Can I use this to Reamp?

[JLondon]

My understanding is the correct impedance matching is about 10x the input for correct headroom.

Mic level at ~600 ohms goes into roughly 10k inputs. (Line level)

Instruments at ~100k or so ohms go into roughly 1M (million) ohm inputs. (Instrument level)

Mic into instrument (multiplies any noise too much? Too much gain required?), and instrument into mic overloads it with hum (no headroom like my focusrite- doesnt handle the guitar well because they didnt go quite to 1M input even on instrument setting)

 

[ecc83]

Impedance "matters" but not in the sense that it is sometimes portrayed..

Let's see if we can first nail the "noisy guitar amp" scenario?
Guitar amps are for the most part noisy fekkers and one almost universal practice is to use shorting jacks on the inputs. Thus the input noise at the grid of the first valve is shorted out and even if you advance the gains the amp will be relatively quiet (if it ain't, it ain't one of "ours"!)

Plugging in a guitar obviously opens the short but the pups and pots present a low enough impedance, about 10k flat out and 100k ish worse case and this is low enough to give a decent signal to noise ratio since of course you now have the string sounds masking much of the hiss.

The amplifier does not give a flying cluck where the source impedance comes from, so long as it is about 100k or less and (MOST IMPORTANTLY!) the signal level is comparable to that of a guitar, the S/N ratio will be satisfactory.

As has been stated, the modern (like last 60yrs!) signal transfer regime is low to high since this preserves the greatest signal VOLTAGE and ideally a 1 to 10 ratio is desired. In practice there is nothing in audio with an op Z higher than about 1k and inputs Z are usually 10k or above. The two special cases are microphone inputs, usually 1.5k and up and of course guitar amps at the "magic" One Meg. Why one meg? Because the valves started life inside radio sets and the detector circuit needed a very high load impedance, Guitar amps are really just the arse end of old radios!

Nothing in audio, not one thing, needs "impedance matching" in the sense of the old telephone or RF days.

Dave.

 

[dudernut]

Impedance "matters" but not in the sense that it is sometimes portrayed..

Let's see if we can first nail the "noisy guitar amp" scenario?
Guitar amps are for the most part noisy fekkers and one almost universal practice is to use shorting jacks on the inputs. Thus the input noise at the grid of the first valve is shorted out and even if you advance the gains the amp will be relatively quiet (if it ain't, it ain't one of "ours"!)

Plugging in a guitar obviously opens the short but the pups and pots present a low enough impedance, about 10k flat out and 100k ish worse case and this is low enough to give a decent signal to noise ratio since of course you now have the string sounds masking much of the hiss.

The amplifier does not give a flying cluck where the source impedance comes from, so long as it is about 100k or less and (MOST IMPORTANTLY!) the signal level is comparable to that of a guitar, the S/N ratio will be satisfactory.

As has been stated, the modern (like last 60yrs!) signal transfer regime is low to high since this preserves the greatest signal VOLTAGE and ideally a 1 to 10 ratio is desired. In practice there is nothing in audio with an op Z higher than about 1k and inputs Z are usually 10k or above. The two special cases are microphone inputs, usually 1.5k and up and of course guitar amps at the "magic" One Meg. Why one meg? Because the valves started life inside radio sets and the detector circuit needed a very high load impedance, Guitar amps are really just the arse end of old radios!

Nothing in audio, not one thing, needs "impedance matching" in the sense of the old telephone or RF days.

Dave.

Wha??? LOL That was supposed to say "what" not "who"

 

[Greg_L]

Look, just worry about matching the level of your reamped signal to the level of what a guitar kicks out so your amp acts like it should.

 

[ecc83]

Look, just worry about matching the level of your reamped signal to the level of what a guitar kicks out so your amp acts like it should.

ABSO-BLOODY-LOOOTLY!
Thank you Greg. You want a good SIGNAL to noise ratio. Get that and "impedance" can go fish.

Dave.

 

[miroslav]

Nothing in audio, not one thing, needs "impedance matching" in the sense of the old telephone or RF days.

Yes....used as originally intedned, the term "impedance matching" would imply that the impedances be similar, and it's agreed that was the case way back in the old days.

However, today we still try to "match"..., we're just matchng low impedance outputs with high impedance inputs.
Most audio gear is already designed that way....but sometimes when we interconnect, things may not match up optimally.
Lke say....guitars, which by the nature of ther pickups, tend to have a high impedance output, and amps therefore have to have an even higher impedance input....than say your typical Line level I/Os.
So yeah...some amount of "matching" still comes into consideration.

 

[ecc83]

"Lke say....guitars, which by the nature of ther pickups, tend to have a high impedance output"

And there, ^ lies one of the root causes of much of the confusion, misinformation and "black art" surrounding the connection of guitars to amps, re-amping* and much else.

Magnetic pickup electric guitars do NOT have a high output impedance.
With the volume pot at maximum the OP Z is about 8 to 15k Ohms. VASTLY lower than the 1,000,000 input resistance (mostly!) of a guitar amp. If the volume pot was the very common 500k then the WORSE CASE (-6dB) OPZ would be 125k but even that considerably modified by tone controls and cable capacitance. Then of course the actual OPZ of any particular guitar at any particular setting is all over the shop and in the lap of the gods. It is never however very close to the 1meg of the amplifier.

But the passive electric guitar is a very special case, quite unlike any other and today any electronics engineer who had never seen one would say "WTF did you do it like that!"

Voltage level is all that matters. The vagaries of source Z and capacitance along the way are peculiar to the guitar and are in the gift of the player to sort by technique and ear.

*Way back in the mists of time, some recording engineer (who I wish had been strangled at birth) connected a pair of audio transformers up such that a guitar in the control room could send a balanced signal down a mic line. The second transformer at the amp end in the studio then turned the signal back into an unbalanced one to drive the amp and also back to approximately the same level, AND SOURCE IMPEDANCE as the guitar. One half of that rig we now call a DI box.

Dave.

 

[miroslav]

And there, ^ lies one of the root causes of much of the confusion, misinformation and "black art" surrounding the connection of guitars to amps, re-amping* and much else.

Magnetic pickup electric guitars do NOT have a high output impedance.
With the volume pot at maximum the OP Z is about 8 to 15k Ohms. VASTLY lower than the 1,000,000 input resistance (mostly!) of a guitar amp. If the volume pot was the very common 500k then the WORSE CASE (-6dB) OPZ would be 125k but even that considerably modified by tone controls and cable capacitance. Then of course the actual OPZ of any particular guitar at any particular setting is all over the shop and in the lap of the gods. It is never however very close to the 1meg of the amplifier.

That's all good...agreed....but it also depends on what you consider "high".

The earlier point was ....a guitar at 8k-15k Ohms is "high" when compared to what a typical line or mic output would be....which is why guitar amp inputs have a MUCH higher input impedance than your typical pream/Line input.....keeping with all that "10 times higher than output" perspective.
So it's all relative to how one matches the different output and input impedances.
Which makes DI and reamp boxes the right ticket for guitar-to-preamp/interface use.

 

[ashcat_lt]

When did we start talking about guitars? That's the other end of the deal and already over at this point. All we need to do now is plug the interface into the amp. There is no impedance issue.

Guitar amps expect very little from their sources. "Line" outputs are prepared to meet some pretty hefty demands and has no problem fulfilling the amp's meager demands. It's practically like paid vacation.

Level is not impedance. It is true that certain impedance standards are attached to certain nominal level standards, but they're not to be confused. A very sensitive microphone can rival the voltage levels of a passive guitar. A weak single coil played softly is in a voltage range that could easily be called mic level. A loud humbucker can put out even 4V when you hit the thing. That's a pretty respectable line level. Most guitar pedals (at least the clean ones) will pass maybe 5 or 6V which is a couple notches above 0db on your +4 meters. A line output will usually put out 20 or more volts if you ask it to. And they will all perform their very best when plugged into something with such a high-Z load as a guitar amp.

But yes, the amp isn't really designed to take 20V inputs. In reamping, we'd usually want the voltage going to the amp to be as close to what's coming out of the pickup as possible. That has nothing to do with impedance. It's a level issue.

And sometimes there's a ground loop. That's a different issue.

A dedicated reamp box actually does help resolve those two issues. There are other ways to do it, but this conveniently does it for you. The method it uses happens also to convert the impedance, but that was never an issue.

There is no impedance issue.

 

[miroslav]

It's a level issue.

Yeah....we covered at the start of the thread.

It's not a question of impedance being a show-stopper "issue"....it's a question of the most optimal connections for best sound quality...if you care about that sort of thing.
Sure, you can jury-rig all kinds of connections and pass signal, sometimes decent enough to use, but maybe not as good as it can be.

No one is saying you can't run a Line out to a guitar amp because of impedance "issues"...but you seem to always reject out of hand the need to use a proper DI and reamp box to get the best possible results with the least amount of fussing around.
That's what I mean about you always having some sort of absolute view about it.

 

[Greg_L]

When did we start talking about guitars? That's the other end of the deal and already over at this point. All we need to do now is plug the interface into the amp. There is no impedance issue.

Guitar amps expect very little from their sources. "Line" outputs are prepared to meet some pretty hefty demands and has no problem fulfilling the amp's meager demands. It's practically like paid vacation.

Level is not impedance. It is true that certain impedance standards are attached to certain nominal level standards, but they're not to be confused. A very sensitive microphone can rival the voltage levels of a passive guitar. A weak single coil played softly is in a voltage range that could easily be called mic level. A loud humbucker can put out even 4V when you hit the thing. That's a pretty respectable line level. Most guitar pedals (at least the clean ones) will pass maybe 5 or 6V which is a couple notches above 0db on your +4 meters. A line output will usually put out 20 or more volts if you ask it to. And they will all perform their very best when plugged into something with such a high-Z load as a guitar amp.

But yes, the amp isn't really designed to take 20V inputs. In reamping, we'd usually want the voltage going to the amp to be as close to what's coming out of the pickup as possible. That has nothing to do with impedance. It's a level issue.

And sometimes there's a ground loop. That's a different issue.

A dedicated reamp box actually does help resolve those two issues. There are other ways to do it, but this conveniently does it for you. The method it uses happens also to convert the impedance, but that was never an issue.

There is no impedance issue.

If you already know this, and actually agree with what everyone has already said, why do you always argue about reamping? You talk yourself into a corner just because you don't like the idea of buying a reamp box.

 

[ashcat_lt]

Nope. I said it's not an impedance issue. Period. You went all over hell and back to tell me I was wrong.

The honest truth is that I believe we should use as few interventions possible and that the simplest solution is always the best unless it doesn't work. A straight wire connection is the simplest solution. If you want to get as close as possible then keep it as close to straight wire as possible. Or go buy the "right gear" for the job, insert transformers, attenuators, gain stages, attenuators, and transformers and if you twiddle each knob just right you might get back pretty close to where you started. A typical DAW system with an instrument DI and a line out is really nothing different from a really big loop pedal with a whole lot of headroom. If you don't need a DI and reamp to run through a loop station...

 

[Greg_L]

Nope. I said it's not an impedance issue. Period. You went all over hell and back to tell me I was wrong.

The honest truth is that I believe we should use as few interventions possible and that the simplest solution is always the best unless it doesn't work. A straight wire connection is the simplest solution. If you want to get as close as possible then keep it as close to straight wire as possible. Or go buy the "right gear" for the job, insert transformers, attenuators, gain stages, attenuators, and transformers and if you twiddle each knob just right you might get back pretty close to where you started. A typical DAW system with an instrument DI and a line out is really nothing different from a really big loop pedal with a whole lot of headroom. If you don't need a DI and reamp to run through a loop station...

I never said you were wrong because I'm not exactly sure what you're stance is besides trying to look smarter than everyone else by being a contrarian. I know you like being outside of the box, even if the box is tried, tested, and true. All I ever cared about with reamping is hitting the amp with a guitar-like signal at an appropriate level so the amp acts like one might predict it should. I actually don't give two shits about impedance.

In my own tests, and from what others have found for themselves, going straight from an interface line out to an amp hits the amp like 10 tube screamers are in front of it. If you're cool with that because one cable is the easiest way possible, knock yourself out. The simple truth is that a reamp box takes care of all the potential problems associated with running a line signal to an amp, so it only makes sense to use one. Even if you have to buy it. Gasp!

 

[miroslav]

Nope. I said it's not an impedance issue. Period. You went all over hell and back to tell me I was wrong.

Not sure if you're responding to Greg or me....either way, I don't see that anyone went to "hell and back" to tell you that you were wrong.
I just asked why your position is always so absolute, and I also posted a couple of SoS articles where they specifically talk about impedance and level considerations when doing reamping....and why going "straight wire" may work, but may also add some hiss to your signal...etc..etc.

You seem to reject all that....and you indirectly reject all the reasons people use the DI/reamp boxes in studios all over the world regularly. You tend to do that in every thread where reamping is discussed.
Not sure why?

Maybe you have the answers that everyone else missed...?....but for myself, purely from personal experience in attempting a variety of interconnections over the years, I found that there's a reason why DIs and reamp boxes work where other approaches may work, but fall short of optimal...and why there's a plethora of various types of "black box" interconnection devices available for use in both live and studio applications....because they do the job well and in an optimal way.

 

[ashcat_lt]

It sounds like an absolute stance because it's absolutely true. In the case of a line out feeding a guitar amp there is no impedance issue. There may be other issues, but impedance is not going to be one of them. The thing you quoted is wrong*. It is deliberately vague because he has nothing to back it up. It is exactly the kind of misinformation that I try to combat in this forum, and it is exactly because these little e "engineers" try to talk about things they don't understand from a position of supposed authority that I end up rehashing this bullshit argument so often.

There is no impedance issue on the reamping end. Focus on the things that do matter.



*The part where he tries to bring impedance into it. The rest is reasonable, I suppose.

 

[Greg_L]

 

[miroslav]

It is exactly the kind of misinformation that I try to combat in this forum, and it is exactly because these little e "engineers" try to talk about things they don't understand from a position of supposed authority that I end up rehashing this bullshit argument so often.

Oh....well why didn't say that right up front. That makes all the difference.
I should have assumed that the editor of Sound on Sound would be totally ignorant of those things.



One other point I'll leave you with...and I'll say right up front that I personally haven't spent any time looking at the math or running extensive lab tests....blah, blah blah...
....but I have noted that some people say that because guitar pickups are inductors with higher impedance they marry up well with the VERY high input impedance of a guitar amp, by design, and the two combine in the complete circuit along with the caps and resistors to form a low pass, mildly resonant filter that is somewhat defined by the impedances and capacitance.
So then if the source output impedance goes much lower (like Line level output impedance)...that drop in output impedance changes that complete circuit and it can then shift that resonant frequency up much higher which can make the amp sound brittle/harsh/bright.

Now one might just reach for the amp's tone control and try to dial that out...but again, getting the impedances in a line source-to-guitar amp to mimic a typical guitar source-to-amp will insure that the tones survive as expected....and that's certainly accomplished with a proper reamp box, which also simultaneously solves all those "other issues" you alluded to.

Of course....you're probably not going to buy any of that either, so to each his own.

 

[ashcat_lt]

The guitar is extremely sensitive to its load. The amp is not sensitive to its source. Once you've recorded the guitar, that resonant peak is already set. Now you just need to get that to the amp.

Impedance considerations do need to be made on the guitar-to-interface side. 470K is a tiny but noticeable difference from 1M, and 10K will be all kinds of suck. That sets the cutoff of the filter with the pickup, and the resonant peak. Once you've captured that, anything else you add to filter the sound - in the DAW, or in an outboard device - is taking you further away from the sound of the guitar plugged right into the amp.

I am well aware that you don't get the math. This is not the second time we've had this argument. I am also aware that "conventional wisdom" and marketing money are on your side. I'm still going to call bullshit when I see fit. The idea that there is any "impedance mismatch" that would cause any of the problems folks run into on the interface-to-amp side of things is bullshit.

 

[JimmyS1969]

I am about to close this thread.

This argument is getting ridiculous IMO. An amp is ABSOLUTELY sensitive to it's source. Especially the signal level. WTF Ashcat?

I don't really give a shit what math anyone tries to use here. Nor do I care about the math.

The fact is if you record a direct signal from a guitar to DAW and then try to get the same tone you would have had by plugging directly into your amp by running the line out of your interface to it, it will likely sound like complete shit.

Why the redundant argument. The fact is that a reamp box is the best route and what works best.

I am not sure why these types of arguments start, but it seems pointless to me and the benefit of the thread now.


Consider this your first warning.

 

[ashcat_lt]

The OP came here concerned because he'd heard that there was an "impedance issue" that might cause some undesirable effect connecting from the interface output to the amp. There isn't. That's really all of I've been trying to say. The discussion of level matching is a completely separate discussion. Important yes, and somewhat relevant to the thread, but not impedance related. The discussion about the other end of the equation - guitar to interface where the whole thing with the inductance of the pickup comes into play - is also important, but not actually to the point the OP was asking about.

The line matching transformers in the OP accomplish none of what a reamp box does well. The impedance step up comes with a voltage step up, which is the wrong way if its already been recorded too loud, and it offers no way to attenuate, so you still have to turn down at the DAW. The transformer adds its own noise and the higher impedance makes the cable run from to the amp more susceptible to EM/RFI noise. The shields of the cables are connected through the barrel of the thing with no ground lift switch so you lose the one benefit of transformer isolation. And all that is best case, assuming that the cheap nasty transformer itself won't change the response in frequencies we care about or add its own distortion.

There is no impedance issue on the reamp side. I'm not the only one in this thread who said so. Close it if you want.