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BATCH's picture
Dallas, TX
Jan 2005
6 years ago

So what exactly is "pwr amp in" "preamp out"? Is it a Fx loop? What's the difference?

Sorry I'm lazy...

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geocox's picture
Seattle
Dec 2004
8 years ago

yes, it's the effects loop.

guitar -> preamp [preamp out ... poweramp in] -> power amp -> speaker(s)

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jimmythescumbag's picture
Florida
Jan 2006
8 years ago

Pre-amp out: outputs your guitar signal after the preamp, but before the power amp. You need to input this into a power amp in order to power a speaker cabinet, unless you are using it to go into a DI box for a gig or recording. If you want to use the tone of a particular amp, you would just use another power amp, and go into the "power amp in"...like this:
gtr-->preamp (preamp out to)-->power amp (or power amp in on another amp to bypass the 2nd amp's preamp)

Power amp in: self explanatory...this is where the preamp out of your amp normally goes, before it is output at the "speaker cabinet outputs" into the speaker cabinet(s). Basically, if you like the sound of an external or rackmount preamp over the one your amp has, hook it up like this:
gtr-->preamp-->(pwr amp in) 2nd amp-->speakrs

FX loop: this is basically an input/output. It allows you to run FX through the in/out (or retun/send respectively) so that your original signal is not altered, but the FX are still audible when engaged. Like this:
gtr-->amp-->(from FX loop send) FX chain-->(into FX loop return)

You can also use the return as a regular input, say if you were using something like a POD or GT-8 or whatnot. Like...
gtr-->POD/GT-8-->(FX loop Return)

Hope this helped some... :)

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pop_n_fresh's picture
Hell
Nov 2005
6 years ago

Originally posted by jimmythescumbag
Pre-amp out: outputs your guitar signal after the preamp, but before the power amp. You need to input this into a power amp in order to power a speaker cabinet, unless you are using it to go into a DI box for a gig or recording. If you want to use the tone of a particular amp, you would just use another power amp, and go into the "power amp in"...like this:
gtr-->preamp (preamp out to)-->power amp (or power amp in on another amp to bypass the 2nd amp's preamp)

Power amp in: self explanatory...this is where the preamp out of your amp normally goes, before it is output at the "speaker cabinet outputs" into the speaker cabinet(s). Basically, if you like the sound of an external or rackmount preamp over the one your amp has, hook it up like this:
gtr-->preamp-->(pwr amp in) 2nd amp-->speakrs

FX loop: this is basically an input/output. It allows you to run FX through the in/out (or retun/send respectively) so that your original signal is not altered, but the FX are still audible when engaged. Like this:
gtr-->amp-->(from FX loop send) FX chain-->(into FX loop return)

You can also use the return as a regular input, say if you were using something like a POD or GT-8 or whatnot. Like...
gtr-->POD/GT-8-->(FX loop Return)

Hope this helped some... :)

Yeah essentially you're right but they are the same thing. An FX loop runs between the pre and power amp, if you wanted the pre of one head and the power of another you would connect them via the FX loop ins and outs.

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BATCH's picture
Dallas, TX
Jan 2005
6 years ago

Thank you so much for clarifying that for me... the only reason i ask is because my roomate has a peavey bandit 112 and it has both fx loop on the front AND "preamp out" power amp in" jacks in the back.

So if he uses a POD, it's better to go thru the power amp in, than directly into the amp?

so guitar>pod>power amp in ?

What is series and parallel fx loops?

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berarduur's picture
Losser, of all places........
Apr 2004
5 months ago

There are numbers and numbers of FX loops

At first, the signal of a preamp is too hot for any stompbox / rackmount to handle. Still, it is well balanced and buffered. So some attenuation is done in an FX loop. Then again, the outgoing signal is too weak to be fed to a poweramp, thus some signal boosting is done after the return

On some amps this is variable with send and return controls.

So this is the difference between FX loop and preamp out, poweramp in.

Sometimes a patch cable between send and return can result in interesting things (as the boosting done in the last stage is louder then the attenuation).

A series FX loop is that the FX loop signal is in series with the preamp out signal (so it will come after the preamp out); a parallel FX loop is a loop in which the FX loop is put parallel besides no FX loop. With a potmeter you can set the mix level (50% clean, 50% FX loop for example).

Parallel FX loops have one downside: phase issues. A lot of pedals (most chrous pedals, tremolo's, phase shifters and delay pedals) will invert the phase of the signal. You normally don't hear a difference as a phase invertion is not hearable. BUT if you mix this with a normal phase signal (as in a parallel FX loop) you get a sound that is OR high in bass / treble and low on mids or vice versa.

This can be fixed by a phase inverter.

Then there are some other FX loops:
- Pre-preamp FX loops (as can be found in many old Peavey heads); this FX loop is placed before the preamp but after some buffer. It is the same as plugging your guitar direct in with the advantage of a buffer. Shame to say is that the buffer is not the best one around :)

- Preamp FX loops (as can be found in a lot of bass amps); this FX loop is placed in the preamp right after the EQ section but brefore any additional gain stages. Has to my ears no advantages above a normal FX loop. Is 99% a parallel FX loop

- Post phase-inverter FX loops; experimental and can only be used in HiFi for Buffer testing and fine tuning

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toma's picture
Cambridge/York, UK
May 2006
2 years ago

why are there two amplification sections to an amp?

what is the advantage of being able to place fx after pre amp amplification, rather than before?

x

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berarduur's picture
Losser, of all places........
Apr 2004
5 months ago

Originally posted by toma
why are there two amplification sections to an amp?

x

Well, just because :)

You can look at it as one whole unit, or as two indicidual units, or as 4 to 9 individual units...... but as two units:
- The preamp shapes the signal. It makes the signal "ready" to be amplified and determines "THE" sound
- The poweramp simply amplifies.

This is very crude as there is more to it then this but I like to keep simple

Originally posted by toma

what is the advantage of being able to place fx after pre amp amplification, rather than before?

x

Because some FX just sounds way better placed in the FX loop compared to after it. Some pedals just like the balanced, slight amplified and overdriven sound more then the weak sound of a pickup; some don't

Tijd zat..., toch?

Quote:

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BATCH's picture
Dallas, TX
Jan 2005
6 years ago

So i tried plugging in my roomate's POD into the pwr amp in.

None of the controls on the amp worked when I had it plugged in this way. I had to control the volume with the POD's "output level" Is there some way to have volume control on the amplifier itself, (not the preamp).

Thanks......

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berarduur's picture
Losser, of all places........
Apr 2004
5 months ago

Volume controls and more are in the preamp stage; poweramp has no controls

So when plugging a POD into the PWRamp in you bypass the preamp thus bypassing the controls.

Tijd zat..., toch?

Quote:

"Berarduur, the self sufficient guitar maan"
"He's Barardurr; he just does"

Technophobia; Analog Audio Solutions; for all your custom builds and mods.
http://technophobia.co.nr/