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Ruben1
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Question on Impedance Matching Between Pre amp and Amp

I have 2 monoblock amps, B&K M200 with an input impedence of 33K ohm. I want to replace my SS preamp with a tube pre amp and was wondering what I need to concider regarding the oputput impedence of the pre Vs the input impedence of the amps? Thanks.

Kal Rubinson
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Re: Question on Impedance Matching Between Pre amp and Amp


Quote:
I have 2 monoblock amps, B&K M200 with an input impedence of 33K ohm. I want to replace my SS preamp with a tube pre amp and was wondering what I need to concider regarding the oputput impedence of the pre Vs the input impedence of the amps? Thanks.

According to the general guidelines, your new preamp should have an output impedance 1/10 or less of the load.

Kal

SAS Audio
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Re: Question on Impedance Matching Between Pre amp and Amp


Quote:

Quote:
I have 2 monoblock amps, B&K M200 with an input impedence of 33K ohm. I want to replace my SS preamp with a tube pre amp and was wondering what I need to concider regarding the oputput impedence of the pre Vs the input impedence of the amps? Thanks.

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

cyclebrain
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Re: Question on Impedance Matching Between Pre amp and Amp

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.

SAS Audio
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Re: Question on Impedance Matching Between Pre amp and Amp


Quote:
The impeadance ratio does not matter if both devices have a constant (flat) frequency vs. impeadance response.

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.

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