Posted 3rd November 2010 at 05:19 AM byjan.didden Updated 3rd November 2010 at 10:20 AM byjan.didden
Just a couple of days ago I posted something to try to debunk that tired old myth that 'feedback always comes too late and therefor can't work'. Apart from the fact that obviously it does work, which makes the first statement pretty stupid to begin with, here's my take on it.
The myth may result from an often repeated misconception that feedback comes 'after the fact' and therefore always comes too late.
This has been shown to not be the case over and over again but if you have no engineering background it may be difficult to grasp the concept. Let me try to help.
Obviously, there is a signal delay in an amp from input to output and back to the input through the feedback loop. Since the feedback loop is generally a pair of resistors, the bulk of the delay is in the amp. That is the case both in non-feedback as well as in feedback amps. Such delays are very small, often fractions of a microsecond, and in this context can be ignored.
In this schemo, Rk is the normal cathode bias resistor. Rl represents the tail load in parallel with the load impedance. Rg is the control grid DC return. The CF gives excellent high frequency performance since Miller Effect is absent, and the Cgk sees very little current since the grid and cathode are always at nearly the same potential. This makes the Cgk effectively smaller than its static value. The main component of input capacitance will be the reverse transfer capacitance: Cgp. With small signal triodes, it is easy to present a Hi-Z, Lo-C load to the driving stage. This isn't just helpful at RF.
This is another circuit which has lately come under unjustified criticism within certain audiophile circles. Much of this is unjustified on the basis that the CF is a negative feedback circuit. This view that all NFB is all bad does have a basis in fact. It has...
Posted 7th January 2010 at 05:10 PM byjan.didden Updated 11th February 2010 at 03:31 AM byJason
There are lots of types of voltage regulators, but in this installment I’ll talk about series regulators.
What’s a regulator? It’s all in the name: it REGULATES the voltage to the circuit to be powered to keep it constant and as free of noise and ripple as practical. The ‘regulation’ means that there is some circuitry that compares a reference voltage, like from a zener diode, to the regulated output voltage, and then uses the difference between the two to adjust another element to null that difference. The ‘compare-and-correct’ is crucial for a regulator, and is done by negative feedback….
Look at Fig 1: is there a regulator in there? No, they are all circuits that try to give a constant, ripple free voltage, but if you start to draw varying currents from them, the output will vary with that current and there is no mechanism that somehow tries to null out that variation. Fig 1c is better than 1b, because Q1 buffers the voltage from the zener reference, so...
Posted 17th February 2011 at 03:44 PM byBoofers Updated 25th March 2011 at 12:42 PM byBoofers
If I could pass one piece of knowledge onto every person in the electronics industry it would be this: always flush cut your cable ties. I am tired of having my forearms sliced up by sharp cable ties every time I reach inside a piece of equipment. So remember, safety first, cut your ties flush. Besides, flush ties just look nicer.
Posted 20th August 2009 at 07:40 AM bykeantoken Updated 20th August 2009 at 09:31 AM bykeantoken(Adding a pretty picture...)
Hi all. Apparently, this is the first blog post of the new DIYAudio (unless the new software is fooling me).
Sooo...... What would someone like me want to blog about? All I can really do is post links to my threads and post pictures of my ideas. I don't really have enough to contribute which would warrant a regular blog...
One thing I think deserves mention is the thread below about the Allison output stage. Surely there are more interesting things to talk about, things more pertaining to audio (there is generally a sort of Zen approach where even though a circuit may measure well, there may be other ways of doing it that sound better).