Need education on amps

[Danster]

Hey guys,
I know almost nothing about amps, and after searching a good while, I cannot find much basic user-level information on the web about amps. Lemme give you an idea about what I don't know, and need to learn about. What is a pre-amp for? Is a pre-amp a part of the amp, or separate, or can be either? (Can it be on board the guitar?). What are different channels for? I think I have figured out what the "head" and the "cabinets" are. I've never paid any attention to amps when I've gone to music stores. The amp I now own is a cheapo practice amp. If you all know of websites that give basic info on amps like I've described above, I'd surely appreciate it if you'd give me a link or two.

Here's one more thing that you guys could tell me. Never having been around professional musicians, I'm ignorant about how you control the amp on stage. I don't see musicians typically walking over to the amp to adjust knobs during songs or inbetween songs, but surely they are not using the same tone throughout a show. Can you control much of the amp settings using foot switches, or how does that work?

Cheers,
Dan

[Bongo Boy]

I found the following site:

http://www.guitarnotes.com

On the home page, see a main heading "Amplification", and under that heading is a link labeled "Amplifier Info". This link provides quite a bit of info re: preamps and power amps, and why you need them, what they do, etc.

Related topics that will help you understand a bit about why these devices are needed include: impedance and impedance matching, and signal levels of common devices around the studio (e.g., microphones and guitar pickups).

Very simply though, anything that produces a relatively low signal level, such as a mic or a pickup, needs to be plugged into a pre-amplifier that "does things" to the signal to make that signal acceptable to power amplifiers. So pre-amps are sold separately for microphones and for guitars, but they are also integrated into guitar amp heads and combo boxes.

Often, the output of those preamps that are provided as part of heads or combos is accessible to the user to send to the input of ANY chosen power amp (or a multitude of other devices)--this will show up as a "Pre Out" jack. On some lower cost equipment this feature is NOT provided.

This is similar to the situation with integrated home stereo equipment, where your front panel allows you to select CD, VCR, DVD, FM, Phono and other music sources. Selecting one of these buttons sends the low-level signal from your CD player, for example, into an on-board pre-amp inside your 'receiver'. The pre-amp output is sent into a power amp inside the receiver chassis, but may also be sent to "Preamp Out" jacks on the back of the unit.

Likewise with home stereo, ALL of these devices may be purchased as separate pieces of equipment--in that case your 'receiver' is separated into 1) a tuner (to receive FM radio broadcast), 2) a stereo preamp, and 3) a stereo power amp.

[EricV]

Hi Danster,

about controlling the amp on stage. There are several ways. Usually, you set the EQ of the amp to a setting where it sounds good. Some players need only one sound, and alter it by turning the volume on their guitar up or down, or they use effects.
Others use amps with multiple channels, so they can switch between i.e. a clean sound and a distortion sound with a foot switch.
Or they use preamps ( i used to use both a Marshall JMP-1 and an ADA MP1 ). Those have a like user presets that you can adjust to give you the sound you need, and you can switch between them with a MIDI board. A MIDI-board also can switch rack effect units ( 19" stuff ).
Also, there are some guys in bigger bands who have their guitar roadie switch the amps for them. ( I am not sure, but I think Kirk Hammett of Metallica is one of them )

About preamps... some basic introduction: a preamp ( pre-amplifier ) has different formats. There are small ones that only boost the signal and do nothing else. Those can be build into the guitar ( Randy Rhoads had a preamp that plugged into the output of the guitar... he used that when he was in Quiet Riot ).
Also, EMG pickups have integrated preamps which boost the signal of the pickup.

Also, preamps are part of every guitar amp. They "shape" the sound. The EQ usually is part of the preamp. So you plug in your guitar, the preamp "shapes" the sound, then the signal gets into the poweramp-section, which amplifies the signal and sends it to the speaker / cabinet.

You can also purchase separate preamps and poweramps, usually those are meant to be put into racks. The signal often goes from the output of the preamps to the effect units, and from there to the poweramp.
The same can be done on regular "all in one" guitar amps... many of them have "effect loops". An effect loop usually has a send and a return. The "send" sends the output signal of the preamp into any effects you connect to it, and then, from the output of the effcts, you go back to the "return", which basically is the input of the poweramp-section.
So, if the amp has a loop, you can split up the amp into preamp and poweramp, and you can put effects between those.
Hope this helps
Eric

[Danster]

I found the following site:

http://www.guitarnotes.com

On the home page, see a main heading "Amplification", and under that heading is a link labeled "Amplifier Info". This link provides quite a bit of info re: preamps and power amps, and why you need them, what they do, etc.

Hey Bongo, thanks for your reply. I waded through some of the stuff in those links, and I s'pose I must be looking in the wrong places, cuz I am yet to find any basic info, but you and Eric have helped a lot in what you have posted here. Gracias!

[Danster]

Some players need only one sound, and alter it by turning the volume on their guitar up or down, or they use effects.
Dang, it seems a shame to have an amp loaded with effects and not use them.
About preamps...
Thanks. The stuff you and Bongo Boy posted helped me quite a bit.