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The features of the Input Selector are listed below.
- Relay-based input selector with up to six stereo inputs.
- Can be built with fewer inputs if desired.
- High channel separation and excellent off attenuation.
- On-board 5 V regulator powers the relays.
- Gold plated relays, designed specifically for small-signal use.
- Connection to volume control by 10-pin, gold-plated connector.
- 3.3 – 5.0 V compatible logic control inputs for audio input selection.
- Except for one SOIC-14 IC, all components are through-hole components.
- Gold plated PCB. Made in Canada.
The parts budget for the Input Selector is just over $25.
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The specifications of the Input Selector are tabulated below.
| Parameter |
Value |
Notes |
| Number of Stereo Inputs |
6 |
|
| Power Supply Voltage |
7.5 – 30 V |
|
| Power Supply Current |
40 mA |
|
Input Impedance
|
10 kΩ
|
With recommended volume pot.
(Note 1)
|
Max. Output Impedance
|
2.5 kΩ
|
With recommended volume pot.
(Note 1)
|
| Channel Separation |
111 dB |
1 kHz, incl. volume control |
| Off Attenuation |
> 113 dB |
1 kHz, incl. volume control |
| Assembled Dimensions |
45 × 112 × 23 mm |
|
| Assembled Weight |
50 g
|
|
Note 1: The input impedance of a passive preamp is equal to the resistance of the volume pot. The maximum output impedance of such a preamp is equal to one quarter of the resistance of the volume pot.
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The amplitude response and gain flatness of the input selector is shown below. As you would expect from a passive preamp, the gain is completely flat and slightly below unity due to the load of the volume pot on the signal source.
More importantly, the left-to-right channel crosstalk is very low as shown below. Note that the crosstalk is the inverse of the channel separation. Thus, the channel separation of the Input Selector is very high.
In addition to providing good separation between left and right channel, the Input Selector must also have good isolation between inputs. Otherwise the signal from an unselected source can leak through to the output. The measurement below shows the leakage from an unselected channel. As you can see, the leakage is very, very low. In fact, it is below the noise floor of the APx525 audio analyzer.
