Hi,
I'm building my first preamp based on the well known LDR+DCB1 couple with unbalanced input.
I'm redesign the input selector and a simple (maybe silly) question came into my mind.
90% of the input selector (relays based) I've seen use a single DPDT relay to connect/disconnect one input, both the channels on the same relay. The grounds of the two channels (for all the inputs) are always connected to the common ground, this way we need one relay for each input we want to manage. Is it the best practice?
During the design of my input selector, I decided to use two DPDT relays for each input, one for left and the other for right channel. This way I can really disconnect unselected signal and related ground, closing the door for any unwanted noise. Is it useless? doubling the relays means better noise rejection or is just a waste of components?
I'm building my first preamp based on the well known LDR+DCB1 couple with unbalanced input.
I'm redesign the input selector and a simple (maybe silly) question came into my mind.
90% of the input selector (relays based) I've seen use a single DPDT relay to connect/disconnect one input, both the channels on the same relay. The grounds of the two channels (for all the inputs) are always connected to the common ground, this way we need one relay for each input we want to manage. Is it the best practice?
During the design of my input selector, I decided to use two DPDT relays for each input, one for left and the other for right channel. This way I can really disconnect unselected signal and related ground, closing the door for any unwanted noise. Is it useless? doubling the relays means better noise rejection or is just a waste of components?
As a rule, I do not short the unused inputs to ground, and in that case I
don't see how it would matter - you would not be using all the pins on the
DPDT switch.
So it's correct to use two relays for each input you want to manage, connecting/disconnecting both signal and ground of each channel?
Well, I have two doubts.
1) connecting all the grounds of the inputs means my cd reader, my turningtable and my other devices will be force to have a common ground.
2) the noise coming form unselected inputs and related connection cables will always be injected into my preamp
When we talk about input stage of an equipment I don't see any relevant difference between balanced and unbalanced. In both the cases we have to manage two wires bringing the signal and in case of unbalanced connection, the ground is also used as shield.
BUT considering that usually in case of unbalanced connection all the grounds are shortcutted... maybe I'm just making things more complex than needed.
1) connecting all the grounds of the inputs means my cd reader, my turningtable and my other devices will be force to have a common ground.
2) the noise coming form unselected inputs and related connection cables will always be injected into my preamp
When we talk about input stage of an equipment I don't see any relevant difference between balanced and unbalanced. In both the cases we have to manage two wires bringing the signal and in case of unbalanced connection, the ground is also used as shield.
BUT considering that usually in case of unbalanced connection all the grounds are shortcutted... maybe I'm just making things more complex than needed.
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