Hi-z input (instrument in) on various interfaces: Lies from manufacturers

Hi there!
After a loong search and help from mr Jim Roseberry, I decided to buy the Edirol FA-101 interface. The most important feature is its round-trip latency. But there are other features i looked in EVERY interface I read about: The instrument input, with Hi impedance (HI-Z) input.
A little bit of story:
Without being OT, let me just mention that since the beginning of the electric guitar era all reasonable good amps, preamps, fx boxes, etc, have had an input impedance of 1 m ohm. That is the minimum passive guitar/bass pickup should 'see'. Why? The reason IS OT. Basically electronic reasons. In short, with lower impedance, you loose high, get more noise because of an IMPEDANCE MISMATCH. Try connecting your guitar directly to a MIC preamp (just mic preamp, not one with Hi-Z) and you will see.....
A LOT of interfaces still insist giving a FAKE INSTRUMENT HI-Z input. The so called universal input accepts mics, line and HIZ. It is amazing that MOST of the interfaces provide a BAD INPUT IMPEDANCE when connecting to it HIZ input. Some manufactures dont even say that value!

Examples: Emu 1820. Presonus inspire and "blue" (Hi z Input 500kohm). M-audio Fast Track, fast track USB, 1814 (500K Ohms), all F.Wire Echo interfaces (102Kohms), U46MKII (200kohm), M-audio Fast Track Pro (220k ohm), RME Fireface 400 (470 kOhm) ,just to mention a few.

The main question (could be stupid,hehe) is: WHY?
Obviously they know this. Some of these brands, have interfaces with 1MOHM input impedance for their more expensive products:

M-audio Fast track ultra, the rack unit interfaces, All Alesis (except IO2), presonus firebox and all rack units,.

Luckily, some interfaces respect that and also have inputs with 1 mohm:

All newer EMU, all TC-electronics, Tascam Us-122/144, All Focusrite units, Tapco.

Interestingly, some brands DONT EVEN MENTION THAT: they just say "Hi impedance input for connecting guitars and basses".

MOTU does not provide that info. I called Tech support they told me it is 220k for the Traveler.
Edirol does not provide that info too. i called them and they dont know.

I might be pick, be obviously a guitarrist does not want another piece of equipment fro mobile situations.

I know some of you have a lot of knowledge and i would appreciatte your thoughts on this. Some will say "22kohm is more that enough".

That things are not so compelling. The best guitars amp today have 1 mohm.

I hope my information helped anyone who want to direct record/ live fx a guitar or bass with those interfaces


Best regards,
Danny Bullo

Edirol does not provide that info too. i called them and they dont know.

That's a disgrace, then. This says this particular Edirol uses 470K ohms Hi-Z, but dunno how typical that is for Edirols. They apparently USED to know such stuff.

http://www.velvetsystems.com/Edirol.DA2496.cfm

[edit fixed link]

Well... you could use a DI. Or, does anyone know if just added a resistor to the cable or in a box would work ? Would you still have enough gain ? Seems like a 500meg resistor should add enough to what is there. Seems like I've seen a little guitar box of some kind to do that but a resistor is so small it should fit inside the 1/4" plug.

They claim 1 Mohm on their website.

http://www.presonus.com/products/Detail.aspx?ProductId=3#

They also see their customers as urchins, for some reason. I won't be buying from them.

.

Great post, bullo, and eye-opening. Some of those brands I would expect better from (RME in particular sticks out like a sore thumb).

This is exactly the kind of thing that leads people to think "old gear sounded better" and that you need to spend megabucks to get decent sound. How many people went from recording bass into a 200kOhm input and then plugged into a fancy boutique DI box and have been wowed by the difference, when simply using a proper Hi-Z input might have had the same or similar effect? How many of those people are now out there posting on internet message boards that there is no way to get good sound without a $500 DI or whatever?

Even a little Rat Shack mixer had proper hi-z inputs 15 years ago. This kind of stuff borders on fraud, but unfortunately there is no FDA for audio. The saddest part is that the very stuff that doesn't post specs is the same stuff that is being marketed to people who don't know how to look for it as "pro" quality.

Great legwork to dig all that up, and very good of you to share. There are such mountains of mumbo-jumbo and pseudo-specs on the web that hard data about basic, important stuff tends to get buried. Hopefully, as "prosumers" start to become better informed, manufacturers will start to have a little more respect for them, the largest market segment for this stuff. Thanks for sharing.

Well, just checked my B-brand V-amps input - 1 M ohm, as it should be. [sigh of relief] I don't use the one on my Edirol anyway, but still - it sucks to think it's maybe only 470 K...

yep - but wouldn't that essentially be the same circuit you would find on the input of an instrument input of one of the interfaces which DOES have 1M Ohm input impedance? I'm thinking that those which do have the correct HiZ inputs are going to have to make that input impedance on non-tube applications by doing the same or similar input circuit as is listed on Roflcopter's link.

.

ORIGINAL: mike_mccue
I have some questions about how many manufacturers are substituting resitance for impedance and then calling it impedance. I haven't even been able to formulate the question but I'm seeing more and more potentiometers offered as variable impedance features in lo cost circuits. It's giving me the willys that I can't make sense of how it's quantifyably different.

When you figure out the question just ask!

In the meantime, impedance and resistance describe how a circuit or circuit element impede or oppose current flow. Resistance is the DC measurement of opposition to current flow. Frequency does not play a part in the definition. A purely resistive impedance will oppose current flow exactly the same at any frequency, of course it turns out there is no such thing as a purely resistive element, but that's a tale for another time!

Impedance is frequency dependent. That is to say in order to specify impedance you must also specify the frequency at which that impedance was measured, otherwise it is pretty meaningless. A 1 ohm impedance at 1000 Hz might be 10 ohms at 10 Hz, or it might be 1000 ohms at 10 Hz.

Impedance is classified as capacitive or inductive. A capacitor will not pass DC, but it will pass high frequencies. In fact, the impedance of a capacitor decreases as frequency goes up. An inductor will pass DC all day long, but starts to impede current flow as frequency increases. The nuts and bolts has to do with whether the current leads or lags the voltage, and that too is fodder for another post.

ORIGINAL: mike_mccue
But the thing that really bugs me is seeing that just about every "value ended" vendor these days seems to cut and paste the gobbly gook from the manufacturers literature onto their sales info and then pretend like they did some kind of service to enhance your purchasing experience. Most vendors now a days are nothing more than financiers investing in the practice of keeping stock in proximity so it's available should you want to acquire it in a timely manner.

It's darn near impossible to get good info about mid grade products.

It's actually much much worse than that. There are a number of companies that simply use the IC vendor's reference design to build their products. If the vendor got the reference design right then at the very least the products will work, but they will all work exactly the same, within the limits of how well the circuit board is laid out, and how complete the reference design is. It's pretty sad really.

This is what the democratization of technology has wrought, along with a frightening reliance on entitlement<G>!

ORIGINAL: mike_mccue
I miss the space race, back then every high school kid at least knew something about technology... certainly they new more than what features the new IPhone has. Manufacturers had to step up and provide real useful info. Now they avoid useful info because it would only discourage up and comers from buying lo-mid grade gear... No one really needs bad gear.

ORIGINAL: cityrat

build yourself one of these:

http://www.till.com/articles/PreampCable/index.html

Tillmans active cable... man I love those things!!!!!! I use them to tame my guitars and my pedals. They work wonderfully!!!

And just to add to my post above, one reason I feel that it's unlikely that the sound interfaces have PASSIVE DI's built into their inputs is because passive DI's require a decent audio transformer for operation. that takes up valuable space and good DI xfmrs are not as cheap as active components. so I think it's likely that all of those sound interfaces which have 1M input "impedance" for their instrument inputs have an active DI built into the input.

ORIGINAL: wst3

ORIGINAL: chefmike8888

I just checked my Onyx 1640. It shows 1 mega ohm.

Mike

Did you measure impedance or resistance?

Bill

Impedance.

Mike

ORIGINAL: mike_mccue

"If there's any inductance or capacitance on the circuit, then the resistance of that input becomes frequency dependant, that's basically the difference between the terms resistance and impedance."

I knew that part. :-)

Sorry, but it is usually safer to assume that some reading this thread don't...

Lately I've been trying to learn more about the practical difference between conductive reactance and capacitance.

Reactance can be either capacitive or inductive, and this is where the phase angle between voltage and current come into play. I will try to write up something later, but you might want to invest in a good Electricity and Magnetism (E&M) text book. I can't remember the author for my college text, but it was good, although quite dependent on calculus and "difficult" equations.

Just as I'm coming to speed on this I've started stumbling on curious claims with regard to input impedance. In these cases when I look at the schematics there's a big honking resistor or potentiometer right before the tranny, transistor, or tube creating a large part of the value that is claimed as "impedance". The manufacturers literally claim that resistance is for all intents and purposes a broad band flat impedance response.
But that's an aside merely explaining why I've been thinking about this stuff in more detail as of late. I smell something fishy.

Strictly speaking, a 1 MOhm resistor, or potentiometer does in fact present a 1MOhm impedance, but it isn't enough, as you've figured out. The "typical" guitar amplifier input presents a complex 1 MOhm impedance, and that is largely responsible for the "sound" of that particular circuit.

What I was speaking of to you is the idea that there may not be an exact substitute for a tube when it comes to explaining how a passive guitar pickup interacts with the input impedance of a guitar amp.

it should be possible to create a circuit with resistors, inductors, and capacitors that mimics very closely, if not exactly, the complex impedance of a tube input stage. All that is required is to measure the complex transfer function of the tube stage, and then build it with passive components<G>! The catch is that a tube input stage will present different impedances with different driving signals. And that too is part of what makes a Fender sound like a Fender<G>!

Sorry, if that had nothing to do with your question. :-) It's just me babbling.

No, we're still talking about the same thing!

edit: I forgot to add:
Jensen makes a really nice 200k:1.5K "direct box" transformer. That's a good example of how a really nice passive design is unlikely to provide a 1Mohm input without some resistance added to fake it.

Careful there... it really isn't "faking" anything. A transformer primary will present an impedance to a source that is in part the "reflected" impedance present at the secondary. Unterminated transformers are uncommon in audio work... in fact I can't think of a single example.

This just makes things that much more interesting<G>!!!!

Yeah, from what I understand you cannot measure impedance with a DC-fed anything, so I am depending on paper specs and google.