I truly do not understand electronics but have been doing some reading. I wonder about a suitable preamp for my Dynaco ST70 and was looking at Bottlehead. Looking there, I noticed their loudspeaker amps have approximately 1/10 of the power of my Dynaco. (Stereomore produces 3.5 WPC) "What gives," I wonder? Then I see this post in another thread:
If true, this suggests the Bottlehead pre (BeePree) output signal is WAY WAY WAY beyond what my ST70 will handle. Are electronic devices (amps and preamps, for example) really this incompatible? It looks like Bottlehead's recipe for hifi sound is to use a preamp that sends a REALLY strong signal to a power amp that has a REALLY wimpy output and then use speakers that are REALLY sensitive.
I must be missing something here. Are hifi systems really this completely different and incompatible? What am I not understanding here?
Most all modern amps can be driven to full power output with less than the signal that's provided by most line level sources, like a CD player or the output from a DAC. So in that case a "passive preamp", which is nothing more than a simple volume control, is all that's really needed. It attenuates, or reduces, the level of the signal going into the amp unless it's turned all the way up.
Despite this, most all preamps have gain, which means they boost the signal coming from the source. But the more they boost, the more of the signal ends up being shunted to ground by the volume control. And this reduces the useful range of adjustment of the volume control, so it's harder to make minor level adjustments.
So why use a preamp? In most cases they allow you to switch between multiple inputs. Older ones might also have tone controls while newer ones might have remote control of various functions. But gain is often not strictly needed when using line level sources. If you use a turntable, its output is very weak so you will need significant gain to boost it up to line level. Some people also find that an active preamp increases dynamics or that it adds a bit of flavor, especially if it's a tube preamp. Others prefer a simple volume control.
As for amplifier power, you may not even be using 1 watt, depending on how loud you listen and how efficient your speakers are. If your speakers are rated at 90 db/w/m, that means they produce 90 decibels with a 1w input at a distance of 1 meter (39"). Of course, if you're further from the speakers you need more power to produce the same db level at your listening position. For every meter you move back, you need 2x the wattage to maintain the level. You will find that 90db is quite loud and it's probably safe to say that most people don't typically listen at such high levels, although I'm sure some might.
Also, if you double the power output, you don't get twice as much volume, you only get an extra 3db, which is not that much. To hear what a 3db increase sounds like just move 1m (39") closer to your speakers. It takes 10x the wattage to make it sound, subjectively, "twice as loud".
So if you want more volume, you can increase the wattage or you can use more efficient speakers, or some combination of the two. So a low wattage amp used with highly efficient speakers can play louder than a higher wattage amp with lower efficiency speakers, even with the same signal level being input from the source.
I don't know what the input sensitivity is for the ST70 and it probably depends on whether or not it's an original version or one of the currently produced versions. The original was obviously meant to be used with the PAS preamp sold by Dynaco. Some of the newer ones can be ordered with simple volume control built in but then they also sell preamps.
Bottom line, try both passive and active and see what you like best. As with everything audio, some pieces work better together than others but they aren't typically incompatible in the strictest sense.
