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Vintage threads from the first ten years
ts9 caps
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 5/4/1999 9:21 AM |
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| Kyle | ts9 caps I'm going to build a DIY ts808, and I'd like to use really good quality parts for this thing. I've got some small 1uf film caps for the sections that have them, but what about the 10uf in the output section? Whay is this value so large? Does it have something to do with the low imp output of the buffer? I'd like to have the math for this circuit if anybody has it. Thanks |
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| 5/4/1999 10:13 AM |
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R.G.  |
If you haven't already, go read "The Technology of the Tube Screamer" at GEO." target="_blank">http://www.eden.com/~keen">GEO. It has to do with the total load impedance of the resistor to ground at the output and any loading of the amplifier. the output may be modelled as a simple RC high pass filter. For more info on how RC high pass filters work, check the "Electronics Onramp" web page. To pass "X" frequency with a -6db loss (half power referredt to voltage) you need a capacitor C = 1/(2*pi*Rload*X) In this case, X= 82 Hz for guitar or 41Hz for bass, and probably you'd choose 41Hz anyway because people like more bass out of these units. So C= 1/(2*3.14159*10K*x) = 0.39uF if you have an essentially non loading amp. In fact, we know that amps do load the output, so we'd have to change Rload to something lower, the parallel combination of the 10K load resistor and the amp input. Most tube amps have input loads of about 1M, so this will not change the results much. Many effects have input resistances that may range from much lower to much higher, so you might want to assume maybe a 50K load on the output of the effect, so the minimum cap becomes about 0.465uF. Really low input effects will run the loading up, so the capacitance must get bigger. Use a 1uF film and try it with your mix of effects and amps. Probably good enough in most cases. | |
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