• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

preamp/power amp matching

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Help, I have a Ming-Da preamp with a stated output of 39V, an output impedance of 50k, and an input? sensitivity of 200mV. It is connected to a Gamma Space Reference 300B power amp of unknown specification. I know that each signal input feeds directly into a 6SN7GTB valve which has a 100k resistor connected from the signal input to one of the other pins on the same valve. I read that there is supposed to be a 200X factor but do not understand this. Can someone please explain what this means and how to optimise the matching of these two components in terms that a relative beginner can understand?


Joined 2003
Welcome to the forum. Now, to your question. It'll work. There, that's simple.

More detail? Well, the 39V is probably the maximum output that your pre-amplifier can produce without distortion. Obviously, the voltage it actually produces is set by how enthusiastic the music is and how far you advance the volume control. The 100k resistor you found is probably the grid-leak resistor of the power amplifier and this is effectively its input resistance. Almost any valve (and any semiconductor) stage should be able to drive this without problems. I haven't a clue what the 200x factor might be. You have nothing to worry about.
Tweeky said:
Thanks for your help guys. The combination goes loud at quite small movements of the volume control so I wanted to be sure that things were ok.

The problem is that you have a preamp with gain, and you don't actually need any gain. It won't cause any problems apart from only being able to use a small bit of the volume control range :)

Are you sure about the 50k output impedance? It sounds very high.

Best regards,

Mikkel C. Simonsen
I am working on my own pre-amp design. I am surprised to hear 39V. I have come to understand that all you need to drive most amps is around 2V p-p.
Given this, is would not surprise me that it is very loud. Either the preamp gain is way to high (my design will be around A=20) or the attenuation of the volume control is not all that well suited for the application
I am hoping that some one can back me up on this.
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