opinions about my design of a complete HI-FI system

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Very impressive write up.

While I am capable of such in depth analysis, I never do it. I do some approximate calculations and then I start breadboarding. I measure, listen, tweak.

I learned when there was no such thing as computer simulations. If I wanted a computer to solve a messy equation, I had to punch cards, turn them in, wait, and pick up the results from my mailbox. I only did it when I had to for an assignment.

Keep up the great work.
echo what has been said by others ...
These write-ups serve a wonderful purpose for the diy community at large so is a very worthwhile effort. The fact that you're eighteen and turned out such a well researched and well explained article is really no small feat - very well done and I for one, will look out for more interesting stuff from you. best,
Hi Davide,

After browsing through your design report, I have the following comments:

1. I'm impressed! I am an electronics engineer who has been building electronics as a hobby since the age of nine, but I wasn't doing anything nearly this advanced when I was eightteen years old. Do you intend to become an electronics professional? You obviously have talent.

2. I find your section about noise somewhat incomplete. For example, bipolar transistors also have base shot noise and base current 1/f noise. You make a general statement about shot noise being negligible, but without explaining under which conditions this is true and whether you mean base or collector shot noise.

3. The distortion plot figure 6 is not showing any distortion, just an FFT calculation noise floor or the FFT of an initial transient. Presumably you need to cut off a larger part of the beginning of the waveform, tighten simulation tolerances and/or reduce the maximum time step further until you actually see the harmonics. Figure 7 looks much better. The graphs in your power amplifier chapter all look fine.

By the way, are your op-amp models supposed to model distortion accurately? Some macromodels are quite primitive.

4. Stability
It is actually possible for an amplifier to have a 360 degree phase shift around the loop at a frequency where the magnitude of the loop gain is greater than 1 and still be stable. This is called conditional stability (in the control-theoretical sense of the word, in RF electronics it means something else). It is used a lot nowadays in sigma-delta analogue to digital and digital to analogue converters and in class D amplifiers. Conditionally stable circuits have the reputation of bursting into oscillation when they clip, but there are ways to avoid that. Besides, circuits that are supposed to be unconditionally stable sometimes do burst into oscillations at clipping. Stability under small signal conditions really doesn't guarantee anything about what will happen during recovery from clipping.

Best regards,
Marcel van de Gevel
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