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Old 15th April 2012, 04:37 PM   #1
kkcinc is offline kkcinc  United States
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Default SSE builder preferences

There are two places where Georges instructions call for whatever values you prefer. One is the volume pot. Why would I choose something other than 50k? The other is the coupling cap. Why would I choose something other than .22 uF?
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Old 20th April 2012, 03:23 PM   #2
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The R value of the volume pot (or an equivalent resistor if you are building a power amp config) is the load that your source will see, so a higher R is easier on the source (it doesn't have to provide as much current), but too high and it gets susceptible to external noise. Typical values are between 50K and 100K, although they can be as low as 25K or lower. If the value is too low, and your source can't provide the current, performance will suffer.

The coupling caps (in combination with the grid leak R) are an RC filter that determines the lower cutoff freq for the amp; this is typically quite low, like less than 10hz. Since the amp output will be -3db down at this freq, you want it to be lower than the audible range (20hz-). However, sometimes cheap/undersized output transformers will benefit from having a higher corner freq so that low freq energy does not saturate them. Changing the coupling cap value will raise or lower this frequency for a given grid leak R. Another example of needing a different coupling cap value is the case where one wants to bi-amp, ie use the amp to drive midranges only, or tweeters only. In that case, the coupling cap value can be chosen to have the lower cut-off freq at 100hz or 1000hz or whatever you choose.

Here is some related reading:

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

http://www.ampbooks.com/home/amplifi...ing-capacitor/

Last edited by boywonder; 20th April 2012 at 03:25 PM.
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