How to select preamp gain

daniel in hong kong one of my favorite cities in the whole world right maybe may be my favorite city in the whole world wish i could go there again stupid covet all right where are we daniel yep hong kong favorite city um he writes and he says while a preamp uh has a line gain switch that is selectable from 10 20 or 26 db is there any rule that helps to choose a good line gain value amongst those choices given that my dac output gain is high and my power amp input impedance is also high all right well first off daniel the fact that the impedance is high that's good on your power but it has nothing to do with this we've tried to go through that before impedance all you want to do on impedance you want to make sure that the input of something has at least 10 times higher impedance than the output of something that you're trying to feed to it and that's pretty typical so a preamp usually has about a hundred ohms output impedance which is very low and a power amp has an input impedance of ten thousand ohms twenty thousand thirty thousand hundred thousand ohms and it's just easy for a hundred ohms to drive a thousand ohms or uh well thousands pushing it i wouldn't want to go any lower than ten thousand dollars but anyway you're okay with that the real issue is gain matching so a couple things going on here first off power amplifiers well all amplifiers of any kind but in particular to this point power amplifiers have a limit how much voltage in is going to equal how much voltage out and usually that's about a about one volt one and a half volts maybe any more than that you're going to clip the output of the amplifier right so this is your input sensitivity and we measure that usually in decibels so the average amplifier gain in decibels is about 26 db ours runs a little hotter about 30 db and 30 is easy to calculate so it's it's a voltage gain of 30 is 30. so 1 volt in equals 30 volts out so that that's always an easy one to remember but you don't want to get let's say that your amplifier's input has some is maxed out at one volt which is kind of typical you don't want to get too close to that first off the amp's going to be playing very loudly and depending on the efficiency of your speakers and also we like to stay kind of down here all right we don't want to get up too close to here so the gain switch on your preamplifier is going to be set such that for the typical source your gain when you're playing at i don't want to say loud listening levels but proper listening levels where you're listening with full attention at reasonably loud listening levels proper levels you want your volume control to be about two-thirds the way up on your preamp so if you if your preamp is from say zero to a hundred you wanna be at about 70 60 or 70 somewhere around there okay maybe 50. i don't i don't want to be a whole lot less than about 50. so set your preamp gain so that when this whole mess comes together that's kind of what you get now sometimes in our situations we'll we'll run the preamp hot at about 40 or 50 but that's just because over time i've found that that sounds the best so given those guidelines just see which one sounds best to you but that's kind of how you want to set that up so you match the power amp by terms of loudness within the room and what you're playing if that makes sense okay thanks for the question talk to you later bye [Music] [Laughter] [Music] you

Channel: Paul McGowan, PS Audio

Views: 21,896

Keywords: high end audio, ps audio, paul mcgowan, stereo

Id: nerR-tIVRzE

Length: 4min 41sec (281 seconds)

Published: Tue Apr 26 2022