15-01-2016, 05:30 PM
One part of the installtion that needs attention is the audio/video router. The current arrangment is both temporary and inadequate.
I'm building a simple relay based router, the photo shows progress to date.
I had plenty of 4PCO relays with 700R 24V coils. Jeremy (Pamphonica) kindly provided some tapped strip to mount them on. The wiring looks a bit rats nest but shoud be fine. It's built for function, not beauty. There are 9 inputs and 4 outputs.
From left to right the outputs are:
To Ch1 Aurora
To Ch9 Aurora
To UHF modulator
Preview
From back to front the inputs are:
BBC1 off air tuner
ITVoff air tuner
BBC2 off air tuner
Testcard for BBC1 (no video normally connected, internal to Aurora in absence of signal)
Testcard for ITV (no video normally connected, internal to Aurora in absence of signal)
Testcard for BBC2
DVD player
COW
Aux
Note that the tuner and testcard inputs are only made available to their respective outputs. Testcard music can be put into the testcard audio inputs when we acquire 1 or more MP3 players.
The video inputs and outputs will be buffered with EL2020 opamps. The audio will not be buffered. The input buffers will be on a bit of matrix board to the right of the relays. The output buffers will be to the front of the relays.
Video crosstalk is minimised by using a pair of CO contacts for each crosspoint. The wipers are earthed via the NC contacts when a crosspoint is switched off. I'll measure the crosstalk when it's all finished. Even with all inputs hostile it should be better than -50dB to 5MHz. I'll be very pleased if I get -60dB . Gain should be accurate to 0.1dB. Frequency response flat to 5MHz within 0.2dB.
Audio uses the same pair of CO contacts technique though probably not essential. I'm not hazarding a guess at audio crosstalk but it should be fine.
I hope I don't get any significant video to audio crosstalk, usually sounds like a buzz on audio.
The ribbon cable carries all the controls to a separate control panel.
Need to mount it in a 2U rack tray and hook it up to an old Cox back panel which has enough holes for all the connectors. I'll need a 12+12 PSU, may well have one in stock, otherwise knock one up out of a toroid, bridge, 7812 and 7912. Actually the relays work perfectly well on 18V so I may use a 9+9 PSU to reduce disspation.
I'm building a simple relay based router, the photo shows progress to date.
I had plenty of 4PCO relays with 700R 24V coils. Jeremy (Pamphonica) kindly provided some tapped strip to mount them on. The wiring looks a bit rats nest but shoud be fine. It's built for function, not beauty. There are 9 inputs and 4 outputs.
From left to right the outputs are:
To Ch1 Aurora
To Ch9 Aurora
To UHF modulator
Preview
From back to front the inputs are:
BBC1 off air tuner
ITVoff air tuner
BBC2 off air tuner
Testcard for BBC1 (no video normally connected, internal to Aurora in absence of signal)
Testcard for ITV (no video normally connected, internal to Aurora in absence of signal)
Testcard for BBC2
DVD player
COW
Aux
Note that the tuner and testcard inputs are only made available to their respective outputs. Testcard music can be put into the testcard audio inputs when we acquire 1 or more MP3 players.
The video inputs and outputs will be buffered with EL2020 opamps. The audio will not be buffered. The input buffers will be on a bit of matrix board to the right of the relays. The output buffers will be to the front of the relays.
Video crosstalk is minimised by using a pair of CO contacts for each crosspoint. The wipers are earthed via the NC contacts when a crosspoint is switched off. I'll measure the crosstalk when it's all finished. Even with all inputs hostile it should be better than -50dB to 5MHz. I'll be very pleased if I get -60dB . Gain should be accurate to 0.1dB. Frequency response flat to 5MHz within 0.2dB.
Audio uses the same pair of CO contacts technique though probably not essential. I'm not hazarding a guess at audio crosstalk but it should be fine.
I hope I don't get any significant video to audio crosstalk, usually sounds like a buzz on audio.
The ribbon cable carries all the controls to a separate control panel.
Need to mount it in a 2U rack tray and hook it up to an old Cox back panel which has enough holes for all the connectors. I'll need a 12+12 PSU, may well have one in stock, otherwise knock one up out of a toroid, bridge, 7812 and 7912. Actually the relays work perfectly well on 18V so I may use a 9+9 PSU to reduce disspation.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
