My understanding is that electric guitars with traditional (passive) magnetic pickups require a high impedance (250k+ Ohm) interface otherwise the frequency response rolls off quickly.
The input spec for an analog input such as the kind found in a Macbook computer says "Input impedance: > 20 kΩ" without giving a typical value or upper limit.
https://discussions.apple.com/thread/1973943?tstart=0
Does that mean that the internals of a typical interface box is nothing more than a high value resistive divider with a small proportion of the voltage tapped off and being fed to the sound card input? Is the assumption that amplification is required within the sound card to compensate for the signal loss?
Looking at the iRig interface in particular (IK Multimedia | iRig 2 - Guitar interface adapter for iPad, iPhone iPod touch, Android and Mac.), it doesn't have any external power and the Macbook analogue input doesn't provide any power aside from a 1.9 - 2.9v bias voltage intended for an electret microphone.
https://blog.faberacoustical.com/2009/ios/iphone/iphone-headset-input-options/
which seems too low to power an op-amp.
Is there any signal buffering happening at all, or is it just a passive resistor arrangement?
The input spec for an analog input such as the kind found in a Macbook computer says "Input impedance: > 20 kΩ" without giving a typical value or upper limit.
https://discussions.apple.com/thread/1973943?tstart=0
Does that mean that the internals of a typical interface box is nothing more than a high value resistive divider with a small proportion of the voltage tapped off and being fed to the sound card input? Is the assumption that amplification is required within the sound card to compensate for the signal loss?
Looking at the iRig interface in particular (IK Multimedia | iRig 2 - Guitar interface adapter for iPad, iPhone iPod touch, Android and Mac.), it doesn't have any external power and the Macbook analogue input doesn't provide any power aside from a 1.9 - 2.9v bias voltage intended for an electret microphone.
https://blog.faberacoustical.com/2009/ios/iphone/iphone-headset-input-options/
which seems too low to power an op-amp.
Is there any signal buffering happening at all, or is it just a passive resistor arrangement?
That device is clearly active, definitely not a plain resistive divider, at all.
Is only 1.9 to 2.9V available from the I Phone?
Then it´s working on that, period.
Of course, it will have some internal converter to any voltage needed ... possible because power consumption must be very low.
Is only 1.9 to 2.9V available from the I Phone?
Then it´s working on that, period.
Of course, it will have some internal converter to any voltage needed ... possible because power consumption must be very low.
I think iRig is a JFET buffer. If you order by the thousands, it is not hard to source JFETs to work consistently at lower voltages. (All electret mikes used to use them.) (In fact you could consider an iRig as a electret mike without the electret capsule.)
With the odd-lot and RF JFETs on the DIY market, it may be easier to work from 9V.
With the odd-lot and RF JFETs on the DIY market, it may be easier to work from 9V.
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