Help with Understanding of Input Sensitivity in Solid State Amplifiers

MikeO

Active Member
Just a bit of background first. I currently have two amplifiers which I like for different reasons. One is a 1990s Exposure XV integrated amplifier which I am struggling to get to sound great in my system. Two is a Vista Audio Spark 20 watt integrated amplifier, probably a few years old, which sounds absolutely excellent in my system. Speakers are either a set of Royd Envoys or Royd Squires, both fairly efficient 8 ohm speakers from the mid to late 90s.

I have had issues in the past with a few of the British amplifiers I have tried, mostly pre-1990s designs, where the gain is too much with my sonos connect set as a line level component. There is little range on the volume control and harshness very quickly kicks in, while it is too loud for low level listening by even 8 o clock on the volume. I have a couple of options, I can use the sonos connect as a volume control and dial it back but it is a digital volume control and apparently affects sound quality as it dials back volume. Two, in the past i have used attenuated cables but unfortunately I got rid of them when I sold the other British amps. The attenuated cables I have bought do seem to resolve the issue, but as always I wonder if some of it is a placebo effect. The Vista Audio Spark just sounds excellent all around but is only 20 watts.

Looking at the specs I noticed that the Exposure lists an input sensitivity of 150 mv which seems quite high for a 2 volt line level device. Usually they seem to be around 300 mv from what I have seen although a lot of the 80s and 90s British gear seems to have high sensitivity. The Spark has an input sensitivity of 600 mv. I can't really say I have seen another amp with that low input sensitivity (not that I really looked deeply into this). But it seems to really work well in my system.

So I guess my question comes down to understanding how important matching input sensitivity to the output voltage of the source is. Am I barking up the wrong tree here or can it make a big difference in terms of sound quality. I do realize it is quite possible I just really like the much newer spark but the Exposure amps are supposed to be a great match for the Royd speakers and I don't get the impression there is anything wrong with the amp. Just a bit harsh. Any help on understanding if the input sensitivity of the Exposure could be the problem and the best way to resolve it, would be greatly appreciated.
 

Tillerman

Junior Member
While not an expert about this, it seems from your description that you have too much overall system gain. Do you know the sensitivity of the speakers you mentioned?
In my own system, I have realized that I face a similar problem, i.e. having to attenuate gain to get reasonable use/range of the master volume control. I have switched from a high gain preamp to an essentially zero gain preamp. This seems to work really well for me and the sources I use.
 

MikeO

Active Member
I have been playing around for the last couple of hours. By changing the volume setting on the Sonos connect to max out at 68 percent, I am able to get volume on the amp to 11 o'clock as a comfortable listen level with no harshness. I was having some success with the Sonos connect at 75 percent but some louder peaks in the music would get harsh almost like it was overloading the amp. 100 Percent is what the fixed gain setting would be and that is supposed to be 2 volts like most line inputs.

I am happy here and it is a major improvement but it does seem that you are correct there is too much gain in the system when I set up the connect as a fixed gain component. My guess is that the issue is the high input sensitivity of the Exposure amp.
 

Tillerman

Junior Member
Older amps and preamps were often designed for much lower source output levels (tape, records, FM). Also, these components were often used with low to medium sensitivity speakers. Hence, it was more common to need more gain throughout the system.
 
A sensitivity of 0.15 volts for (presumably) full rated output is very high these days. It sounds like you are a prime candidate for an in-line attenuator. This plugs into your amp input jack, and the cables from your source plug into the back of the attenuator. It has a series resistor and a shunt resistor inside that reduce the level by a fixed amount. I am pretty sure they are available with different amounts of attenuation. In your case, I would be looking for a 10db attenuator. That would reduce the effective sensitivity to 1.5v.
 

MikeO

Active Member
A sensitivity of 0.15 volts for (presumably) full rated output is very high these days. It sounds like you are a prime candidate for an in-line attenuator. This plugs into your amp input jack, and the cables from your source plug into the back of the attenuator. It has a series resistor and a shunt resistor inside that reduce the level by a fixed amount. I am pretty sure they are available with different amounts of attenuation. In your case, I would be looking for a 10db attenuator. That would reduce the effective sensitivity to 1.5v.
Thanks. I have used 10 db attenuated cables in the past with a couple of other older British amps with good results. But I had just guessed to the correct level of attenuation. Thanks for confirming 10 db is what I want in this case.
 
I would be skeptical about the Sonos volume setting. I am guessing it uses a digital attenuator which will introduce some distortion at less than maximum volume.
 
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