Pre/Post Amp Clarification

[smbarrett3]

At the risk of sounding very dumb, I am looking for a bit of education here. My basic understanding of a preamp / power amp configuration is that the preamp attenuates the signal to a portion of the power amp's full capacity. But in actuality, I don't know how a pre-amp is any different from an integrated amp.

My integrated has pre-amp outputs. I understand I can send out a signal to a dedicated power amp. But what exactly is this sending?

If I were to buy/build a low power tube amp, could I use this as a preamp and connect it to my integrated amp for additional amplification (i.e., acting as a power amp)? The reason why I would want to try is to hear the different character of the amplification, tube v. Class A v. Class D.

If my understanding of electrical engineering isn't totally misguided, volume controls are potentiometers which controls how much energy is being dumped a resistor. So is a full blast integrated amplifier essentially a power amp?

 

[gadget73]

A preamp can actually boost the signal. It depends what the source is, and how much drive the amplifier requires. CD players typically have enough output to drive most amplifiers. A phono cartridge does not, so it gets boosted quite a bit. they also don't put out any sort of current. Speakers are rated in wattage, which is voltage * current. A preamp can give a couple volts of output, but at very low current which results in very low wattage. A power amp boosts both so you can drive speakers.

An integrated amp is a preamp + power amp in one box. The pre-amp output would be a low power signal that would drive a power amplifier to feed the speakers. Output is somewhere about 1 volt at essentially no wattage. It would probably drive a set of headphones, but thats about it. It would also be OK to drive a separate power amp.

 

[g..v]

A pre amp provides gain to drive a power amp. The volume control is limiting the gain within its range once past the first stage or stages. Many power amps will operate to full output with 1/2 volt input. Some will require more.

If you tried to use a phonograph with an output measured in millivolts you would never drive a power amp to produce enough to drive most speakers.

Integrated amps have a preamp built in.

A low power power amp will still need a preamp.

Your integrated amp with "pre" outputs can drive you suggested power amp but you're duplicating the circuitry for little reason.

Preamps provide voltage gain. Power amps deliver power, or watts of output.

Volume controls definitely do not dump energy into a resistor as their mode of operation.

The integrated amp is a combination of both pre and power amps.

 

[smbarrett3]

Thanks for the info. So is there a difference between a tube pre-amp and a low wattage tube amp?

And would I be able to use a tube pre-amp and send it to my integrated amp to use its power to boost?

 

[g..v]

"So is there a difference between a tube pre-amp and a low wattage tube amp?"

The first provides voltage gain, the latter power gain.

Yes you could.

 

[JoeESP9]

Yes there is a difference. One is made to drive a power amp the other is made to drive speakers.

If your integrated amplifier has pre out power in jacks, yes. You can use just the power amp section via the power in jacks. Otherwise no.

 

[Blue Shadow]

Let's start with different levels of signal.

Tape head is a very low level and not used much at all as most tape machines have amplifiers in there but some old preamps/integrated amps/receivers have tape head inputs.

MC phonos have very low, low and high level outputs as designed by the manufacturer. Very low is less than 0.1mV, low is 0.2-1.5mV and high level is 2.0mV and up. These are amplified by different devices whether that be a moving coil amplifier to add 20-35dB for input of low output units into phono inputs, a phono preamp with adjustable gain, 40-70dB to take a cartridge signal to line level avoiding the phono input (these units have phono EQ built in)

Then there is line level, the level for CD, Tape, Tuner, DAC, MiniDisc and all sorts of things including AUX. This level is 1-2Volts.

A power amp needs 0.5-1.5V to achieve FULL output so the preamp will be an attenuator of line level signals for input to power amps but the preamp will have amplification for the tape head, LOMC, HOMC and phono inputs. These will also have equalization in them to allow them to conform to industry standard EQ curves.

The next thing you need to look at is the impedance of the LOAD that the amp, preamp, phono amp and such sees. The amplifier wants to see a 2-16Ω load roughly, more commonly 4-8Ω. Most amps don't want to see a 25,000Ω load...but this what an amp presents to the preamp, roughly. Lots more on this and with more knowledge you can see that one is as stated for voltage gain (all the preamps) and power (wattage) gains are for the power amp.

In many cases any preamp will drive any amplifier but there is more to it than that. We'll talk about that next time when you are comfortable with the amp/preamp/integrated amp information.

 

[SuperjazzyJa]

Basically, like others have said, the preamp is usually a single gain stage. There are also passive preamps that are nothing more than control centers for your system. Either way, the preamp is your control center. The source selector, volume control, tone controls and any other so called "features" reside here and external "enhancers" like equalizers, dynamic range expanders, etc are connected through the preamp's tape loop. Whether you're listening to a transistor radio, a half million dollar high end system or anything in between, the basic signal path is the same: source, preamp, power amp, speakers.