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Hi-Z Input

Discussion in 'Recording' started by Si Cassidy, Aug 25, 2014.

  1. Si Cassidy

    Si Cassidy Active Member

    When using an Amp simulator in Sonar x3, I have switched the Hi-Z input on my Roland Quad Capture to on, and plugged my electric guitar into said input.
    When miking my amp, I have switched the Hi-Z input to off.
    I want to try and use the Emulated Line Out on my amp (Marshall MG 50DFX), to plug into the Hi-Z on my Quad Capture, instead of an Amp simulator.
    The queation is: Hi-Z on or off?
    Has the impedance changed to low, (Hi-Z off) now that the signal has gone through the amplifier.
    Or is it still high impedance, (Hi-Z on)
    I liked the sound of the miked amp, as oposed to the simulator, just not sure the neighbours shared my enthusiasm.

    Simon :)
     
  2. paulears

    paulears Well-Known Member

    In general for the input device to have the smallest impact on the guitar pickup, it needs to be very high impedance. On guitar amps this means around or above 1MOhm - which is about as far away from a short circuit that you can get. Ordinary line level impedance might be between 25KOhms and maybe 100KOhms, and this will have a padding effect on the guitar pickup, dulling the top end and even being enough of a load to present a damping to the actual strings. Switching on the guitar pickup very high impedance switch if you have one is a good thing. So in the kit we use often, we have low impedance for mics, high impedance for line level stuff like keyboards, synths and playback kit, and very high impedance for guitar connections.
     
  3. dvdhawk

    dvdhawk Well-Known Member

    The manual is pathetic. But what is stated clearly is, it's a relatively hot +4 signal out of the emulator, so set your Capture to low-z, or line level. Start with all of your levels low as a precaution.

    What is unclear is whether or not it's quasi-balanced TRS or not. Since it doubles as a headphone output, we can probably assume the jack on the front-panel is TRS. In headphone mode, it's likely sending +Right Channel to the Tip, +Left Channel to the Ring, and they share the common shield. I'm not sure how it would behave with a TRS male to XLR male, (or TRS male to TRS male) cable between the Marshall and the recording interface, since the Left/Right are surely in-phase with one another for headphone purposes. Perhaps it is designed to send +4 via an ordinary TS instrument cable, or employs some auto-sensing. Maybe Boswell or Mr. Ease can shed some light on that for us.
     
  4. RemyRAD

    RemyRAD Well-Known Member

    Typical rule of thumb is, most all outputs that are not coming from passive guitar pickups are already a rather low impedance, output. And we generally want these lower impedance outputs, feeding higher impedance inputs. Be it line level or even high Z, inputs. Line level inputs are typically around 10,000 ohms to 100,000 ohms. On professional broadcast and recording equipment, earlier studio items frequently had a 600 ohm input load.

    Any passive output devices are frequently high Z outputs. Which means you cannot load them down with lower Z line level input devices. Without some kind of loss in level or loss in frequency response from low to high. But sometimes that can actually work for ya when that happens. Not generally though.

    When we talk about amplifier outputs, those designed to power speakers are designed to drive an extremely low impedance load like 4 or 8 ohms. So Speaker drive output amplifiers are pushing a lot of current. They are generally too high in current, to even feed 600 ohm inputs much less, 10,000, 20,000, 100,000, 1 million, 2,000,000 ohm loading input devices. There is a difference between current drive amplifiers and voltage drive amplifiers. One deals with power output. The other deals with voltage output. And voltage times current equals Watts. Of which no one needs kick ass wattage outputs to feed, lower voltage input devices. Such as line input and high Z, input devices. Those don't need powerful outputs plugged into those lower-level inputs. Not that one can't do that, you can. But if you're not sure what you're doing? There is the potential for burning up and/or damaging the inputs of devices, that don't need the kind of powerful drive, the speakers need.

    Certain Direct Injection (DI) boxes, designed to take a lower level output device or passive guitar pickup outputs, can sometimes, depending on manufacturer and design type, be able to take the output from a guitar power amplifier. Usually involving an extra switch on the DI box to knock down the power level of the power amplifier outputs. Which allows one to then plug it into a 600 ohm, 250 ohm, 150 ohm, 50 ohm, extremely low level microphone type or high Z, input items, without fear of damage. Sometimes all ya might need is just a couple of resisters. Especially when one is dealing with high Z, unbalanced, guitarlike, inputs.

    There are quite a few ways to deal with your inquisitive question. One can do it both the right way and the wrong way and still get good to even great sounding recordings. Will the sound of the instrument be altered in any way that might compromise its sound? Sure... but who cares? Does it do the job you want it to do or not, is all you really have to worry about. Sometimes the damping of frequency response or the sound of an instrument, works just fine. For others with technical obsessive-compulsive disorders, could never even think of even a 1 db compromise. And that's their problem.

    The reason I say that is, back in the 1970s, we really didn't have, active input, high Z, direct boxes, from which to take a direct output from a bass guitar or lead/rhythm electric guitar or acoustic guitars. What we had were 50,000 ohm input transformers. While 50,000 ohms is considered high impedance, or passes pick up guitar outputs, those usually wanted to see the input to a tube. And those tube inputs are typically 1-2,000,000 OHM inputs. So 50,000 ohms will load down those passive guitar outputs. But not so badly that they are not still usable. What the heck do you think we used back in the 1970s? 50,000 ohm transformers. And plenty of hits were made that way.

    So if you want the utmost in technical perfection? See a psychiatrist. You're going to need one LOL. It's almost like germ phobia. Oh no! I'm down 1 DB at 20 kHz and 100 Hz! How can I live with that??? Ya live with it. And you'll sleep just fine.

    Lullaby and good night.
    Mx. Remy Ann David
     
  5. paulears

    paulears Well-Known Member

    My first electric guitar went into an old valve (tube) radiogram, with an external speaker - it made a great sound, apart from my playing. Nobody really cared about the frequency response, the signal to noise, and back then I'd not studied electronics so had no idea what impedance was. Probably everything about it was compromised, but it didn't matter. Nowadays I do get the feeling people don't experiment, and only do things that are in the manuals or shown in a video on youtube. I couldn't even solder, and twisted wires and tape worked fine!
     
  6. Boswell

    Boswell Moderator Distinguished Member

    The TRS output from the Marshall MG50DFX amp is mono, both the tip and ring being fed the same signal through separate 470R resistors. You can take this output using a standard guitar cable (TS jack lead) into the Hi-Z input on an interface provided the gain can be set low enough. Don't use a balanced microphone input or balanced line input as you will get no signal unless you put an unbalanced-balanced signal transformer in the path.
     
    dvdhawk likes this.

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