[lowers head in shame] could some one explain what a pre-amp is?

[lucien]

okay - this is going to sound terrible, especially from someone who gets off on high end audio stuff, but there's something that never quite added up for me:

what the hell is a pre-amp for?

would someone mind explaining what they do, whether they're necessary, what advantages they offer, and why marc levinson ones cost so much???

thanks.

 

[RGA]

I can't comment on Mark Levinson's pricing...other than the rich need to buy something with all that money otherwise they might discover that money isn't everything in life...some of us figured that out at 20...some never do. Where is Socrates when you need him?

A preamp(and this is going to be an oversimplification) basicall controls what you want to do with the sound coming from your source(CD or LP etc). It controls volume(it does not provide power it just tells the power amp how loud you want it). It also controls BASS and Treble (if they ar on the preamp). Ideally, a preamp should take the signal from the source and send the information(volume level preferred) to the power amp with as little distortion as possible. Obviously some do a better job at this than others, but spending obscene amounts on one is silly....they should impart NO SOUND to the original signal...and many around the 1k mark...at least on spec...are as good as ones at 20 times that price.

 

[jude]

Quote:

Originally posted by RGA Obviously some do a better job at this than others, but spending obscene amounts on one is silly....they should impart NO SOUND to the original signal...and many around the 1k mark...at least on spec...are as good as ones at 20 times that price.

I find the preamplifier to be one of the most important parts of the chain as it comes right after the source components and has the rather difficult charge of doing just what RGA mentioned -- taking multiple line level inputs from your source components, and providing gain for them as the volume is turned up and feeding it to the amplifier which responds in kind. And, as RGA suggests, a preamp is generally expected to do this without imparting its own color to the signal, which can be one of the most challenging responsibilities for any component in the chain. After the digital source component, the preamplifier is sometimes the most complex piece of gear in the chain.

lucien, a "receiver" is essentially a tuner + preamplifier + amplifier all in one chassis. An integrated amplifier is a preamplifier + amplifier in one chassis. And with integrated amps, most audiophile types will be just as concerned with the preamplifier part's performance as the amplifier part's.

 

[lucien]

thanks, this is starting to make some sense...

so if a receiver has a pre-amp in it, why bypass it if it is to make no change whatsoever to the sound? i'm having trouble figuring out why it takes an expensive part to tell the amp what volume it should use.

that bit doesn't sound right either. surely the amp takes a line level source and amplifies it according to its own controls, not those of a separate component?

and how can it control bass and treble without changing the source signal?

 

[bootman]

Quote:

[lowers head in shame] could some one explain what a pre-amp is?

No shame here.

I'm sure that there are other members/guests that have asked themselves the same question but have not had the courage to post it. Hey, thats why we are here!

As far as answering the question, Jude and RGA have pretty much covered it.

 

[joelongwood]

Quote:

so if a receiver has a pre-amp in it, why bypass it if it is to make no change whatsoever to the sound?

The reason you might want to bypass the pre-amp is because, even though the goal is to "make no change whatsoever to the sound," that is not often attained. Every component imparts some coloration to the sound. By eliminating one component in the chain, the signal remains that much purer. But if you bypass it, you lose the ability to control volume, bass, treble, etc.
Quote:

surely the amp takes a line level source and amplifies it according to its own controls, not those of a separate component?

An amp does take a line level source and amplifies it further to drive the speakers, but power amps do not have their own controls. That job is left to the pre-amp.
Hope this helps.

 

[dhwilkin]

Quote:

lucien said... so if a receiver has a pre-amp in it, why bypass it if it is to make no change whatsoever to the sound? i'm having trouble figuring out why it takes an expensive part to tell the amp what volume it should use.

You would bypass the receiver's pre-amp for exactly the reason that jude mentioned. Namely, not changing the signal is actually quite difficult. And since a receiver is expected to do so many different jobs, none of them will be done as well a single component that only has one job. This is why so many people have separate amps and pre-amps instead of receivers.

 

[DanG]

I have a Creek 5250 integrated amp that I got to drive my Axiom Millenia M3Ti speakers. When I first tried just to use the 5250 as pre-amp and power amp, it sounded very good. I then got the crazy idea to use my headphone amp, the Wheatfield HA-1, as my pre-amp, thereby bypassing the pre-amp in my 5250. The sound was far better.

One way to think about it is this: an active pre-amp provides, usually, no more than 500 mW of power at output. This, in fact, is the amount of gain that most headphone amps provide! However, loudspeakers need more power than 500 mW, and so a power amp in a way gives the "ten fingers" to the signal so that it can drive a loudspeaker. While many people think a pre-amplifier should be the part where it's easiest to pass on the signal untainted, I think it is in fact the opposite way around. Providing a variable-level signal with so little distortion that amplifying it 70-200 times will provide a clear signal is very difficult. A power amp, on the other hand, basically just needs a positive feedback loop (okay, extreme oversimplification, but you get the idea). That's why many people think the pre-amp has more influence on sound than the power amp.

 

[thomas]

I really don't see the point of a preamp, unless you need the voltage gain for a turntable.

All modern CD players have line level outputs, which do not need any further amplification. Adding an extra gain stage can only add distortion, maybe this distortion is plesent sounding, but it certainly isn't more accurate.

All power amplifiers should have a very high input impedance, which means no matter how powerful the preamp is, it doesn't matter because none of it will go to the amp.

Unless you need the gain for a phono stage, i can't see how a preamp can be better than a passive volume control/stepped attenuator and a switchbox.


And BTW, a preamp is not more complex than a poweramp, its just a simple opamp / tube equivatent with a DC blocking capcitor. It does not need to source any current, so the design is very simple compared with a powerful power amp.

 

[morphsci]

Quote:

Originally posted by thomas I really don't see the point of a preamp, unless you need the voltage gain for a turntable. All modern CD players have line level outputs, which do not need any further amplification. Adding an extra gain stage can only add distortion, maybe this distortion is plesent sounding, but it certainly isn't more accurate. All power amplifiers should have a very high input impedance, which means no matter how powerful the preamp is, it doesn't matter because none of it will go to the amp. Unless you need the gain for a phono stage, i can't see how a preamp can be better than a passive volume control/stepped attenuator and a switchbox. And BTW, a preamp is not more complex than a poweramp, its just a simple opamp / tube equivatent with a DC blocking capcitor. It does not need to source any current, so the design is very simple compared with a powerful power amp.

Very true. In fact in many cases line-level preamps are really misnamed because they are nothing more than switchboxes with a nice volume control. A preamp can also provide some ergonomic benefits such as remote control or zone switching capabilities. Lastly some preamps can be used for "matching" source outputs and amp inputs, especially on some of the esoteric (read damn expensive) power amps.

 

[lucien]

ahhh....

that makes more sense, guys. thanks. i had always figured that the amp was the one controlling the volume, not that its amplification rate was constant, and that the source level was variable.

thanks for your information. and your speed. cripes... post a message, get a response in 20 mins, then go to bed and see pages of explanation in the morning. great fun.

thanks,
lucien

 

[squirt]

licien, till a month ago i didn't know what the preamp was for too...you may find this book of interest. it will answer many of the questions concerning just about anything audio.

here

ps. you can get the same book a bit cheaper at Amazon.com

 

[jaskin]

I just received that book a few days ago. Haven't really had the time to read it yet. It's quite thick and very concise from the browsing I'm been doing.
BTW how about let's say you buy a integrated amp first then later you upgrade to a power amp. Could you use the Integrated amp as a Preamp? Also could you use both amps to bi-amp or bi-wire the speakers.

Thanks
Jason

 

[DanG]

Most integrated amplifiers allow you to use either the pre-amp or power amp stage alone. However, you could not bi-amp if you have one integrated amp and one power amp. A power amp needs a variable input signal, which means it needs a pre-amp or a CD player/DAC that can send a variable output signal. If you use the pre-amp stage from your integrated amp with your power amp, you won't be able to use the power amp part of the integrated amp (as far as I know).

One warning, though -- I've found that the pre-amp stage of my Creek 5250 is far inferior to my Wheatfield HA-1's preamp stage. It may be a better bet to get a good pre-amp to use with the integrated amp's power amp rather than to get a good power amp to use with the integrated amp's preamp. Unless, of course, you just need more power for your speakers.

 

[DanG]

Oh, another thing. If you want to bi-wire speakers, you only need one amp.