Why do I need a preamp?
Posted 14th May 2015 at 07:22 AM by cspirou
One of the things that confused me a bit when I started this hobby was the distinction between a preamp and an amp. Looking up info on a preamp usually was met with a definition that a preamp controls volume and switches inputs, which never made sense to me because my amp always had volume control and multiple inputs.
Well it turns out that what I (and most people) considered an amp was actually an integrated amp. It never really made that much sense to me to separate the functions in a separate chassis and I would roll my eyes seeing preamps worth at least as much as the price of a good amp. Discussions about the different sound of a preamp are a bit weird for me too. While I don't doubt that different preamps sound different, it seems like people are just separating components to do some mix and matching.
However after being in this hobby for a bit of time I have discovered some solid reasons to have a separate preamp(besides wanting to separate everything) and why someone would want one in their setup. I am making this post for people that might also be wondering why they would want to add a preamp to their setup.
*If you are using monoblocs - I guess you could have integrated volume in each monobloc amp which would basically double as a sort of balance control. But I assume most people don't want to go through that process.
*if you are using powered active speakers - multiply your issues with monoblocs by 2-4. Speakers with an active crossover have an amp per driver and any volume control must be done at the level of the input signal. Maybe if you plug in directly to a computer or TV and only use digital volume control, but a preamp lets you use other sources.
*if your amp requires XLR-Most people typically have RCA outputs on their sources but could have an amp that has XLR inputs. A separate preamp that outputs XLR would be a good way to make a balanced signal from an RCA input.
*If you are doing DSP processing-This section should probably go with the active monitors, however many DSP setups are separate like miniDSP. DSP projects typically use multiple amplifiers and you need to find a way to control the volume of all those amps.
*multiple channels and mixing amps-A integrated amp for 5.1 or 7.1 channels will usually have the same power for each channel. Which is fine but you might have some huge front speakers that need a lot of power and some small satellite speakers that don't need as much. a separate preamp allows you to mix and match. Your front channels can use a nice high power amp while your satellite channels can use something lower powered. Or you can experiment with tube amps on the main speakers and use Class D for the subwoofer.
*In extremely rare cases where your integrated amp has an input impedance that is usually low and the output impedance of your sources is high and you absolutely must use this amp. Then you would need an active preamp that can match the impedance of the source and the amp.
TLDR-Basically if you have something that gets more complicated than two passive speakers and a stereo amp, a separate preamp becomes a necessity.
Well it turns out that what I (and most people) considered an amp was actually an integrated amp. It never really made that much sense to me to separate the functions in a separate chassis and I would roll my eyes seeing preamps worth at least as much as the price of a good amp. Discussions about the different sound of a preamp are a bit weird for me too. While I don't doubt that different preamps sound different, it seems like people are just separating components to do some mix and matching.
However after being in this hobby for a bit of time I have discovered some solid reasons to have a separate preamp(besides wanting to separate everything) and why someone would want one in their setup. I am making this post for people that might also be wondering why they would want to add a preamp to their setup.
*If you are using monoblocs - I guess you could have integrated volume in each monobloc amp which would basically double as a sort of balance control. But I assume most people don't want to go through that process.
*if you are using powered active speakers - multiply your issues with monoblocs by 2-4. Speakers with an active crossover have an amp per driver and any volume control must be done at the level of the input signal. Maybe if you plug in directly to a computer or TV and only use digital volume control, but a preamp lets you use other sources.
*if your amp requires XLR-Most people typically have RCA outputs on their sources but could have an amp that has XLR inputs. A separate preamp that outputs XLR would be a good way to make a balanced signal from an RCA input.
*If you are doing DSP processing-This section should probably go with the active monitors, however many DSP setups are separate like miniDSP. DSP projects typically use multiple amplifiers and you need to find a way to control the volume of all those amps.
*multiple channels and mixing amps-A integrated amp for 5.1 or 7.1 channels will usually have the same power for each channel. Which is fine but you might have some huge front speakers that need a lot of power and some small satellite speakers that don't need as much. a separate preamp allows you to mix and match. Your front channels can use a nice high power amp while your satellite channels can use something lower powered. Or you can experiment with tube amps on the main speakers and use Class D for the subwoofer.
*In extremely rare cases where your integrated amp has an input impedance that is usually low and the output impedance of your sources is high and you absolutely must use this amp. Then you would need an active preamp that can match the impedance of the source and the amp.
TLDR-Basically if you have something that gets more complicated than two passive speakers and a stereo amp, a separate preamp becomes a necessity.
Total Comments 1
Comments
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A preamp makes more sense in an historical perspective: consider LPs and the need for a phono preamplifier. Yes you can do it all in one chassis, but do you really want your phono preamp circuit running off the same power supply as your power amp, in proximity to high currents and noise of that circuit?
That and physically all the components for the phono stage, line stage, tone controls, and headphone amp found in a high end preamp literally required so much space that a separate chassis was needed.
Today with microelectronics, remote volume controls, and most people choosing to have a phono preamp or headphone amplifier external to their preamp, the need is simply not the same. The remaining components: line stage, volume control, input selectors ... can easily be put in together with the power amplifier. Even the line stage isn't really needed, since its purpose was to buffer the output of the volume control and drive the interconnects ... just increase the gain in the amplifier stage to compensate.
I think it was Wes Phillips at Stereophile who many years ago made the most eloquent case for why you would want to invest in a really nice preamp. Basically he said, look, this is the bit you physically interact with. It's also the bit that all your audio signals pass through. Get a really nice preamp and you get all the functionality (phono, headphone amp, mute or balance) in an elegant, uncluttered chassis with the transparency to be able to truly hear all the other components in the system.
I never did get around to following his advice since I'm forever putzing around with phono stages and headphone amps, but I've always thought it was a wonderful goal.Posted 16th May 2015 at 12:48 AM by rjm
Updated 16th May 2015 at 12:51 AM by rjm
