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Re: How does ground loop voltage changes with ground loop impedance
Anyone has any idea? According to Faraday's law a voltage is induced proportional to the loop inductance L and the rate of change of the magnetic flux. So the induced voltage is apparently not a function of loop impedance. So...
How does ground loop voltage changes with ground loop impedance
Hi,
I have a question about ground loops. One thing I don't understand is how an "isolation" resistor can eliminate ground loop problems. Take the following setup:
If a certain voltage (Vg) is induced in the ground loop (for...
The way I see it, is that as frequency goes up more of the signal current from the input stage flows into the compensation capacitor and that the current flowing into the base decreases with rising frequency. Is this correct? What I don't see is how it makes the VAS more linear.
Hi,
Lately I'm reading a book on (audio) amplifier design. I have some questions about the Miller capacitor in the attached schematic.
From this audio book I read:
"The global (overall) feedback factor at low frequencies is sufficient to linearise the VAS, while at high frequencies shunt...
Hi, I had a question about the calculation of HF gain in the attached amplifier schematic. I found the following formula for calculating HF gain of the first two stages (input pair and Voltage Amplification Stage (Q4)):
HF-gain = Gm/(w*C)
Gm = transconductance of input pair
w = 2 * pi *...
Yes my question wasn't very clear. I looked into the schematic a bit further. I drawed arrows (blue/red) on the schematic to indicate where the signal current flows. The red arrows indicate the signal current path where the compensation capacitor gets charged and the blue where the cap gets...
Hi
I have a question about the Miller capacitor in the attached schematic of an audio amplifier. I read from a book on audio amplifiers "At higher frequencies, virtually all of the signal current from the LTP (differential input pair) flows through C1". My question is: Where does this signal...
I can see that the current source (Q6 and Q7) wants to provide 10mA through the circuit. But this current also depends on Q4 itself right? Q4 itself functions as a variable current sink set by its base voltage. So the amount of current Q4 let's through its collector depends on its base voltage?
I see how the negative feedback sets the bias point now. Then how can we determine the quiescent collector current through Q4? As i see it there are actually two opposing current sources. One is a current sink (Q4 itself) and the other is the current source (Q6 and Q7). So which of them sets the...
Hi, I'm still struggling with some things in the attached amplifier circuit:
1. How can we find the quiescent bias collector voltage of the VAS transistor (Q4) of this circuit?
2. With the "bias spreader" we create a voltage of 4*Vbe to bias the driver and output stage. How do we make sure...
Isn't the input impedance of Q4: (beta + 1)*R6 ? The datasheet of Q4 (2N5551) lists a beta between 80 and 250. With R6 being 22 Ohm then max. input impedance would be 5.5 kOhm and min. 1.7kOhm. I assume you took an arbitrary value for beta?
Just for a calculation example: If we would have an 8...
@ Audioguru: Yes i was aware of that, but probably you asked this for a reason :-)
@ chuckey: I didn't fully understand your answer.
Where does this 3K value come from, I can't see that in the schematic.
OK, so the collector load is mainly determined by the input impedance of the...
Hi,
I have a question about the voltage amplification stage of an (audio) amplifier. I just took this attached schematic as an example. The VAS transistor Q4 is driven by the output current from the input pair. It is said the VAS (Voltage Amplification Stage) is a transimpedance stage...
Thanks for your answers. That transistor manual looks interesting. I didn't find specific info in it about the factors that determine how to calculate these bias resistors. If anyone has more input on how to dimension these base resistors then please let me hear.
Hi all,
I have the following schematic attached of an AC-coupled differential pair. I would like to know how to choose the right value of the base DC bias resistors (Rb)? Many times I see values used between 10K - 100K. What factors decide how we should choose the value of these resistors...
I made a drawing in Paint. You are right that the input can be a weak high, due to a pull-up resistor. But if it is low-active signalling then i would suspect that if input A and B measures high (4.7 V) pin C should measure 0V (GND). So when a connection is made through the switch between either...
Hi all.
At the moment I'm working on a simple LED indicator (up/down) for a motor controller. It has to indicate if the motor is going in one direction or the other. On the controller there is a control port (D-SUB9) and a switch is connected through a three wire cable to this control port to...
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