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

[zappazapper]

Apologies if I've already asked this question...

 

https://line6.com/data/6/0a020a4112bbf5fb6a519e8b18/application/pdf/HX Stomp 3.0 Owner's Manual - Rev C - English .pdf

 

I don't own a Stomp, but before I got my LT I was looking at all the manuals for the different products in the Helix lineup, and I was reminded of this today when I was checking the Mesa Boogie Board to see if there was any new responses to posts I've made there.

 

From page 9:

Quote

The effects loops on most amplifiers run at instrument level.

 

This is contrary to my own understanding of what a guitar amp preamp does. It seems to me that, besides shaping the signal coming from the guitar, the job of a preamp in a guitar amp is to bring the level of an instrument-level signal to line-level. And so what comes out of an Effects Loop Send on an amp would be line-level, and what an Effects Loop Return would expect would also be line-level.

 

So I have a few questions:

• Is this a typo in the Stomp manual?
• Are most effects loops indeed instrument-level?
• Is there a way to use a multimeter to find out the signal voltage and impedance of different points in the signal chain of an amplifier?

[CraigGT]

My 4CM patches are set to instrument level and they were very carefully matched to the amp.

Just set it so with everything bypassed on the Helix there's no difference in level whether there's anything plugged in to the amp loop or not.

 

 

 

[PierM]

There are amps running FXloop at instrument level, and there are amps running loop at Line level....and then there are amps where you can switch between the two.

[CraigGT]

2 minutes ago, PierM said:

There are amps running FXloop at instrument level, and there are amps running loop at Line level....and then there are amps where you can switch between the two.

 

And then there's Boogies running parallel loops!

[rd2rk]

Once upon a time there were two different types of effects.

 

Amps in those days did not have effects loops. All guitar effects were placed before the amp input, and were designed to take a signal from an instrument and send it to an amp that was also designed to take an instrument level signal.

 

Studio gear, OTOH, was designed to receive and send a Line level signal for use in a studio.

 

But guitarists wanted to use Studio gear too! Especially time based effects like delays and reverbs. Amps started appearing with FX Loops for that purpose. Some were Line level, and some had switches so that users could CHOOSE whether to use Guitar FX or Studio FX in the Loops.

 

Eventually, the quality of Guitar FX started to catch up with that of the much more expensive Studio gear. Everybody started using guitar FX in their loops. Amps with only Line level loops were quickly replaced with Inst level FX Loops.

 

Today, most FX Loops on Guitar amps are Instrument Level, because few guitarists still use Studio gear in their loops, and lots of Studio Gear have Inst/Line level switches, as do many Guitar amps (Blackstar for instance).

 

Modeler designers are aware of this history and, in order to allow players maximum equipment flexibility, provide options for both Inst and Line level signals.

 

It is truly a great time in history to be a musician!

 

 

[zappazapper]

21 hours ago, CraigGT said:

My 4CM patches are set to instrument level and they were very carefully matched to the amp.

Just set it so with everything bypassed on the Helix there's no difference in level whether there's anything plugged in to the amp loop or not.

My question is WHY are you using instrument-level? Do you know for a fact that your amp's loop is instrument-level? Or is it a purely sonic reason? If it is, is there an obvious issue with using line-level, like some kind of audible distortion, or is it a purely subjective choice? "It just sounds better"?

 

21 hours ago, rd2rk said:

It is truly a great time in history to be a musician!

Provided you know whether your amp's loop is instrument-level or line-level. Check out the contradictory pile of garbage going on in the manual for my amp. 

 

https://mesa-boogie.imgix.net/media/User Manuals/50 Caliber Plus.pdf

 

From page 4:

"EFFECTS SEND & RETURN These jacks provide a low-noise patch loop within the 50's preamp for connecting external accessories. Compatibility is quite good with most line-level or rack-mount devices..."

 

Quite good? If it were line-level, wouldn't compatibility be PREFECT?!

 

"...although some will require you to trim down their input attenuators to prevent overload."

 

OK so then line-level signals are too hot, so that must mean the loop is instrument-level. Right? 

"(Pedal-type effects are designed to handle the low-level signals emanating directly from your guitar; therefore this type of device should be connected “in front” of the amplifier, rather than in the Effects Loop.)"

 

OK, so the loop isn't instrument-level either? Ffs.

 

"Some manufacturers offer rack-mount multi-effects units for guitar which include compression, distortion, overdrive, etc. Although a good-quality compressor can be used effectively in your Boogie's Effects Loop, we do not recommend the use of multi-effect "guitar processors" in the Loop, as their inputs are often too sensitive and their added gain stages will tend to contribute some noise.
If you wish to use this type of device with your Boogie, it should be patched in between the guitar's output and the amplifier's input."

 

K wait. You just said that pedals should be plugged into the front panel input because pedals have "low-level" (instrument-level?) signals, and now you're saying multi-fx units should be plugged into the front panel because their signals are too hot for the loop. 

 

So ya, there's really nothing I can gleen from the manual on this subject. Which is why I'm after a way to test it myself.

[Schmalle]

22 hours ago, zappazapper said:

Apologies if I've already asked this question...

 

https://line6.com/data/6/0a020a4112bbf5fb6a519e8b18/application/pdf/HX Stomp 3.0 Owner's Manual - Rev C - English .pdf

 

I don't own a Stomp, but before I got my LT I was looking at all the manuals for the different products in the Helix lineup, and I was reminded of this today when I was checking the Mesa Boogie Board to see if there was any new responses to posts I've made there.

 

From page 9:

 

This is contrary to my own understanding of what a guitar amp preamp does. It seems to me that, besides shaping the signal coming from the guitar, the job of a preamp in a guitar amp is to bring the level of an instrument-level signal to line-level. And so what comes out of an Effects Loop Send on an amp would be line-level, and what an Effects Loop Return would expect would also be line-level.

 

So I have a few questions:

• Is this a typo in the Stomp manual?
• Are most effects loops indeed instrument-level?
• Is there a way to use a multimeter to find out the signal voltage and impedance of different points in the signal chain of an amplifier?

You are right in that an amplifier that needs to tame the signal it carefully amplified to provide a low signal for FX gear isn't that great of a design. A modern amp like a 5150 III i.e. has a tube preamp, an intermediate OP amp based FX loop/preamp send/headphone buffer stage and a tube power amp to do that.

 

Is there a way to use a multimeter to find out the signal voltage and impedance of different points in the signal chain of an amplifier?

- Yes, you need a multimeter, a potentiometer or a collection of resistors and a test signal generator for sine waves (a synth/PC/phone will do the job). Then do this.

 

[PierM]

I see nothing wrong in that Boogie manual quotes. They are not saying multieffects are too hot. They are saying there are effects, in those devices, that are using a gain stage, which would sound crap in a loop. This is an universal thing.

 

Compressors, Distorsion, and any other similar effect (doesnt matter if its a stomp or part of a multiFX rack), should not be used in the effect loop of anything, as they have a gain stage. They needs to be before the amp.

 

Time effects, modulation etc, they are fine to go in the loop.

 

 

[zappazapper]

36 minutes ago, PierM said:

I see nothing wrong in that Boogie manual quotes. They are not saying multieffects are too hot. They are saying there are effects, in those devices, that are using a gain stage, which would sound crap in a loop. This is an universal thing.

 

Compressors, Distorsion, and any other similar effect (doesnt matter if its a stomp or part of a multiFX rack), should not be used in the effect loop of anything, as they have a gain stage. They needs to be before the amp.

 

Time effects, modulation etc, they are fine to go in the loop.

 

 

Fair enough. I don't know if there was a multi-fx in existence that had its own effects loop that would allow you to place some effects before the preamp and some after when this amp was designed (late 80s). I will disagree with you about using compressors in the loop, though, although clearly one has to be mindful of the output level. 

 

So from what it says there, would you say it's an instrument-level loop or a line-level loop? 

[CraigGT]

50 minutes ago, zappazapper said:

My question is WHY are you using instrument-level? Do you know for a fact that your amp's loop is instrument-level? Or is it a purely sonic reason? If it is, is there an obvious issue with using line-level, like some kind of audible distortion, or is it a purely subjective choice? "It just sounds better"?

 

Because using it like that gives unity gain through the Helix.

If the amp was sending a line level then it would overdrive the Helix

If the Helix was sending line level it would overdrive my amp.

 

Like PierM says, you don't really want to changing gain in the loop.

[zappazapper]

2 minutes ago, CraigGT said:

If the amp was sending a line level then it would overdrive the Helix

If your amp was sending a line-level signal to the Helix and the loop on the Helix was set to receive line-level signals, why would it overdrive the Helix? 

 

3 minutes ago, CraigGT said:

If the Helix was sending line level it would overdrive my amp.

How did you reach this conclusion? Because the manual for your amp says the loop is instrument-level? What amp are you using? 

[zappazapper]

1 hour ago, Schmalle said:

Is there a way to use a multimeter to find out the signal voltage and impedance of different points in the signal chain of an amplifier?

- Yes, you need a multimeter, a potentiometer or a collection of resistors and a test signal generator for sine waves (a synth/PC/phone will do the job). Then do this.

Awesome. I'll have to read that article about 100 more times before I understand it, but ya. That should work. I'd also like to test the Helix's loops and outputs because I've never really seen a clear answer as to whether the Instrument/Line settings actually do anything as far as impedance goes. 

[CraigGT]

1 hour ago, zappazapper said:

If your amp was sending a line-level signal to the Helix and the loop on the Helix was set to receive line-level signals, why would it overdrive the Helix? 

 

How did you reach this conclusion? Because the manual for your amp says the loop is instrument-level? What amp are you using? 

As I said, my Helix is set up for Instrument so a line level signal would be too high. So knowing that it's sending at instrument level it follows that I need to send the same back to it.

It's a Cornford Roadhouse.

 

I do think you're overthinking this,

 

Set up an empty patch, set the relevant ins and outs to Instrument, play a note and unplug the cables from the amp and nothing should change.

Do the same with Line levels, decide which is best and stick with it.

 

Some amps have the Master Volume before the Effect Send which makes it all irrelevant anyway.

 

 

[CraigGT]

I just looked at a schematic for your amp and the effect send is after the Vol (Gain) and the switchable Lead Master Vol but before the Master Vol .

That means that the send level is completely dependent on the settings of those amp controls. It's probably line level when they're on 10 but somewhat less at other times.

 

If you put a compressor in there it's going to be unpredictable because there are too many variables before it. That's why PierM said what he did.

 

 

[CraigGT]

2 hours ago, zappazapper said:

I've never really seen a clear answer as to whether the Instrument/Line settings actually do anything as far as impedance goes. 

No they don't, they're 1Meg there is no need for them to be anything else

[zappazapper]

2 hours ago, CraigGT said:

I do think you're overthinking this,

Ya, I get that a lot XD but hey, just so you know, part of the reason I'm probably overthinking it IS that I'm interested in the science and engineering part of all this, not just so I can get "good tone" but also just for the sake of knowledge. And if I sound (read?) like I'm trying to find holes in your responses just so that I can win an argument, I apologize, because I'm really just trying to learn about this stuff. That's why I keep asking "why?" every time you answer my last "why?". Hope you understand.

 

2 hours ago, CraigGT said:

As I said, my Helix is set up for Instrument so a line level signal would be too high. So knowing that it's sending at instrument level it follows that I need to send the same back to it.

Hmm. So ya, that's something that doesn't fit with my own understanding of what a guitar preamp does. I mean, a guitar preamp is not that different than a mic preamp, and a mic preamp (generally) takes a low-level high-impedance signal and amplifies it to a high-level low-impedance signal, right? So I guess I made an assumption that a guitar preamp also does that. And I had to take a look and remind myself what the "Instrument/Line" option is on the Helix: It's an option for the complete loop. There's no separate option for the Send and another for the Return. And assuming that L6 knows that a good percentage of users will be using the loop for 4CM (I mean, it's in the manual), clearly they would have provided separate options for the Send and Return if it was necessary.

 

2 hours ago, CraigGT said:

It's a Cornford Roadhouse.

https://www.zikinf.com/manuels/cornford-roadhouse-30-head-manuel-utilisateur-en-32271.pdf

Quote

Effects Loop: Series effects loop. Send level is a nominal –6 dBV. Send impedance is 33k ohms. Return impedance is 145k ohms.

 

1 hour ago, CraigGT said:

No they don't, they're 1Meg there is no need for them to be anything else

OK so this is where I'm getting confused, and it's not just because the concept of mismatched impedances having an effect on frequency response makes sense to me, but because I have my own anecdotal experience with impedance mismatches having an effect on frequency response: back when I started experimenting with 4CM, I had an X3 Live.

http://www.benvesco.com/blog/the-digital-age/2007/pod-x3-specs-revealed/

Quote

FX Send: 100 kOhm

https://www.soundonsound.com/techniques/understanding-impedance

Quote

Since the pick-up presents a relatively high output impedance, it is normal to provide guitar preamp and DI inputs with a hugely high input impedance. A minimum value is typically 470kΩ, but many are over 1MΩ...

When I connected the X3L and the amp in 4CM, the tone was "screamy", for lack of a better word. It certainly had more gain, but when I tuned the Send Level in the "Loop" Block down to a point that I know had less gain than the amp should have had at that setting, it still had this screamy character. And so after some research I learned about impedance mismatching, and considering the values that I quoted, it made sense to me that the impedance mismatch between the FX Send of the X3L and the front panel input of my amp was resulting in an increase of high frequency content (or more correctly, a LACK of high-end roll off associated with high impedances, which a guitar amp preamp is specifically designed to compensate for), resulting in the "screamy" character I was getting. And so the solution seemed to be a reamp box, since reamp boxes are designed to convert low-impedance "line-level" signals to high-impedance "instrument-level" signals. And lo and behold, after I bought this...

https://artproaudio.com/framework/uploads/2018/06/om_dualrdb.pdf

...all of a sudden my amp sounded exactly like my amp again. 

Now, when I started looking into the Helix line, I noticed this "Instrument/Line" option for the FX Loops and figured that L6 must have had enough feedback about the impedance issue to include circuitry that would deal with it, but when I got my LT and connected it in 4CM with my amp without the reamp box, I got the same screamy tone regardless of what setting I used. Which is why I've mentioned in numerous places on the forum that I'm not sure the "Instrument/Line" option does anything to the impedance of the signal coming from the Send. Now you're saying the impedance of the Loops are 1M, regardless of the setting. Again, not to question your credibility, but I'd really appreciate if you could provide a link to where you got that information because I can't find it. At any rate, if it was 1M, it wouldn't explain why I still get that screamy tone from my amp in 4CM without the reamp box. 1M would seem to be a better impedance match with a front panel input on a guitar than the 100k of the X3L, and certainly shouldn't result in an increase in high frequency content. I'll have to test that out again on my rig.

 

2 hours ago, CraigGT said:

I just looked at a schematic for your amp and the effect send is after the Vol (Gain) and the switchable Lead Master Vol but before the Master Vol .

Confirmed.

 

2 hours ago, CraigGT said:

That means that the send level is completely dependent on the settings of those amp controls. It's probably line level when they're on 10 but somewhat less at other times.

I think what I'm trying to say is that I'm more concerned about the impedance portion of "line-level" and its effect on frequency response. Signal level can be easily dealt with, and it wouldn't even offend me if it were some arbitrary setting on a digital level control in the Helix. But yes, I can confirm that the level coming back from the preamp is about the same as having the Loop block bypassed.

 

2 hours ago, CraigGT said:

If you put a compressor in there it's going to be unpredictable because there are too many variables before it. That's why PierM said what he did.

Sorry, I just can't see how a compressor between a preamp and a power amp would be such an uncontrollably disastrous thing. In fact, I use one often. In fact, my X3L had a unmovable LA-2A model right after the Loop block in the "Pre" position, which is where I always used it (after gate, wah, distortions, before EQ, before mods, reverbs, delays in "Post" position), which I used often. Again, one has to be careful with a compressor REGARDLESS of where it is in the signal chain. I made sure it worked.

 

Anyway, at this point, I have more questions than answers. That's fine. It usually means I'm about to learn something. Unfortunately, I'm too tired for a night of deep-diving my gear. I appreciate your responses and I look forward to more.

[CraigGT]

Damn you're good with the quotes :-)

 

The fundamental issue here is that audio systems don't use matched impedances, matched impedance systems are used for higher power/higher frequency systems when power efficiency/lack of reflections are desirable. (maximum power transfer)

 

Audio systems use a lower impedance source feeding higher impedance inputs,  eg my Strat measures less than 6k but that feeds into a 1M tube amp input. (maximum voltage transfer)

 

I've also remembered that when I used a normal Helix patch into my amp effects return it was far too loud on line so I used instrument level instead, yes my amp maybe a "nominal" -6dbV out (somewhere between line and instrument) but what is nominal? with the gain and boost flat out with a Les Paul or with lower setting and a Strat? that's a much bigger difference than the difference between line and instrument level definitions. 

 

Your understanding of a preamp (amplifying voltage) is correct but in the case of the Roadhouse, there are four stages of amplification before the loop but there is also the tone stack which reduces the signal level considerably.

 

The point about the compressor is that you would set it up to work how you like it at a certain input level and changing any gain settings on your amp affects that operating point considerably. if you put it between the guitar and amp it would behave more consistently. Of course that's thinking technically, if you like how it sounds then it's good.

[Schmalle]

1 hour ago, CraigGT said:

The fundamental issue here is that audio systems don't use matched impedances, matched impedance systems are used for higher power/higher frequency systems when power efficiency/lack of reflections are desirable. (maximum power transfer)

This. Audio signal transmission is not about maximizing the transmitted power - which would be impedance matching. It's about maximizing level (high voltage) at the input with high fidelity (low current). This is called high impedance bridging / voltage bridging.

[zappazapper]

13 hours ago, CraigGT said:

Audio systems use a lower impedance source feeding higher impedance inputs,  eg my Strat measures less than 6k but that feeds into a 1M tube amp input. (maximum voltage transfer)

 

12 hours ago, Schmalle said:

This. Audio signal transmission is not about maximizing the transmitted power - which would be impedance matching. It's about maximizing level (high voltage) at the input with high fidelity (low current). This is called high impedance bridging / voltage bridging.

 

On 3/30/2021 at 6:50 PM, CraigGT said:

No they don't, they're 1Meg there is no need for them to be anything else

Quote

Since the pick-up presents a relatively high output impedance, it is normal to provide guitar preamp and DI inputs with a hugely high input impedance. A minimum value is typically 470kΩ, but many are over 1MΩ...

So in the case of 4CM with the Helix, we have a high impedance source from the Helix FX Send feeding a low impedance front panel guitar amp input, right? And what would be the result of that mismatch, which seems to me to be the opposite of the "impedance bridging" being described? 

[Schmalle]

6 hours ago, zappazapper said:

So in the case of 4CM with the Helix, we have a high impedance source from the Helix FX Send feeding a low impedance front panel guitar amp input, right? And what would be the result of that mismatch, which seems to me to be the opposite of the "impedance bridging" being described? 

No, the opposite: a low impedance of the Helix is driving a high impedance input of the amp.

[CraigGT]

6 hours ago, zappazapper said:

 

 

So in the case of 4CM with the Helix, we have a high impedance source from the Helix FX Send feeding a low impedance front panel guitar amp input, right? And what would be the result of that mismatch, which seems to me to be the opposite of the "impedance bridging" being described? 

No you've got that the wrong way around, it's a low impedance source feeding an high impedance input which is correct.

 

The effect of feeding into a lower impedance would be less level and possibly some loss of high end.

This would be more pronounced with a straight guitar signal which is why some of the old fuzz's have a lower input impedance.

 

PS I made an error earlier, The Helix Returns are 1M on instrument and 10K on Line

[zappazapper]

3 hours ago, CraigGT said:

PS I made an error earlier, The Helix Returns are 1M on instrument and 10K on Line

OK. And you're sure the Send is 1M no matter what setting is being used? I guess that'll be the first thing I test when I actually get time to take a look at @Schmalle's article in any depth.

 

3 hours ago, CraigGT said:

No you've got that the wrong way around, it's a low impedance source feeding an high impedance input which is correct.

Assuming that the send is 1M, and the Sound On Sound article I linked is correct about a typical guitar amp input being 470k or higher, then I'm right, aren't I? 

[PierM]

Sorry, he has to say that; (j/k)

 

 

 

[CraigGT]

5 hours ago, zappazapper said:

OK. And you're sure the Send is 1M no matter what setting is being used? I guess that'll be the first thing I test when I actually get time to take a look at @Schmalle's article in any depth.

 

Assuming that the send is 1M, and the Sound On Sound article I linked is correct about a typical guitar amp input being 470k or higher, then I'm right, aren't I? 

 

I just measured the send and it's 2K

[zappazapper]

4 minutes ago, CraigGT said:

 

I just measured the send and it's 2K

For both Instrument and Line settings? 

[CraigGT]

10 minutes ago, zappazapper said:

For both Instrument and Line settings? 

Yes.

[zappazapper]

9 hours ago, PierM said:

Sorry, he has to say that; (j/k)

 

 

 

Thanks, I've already mentioned that I'm just as interested in the science and engineering of music and music equipment as I am in shutting up and playing my guitar. And by the way, Frank was at the forefront of musical science and engineering for his entire career and if you're suggesting that I should model my approach to his, well then I guess I have to start asking even more questions.

[zappazapper]

6 hours ago, CraigGT said:

Yes.

This is all really interesting to me and I'm excited to test the input of my amp and see how that compares, but I had a particularly rough day at work and am not really in the state of mind for such technically minded stuff right now. However, in my excitement I did pull out my X3L to do a comparative test between its FX Send, the Helix FX Send, both with and without the reamp box, and plugging straight into the front panel input of my amp. Gain 10, Treble 10, but Master and Lead Volumes at 0, for your typical metal "chug" but not nearly loud enough to feed back because it's too loud. Yes, I know Gain and Treble at 10 are not even remotely reasonable settings at performance volume (even the manual will tell you that) but it's the best setting for exaggerating the differences between the different configurations. 

 

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'm more than willing to accept the logic you guys have presented to me about impedance bridging, and it was more than backed up by that Sound On Sound article I posted earlier, but I can't ignore my ears. And it doesn't make sense because the FX Send impedances of the two multi-fx units are wildly different compared to a typical guitar signal. The SOS article says that a typical output impedance for an electric guitar with standard magnetic pickups would be anywhere up to 10k. The Helix Send is lower than this at 2k and the X3L Send is higher at 100k, yet they both yield the same bad result. As for the reamp box, the only place in the manual that mentions an impedance spec at all is under "insertion loss", and it gives two numbers - 100lk and 600 ohm. Neither of them anywhere near the 10k that would make it make any sense for me. And the difference in these numbers is quite insignificant compared to the likely input impedance of my amp (1M-ish?), making every configuration easily "impedance bridged", which makes it even less likely that impedance would cause such an issue in frequency response.

 

Again, I have even more questions than answers. Until I get them, I guess I'll just continue to use the reamp box because "it just sounds good" XD

[CraigGT]

But you're not dealing with a guitar signal on the loop send of your amp, it's a robust amplified signal that should be largely indifferent to minor impedance mismatches.

 

Have you tried just plugging a cable between the send and return of your amp? it's not unknown for the jacks to be faulty? 

[zappazapper]

Ya, I'm getting a little off topic here. The thread's about the FX Loop in my amp and I'm testing the loop on the Helix into my front panel. My thinking was that since the Instrument / Line setting is for the entire loop, not the Send and Return separately, choosing one setting over another for the sake of the signal coming from my amp's EFFECTS SEND to the Helix Return would force that choice on the connection between the Helix Send and the front panel of my amp. At this point it makes sense to me that the signal coming from the EFFECTS SEND of my amp is indeed instrument-level, but using the Instrument setting doesn't give me the best sounding option for the connection between the Helix Send and the front panel input of my amp. The best sounding option was the Line setting into a reamp box. Instrument setting into a reamp box results in less gain. It's possible that turning the Send Level slider to max will fix it. 

[CraigGT]

I'm kind of lost with what you're trying to achieve now.

[zappazapper]

24 minutes ago, CraigGT said:

I'm kind of lost with what you're trying to achieve now.

Sorry, I'll try to do a better job of explaining, because your input has been very helpful and I want your continued participation in this discussion.

 

Basically what I'm looking for is anything that will make my 4CM experience better. By "better" I guess I mean more accurate to how my amp behaves just on its own. So when I have a Helix Preset with just a Loop Block enabled, it should sound exactly how my amp sounds when I'm plugged into the front panel input with nothing else connected. I think that's a good starting point for building Presets. I'm not suggesting that needs to be a concern for everybody who uses 4CM, but it's a concern for me, and I don't think I've ever really found a solution that got me there.

 

And so even though this thread started as a discussion about the impedance of guitar amp effects loops, the ultimate topic, at least for me, is 4CM "in general". Part of what got me to the issue of the connection between the Helix FX Send and the front panel input of my amp is the fact that the Instrument / Line setting is shared between the Send and the Return, so even though this thread started as a discussion on interfacing with the effects loop of a guitar amp, the choice you make between Instrument and Line for the connection between the effects send on an amp and the FX Return on the Helix forces one to use that same setting for the connection between the FX Send of the Helix and the front panel input of an amp.

 

So once I became convinced, in no small part due to your contributions to this discussion, that the signal coming from the EFFECTS SEND of my amp was in all likelihood an instrument-level signal, the next question that entered my mind was whether or not the Instrument setting was going to be the right setting for the connection between the FX Send of the Helix and the front panel input of my amp. At that point it's possible that I should have maybe started a different thread to discuss that topic.

 

I hope that better explains where my thinking has been in the last couple of posts. Suffice it to say that it's a completely different discussion and when I'm ready to start a thread on that topic I will. In the meantime, I'm looking around to see if I even have a 1M pot to build this testing rig from the article that @Schmalle posted. I might have to go out and buy one.

 

Here's a question for @Schmalle - since some of the impedances we're dealing with are in the neighborhood of 1M anyway, does it make sense to use a pot with a higher resistance to build this testing rig so that we're able to measure a higher impedance if it happens to exist somewhere? 2M? 10M?

[CraigGT]

Then do it one step at a time starting with an empty patch.

Guitar -> Helix guitar in 

Helix Send 1 (set to Instrument) -> Guitar amp in

With nothing in the amp effect loop it should sound the same as plugging the guitar in the amp (make sue Helix Pad is off)

 

Then 

Amp FX Send -> Helix Return 1

Helix Main Out -> Amp FX Return

The sound should still not change however overall level will be dependant on the Helix main Volume knob.

 

I've attached a preset

When it's all working, before amp effects go on the top line

Effect loop effects going on the bottom.

4CM Start.hlx

[CraigGT]

3 hours ago, zappazapper said:

Here's a question for @Schmalle - since some of the impedances we're dealing with are in the neighborhood of 1M anyway, does it make sense to use a pot with a higher resistance to build this testing rig so that we're able to measure a higher impedance if it happens to exist somewhere? 2M? 10M?

Why would you need to get a pot and do the tests?

We've given you the facts, it's science, it's not debateable.

[zappazapper]

1 hour ago, CraigGT said:

Why would you need to get a pot and do the tests?

We've given you the facts, it's science, it's not debateable.

Hmm. Well, science is inherently debatable, but I digress...

 

I'm going to do the tests because I've never done such a test and I'd like to know how it's done and how it works; I'd like to test my OWN amp and see what the values are; I'd like to test my OWN Helix and see how the numbers I get compare to yours, as variation undoubtedly exists between units to some degree.

 

And lastly, because your "facts" have already changed a couple of times during this discussion. First you said they were all 1M, now some are 10k, some are 2k. Do you really begrudge me the opportunity to test them myself for my own piece of mind? I've thanked you a number of times for participating in this discussion and I hope you will continue to do so, but I don't think anybody around here has the stature to give me "facts" and have me just blindly accept them as indisputable law when I can easily test them myself. Does that seem to you to be an unreasonable position or can we continue to have a respectful discussion among adults? Because adults can and do skepticize the things they're told and seek truth themselves.

 

I hope you understand. 

[CraigGT]

Feel free to test them but I haven't really changed my facts, I said that Helix Returns are 1M but didn't realise at the time that they changed to 10K when set to Line. 

I never said they were 2K, that's for Sends.

 

I already know what they are for your amp, We can compare results later :-) 

 

Of course I understand - carry on :-)

 

Ps maybe they're not facts but they are actually little resistors with 1% tolerance :-)  

[zappazapper]

19 hours ago, CraigGT said:

I already know what they are for your amp, We can compare results later :-) 

You know what the impedance specs are for the effects loop of MY amp? By all mean, please enlighten me...

[CraigGT]

The send is around 22K and the return is 47K, the front jack could be anywhere between 2.5M and 0 depending on what frequency you test it with. 

[zappazapper]

8 minutes ago, CraigGT said:

The send is around 22K and the return is 47K, the front jack could be anywhere between 2.5M and 0 depending on what frequency you test it with. 

I'm assuming you got those from the schematic? 

 

What's the impedance of the Helix 1/4" output then? 

[CraigGT]

Yes from the schematic,

I've not measured the 1/4" outs but you can be sure that they'll be low enough to not be of any concern.