In this Gear Page thread I suggested folks running the POD HD500 as a pedalboard before an amp can reduce hiss and get a better signal to noise ratio by making sure the mixer pan controls are both set to centre.

I've been fiddling around with HD Edit and headphones this evening and I came up with some other things I thought worth sharing away from that thread, because they apply whether running amp models or just FX.

It seems a lot of the hiss you may be hearing is actually coming from inactive inputs adding noise into the signal chain. Most default empty patches seem to be set as follows:

Input 1: Guit+Aux+Varx Ch1
Input 2: Same

And this seems to introduce hiss and unwanted noise.

...

Now try the following (assuming you've one guitar plugged into the regular 1/4" input and are not using a Variax):

Input 1: Guitar
Input 2: Mic

then:

Input 1: Guitar
Input 2: Aux

and finally:

Input 1: Guitar
Input 2: Variax

If you're using a patch with some gain in it you'll certainly notice hiss, decreasing as you try each example above. With the final one Guitar/Variax being the quietest.

Now from that setting try:

Input 1: Guitar
Input 2: Guitar

Notice how much louder your signal suddenly gets? (You'll notice these examples more with headphones on). Perhaps this is one of the reasons some folks have been having issues with clean sounds not being as clean as they hoped. Setting Guitar/Guitar seems to put your signal through stronger. For low noise and low hiss it seems that you're best setting the HD inputs to 1: Guitar / 2: Variax (or an equivalent if you're using a Variax - the general principle being to use a second input that doesn't have anything actually running into it).

Now going back to my suggestion in the previous thread, I believe I was wrong when I said centring the mixer pan controls isn't relevant when using the amp models. I believe that the signals don't seem so much quieter when panned compared to FX only, but I believe it's the setting of two guitar signals as inputs that compensates for that so the earlier principle of centring controls still stands.

So what's the practical upshot of all this waffle? I've just gone through all my patches on HD Edit and centred the mixer pan controls (double clicking them does this quickly). Obviously you won't want to necessarily do this on patches where you've placed FX/Amps in the left and right channels, but try it on the ones you haven't I've also changed every patch so that the inputs are set to:

Input 1: Guitar
Input 2: Variax

I chose Variax as this offered less hiss than an unused Aux or Mic setting and I don't have a Variax. Line 6 really needs to add the option to switch inputs off completely rather than allowing them to add noise into the signal chain.

Anyway the result for me of changing all the patches to (1) Guitar/Variax input and (2) centred mixer pan controls is that all the patches are much less noisy and feature much less hiss. This seems to be a very good solution to some noise issues for me - and seems to result in a more pure signal chain from which to begin building patches. It seems foolish that Line6 has the empty patches defaulting to settings that introduce noise into the system.

I hope my experimentation helps some of you.

PS: Those worried about losing stereo separation by centring the mixer pan controls needn't worry. They are only for setting the stereo position of FX within those left/right channels. Any stereo effect after the mixer works in stereo as normal whatever the mixers settings are.

UPDATE: I thought I'd update this piece with a few more of my findings and quotes from the manual. I've been in forum discussions with some users who believe the above settings prevent the PODHD from feeding a stereo power amp. However as I will show - whether the POD outputs a stereo signal is not based on the number of inputs - but on the positioning of amps and effects in the signal chain.

I thought it was worth posting this section from the HD500 manual. I think it makes it clearer why we may or may not experience different things when routing inputs and using stereo outs depending on the patches we are trying to create. From what it says here it's clear that no matter how many inputs you are using it still should be possible to get a stereo output - it's all down to block positions within the signal chain in relation to the a/b paths and mixer block.

About Source Input Signal Routing: It is important to note how POD HD500 actually routes Source Inputs 1 and 2 through Amp & FX Blocks that are positioned “Pre” position. The following behaviors apply:
• In a configuration with no Amp or FX Blocks in Pre, Input 1 is fed only to Path A and Input 2 only to Path B. Therefore, this is the best configuration if you want to retain discrete Input Sources into Paths A & B.
• Placing an Amp Block or an active mono FX Model in Pre results in a “mix-down” of Input Sources 1 & 2, feeding the same, combined signal into each Path A & B.
• Placing a Stereo FX Model in Pre results in the left channel FX output being fed to Path A and its right output to Path B.
• The Mixer Block’s Volume and Pan options provide independent control for Path A & B outputs before they are fed through any Blocks positioned “Post” the Mixer.
• By setting Input 2 to “Same,” this effectively routes your Input Source to both stereo Paths A & B (which is how you can feed one guitar input into two Amp Models and/or parallel FX, for example)

I've just performed a quick experiment to check the following.

First set Input 1 to Guitar, and input 2 to Variax. Keep both channels panned full left and right as normal. Start with a clean patch with no used blocks.

There are three positions an amp (or effect block) can hold. Before the point where the channels split left and right - the pre position, in either the left or right path, and finally after the mixer - the post position.

If you put an amp block now in the pre position, even though only one guitar is set as input, you will get a stereo signal coming from your HD500. I've just checked this. It works. You still get sound from the left and right outputs. If you put an amp block after the mixer - that is in the post position - you will also get a stereo signal coming from your HD500.

Where you will lose one side of your stereo signal is if you just put that amp block in the a or b stereo paths before the mixer. Input 1 goes down the top line (left by default) and input 2 goes down the bottom line (right by default). If your patch makes use of the a and b paths then yes, switching a guitar input off will mean you get nothing down that particular route. I tried this for myself. With input one on guitar only the upper channel is fed, with that set to variax and input 2 set to guitar it was the lower channel that was fed. So whenenver you have a patch using these parralel paths - switching an input off will kill one of these side channels.

But again, if you are not putting amps and effects in those a/b channels then the following is true - , you only need one guitar input, either on input 1 or input 2, and seconldy you will still send a stereo signal. There is no need to feed two guitar signals through a patch that is not using the a and b channels and as others have found - it sounds better if you don't. Having two guitar inputs is clearly designed for driving two amps - one in each side channel. Running two inputs into one single amp leads to unwanted early distortion.

I just made a patch with one guitar input only (I set the second to Variax) and then placed an amp in the PRE position. I then placed a delay in channel A and an Octisynth in channel B.

Putting an amp (or any other mono effect) in the pre-position has the following effect according the the manual - "Placing an Amp Block or an active mono FX Model in Pre results in a “mix-down” of Input Sources 1 & 2, feeding the same, combined signal into each Path A & B."

As long as your amp in the patch is in the pre-position - that is not in A or B - then your setup should work find with one input. Just for the sake of completeness I will just go upstairs and try exactly what you described.

One input only. Amp in pre-position. One delay placed in channel A. The result - it worked perfectly fine with one guitar input and I get a normal stereo output (with dry amp one side and delay in the other) in my headphones.

So in conclusion of this section - it is possible to run one input into the PODHD and still feed a stereo power amp. The issue is all about where you place the amp/FX blocks.