100K load in the audio passband. Yet the very same preamp according to ARC should not be asked to drive anything less than 30K.

Your claim to which I was objecting was that the higher output impedance of tube preamps leads to frequency response errors and the simple fact is this is not so- it depends more on the timing constant that may or may not be present at the output of the preamp in question.  I showed the math. If you wish to refute this, then show the math.