Setting up Amps live for Guitar Processors

I've recently dug out one of the posts I had made on gigpad(dot)com forum somewhere in 2004. The post is now buried somewhere amongst thousands of other posts and hence, I have reproduced it here in case it may benefit someone else who is struggling to find the real sound that they want or tweak around with their sound settings.
The patch (i.e. sound setting on guitar processors) setting on a processor will never sound the same when played through other amps because the processor have their own preamps set to a certain values (eg, bass, treble, EQs etc).

To move further on, let us classify amplifiers into two types: pre & power which may be combined or separated as separate power amp, separate pre-amp or pre & power combined together as a combo. Most of the guitar amplifiers that we use are of the last kind (combo) which has both the pre & power amp combined.

Now, when you connect the processor to the combo, the preamp setting of the processor will not sound the same because the sound will be coloured by the preamp setting of the combo. I think this is the main reason people with awesome processors/amp sims connect directly to the PA System to reproduce the sound that they have created at home/studio as close as possible. Here, since there are no preamp section of the amplifier to go through, the sound will be very close to what you have made. Only a few minor adjustment at the mixing desk will get you closer.

Based on what I have read, tried some from Barry Pearce's Manual, I will try to give a few suggestions. I hope this will be useful for others too.

TERMINOLOGY: Let us get familiar with the amps terminology of most combos (guitar amplifier with both preamp & poweramp) first so that there is no confusion.
1. Preamp Input: Guitar In/Input
2. Preamp Output: Send
3. Poweramp Input: Return/Main In/CD Input (For smaller amps like Marshall 15W, 30W etc, I believe this is the poweramp input as it bypass the preamp section)
4. Poweramp Output: Speakers.

Now, we will look at the different connection options available.

1. PROCESSOR IN FRONT (Mono/Stereo) - This is the simplest of connections. Just connect from your processor main output to the amplifier. This set up works well for keyboard amps or studio power amps which goes into guitar cabs.
PROS: Simple and you can use the preamp of your amplifier to modify your tone.
CONS: You cannot remove the preamp colouration of your sound (guitar amplifier), hence it will be difficult to reproduce the same sound if using different amps.

2. EFFECTS RETURN: Instead of connecting the main output of your processor to your amp main input, connect the processor's output to the RETURN socket of your amp. (this should be same as the CD IN of the smaller amps). By doing this, we are effectively bypassing the preamp section of the guitar amp. This will remove the colouration of the processor's patch settings.
PROS: Uncoloured sound from your guitar, simple. The patch you set at home will be as closely replicated as possible (provided you set your patch using the same connection).
CONS: Your guitar amp's volume may not work. Hence, all volume control will have to be done from your processor.

3.OTHER EFFECTS LOOP: This is when you want to put your processor in the loop of other equipments. Hence, your processor will act as more of a secondary effec device ie. you use your processor for the effects only and not necessarily for preamp/distortion. Connect your guitar to the other device input (this may be your amps/any device main input). Connect the device's loop send to your processor's MAIN IN and then, the processor's OUTPUT to the return of the device. If the device used here is not an amp, then you will have to run another cable from your device to your amp to complete the loop.
CONS: Preamp of guitar amp is not moveable in the signal chain.

4.4 - CABLE METHOD (MONO): This method allows you to use an external preamp in the middle of your processor's effect chain. This is useful for those people who have great amps and loves the sound that they obtain from their guitar amp (like Marshall's high end tube amps, Soldano, ORANGE, Fender Hotrod, MESA BOOGIE ) but still want to use the processor for its other effects.
Connect your guitar to the input of your processor. Processor's SEND goes next to amps INPUT. Amps SEND to processor RETURN. Then processor main OUTPUT to amps RETURN.
PROS: The power & capability of your great amp is not lost.

5. POWER AMP ONLY & PROCESSOR EXTERNAL EFFECTS LOOP: This is almost the same as the 4 - Cable method. The only difference is that the effect in the loop here is a preamp from another device/amps set up, and instead of going to the same device/amps, the main OUTPUT from the processor goes to a second guitar amplifier. Any effect/preamp/preamp rack system can be used in this loop.
CONS: A good quality cable is required as more cabling leads to more noise.

6. PA/Mixing Desk: This is a direct connection from the processor to the PA. The main OUTPUT from the processor goes directly to the PA system/Mixing desk. If the distance between the stage and the Mixing Desk/PA system is far, then it is important to use a DI Box (Direct Injection) to minimise sound & signal loss because of the long cables involved. If your processor does not have a speaker simulator, it would be advisable to get an external one as distortion will not sound at its best without them.

THERE WAS ONE PARTICULAR QUESTION ASKED ON THE POST WHICH GOES AS FOLLOWS:

Should the amp sim be kept on or off?
Micing the amp- Amp sim on or off(which one is it?)
Line out- Amp sim on or off( which one is it?)

TO THIS QUESTION, WARREN ADDS THE FOLLOWING REPLY:

*I would suggest keeping two sets of patches:

*One with the speaker/amp sim off for use with amps and when the amp is miked

*One with the spkr/amp sim on when the amp has a line out to the mixer or when your processor goes straight to the mixer.

*The reason being your speaker simulated patches generally don't work well when connected to the front end of your amp.

*Fiddle with the amp to get your sound. the knobs are meant to be moved.

*If the amp has a fx loop try plugging your processor into the fx return of the amp. you may need to turn the volume up on your processor [usually the output volume].

Use only as much gain as you need. Too much gain turns your tone to mush.

Don't go overboard on the chorus-reverb-delay thing. too much of any causes your tone to lose its in-yer-face attack.

Above all: use your ears.