Whatever works best with the preamp (allows you to play softly and loudly).
9 responses Add your response
As Shadorne says, you adjust it so that your preamp's volume control has the most range. If at 32dB, you only need to turn your volume 10% to make it loud, then changing to 26dB will allow you to turn the volume to say, 30% to make it loud. You should set it to whatever you find better. You may not need lower gain (although all things being equal, 32dB is a lot for an amp).
Keep in mind that using the higher 32 dB gain setting does not increase the power output of your amp. The max is the max no matter which you choose.
As noted in a previous response, the switch is simply there to give you more flexibility in matching to your preamp. I'd recommend turning your preamp volume knob about half way up and then choose the amp gain setting that gets you closest to your desired average listening level. If the 32 dB setting is way loud, use the lower amp gain. That will allow your preamp volume knob to give you the best volume fine-tuning in it's "sweet spot."
My guess is the higher gain setting is primarily for passive preamp situations.
Generally, with variable gain on power amps, one sets the gain as low as possible for the max volume level one wishes without demanding more than whatis posible from the preamp. This gives the best SN at the speakers.
In your case, use the 26db if that doesn,t cause the preamp settingto be too high for the volume that you wish at the speakers.
I can think of no technical reason that the gain setting would tie to dynamics as you describe unless you are just horridly mismatched.
When you look at an amp's specs, you'll see a sensitivity value. For example, my amp needs 1.5 volts at the input jack to produce full power output of 150 watts per channel. While my amp is not gain switchable, if it were and I changed it to where 0.75 volts now gave the full 150 watts, I'd still have the same power but I'd be running with the volume knob on my preamp at a much lower setting.
The catch is that increase amp sensitivity is also amplifying the preamp and source background noise as well as the signal. If your higher amp sensitivity setting ended up elevating your noise floor, you could actually end up with less dynamic range as the quiet passages would end up degraded by the poor signal noise ratio.
People also have interesting psychological expectations regarding the position of a volume knob. Some get uncomfortable with the knob in a very high position (say 3 o'clock or higher on a traditional knob) so they acutally back off and end up listening at a slightly lower actual volume. In that case the person ends up inaccurately matching volumes between the two settings and is in reality listening to the high-gain setting at a higher volume. This would give the impression you noted.
Chris, only if your preamp is incapable of driving the amp to full output at the lower gain will dynamics be affected by the lower gain in the power amp. For example, if the gain at 32db settings means that .5 volts at the preamp output will drive the amp to full power, then 2.0 volts will drive the power amp to full power at the lower 26db gain. If your preamp, however, is incapable of producing 2 volts into the power amp, then it will not be driven to full power, hence 'lack of dynamic'. This not a problem, usually and therefore the more the signal is amplified before the power amp the better the SN at the speakers will be, especially with very sensitive speakers.
In other words, use the lowest gain that does not drive the preamp into distortion for the highet volume that you will be using.