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Old 13th August 2003, 10:09 PM   #1
wrl is offline wrl  United States
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Default What exactly does a preamp do?

Ok, I know that this makes me sound like a moron, but what is the purpose of a preamp? I have built an active crossover for my ESL's that I tell me non-audio friends is a preamp because it easy to explain that way, but other than volume control... what does a preamp do?


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Wes
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Old 13th August 2003, 10:21 PM   #2
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Default Re: What exactly does a preamp do?

Quote:
Originally posted by wrl
Ok, I know that this makes me sound like a moron, but what is the purpose of a preamp? I have built an active crossover for my ESL's that I tell me non-audio friends is a preamp because it easy to explain that way, but other than volume control... what does a preamp do?
Naaaaah. Morons don't ask questions.

A preamp, at least those of the non-passive variety (passives technically not being preamps in the first place) are intended to provide additional voltage gain of the signal before it gets passed on to the power amplifier.

They're somewhat archaic in a way today seeing as most source components have healthy output voltages and most power amps have healthy input sensitivities (i.e. they don't require a great deal of input voltage to make full power).

Back when typical source components had much lower output levels, preamps were more of a necessity if one wanted to get full power from their amplifiers.

From J. Gordon Holt's Audio Glossary:

preamp, preamplifier A device which provides amplification to raise a low-level signal to line level. The term is usually applied to a line controller which has a built-in preamplifier/RIAA equalizer for a magnetic phono cartridge.

se
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Old 13th August 2003, 10:24 PM   #3
wrl is offline wrl  United States
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Cool, thanks. I suppose this explains why I hadn't had any experience using one since I only got into the hobby recently.
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Old 13th August 2003, 11:01 PM   #4
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Quote:
Originally posted by wrl
Cool, thanks. I suppose this explains why I hadn't had any experience using one since I only got into the hobby recently.


In the broader mass-market, which is dominated by "receivers" which combine all the various functions into one unit (tuner, preamp, power amp, etc.), the term "preamp" just doesn't come up much in conversation.

Oh, and welcome to the hobby!

se
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Old 13th August 2003, 11:14 PM   #5
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another thing i didn't know until i'd researched a bit is that an 'integrated' amplifier is one which incorporates the preamp and amp in one body. i guess these are usually stereo as well - as opposed to monoblock. (that just wouldn't make sense.)

the other function 'preamps' usually contain is input selection. sometimes preamps are also called 'control amps', because they control the signal as opposed to simply amplifying it.

if i'm not mistaken, equalizers / tone controls / signal processors also function at the 'preamp' level, although i guess they normally have their own box.

to the purist, i suppose a straight amplifier has only 3 things connected to it: power in, signal in, and signal out.

is that a fair summary?

/andrew
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Old 13th August 2003, 11:37 PM   #6
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Hi,

Quote:
i guess these are usually stereo as well - as opposed to monoblock. (that just wouldn't make sense.)
Generally, no...still these monoblocks could be useful in some situations.
Admittedly rather rare.

A preamp, as the name suggests is just a stage that elevates the lowish signal level from tuners, tape devices to a level high enough to drive an amp.

Historically it was the logical place to include source selection and volume control, in a way it still is.

Nowadays, CD based sources are well at levels capable of driving amplifiers to full output.

Since we still need to control the listening level we had so-called passive preamps in all their incarnations.
These worked fine in one system but not necessarilly in another.

Moreover the preamp idea is so common that most people feel their system to be incomplete without one.

To me, a preamp in a system with modern sources such as a CDP is best served by a VC followed by a buffer.

The buffer provides for current drive of the cables and provides a nice low Z source for the amp to work with.

Cheers,
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Old 13th August 2003, 11:37 PM   #7
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Quote:
Originally posted by faustian bargin
is that a fair summary?
Yup. You nailed it.

se
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