Capacitor Sizing

[markc2]

How do you size capacitors, I've just built a quickie and was wondering how you decided what to put where as you upgrade.

Thanks

Mark

[earwaxxer]

lots of posts on capacitor ramblings here, but basically the 2.2 coupling caps are the place to start. I used Mundorf silver/oils in that spot. If you have the bucks, you can have some fun with that one (you can spend several hundred bucks on that)! The electrolytic 1000uf can be replaced with a good foil cap around 56uF or so. The physical size of the caps will be much bigger by the way.

good luck my friend, and god speed! - Eric

[Paul Birkeland]

Here is a good calculator for the 2.2uF coupling caps:

http://www.v-cap.com/coupling-capacitor-calculator.php

The load impedance would be the input impedance of the amp after the Quickie (which can be really high for Bottlehead gear, but much lower for others).

The 1000uF cap on the cathode was put there because it was already in our inventory, but this part can be much smaller.  Here's a fun tool to play around with to see how changing that part changes the frequency response of the amplifier:

http://www.ampbooks.com/home/amplifier-calculators/cathode-capacitor/

[earwaxxer]

Thanks Paul! - love that stuff!

[Paul Joppa]

The link is for cathode bypass caps, not coupling caps. Hit "select another calculator" for coupling caps. Output impedance is around 600 ohms for BeePre and Foreplay III, 2K for Quickie, and 4K for Quickie with PJCCS. The load impedance is called "volume control RV" on this page; be sure to set the volume at 100%. (All our preamps have the volume control at the input of the preamp, not the output as in this site.)

There is another consideration besides frequency response in choosing a cap. That is, the impedance of the output line should be as low as possible - I like to make it equal to the preamp output impedance at 120Hz; this is the point of diminishing returns for hum pickup. So I would not use a much small cap than stock even if the power amp input impedance is very high.

[markc2]

Here is a good calculator for the 2.2uF coupling caps:

http://www.v-cap.com/coupling-capacitor-calculator.php

The load impedance would be the input impedance of the amp after the Quickie (which can be really high for Bottlehead gear, but much lower for others).

The 1000uF cap on the cathode was put there because it was already in our inventory, but this part can be much smaller.  Here's a fun tool to play around with to see how changing that part changes the frequency response of the amplifier:

http://www.ampbooks.com/home/amplifier-calculators/cathode-capacitor/

I used this guide when I found out what the MC275 uses Input Impedance (90,000 ohms unbalanced inputs) which puts the ideal capacitor at .88 uf. I am going to use a 1.0 uf and see what happens. Thanks for the help!!!

Mark