Old Distortion Analyzer and Audio Analzyer

[walters]

To properly bias transistors you have to match the baising resistors to have a perfect sine wave going in and out of the transistor without clipping or asymettical clipping only one cycle or one half of the waveform but thats just sitting there experiment with different values to come up with the right biasing resistors for the perfect Q point of the transitor

 

[audioguru]

To properly bias transistors you have to match the baising resistors to have a perfect sine wave going in and out of the transistor without clipping or asymettical clipping only one cycle or one half of the waveform but thats just sitting there experiment with different values to come up with the right biasing resistors for the perfect Q point of the transitor

Mostly correct, but in most transistor circuits the base biasing resistors are not matched with equal values.
Experimenting isn't necessary if the transistor operates at low levels or if it has negative feedback. Then a transistor is linear and its Q point in a circuit can be calculated.
It is difficult to set a perfect Q point of a transistor that operates at high levels and doesn't have negative feedback. Then the transistor is non-linear, the output is asymmetrical and the even harmonics distortion is high.

 

[_3iMaJ]

my college didn't or book didn't teach this stuff sorry

Ask for your money back.

 

[audioguru]

my college didn't or book didn't teach this stuff sorry

Ask for your money back.

:lol: :lol: Hee, hee, hee, hee! :lol: :lol:
A very good one.

 

[walters]

So not having the bottom or lower half of the half waveform= 2nd harmonic distortion?


Why is the 2nd harmonic distiortion so special? why do u measure it?


When looking on the scope i can't tell what the 2nd harmonic looks like where is it and what does it look like please?

If the Transitor is Linear why does it have 2nd harmonic distortion?

If the transistor is "not" linear does the 2nd harmonic distortion increase or decrease?

 

[audioguru]

So not having the bottom or lower half of the half waveform= 2nd harmonic distortion?

No. You con't understand distortion. If the upper half or the lower half of a waveform has a different amplitude from the other half, then there is even harmonics distortion caused by non-linearity in the driving device. If half the waveform is missing completely then the device performs like a rectifier and the even harmonics distortion is extremely high.

Why is the 2nd harmonic distiortion so special? why do u measure it?

It shows that a device is non-linear. 1% even harmonics distortion can be heard but can't be seen on a sine-wave on a 'scope. Since a distortion analyser nulls-out the fundamental then the distortion is very clear and easy to measure.

When looking on the scope i can't tell what the 2nd harmonic looks like where is it and what does it look like please?

I posted a sim of a distorted sine-wave. Its even harmonics distortion was 40% because the top half of the waveform was grossly reduced in amplitude, compared to the normal higher amplitude lower half.

If the Transitor is Linear why does it have 2nd harmonic distortion?

No. Transistors are not linear. They have 40% even harmonics distortion at a high level like I showed. Negative feedback is used to reduce the distortion like my sim showed.

If the transistor is "not" linear does the 2nd harmonic distortion increase or decrease?

Duh! Guess.

 

[walters]

Thanks alot for the help

so u have to "null" out the fundamental frequency and then hook the circuit to a oscilloscope to see the distortion?

How do u measure the THD distortion?

What about all the other harmonics like all the even and odd harmonics
1,2,3,4,5,6,7,8,9, harmonics how do we measure them?

I'm still confussed about how a transistor can have even and odd harmonics how does a transitor circuit when biasing the transistor can produces odd harmonics again please?

Does it depend on the Biasing to produces even or odd harmonics?

 

[audioguru]

There is no reason to individually look at each harmonic of a distorted waveform. Just the total of all harmonics are measured on an AC voltmeter as a percentage of the fundamental's amplitude.
Negative feedback reduces both even and odd harmonics distortion. Using devices in a push-pull or differential mode cancels even harmonics distortion. A push-pull or differential circuit produces odd harmonics distortion because each half of the waveform has exactly the same non-linearity. Both the tops and the bottoms are compressed.

 

[walters]

Thanks for the help

Both the tops and the bottoms are compressed

whats causes the compression?

Why is the tops and bottoms compressed?

 

[audioguru]

Both the tops and the bottoms are compressed

whats causes the compression?

Why is the tops and bottoms compressed?

Non-linearity of push-pull transistors when they are conducting the most at the peaks of the waveform.
I just finished making a simulation but the stupid sim software made a perfect output without any distortion.

 

[walters]

"conducting the most at the peaks of the waveform"

This is what causes the Compression?


"Non-linearity of push-pull transistors"


The Non-linearity causes the compression?


Or the Push pull causes the compression?


What causes the compression?

 

[audioguru]

Transistors are non-linear. The higher the current then the lower is their gain. Therfore the waveform is compressed at the peak when the transistor's current is its highest.

Push-pull transistors alternate during the waveform. One transistor conducts current when the waveform goes upward, then the other transistor conducts current when the waveform goes downward.

Transistors are used in a push-pull mode to cancel even harmonics distortion, since the upper and lower parts of the waveform are the same.

 

[_3iMaJ]

I don't think our friend Walters has a clue as to what you mean by "non-linear." Knowing is half the battle.

 

[audioguru]

I don't think our friend Walters has a clue as to what you mean by "non-linear." Knowing is half the battle.

I thought about those curved mirrors at the circus that make you appear fat or thin. Maybe Walters hasn't seen a circus.

 

[_3iMaJ]

I think that 2*f(x) != f(2*x).

 

[audioguru]

I think that 2*f(x) != f(2*x).

2 is a majic number. Add itself, multiply or square itself and the answer is the same.
Root it (route?) and you get another majic number that is good for sine-waves.

 

[walters]

Thanks guys for the help

What is transistor non-linear mean please?

I thought the Baising resistors made the transistor Linear?

"Transistors are used in a push-pull mode to cancel even harmonics distortion, since the upper and lower parts of the waveform are the same."

How does the push pull mode "cancel" out the even harmonics?

Does push pull mode "Cancel" out the Odd harmonics?

 

[walters]

"Push-pull transistors alternate during the waveform. One transistor conducts current when the waveform goes upward, then the other transistor conducts current when the waveform goes downward. "


Using a Single Transistor in normal mode "conducts" current upward and downward whats the difference between Pull-pull VS normal mode?

Because they both "conduct" upward and downard waveforms

 

[audioguru]

What is transistor non-linear mean please?

Linear: 1V in= 1V out. 2V in= 2V out. 3V in= 3V out. 4V in= 4V out.
Non-linear: 1V in= 1V out. 2V in= 1.5V out. 3V in= 2V out. 4V in= 2.5V out. Non-linear causes compression at high levels like that.

I thought the Biasing resistors made the transistor Linear?

A little. You can bias a transistor away from the worst non-linear part of its gain curve. Negative feedback makes transistors much more linear than biasing changes. We are't talking about a gross biasing error that cause a transistor to clip asymmetrically like in the FuzzFace.

"Transistors are used in a push-pull mode to cancel even harmonics distortion, since the upper and lower parts of the waveform are the same."

How does the push pull mode "cancel" out the even harmonics?

When the upper and lower parts of a waveform are the same (even if they are compressed or clipped) then there isn't any even harmonics distortion.

Does push pull mode "Cancel" out the Odd harmonics?

No. Compression of both upper and lower parts of a wavedorm equally, and symmetrical clipping causes odd harmonics distortion.

Negative feedback reduces any kind of harmonic distortion.

 

[_3iMaJ]

I think that 2*f(x) != f(2*x).

2 is a majic number. Add itself, multiply or square itself and the answer is the same.
Root it (route?) and you get another majic number that is good for sine-waves.

Its actually one of the axioms of linearity, written generally a*f(x) = f(a*x) for linearity to hold.