I would appreciate if someone can disseminate the consequence of this low impedance on the devices to associate with this preamp. I am not an expert in such matters.
thanks in advance
Why 2k?
A 2k input impedance perhaps indicates the use of an opamp in the inverting mode, rather than voltage follower mode. 2k is chosen as the input resistor to the virtual earth input of the opamp in order to reduce noise. This configuration which does give a low input impedance however does not rely on the common mode rejection ratio (CMRR) of the differential I/P of the opamp which is the case in voltage follower mode where the differential input pair follow the input voltage resulting in sensitivity to the CMRR parameter and hence a marginally higher distortion.
The consequences for the driving source?
1. If fed from a high quality opamp (capable of sink/sourcing several mA) in the signal source with a low value series resistor between the opamp and the O/P terminal of the signal source (as in the D90 for example), then it works perfectly.
2. If the series resistance is higher then signal level is lost: so if for the sake of argument the O/P Z is 2k you lose 6dB of gain
(and add inconsequentially to the noise)
3. With only 10dB of gain and the above signal loss you may lose out on the ability to fully drive your power amp if it’s not sensitive. So check the drive levels of the signal source - some were designed in the past to work with line input sensitivities of ~250mV on an integrated amp
4. To drive 2v rms sine wave into 2k load then your source needs to be able sink/source 1.41mA with low distortion so sources which don’t have a feedback opamp with a complementary O/P stage will suffer severe distortion. Such a stage might be an emitter follower O/P which was used in the past when a high impedance load was anticipated