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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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7th Jun 2016, 12:46 pm | #21 |
Octode
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,764
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Re: 1 deck, 2 preamps?
Some more pondering on this matter (and googling). It seems this is indeed a common method to avoid crosstalk with source selection switches in audio equipment. Looking at how the input board connects to the main mixer board, I can see how this could be an issue. Its an unshielded ribbon cable with the 2 sources (phono and line) running directly next to each other for a good 40cm or so.
So I suppose if I replace the ribbon from the I/O board with shielded cable up to my switch, I should prevent that happening. As I understand it this is more likely to be caused by cable runs or PCB tracks next to each other over a length |
20th Jul 2016, 4:07 pm | #22 |
Octode
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,764
|
Re: 1 deck, 2 preamps?
Just to close this off, I did manage to achieve this modification. As the main source switch for each channel shorted the unused inputs to ground, I added an additional switch BEFORE this to select either the "timecode" return signal, or the untouched signal from the preamp section.
The output for each timecode was buffered with a TL072 operating in unity gain, and powered by the mixers dual supply. I used shielded cable wherever possible and mounted 4 phono sockets, and the switch on each respective side of the mixer. The switches I took from a donor mixer of the same brand and are the same to maintain consistency. All in all it does the job and works very well. It seems most people achieve this by splitting the phono signal with a "Y" cable to effectively send it to 2 preamps, I cant see how that can retain decent sound quality myself however |