1413
Variable Input Impedance
One stand-out feature of the ASP880 is the
variable input impedance (Z) control.
There are three impedance load settings on
the unit, and these can be used to extract
various voicings from your mic collection by
loading the mic’s output stage differently.
Notably mics with transformer outputs such
as SM57 / SM7 dynamic mics or Coles
4038 ribbon microphones often provide
quite noticeable changes in tone when
operated into various loads.
The three settings on ASP880 are:
• LO 200Ω
• MED 1400Ω
• HI 3600Ω
Take the dynamic output impedance of an
SM57 for example (illustration only):
Variable Input Impedance - Listening
When listening, this diagram may come in
helpful if trying to train your ear to hear the
differences.
Listen for the following:
1. Change in Level
2. Change in Speed (Transient Response)
3. Change in Tone (Frequency Response)
4. Change in Detail
Please be aware that some microphone
types (transformerless condensor types)
may not produce audible changes due to
their electronically buffered output stages
which have linear output impedances with
regards to frequency and therefore are less
susceptible to changes in loading.
If in doubt, consult your microphone
datasheet & manufacturer.
The source (microphone) and load (mic pre-
amplifier) form a bridging voltage divider,
that contain different values of resistance
for the source at different frequencies - thus
creating a varying frequency response (or
different output levels for each part of the
SM57 impedance curve) and thus a change
in tone can be perceived.
Typically there is some change in level,
timbre, punch and tone when changing Z.
Ribbon mics are known for liking HI-Z inputs.
Ω
Hz
20 20k
310 Ω
0
2k
OUTIN
MIC - SOURCE
310 Ω @ 1kHz
Varying at all frequencies
PRE - LOAD
200 Ω
1400 Ω
3600 Ω
GND
Hardware Features
dB
Hz
20 20k
∞
-20
LOAD = 200 Ω
LOAD = 1400 Ω
LOAD = 3600 Ω
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