effects from coupling capacitors in audio circuits

The video shows the "bandpass" from different capacitor values used as coupling capacitor in audio circuits (20 Hz - 20 KHz). The "sound" changes completely with different values, and 1 series capacitor in the audio signal line can be used as audio filter (though the characteristic is far from ideal, complete audio bands are shut off, so not very selective!). More about audio in my book: "Schematics 2, audio amplifiers and loudspeaker boxes" (author Ko Tilman, ISBN 978-1-4475-7336-4. Please note: the capacitor value and its effects also depends on the input resistance from the electronic stage to which it is connected (4-pole-theory). This means that with a high-impedant input stage (like a tube grid or a FET gate), the effects will be (somewhat) else. In the showed demo the input resistance is approx. 3-4 K (bipolar transistor). This low impedance input gives damping.

Category:

Science & Technology

Tags:

• coupling
• capacitor
• audio
• sound
• characteristic
• amplifier
• amplifiers
• typical
• radiofun232

[vibra64]

Great video. Can you tell me what is that white looking gel on your breadboard?

[radiofun232]

@vibra64 It is transparent silicon kit, used to fix the capacitors to the borad. It has good properties for isolating electronic circuits.

[teflondon91]

What happens when you use really big caps in the like 10,000uf? I have seen in some HIFI amps they use multiple caps of different values on the output of a tube stage... here is an example of what I am speaking about: tubecad.com/2009/10/11/srpp+%2­0mosfet.png

[radiofun232]

@teflondon91 cannot find the link to a mosfet circuit on this website.

[teflondon91]

Hello Mr. Tillman, I wanted someone to do this! I found a very interesting paper you might want to check out also: tech.juaneda.com/en/articles/e­lectrolyticcapacitors.html

[radiofun232]

@teflondon91 I saw today it was a test for supply capacitors, that is why he used the resistor. So far so good.

[perazaroberto2]

It is the most intelligent explanation I've seen in my life, rustic, but very intelligent teaching. thank you very much!.

[radiofun232]

@teflondon91 As far as I could see these capacitors are used as power supply capacitors, connected to the bridge rectifier. They are used to keep the hum level low without using a stabilizing circuit with a transistor.

[teflondon91]

@radiofun232 Did you see the 3 caps in parallel on the ouput what method is used here?

[radiofun232]

There is a difference between the output and the input of an amplifier. On the output (non electrostatic amp.) a current has to drive a low impedance load, let us say a 4-32 Ohm coil. This means a "heavy" current, this can only be supplied via a high value capacitor (1000 uF-10000 uF), capacitive reactance. On the input all audio frequencies are delivered to a 3-4K (bipolar transistor amp input) or 500K-1M (triode tube amp input) stage. The coupl. cap. can be less if so.

[radiofun232]

@teflondon91 Thanks, I am gonna search and read it.