[LAU] checking passive input frequencies on non Hi-Z connection
termtech at rogers.com
Sat May 20 15:12:32 UTC 2017
On 05/18/2017 07:15 PM, Wayne DePrince Jr. wrote:
> ahoy all,
> i have been testing out a Zoom H5
> which (along w/ the H6
> for that matter) is advertised as NOT supporting passive instrument
> connections on the TRS inputs. to quote the manual: "Direct input of
> passive guitars and basses is not supported." thus i assumed that i
> would need a DI box/effect box/etc. to record well any directly
> connected passive electric guitar or bass.
> however, when i connect my electric guitar (Lace Sensors and Alumitone
> pickups) and electric bass, both passive, to the TRS connections on
> inputs 1 & 2 of the H5 with gain only at 5 of 10, i get a good sound
> and strong signal, /seemingly/ the same as when they are connected to
> an interface (in this case a Zoom U-44
> that supports Hi-Z connections.
> i first contacted Zoom support and they replied:
> "There is no issue connecting a passive guitar to the 1/4" input on
> the H5.
> There may only be an issue with level or noise, but if you are
> satisfied with the audio quality then there is no problem."
> now while i do not yet have a good understanding of Lo vs. Hi-Z, i
> have read various
> about it. they seem to indicate that the passive guitar signal would
> lose some frequencies with this kind of connection and thus this setup
> is undesirable.
> but again as it "sounds the same", i had some questions before
> investing in a DI box or getting a different interface:
> * would the fact that the pickups are Lace Sensors and Alumintones
> have anything to do with the passive signal being picked up fairly
> well by the non Hi-Z input?
> * is there a way to check (preferably in software) if frequencies
> are actually missing or if the signal quality is indeed reduced
> when compared to one from a Hi-Z input?
> * is it possible that the H5 has good enough preamps/whatever that
> the gain on the inputs is enough to make the passive signal OK?
> so to summarize: is this an acceptable solution for recording a
> directly connected passive instrument (in this case an electric guitar
> and bass) even though the H5 does not officially support it?
> thanks, w
> PS: for those wondering the H5 works great w/ GNU+Linux as an audio
Hi. According to the Zoom HS specs, the input impedance on Mic/Line In is
2 Kilo Ohms or more while Inputs 1/2 are 1.8 Kilo Ohms or more.
This is terrible for a guitar pickup.
The pickup's coil and the input impedance of the device it is plugged into
form a low-pass filter. The higher the input impedance the better.
That's why guitar inputs are always 1 Mega Ohm or more.
But it is bad for another reason as well:
Most guitar pickups have between 6 and 12 Kilo Ohms resistance.
When fed into your 1.8 Kilo Ohms input, it forms a voltage divider
which will severely lower the overall output of your pickup.
Get a DI box.
If you want the maximum possible frequency response and you
want the most out of your pickups, get an active DI box.
It may introduce a bit more noise due to the active circuit.
On the other hand, if you want convenience of no batteries
and just plug and go, get a passive DI box.
It may introduce a bit of noise due to non-linearity of the
passive transformer, and the frequency response may not
be as full or flat as an active DI box.
Mine is a Radial Engineering DI box. I am happy with it.
Even though the sound is slightly coloured by the
passive transformer, it is far better than no DI box at all.
As for measuring the differences, that's a tough one.
I was able to see clearly a difference simply by using
my oscilloscope and plucking strings.
With the guitar plugged into a 10 Kilo Ohm mixer input,
I could clearly see less high frequency content (harmonics etc.)
than with the guitar-to-scope alone. (The scope probe has
1 Mega Ohm input impedance.)
A more scientific method might involve simultaneously
recording the un-loaded pickup signal and the loaded
signal and then comparing with software.
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