Customize your output caps to your gear:
Tubed preamp, DAC and CD player manufacturers anticipate their gear will be used to feed components with a wide range of impedances. Because of this, many will use output coupling capacitors larger than necessary for many components (especially tube amps). While this makes perfect business sense for the manufacturer, as a hardcore solder-slinger, YOU have the ability to optimize your output coupling cap value to your own gear. The calculators above help you do this.
Coupling capacitors are used to block D.C. (D.C. = bad Ju-ju) , and pass A.C. (A.C. = the music signal). However, a coupling capacitor acts as a high pass filter, meaning it will attenuate frequencies below a certain point. The point at which the frequency rolloff is down -3db (corner frequency) is dependent on the input impedance of the component it will be feeding (the load). Once you know this, the calculator above comes in handy.
What is the input impedance of the component you'll be feeding?
First, you need to find the input impedance of the component you'll be feeding with this capacitor (owner's manual, search online or contact manufacturer). Once you know the input impedance, you have a decision to make: Do you want to modify your gear away from the "stock" cap value, and customize to the gear you own AT PRESENT, or do you want a more "universal" approach, as the manufacurer likely took, in order to have your component compatible with gear that has a wide range of input impedances?
Let the calculating begin...
After you know the input impedance, and have made the decision to go for fully "custom", the fun begins. Simply enter the input impedance of your load in the first row of the first calculator above (Solve for -3db Frequency). In the next row of the same calculator, enter the uF value of the capacitor that is in your unit right now. In most cases, this value will be at least 2 uF, and may be as high as 10 uF or more. This calculator automatically solves for your current -3db corner frequency, to use as reference for the next calculation.
Optimizing for your gear...
For this step, you'll enter the input impedance of your load into the calculator on the right side (Solve for Capacitor Value). Then, move down a row and enter your desired -3db corner frequency. This is where things get interesting. While most intuitively think good system response is from 20 Hz to 20 Khz (yes, we hear the SACD guys groaning...), we DON'T want to use 20 Hz as our -3db point. The reason for this is because we're audiophiles, and we don't want no stinkin' response down to 20 Hz, when we can get LF response suitable for Elephant ears! No, not really... The real reason we don't select 20 Hz is because near the the -3db point, there may be some phase anomalies introduced into the signal, and therefore we want to operate with a buffer from this ragged edge. We recommend using a -3db point of 1/10th of your desired low frequency response. For the Human beings with audio systems manufactured on Earth, that would be 1/10th of 20 Hz, or 2 Hz. If you enter the number "2" into the -3db frequency field, the capacitor calculator will automatically calculate your optimal value so you will have great sound from 20 Hz and higher.
Compare the results from the two calculators:
If you compare the values from the second calculator to the values calculated from the first calculator, you may realize a substantial increase in performance, without any penalty in LF response, if you swap out to a smaller uF value output capacitor. You'll also likely save a bit of dough in the process. Note: The voltage rating of the new capacitor should be equal to or greater than the capacitor that is being replaced, unless you determine that a lower voltage may be used (contact manufacturer).
Try not to be "that guy".
You know who you are- you're the guy tempted to take that -3db point down to the aforementioned Elephant ear territory. Here's the reason why more isn't always better: The lower your -3db point, the higher the capacitor value must be. The higher the capacitor value, the more material in the signal path. The more material in the signal path, well, you know where this is going... the less transparent the signal becomes. When it comes to output coupling caps, less is more, as long as you've achieved a reasonable -3db point.
Disclaimer: A 2Hz -3db point is a general guideline, based on our own experience, as well as the experience of many audiophiles, and modificaiton professionals who have shared their experiences with us. As with all things in high end audio, there is no magic bullet or perfect fix for every system and every application. We encourage you to experiment (with many different values and series of V-Caps, of course), listen for yourself, and reach your own conclusions.