The output impedance of most professional microphones is low, generally in the range of 150•, so mic preamps should have an input impedance of about 1,500• or 1.5 kilo-ohms (k•). (Some mic preamps have an input impedance as high as 10 k•, but the range from 1.5 to 3 k• is more typical.) Line-level devices, such as synths, also exhibit low output impedances in the 50 to 100• range, and they operate well with any input impedance more than 1 k•. Older synths and some consumer hi-fi equipment often have output impedances in the 100• to 1 k• range, which requires the destination device to have an input impedance in the 1 to 10 k• range.
An electric guitar's output impedance depends on the pickup design, the settings of the volume and tone controls, and the frequency produced. When the volume knob is turned up (which is usually the case), the guitar's output impedance is typically 3 to 10 k• at low frequencies and 100 to 500 k• at 10 kHz. When the volume is down, the output impedance is more constant, but it still varies by a factor of ten from low to high frequencies.