re: effects loop impedance - this seems wrong to me...

[zappazapper]

So I was reading that article that @Schmalle posted (https://www.harmonycentral.com/articles/effects/how-to-test-input-impedance-for-guitar-effects-and-amps-r428/) and I came across this:

Quote

...low frequency signals may not be attenuated that much, but high frequencies could get clobbered.

Buffer boards and on-board preamps can turn the guitar output into a low impedance output for all frequencies, but many devices are already designed to handle guitars...

 

It is possible that the reason I'm getting a "screamy" tone in 4CM without the reamp box, regardless if I use my X3L at 100k or the Helix at 2k, has less to do with the impedance and more to do with the fact that both multi-fx units are outputting a buffered signal at their Sends when my amp's front panel input is expecting an unbuffered signal? And therefore is designed to compensate for the lack of high end in an unbuffered signal, and so is adding high end to a buffered signal that isn't experiencing high frequency loss in the first place?

[CraigGT]

That is all irrelevant, differing Impedances only affect frequency response when the source is inductive which none of these are.

[HonestOpinion]

On 4/1/2021 at 7:30 PM, zappazapper said:

...

 

Anyway, some observations:

• Out of all the possible configurations, the one that sounds the least like plugging straight into the amp is the X3L without the reamp box. I wasn't imagining it. Besides the obvious level mismatch (way more gain), there is something else going on frequency wise that you can't miss
• Using the X3L with a reamp box sounds exactly like my amp
• The Helix using the Line setting without the reamp box sounds like the X3L without the reamp box - more gain, and "screamy"
• The Helix using the Instrument setting without the reamp box sounds better than the Line setting because the gain is now comparable but there is definitely something different frequency wise, and it's easy to tell because it feeds back easier even though it's almost exactly the same amount of gain
• The Helix using the Instrument setting with the reamp box results in noticeably less gain, but frequency-wise sounds the same as plugging straight into the amp...  it just sounds like I turned the gain down
• The Helix using the Line setting with the reamp box sounds exactly like my amp

...

 

I have no where near the expertise that the electrical engineers weighing in here bring to the table but when I look at your observations above regarding your sound with the reamp box it looks to me like this could be more about what signal level your amp is ultimately getting hit with. Is it possible impedance may be playing a negligible role?

[zappazapper]

1 hour ago, HonestOpinion said:

 

I have no where near the expertise that the electrical engineers weighing in here bring to the table but when I look at your observations above regarding your sound with the reamp box it looks to me like this could be more about what signal level your amp is ultimately getting hit with. Is it possible impedance may be playing a negligible role?

There definitely is a difference in signal level but even when you turn the Send Level down to a point where it's now noticeably lower than plugging straight in, you still hear it. And then you plug the reamp box in and it's just right, except like I said in a subsequent post, I did end up noticing that there was a little bit less gain with the reamp box, but turning the Send Level up to +6.0 fixed that. 

[zappazapper]

It took me a while to get the testing rig together. I bought a 1M pot, soldered everything together, then realized my multimeter's AC voltage setting options are limited to 750v and 200v. So I had to get a different multimeter and they've put restrictions on stores here in Ontario that sent me on a little bit of a wild goose chase. By the time I got everything together today I only managed to test the front panel input and the effects return on my amp before I had to meet with my girlfriend for dinner. 

 

Front panel input - 370k

Effects return - 41k

 

I did the tests with a 1 kHz tone. I don't know what kind of effect frequency has on this test and didn't have time to experiment. Maybe someone can chime in on the subject. Also, I don't pretend that these are definitive numbers since I haven't done the test enough to fully accept the numbers myself. Just wanted to put them up here and see what reactions they get. 

[zappazapper]

OK, I have to apologize.

 

My thinking on this subject has been too linear. Our use of the signal may travel in one direction, but signal and its associated phenomenon are bi-directional. When I was thinking that the problem was between the Helix FX Send and my amp, I should have been thinking more about the interface between my guitar and whatever it's plugged into. The impedance of my amp's front panel input is irrelevant as far as the Helix FX Send is concerned. All I'm doing by using a reamp box is incorrectly loading the signal coming from the Helix - not only does this not load the pickups on my guitar correctly, but it incorrectly affects the signal coming from any blocks I place before the Loop (not to mention that there is at least a remote possibility of damaging either my Helix or my amp). It was suggested on this thread to experiment with the input impedance setting on the Helix, and I quickly dismissed it - "that's not the problem!!" Part of the reason is that there was no option to select input impedance on my X3L, and using a reamp box was the next best thing to accepting the "screamy" tone I would get in 4CM, and so it was hard to let go of the interface between the Helix Loop and my amp being the source of the problem.

 

I tested the front panel input on my amp using a range of test-tone frequencies. The results vary but it's safe to say that it's far below 1M. If I had to pick an average I'd say it's around 400k. The next highest option to 1M for "Guitar In-Z" is 230k. With the Loop set to "Instrument" and the "Guitar In-Z" set to 230k, it definitely sounds as close to plugging straight into the front panel as I've ever heard with a reamp box. So I consider this issue to be resolved to my satisfaction, and again I'd like to apologize for being so dismissive and difficult, if that's the impression I was giving.

 

Further to that, I was considering the implications to input impedance and the "first active block" option. If I have to set my input impedance to 230k to get my amp to sound right, then I am no longer able to take advantage of the variable impedance of the Auto setting. I had an idea that there could be a setting on the Loop blocks that would tell the Helix what impedance it should use when the Loop is the first active block and "Guitar In-Z" is set to auto. I plan on posting an IdeaScale article soon. Now that 3.1 is on the books, I feel compelled to embark on a lobbying campaign to have a few of my IdeaScale ideas at least be considered for 3.2, and this is near the top of the list.

 

Thanks again for all the patience you had with me.

[CraigGT]

Got there in the end :-)