[Ashkii21]

I just finished building my second Cmoy and I was wondering which resistance to use to figure out the frequency of bass roll-off. I am using a 10k pot and have 100k for R2. Which do I use in the formula, f=1/(2 x pi x R x C)? Is it 10k from the pot, 100k from R2 or is it something else? (9090?) Are there any benefits from using a 50k pot instead of the 10k pot and changing R2 to around 500k?

 

[Vizzini]

Use the value of R2. The pot determines the input impedance of the amp, but has no effect on the roll-off freq. The higher the value of R2, the lower the corner frequency, but at the cost of some noise. Tangent has a noise calculator on his site that's informative to play with: http://www.tangentsoft.net/audio/calc.html

 

[sanderx]

BTW, you don't have to use a resistor that is exactly 10x larger than the pot. You can easily select inbetween 5x and 20x.

 

[Ashkii21]

Thanks!

I am planning on making another Cmoy amp and was deciding on using either a 10k or 50k pot. I am using headphones with 32 ohms Impedance and was wondering if the 10k pot or 50k pot would work better with them or if it even matters. From what I read, 60 ohms and below are considered low impedance headphones. In the Cmoys that I've made, I used a gain of 3 and the other a gain of 5. I also just used a jumper (no resistor) for R5. Also I use the TLE2072 opamp, and only a single 9V battery.

I tried the link to Electronics Calculators, but it doesn't work for me. I am using Windows 7, tried it on Firefox and IE8 but the calculators wouldn't show up. (I have the latest Java update from Sun)

 

[Vizzini]

Quote:

Originally Posted by Ashkii21 /img/forum/go_quote.gif Thanks! I am planning on making another Cmoy amp and was deciding on using either a 10k or 50k pot. I am using headphones with 32 ohms Impedance and was wondering if the 10k pot or 50k pot would work better with them or if it even matters. From what I read, 60 ohms and below are considered low impedance headphones. In the Cmoys that I've made, I used a gain of 3 and the other a gain of 5. I also just used a jumper (no resistor) for R5. Also I use the TLE2072 opamp, and only a single 9V battery.

The input impedance of the amp (determined by the pot and R2) has no effect how how the amp drives your headphones. Increasing the supply voltage (use two 9V batteries) might have an effect depending upon the headphone, but you're still limited by the amount of current that a TLE2072 can put out. With low impedance headphones a different amp design might produce better results. The "Apheared 47" is only slightly more complicated than a Cmoy and reportedly works well with low impedance Grados (see How to build the Apheared 47 Headphone amplifier for Grado Headphones). Or you could build a PIMETA or Mini3.

Quote:

I tried the link to Electronics Calculators, but it doesn't work for me. I am using Windows 7, tried it on Firefox and IE8 but the calculators wouldn't show up. (I have the latest Java update from Sun)

The calculators don't show up for me either. I've emailed Tangent with the Java Script error that I'm getting.

 

[Vizzini]

Quote:

I tried the link to Electronics Calculators, but it doesn't work for me. I am using Windows 7, tried it on Firefox and IE8 but the calculators wouldn't show up. (I have the latest Java update from Sun)

I noticed the same problem and notified Tangent. He has corrected the problem. (You may have to force your browser to reload the page to get the updated javascript file.)