2. amps-preamps
  3. 181941-2029

Impedance and Sensitivity

Hi All,

I have made a move from inefficient speakers and large amps with high current supply to smaller amps and more efficient speakers. Think like 300 to 500 WPC at 8 ohms changing to 25 or 50 WPC at 8 ohms and speaker efficiency increasing to 98 or 100 Dbl from 87 Dbl.

I have always kept an eye on the output impedance of the preamp compared to the input impedance of the amp. I understood that if the input impedance of the amp was not at least 10X of the output impedance of the preamp, I could experience a negative impact on the bass response of my system.

As I try different preamps and amps with more efficient speakers, I have run into a new problem. This problem is that the gain of one of my preamps is 26dbl and, pairing it with a tube amp with an input sensitivity of 0.5 volts, results in not being able to adjust the preamp volume control so that my system plays more quietly. I run out of clicks for it to play more quietly.

I realize that either a preamp or a amp change can fix this. Not sure if in line attenuators is an answer as I suspect it adds a distortion or tonal coloration.

In the meantime...does this "gain" imbalance impact sound quality or is it just a loudness problem?

Thanks for listening,

Dsper

 

 

 

 

dsper

Showing 2 responses by atmasphere

atmasphere's avatar
atmasphere
11,632 posts
 

My problem is that I do not know how to relate amp input sensitivity to preamp gain. One Volt less of amp input sensitivity equals how many preamp dB?

In preamps, 6dB one way or another is a doubling or halving of the voltage. From 1 to 2 volts is a 6dB increase and so on.

You have so much gain (especially with speakers like that) that you might consider a passive volume control. I'm not a big fan of them; an attenuator would work but means that you would be amplifying and then knocking the signal back down. If you keep the passive volume control as close to the amp as possible that seems to work better.

atmasphere's avatar
atmasphere
11,632 posts
 

@dsper You have put your finger on why lower powered amps also have less gain, since its an expectation they will be used with a more efficient loudspeaker.

A higher powered amp usually needs more gain since its more likely to be used with a low efficiency speaker. When you start mixing the two you run into problems like this.

What you might notice here is that the amps and speakers have differences in gain and sensitivity while the gain of the preamp can usually remain a constant, although in the last 25 years the gain of the preamp hasn't been as important. 26dB is a lot of gain in a preamp line stage these days.

More to discover