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October 11, 2008 - 6:49am
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Question on Impedance Matching Between Pre amp and Amp
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According to the general guidelines, your new preamp should have an output impedance 1/10 or less of the load.
Kal
Hi Ruben,
I agree with Kal. The RCA Radiotron Designers Handbook recommends approx 5 to 1 min ratio, but I like an extra margin of safety and recommend 10 to 1.
I have seen 100 to 1 mentioned, but that ratio is actually detrimental in most cases.
I have an entire section devoted to this subject, with engineering reasons included. Scroll down to G), "I use the 10:1 ratio to be safe."
http://www.sasaudiolabs.com/sasaudio.htm
Hope this helps Ruben.
Steve
The impeadance ratio does not matter if both devices have a constant (flat) frequency vs. impeadance response. In the real world (not flat), a higher ratio negates any effect caused by the change in the loads impeadance. Simple ohms law stuff. 10:1 works pretty good, but audio equipment impeadance values are not always a useful spec. An impeadance vs. frequency plot would be more useful.
Same thing as the relation between the output impeadance of an amplifier and a speaker.
Actually it does as the ratio lowers, the loadline changes and distortion increases. For instance, if the ratio of RL, plate resistor, is 1:1 with the load resistance, the distortion rises rapidly.
I guess my main concern is that the 100:1 ratio as some tout is actually more detrimental than helpful because an extra stage, usually a buffer, is needed.
Otherwise I do not worry since I have plenty of drive current, excellent FR, and super low distortion.
However, I may be not expressing concerns others might have using different tubes and configurations.
Thanks Cyclebrain.