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-   -   GK-2 cutoff frequency for SS section (http://www.diyaudio.com/forums/aksa/228989-gk-2-cutoff-frequency-ss-section.html)

Jens A. 30th January 2013 10:09 AM

GK-2 cutoff frequency for SS section
 
Hi Hugh,

When I created the SS output on my GK-2, I used a 1 uF teflon cap. When we discussed this prior to my implementation, I remember you said it should just be between 1 and 10 uF.

Just out of curiosity - what would the cutoff frequency (- 3 dB point) for the SS output be with the 1 uF cap?

It is looking into the Ground Sound filter's 20 k input impedance.

I do not feel there is a problem, but since I have already implemented a very steep (48 dB/octave) sub filter at 10 Hz in the Ground Sounds, there is no need for additional sub filtering, and if that turned out to be the case I would simply change the SS output cap value to ensure I do not "get too much of a good thing" ;)

Cheers,

Jens

Osvaldo de Banfield 30th January 2013 12:08 PM

Simple: the -3dB roll off frequency is when the reactance of the capacitor (1/(2 * pi *frequency * capacitance)) equals load resistance. In this frequency, phase angle between voltages becomes 40 degrees and voltage across loads becomes .7071 of the input voltage.

If you get a calculator, then F 0 1/(2 pi capacitance [microfarads] * resistance[mega-ohms]) will give frequency in hertz.

Fortunately, this calculae is independent of capacitor brands and personal tastes. Is as is.
Good luck.

Jens A. 30th January 2013 12:59 PM

Quote:

Originally Posted by Osvaldo de Banfield (Post 3348511)
Simple: the -3dB roll off frequency is when the reactance of the capacitor (1/(2 * pi *frequency * capacitance)) equals load resistance. In this frequency, phase angle between voltages becomes 40 degrees and voltage across loads becomes .7071 of the input voltage.

If you get a calculator, then F 0 1/(2 pi capacitance [microfarads] * resistance[mega-ohms]) will give frequency in hertz.

Fortunately, this calculae is independent of capacitor brands and personal tastes. Is as is.
Good luck.

Errr, well, yes ...

Unfortunately, I'm not much of a mathematician and have never used a scientific calculator, so for me this is not simple.

So what is "F 0 1"? And what "resistance" are we talking about?

Cheers,

Jens

Osvaldo de Banfield 30th January 2013 01:54 PM

Quote:

Originally Posted by Jens A. (Post 3348561)
Errr, well, yes ...

Unfortunately, I'm not much of a mathematician and have never used a scientific calculator, so for me this is not simple.

So what is "F 0 1"? And what "resistance" are we talking about?

Cheers,

Jens

OK, it was a typo I would write f= 1/ 2 * pi * Capacitance * resistance, and it gives you frequency. Resistance must be considered the equivalent resistance to any ground before the capacitor in the way of signal flow. Example:
lets consider a 1 microfarad ( F, or 10E-6) farad and a 20Kohms load.

So the "corner" frequency, say, the frequency at which the signal after the cap is -3dB (.7071 times) respect to the signal before the cap will be:

f = 1 / ( 2* pi * 20000 ohm * 10E-6F) = 15.91Hz.

Then, at about 16Hz, it is considered the lowest frequency your circuit will pass without "severe" attenuation and or distortion.

It is independent if the load resistor is a single 20000ohm or two 40000 in parallel, or or two 10K in series, or any other combination of resistances that gives you 20000ohms as result.

Aclareta: 1E-6 means .000001 in scientific notation, or 1/1 million or 1 millionth part of any measure.

Jens A. 30th January 2013 03:09 PM

Quote:

Originally Posted by Osvaldo de Banfield (Post 3348615)
OK, it was a typo I would write f= 1/ 2 * pi * Capacitance * resistance, and it gives you frequency. Resistance must be considered the equivalent resistance to any ground before the capacitor in the way of signal flow. Example:
lets consider a 1 microfarad ( F, or 10E-6) farad and a 20Kohms load.

So the "corner" frequency, say, the frequency at which the signal after the cap is -3dB (.7071 times) respect to the signal before the cap will be:

f = 1 / ( 2* pi * 20000 ohm * 10E-6F) = 15.91Hz.

Then, at about 16Hz, it is considered the lowest frequency your circuit will pass without "severe" attenuation and or distortion.

It is independent if the load resistor is a single 20000ohm or two 40000 in parallel, or or two 10K in series, or any other combination of resistances that gives you 20000ohms as result.

Aclareta: 1E-6 means .000001 in scientific notation, or 1/1 million or 1 millionth part of any measure.

Hmmm - I am afraid I still do not understand. If "1 /" means "1 divided by" then I cannot see how you get to the result shown. If I divide 1 by the result in the brackets, I get less than 1.

But I probably do not understand the notation ...

Anyway, since we do not know the resistance, I guess we can just as well wait for Hugh ;)

Cheers,

Jens

Osvaldo de Banfield 30th January 2013 03:44 PM

Quote:

Originally Posted by Jens A. (Post 3348692)
Hmmm - I am afraid I still do not understand. If "1 /" means "1 divided by" then I cannot see how you get to the result shown. If I divide 1 by the result in the brackets, I get less than 1.

But I probably do not understand the notation ...

Anyway, since we do not know the resistance, I guess we can just as well wait for Hugh ;)

Cheers,

Jens

Go to the windows calculator, and in the menu "view" click scientific, you will see the calculator expands.

Then, in the numeric right keyboard type (or in the calculator drawing press with the mouse the number) 2, then the asterisc that operates as a multiplier sign, with the mouse click the "pi" button, the * again, then type the value of the resistance load in ohms, the *, then the capacitance in farads (Again, 1F is .000001F). Then, press equal button.

Once did it, press with the mouse, the 1/x button, and you'll get the value I post in the previous msg, (15.91xxxx) with lots of decimal numbers. In practice, only the first or two first digits are of interest.

But, if you don't know the load impedance form the output of the cap to ground, all this thread is meaningless.

Cordially, Osvaldo :headbash:.

Jens A. 30th January 2013 05:26 PM

Quote:

Originally Posted by Osvaldo de Banfield (Post 3348731)
Go to the windows calculator, and in the menu "view" click scientific, you will see the calculator expands.

Then, in the numeric right keyboard type (or in the calculator drawing press with the mouse the number) 2, then the asterisc that operates as a multiplier sign, with the mouse click the "pi" button, the * again, then type the value of the resistance load in ohms, the *, then the capacitance in farads (Again, 1F is .000001F). Then, press equal button.

Once did it, press with the mouse, the 1/x button, and you'll get the value I post in the previous msg, (15.91xxxx) with lots of decimal numbers. In practice, only the first or two first digits are of interest.

But, if you don't know the load impedance form the output of the cap to ground, all this thread is meaningless.

Cordially, Osvaldo :headbash:.

Ah, that's how to do it! Thanks :D

Not all in vain - once Hugh tells us what the resistance is, I'll use your calculation to adjust my cap value, if necessary ;)

Thanks,

Jens

Osvaldo de Banfield 30th January 2013 05:38 PM

Quote:

Originally Posted by Jens A. (Post 3348874)
Ah, that's how to do it! Thanks :D

Not all in vain - once Hugh tells us what the resistance is, I'll use your calculation to adjust my cap value, if necessary ;)

Thanks,

Jens

Congratulations, guy!!!

andyr 30th January 2013 06:53 PM

Hi Jens,

There's an easier equation to remember/use - although it's a slight approximation. This is: 160,000 / R * C (where C is in microFarads).

But, yes, this gives the -3dB roll-off of the R-C pair but you need to remember that the effects of the roll-off (in terms of phase) will extend up to 10x the -3dB frequency ... so in Oswaldo's example, this would be 159Hz.

Which is much too high.

The output cap in the GK-1/GK-2 is 1uF, so when combined with the 43K input impedance of my Lifeforce/Maya amps, produces approximately 4Hz - much better! :D

So, in your case - looking into the 20K input impedance of the Ground Sound filter - I would use 2.2uF as a minimum.


Regards,

Andy

PS: Don't forget that if you are using the "Sub out" facility to feed your bass drivers or subs, you also need to put an output coupling here (whose value depends on the Zin of the amp driving them).

Jens A. 30th January 2013 07:46 PM

Quote:

Originally Posted by andyr (Post 3349024)
Hi Jens,

There's an easier equation to remember/use - although it's a slight approximation. This is: 160,000 / R * C (where C is in microFarads).

But, yes, this gives the -3dB roll-off of the R-C pair but you need to remember that the effects of the roll-off (in terms of phase) will extend up to 10x the -3dB frequency ... so in Oswaldo's example, this would be 159Hz.

Which is much too high.

The output cap in the GK-1/GK-2 is 1uF, so when combined with the 43K input impedance of my Lifeforce/Maya amps, produces approximately 4Hz - much better! :D

So, in your case - looking into the 20K input impedance of the Ground Sound filter - I would use 2.2uF as a minimum.


Regards,

Andy

PS: Don't forget that if you are using the "Sub out" facility to feed your bass drivers or subs, you also need to put an output coupling here (whose value depends on the Zin of the amp driving them).

Hi Andy,

This whole thread is in fact about the "Sub Out" (= SS output) ;)

The capacitors I am talking about are on the SS output, as recommended by Hugh, but they may need to be a somewhat higher value anyway.

Let's see what Hugh says!

Cheers,

Jens


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