It is very rare for an amp to have insufficient gain to reach full volume even with a very quiet bass. The only way you'll get a 35W bass amp to be heard over a drummer is by sticking the amp in the corner of the room for maximum bass reinforcement, cut back your lows, add midrange, and give the drummer hotrods or very light sticks.
Gain and volume (or more accurately Sound Pressure Level) are two very different things. It works like this:
Movement of strings due to plucking generate peak voltage of, say, 1V in the pickups. This goes to the preamp part of the amp which adds, say, 5x gain, with the knobs at 12 o'clock. Thus the voltage is now 5V. This goes to the power amp section which adds gain of say, another 5x, with the knobs at 12 o'clock. The voltage is now 25V. This power amp is driving an 8 ohm load. 25V into 8 ohms equals (25×25)/8=78W.
Now, say this amp has a maximum output of 100W. This means its maximum voltage output is 28V. Let's say that if you turn the preamp gain to max you get 10x gain. Let's say that if you turn the power amp gain to max you get 10x gain. This means that the amplifier has a maximum gain of 100x. So if you put your 1V signal in the amp will try to put 100V out - BUT IT CAN'T because the maximum voltage output is only 28V.
If you put a preamp or booster in front of the amp you might be able to put 10V into the preamp but you still won't be able to get more than 28V out of the power amp.
If an amp is not loud enough, no amount of louder effects pedals, outboard preamps, pickups, will make it louder.
There is one thing that will make it louder and that is more sensitive speakers, or simply MORE speakers! The more sensitive the speakers the more dB SPL out you will get for the voltage in. So if you were to plug the power amp output of your little 35W combo into a very large efficient speaker cab or two (like a BFM DR280 on top of a Titan 48) then you would actually get enough volume to easily keep up with a drummer. But you wouldn't want to have to move that…
This is made worse by the habit that many manufacturers have of mis-labelling the controls on amplifiers.
First let's deal with the worst culprits. It seems to be a commonly held view among certain companies that in selling to musicians, they are ipso facto selling to idiots who are easily impressed by shiny objects and flashing lights, and to whom they can pretty much spin any nonsense they wish. This leads to products on which perfectly normal Signal Level and EQ controls have been given stupid, subjective names like “bite”, “heat”, “balls” etc. Does anyone really find such descriptions useful? I doubt it. Personally, I just find them embarassing, and I'm sure I'm not the only one who immediately ignores any product with such twaddle printed on its panel.
However, even among those companies who avoid such inanities, there is still a common practice of mis-labelling going on, and one that leads to endless confusion among non-technically minded users. I'm talking about all those amps (including well-respected, high-end products) that have an input level control which, bizarrely, is labelled “Gain”, and may well be accompanied a bit further down the panel by another knob marked “Master Volume”, “Master Gain” or “Output Level”. In nearly every case, such labels are wrong!
And let's not forget that old favourite, “Volume Control”. We're all used to saying that, aren't we? Yet even that is a piece of 'creative' labelling - a hangover from the days of domestic wireless sets.
In a typical instrument amp, the first “Volume Control” you find is simply a pot placed in the signal path - just like the one we find in a passive guitar or bass, between the pickups and the jack socket. All it does is act as a potential divider: a variable resistance that bleeds some of the signal away to earth and allows the rest through to the next amplifying stage. Turn it up full, and all (or nearly all) of the signal gets through. Like a water tap, it's a purely passive device. It can't give out more than is being fed in. In some amps this first pot is positioned directly after the jack input itself, but more commonly these days it is placed after an initial amplifying or buffer stage. Either way, the effect is the same.
Likewise, the “Master Volume” or “Output Level” control is another passive pot, placed at the point where the signal leaves the pre-amp/EQ circuitry and is being fed to the input of the Power Amp.
What it doesn't do, in either position, is alter the GAIN of the amplifying stage of which it is part …but that doesn't stop some manufacturers calling it a “Gain” control.
Confused? I'm not surprised!
So, just for the record: A true Gain control works by modifying the operating conditions of an amplifying device (varying a DC control voltage on an Op-Amp, for example) and in so doing actually determines how much gain that device can apply to whatever signal it is being fed. Genuine Gain controls are usually only found on professional studio equipment, mixing desks and so on. They are not used alone, or instead of passive pots. Both are used together, as they have different roles to perform. They're part of the variety of control options that make such equipment flexible enough to accept and process signals from the widest possible range of sources, and do it efficiently, with the best possible signal-to-noise ratio.
