Sounds like you need the mode that goes rec/dub/play:
to initialize
REC/DUB/PLAY
mode:
1.
Unplug the power jack.
2.
Simultaneously plug in the power jack while holding
down the ½ SPEED
button for three seconds.
3.
The digit display will show the sequence “o – o – 2
– 2”
4.
The power on cycle will continue as usual.

I see
well what I do for loops that are drones is record silence first for say two bars and the go into dub mode then swell your guitar in with your guitar volume.
I did that here at 3:60 in on this video:

Lord
Well no mater what it will have to get to the end of a loop and start over.
So if you record a blank loop of 10 seconds and fade in a swell with a filter going down at some point it will get back to the start of the filter sweep. Swelling in will not cause an abrupt start over.
In the dub mode it records over the start point so I staggering phrase and it records over the original start. Does that make sense?

Lord just do it and you will hear what it sounds like. Its piling loops on loops.

I bought a S/H freeze pedal to do just that – works really well if you draw a blank with your 720 looper.

I think you might have a basic misunderstanding. The first recording, that is the first layer if you’re dubbing, sets the length of the loop. Overdubbing does not change the length of the original loop. So, if you start off with a 5 second loop and you dub 10 seconds on top of it, you still only end up with a 5 second loop. While the 720 is overdubbing, it just starts the first loop over again and only keeps the last 5 seconds of your overdub like this:

Original:
Layer 1 – 1 2 3 4 5

When Dubbing:
Layer 1 – 1 2 3 4 5 1 2 3 4 5
Layer 2 – 1 2 3 4 5 6 7 8 9 0

Stop Dubbing:
Layer 1 – 1 2 3 4 5
Layer 2 – 6 7 8 9 0

So, it just loops to the beginning and records through it. The total length of the original loop will never increase, and by the way, only the length of the original loop is subtracted from your total loop time of 720. Overdubbing does not subtract from your total storage.

I don’t have the 720, so I might be wrong, but I’ve noticed with my 360 that it tries to do some sort of auto leveling of the volume when it begins recording, so that even if you start recording even after you’ve struck a cord, you will hear a pulse at the beginning of the loop. It’s a bit better if you use a compressor before the looper to get a very even volume throughout the recording, but it still doesn’t go away completely. So, here’s how I’ve gotten the best drone results with my 360.

1. Use a compressor, or very compressed OD/Distortion/etc, before the looper.
2. Use a very short initial loop – as short as possible.
3. Record silence on the first loop.
4. Fade overdubbed layers in.

Here are the specific steps I use after everything is plugged in and ready to go. This is assuming a REC/PLAY/DUB workflow since I can’t switch to a REC/DUB/PLAY workflow on my 360. I want to build an Asus2 triad.

— Record blank loop to equalize volume. —
1. Turn down the volume on my guitar to record a silent initial loop.
2. Tap the footswitch (LOOP on the 720) to start recording a short silent initial loop – about 1 second or so. Tap it again to stop. The PLAY LED will be lit and it will be flashing on the 360 to indicate the start of the loop. The PLAY LED will be lit on the 720 and it will indicate that the loop is playing.

— Add the first note of the drone. —
3a. Play the root (A) on my guitar with volume turned down all the way.
3b. Quickly tap the footswitch (LOOP on the 720) to start first dub.
3c. Quickly fade in the root note with volume control on my guitar. Let it ring past the beginning of the loop.
3d. Tap the footswitch (LOOP on the 720) to stop the first dub.

— Add the second note of the drone. —
4a. Turn down volume on my guitar.
4b. Play the second note ( on my guitar with volume turned down all the way.
4c. Quickly tap the footswitch (LOOP on the 720) to begin second dub.
4d. Quickly fade in the second note with volume control on my guitar. Let it ring past the beginning of the loop.
4e. Tap the footswitch (LOOP on the 720) to stop the second dub.

— Add the third note of the drone. —
5a. Turn down volume on my guitar.
5b. Play the third note (E) on my guitar with volume turned down all the way.
5c. Quickly tap the footswitch (LOOP on the 720) to begin third dub.
5d. Quickly fade in the third note with volume control on my guitar. Let it ring past the beginning of the loop.
5e. Tap the footswitch (LOOP on the 720) to stop the third dub.

That’s a lot of steps, but I’ve discovered that if you build the drone up in faded-in layers, they kind of blend together and the restart of the loop is smoother and less noticeable. It becomes more like a shimmer.

You might be able to do this more easily on the 720 with a REC/DUB/PLAY flow as Bill suggested, but I don’t have that to try, so you’ll need to experiment. Also, the Freeze is of course designed to do exactly this with a single press, but you lose the ability to layer your individual drone notes. For instance with the 360/720 you could do the root with an octave down to simulate a base, or use different effects for each layer, or if you use the same modulating effect like a flanger for each layer it would be at a different part of its cycle which can create a richer drone than just freezing a single chord.

Finally, although you can use a looper as a drone machine with some effort since the Freeze is really just a very short looper without overdubing, the ultimate EHX drone machines are really the: Freeze, the Ravish Sitar, the Superego, and the Superego+. If drone is really what you want, you might consider getting something that’s designed specifically for it.