Help me understand Amp Spec sheet

I am in the process of getting a Receiver/Pre-amp as my current one is having issues. Now, for matching the pre-amp to my power amp, WHAT are the specs to match? Impedance, gain, sensetivity, etc…?

Here’s my Classe’ CA-2100 Amp specs. Could someone explain what do each of these specs mean? Specifically if it helps find a better matched pre-amp

  • Voltage Gain
  • Sensitivity
  • Input Impedance

I understand the rest.


Any current receiver or preamp/processor with preamp outputs will work.

1 Like

Of the specs you ask about, the two I find amusing are the gain and sensitivity. Why? Because they are redundant. I just did a calculation of gain from the sensitivity and sure enough got 29.1 dB. Not sure why manufacturers would do that except perhaps that they believe the average audio consumer doesn’t know voltage gain = 20log(Vout/Vin) and power=V^2/R. They may be right, but for those like me who know the relationship and meaning of specifications it is just … annoying. The good news is the input impedance of 100k is high enough I can’t see incompatibility with any preamp you might consider, unless it has a crazy high output impedance of, say, 10k+. You want the ratio of amp input impedance to preamp output impedance to be high to avoid ohms law frequency response deviations and premature rolloffs at the frequency extremes.

Thanks, one of the reasons I am asking, is that it looks like Receivers, and I assume not very well designed pre-amps seem to CLIP when driven past 1 VRMS on many brands! So, if an amp requires more than 1V to drive it to max power, it would distort beyond a certain point. Some amps require 2 VRMS or even 4 VRMS, and I guess mine having full power at 1v is easier to drive.

Now how does 100k input impedance help pre-amp?

High input impedance on the amp makes it easy for a preamp to drive and maintains a flat frequency response.

The rue of thumb is the input impedance should be at least 10x that of the output impedance of the source component.


Thx for the assist Elk. Yep, that is indeed the rule of thumb. Which is why with the 100k input impedance of his amp he wouldn’t want to be using a pre with an output impedance of 10k+. The only preamps I can think of, as a class, that might push that are zero feedback all tube types. And typically only at the low end due to decoupling cap limitations.

1 Like

Thanks guys, very helpful! I guess then my amp choice was a good one. As a younger, poorer person I was always AMAZED how the large Classe’ amp sounded at my dealer, so when I could get one (albeit smaller) later on, jumped on it. It’s an amazing piece of audio equipment. I hope the new Classe’ revival will bring them back to the glory days!

Hay buddy. Yes it is a good SS amp. 20+ years ago the CA 100 was my first amp (still have it, still works). I paired it with a tube preamp (Audible Illusions 3, still works, still have it too). If you are at all interested in exploring the tube sound, you may want to consider a tube preamp. But almost any quality preamp will work with that baby. Enjoy the music friend!


Can you show me that calculation…?