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The "DAC-as-Preamp" Trap: Why DAC Buffers Bottleneck High-End Amplifiers

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Yes. A-B-C-D-E - very long...
You completely missed my point. Or maybe you are trying to be funny. I am talking about sudden change in amplitude and frequency of signals or sudden high dynamic shifts in the waveform - this is something that will put stress on the circuits carrying source signal coming through the preamp.
I read your point as being that microsecond scale changes in voltage (which you related to musical notes) would cause audible distortion. My point is that microsecond scale changes in voltage don't even exist in band limited audio, and especially not because a low note follows a high one, an event thousands of microseconds long at minimum.
 
So far I have heard:
Power amp input impedance = 20–50 kΩ
I = V/R = 2 V / 20 kΩ = 0.1 mA
Therefore 20 mA output from a DAC is “plenty”.
But this is DC math on a AC wide-band system (at least 20-20k Hz with varying amplitudes) and ignores capacitance, transients, RF, feedback and stability... signal has a chaotic nature and user can increase volume as high as he/she wants. As an engineer, I feel I want to have good scientific understanding of what variables matters and where I need to ensure I have taken necessary buffers.

My thoughts are: this ignores capacitance, slew rate is about being able to charge the capacitance within the limits of the output impedance, voltage and current delivery. Especially if you look at the end to end signal path.
Low current will give low slew rate that can lead to high frequency losing fidelity, or is this where I am wrong? At least if I try to remember my class from university when we were studying transistors, this was the case....

I don't believe it is audiophile myth. It’s basic analog electronics, unless I am going demented.

So please, let me know what I have misunderstood or mistaken.
 
In addition, there is no such thing as "zero" feedback. There are badly designed amps without global feedback, but they all have local feedback implicitly through emitter degeneration resistors and such.
I always find it a bit funny when I see "zero negative feedback" tube amps with triodes. Unless the anode voltage is held constant, triodes have quite a bit of internal negative feedback even without cathode degeneration.
 
I always find it a bit funny when I see "zero negative feedback" tube amps with triodes. Unless the anode voltage is held constant, triodes have quite a bit of internal negative feedback even without cathode degeneration.
I've upset some "audiophiles" pointing that out.
 
I read your point as being that microsecond scale changes in voltage (which you related to musical notes) would cause audible distortion. My point is that microsecond scale changes in voltage don't even exist in band limited audio, and especially not because a low note follows a high one, an event thousands of microseconds long at minimum.
I appreciate your point — and I actually agree with part of it.
We don’t have microsecond‑scale musical events. That part is clear.

My point was more about the electronics behavior. Even if the audio wave itself is slow, the electronics in the signal path deal with fast edges, charging/discharging of capacitances, and transient current demands due to how the eletronic circuits are built (capacitors, resistors, buffers, transistors, compensation networks, JFETs, attenuators, etc... this part I know well and I like to solder and repair equipment... as an old solder certifier in telecoms industry).

Any analog output stage (op‑amp, discrete, tube, whatever) has limits. When you get close to those limits, distortion increases — even if the audio signal itself is “slow.” Tubes are a great example, they are very slow by nature (compared to transistors), it rounds out the edges and makes the sound a bit softer. However side effect they have a tendency to introduce (good in some cases) distortion

You can attack my wording on these facts, and maybe semantics on tube behavior, but nothing here is factually incorrect I believe, at least from my experience.
 
I've upset some "audiophiles" pointing that out.
Negative feedback indeed :facepalm:

So please, let me know what I have misunderstood or mistaken.
Merely listing capacitance, transients, RF, feedback and stability doesn’t demonstrate that any of them presents a problem.

But this is DC math on a AC wide-band system
That isn’t really the argument. Just replace R with a complex impedance and redo the calculation. You can do the same for the max vd/dt of a band limited signal and get the resulting capacitive current.
 
I always find it a bit funny when I see "zero negative feedback" tube amps with triodes. Unless the anode voltage is held constant, triodes have quite a bit of internal negative feedback even without cathode degeneration.
Yes it is funny for me too as an electrical engineer... of course there is no such thing as zero feedback!
By the way this is confirming my point.
In the audio world (which isn't always correct from a factual point of view), there is such a thing they call a zero feedback amplifier which is more correctly an open loop amplifier... i.e. an amplifier without a feedback loop to the source...
 
Oh my...
We really gonna hit rock bottom if the future of ASR is posts challenging AI VS AI. What the heck, guys ?!
 
Oh my...
We're really gonna hit rock bottom if the future of ASR is posts challenging AI VS AI. What the heck, guys ?!
All the nonsense from the internet dragged to our doorstep. It's like having a technical cat :)
 
Negative feedback indeed :facepalm:


Merely listing capacitance, transients, RF, feedback and stability doesn’t demonstrate that any of them presents a problem.


That isn’t really the argument. Just replace R with a complex impedance and redo the calculation. You can do the same for the max vd/dt of a band limited signal and get the resulting capacitive current.
Let's take capacitance as example! I like it because I love making cables... If capacitance never mattered, a 200 m long 0.1 mm RCA cable would work perfectly. (I know a stupid example, but it made me chuckle...)

Of course it would not work well because capacitance is one of the parameters that defines how much current and slew rate the output stage needs. Whether it becomes a “problem” depends on the design margin.
My original question was around thoughts I have had why no-one talks about current reserves in preamps and why everyone only looks at output voltage and say - hey it's 2Vrms - this can drive my poweramp! We have now drifted far away from my original thoughts... but I enjoy it!
 
ASR really should be an AI-free zone.
But, I guess that ship has already sailed.
Disappointing.
If you are afraid of AI, I think you need to throw away your laptop and mobile phone and live in the forest. It is here.
 
capacitance is one of the parameters that defines how much current and slew rate the output stage needs.
It has nothing to do with slew rate. Peak current for a given dV/dT into a given capacitive load is trivial to calculate. Try it and you'll see that your assertions are unfounded. Remember that the maximum demanded dV/dT is strictly limited for a given peak voltage and sample rate unless your DAC has no output filter.
 
My original question was around thoughts I have had why no-one talks about current reserves in preamps and why everyone only looks at output voltage and say - hey it's 2Vrms - this can drive my poweramp!
This is because there's no problem at all. As has already been shown to you any decent DAC output stage is able to feed any decent power amp input including a cable with sufficient length in domestic settings. Very few power amps need more than 4V rms and some DACs are not able to deliver 4V rms, so those combinations are unable to reach full output but would still sound fine without those distortions you claim.
 
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