Preamp is an amplifier too, right???

Tube preamps typically have a far higher maximum output level than the mass majority of SS designs. As such, the only thing that i can think of is that the tonal balance has shifted due to different power transfer / loading conditions and you seem to like those changes.

Other than that, a preamplifier is nothing more than an amplifier designed to work with a lower input signal and a lower output signal. Think of a preamp as an "intermediary gain stage". It can take a weak signal and boost it enough to drive the next gain stage or it can regulate a signal that may otherwise overdrive the next gain stage through attenuation. Pre-amplifiers got their name as they are nothing more than an amplifier stage prior to the main amplification stages, hence "pre" ( before or prior to ) amplifier. As such, most do not consider "passive units" to be pre-amps as they have no amplification stages. However, one "could" say that they go "before the amp", so in effect, it is still a "pre" amp.

Other than that, there are preamps with enough voltage swing and a low enough output impedance that they can drive speakers. They will typically sound like tin cans vibrating when doing so, but you might be surprised what comes out of the speakers if you were to try doing this. This is NOT a suggestion to try driving the speakers via a preamp even though i have. For the record, i did this as a "yout" ( pronounced "youth" ) when i didn't know better. Sean
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Preamps do not increase power, only voltage. A preamp drives a load of thousands of ohms, which is far larger than its own output impedance, and that, along with a smaller power supply, decreases the power produced and transferred. Instead, it increases the voltage, so it is a small signal (voltage) amplifier not a "power" amplifier. A power amp drives loads of less than 10 ohms, which require a lot of current at a given voltage - so there is substantial power transferred. That's the basic difference - one amplifies voltage and the other power (voltage and current).

Funny, I never thought of it until reading this post, but I guess that is why it is called a (pre)amplifier! I like days when I a lightbulb goes on in my head (Lord knows there are not enough of them!) Good Listening!! :-)

You could always simply be choosing unequal volume settings between the two preamps, maybe unconsciously, based on their sounds. But it could be that the SS preamp is just doing a better job of driving your interconnects and amp inputs, which would presumably be due to its lower output impedance, not higher or lower gain (which is ultimately limited by where you set the volume control anyway, usually well below the available maximum).

In other words, even if you were to volume-equalize the two preamps at 1,000 Hz (the ear's most sensitive range), the tube preamp might suffer from an impedance mismatch - relatively speaking - driving its load as compared to the SS preamp, which would tend to slightly roll-off its response in the 'power range' of frequencies below the midrange which give music its "balls", as you say, causing it to sound a bit more lightly-balanced.

Another possibility (not mutually exclusive) is that the tube pre is suffering from a bit of dynamic compression, again relative to the SS pre, which is limiting its amplitude response on musical peaks and making it sound 'quieter' overall (in the sense of being less loud, not less noisy). Time for new preamp tubes, maybe? But even if neither of these scenarios is the case, SS preamps will commonly have somewhat firmer low bass than tubed models, and also better S/N ratios, and I suppose the results could sound like "more balls" to some listeners, even if volumes were broadly equal.

Seems strange no one mentioned that in the days of vinyl only, the preamp had two basic and indispensable functions: to amplify the very small signal coming from a cartridge and to equalize it to the RIAA curve. Preamps seemed more of a "real" component to me in those days than the line stages today that are, more or less, required with higher output sources such as CD, DVD and SACD. I kind of liked the term Yamaha used years ago of a "control amplifier" since it is where the other components are plugged into and where you have the controls.