so i'd like to built a really simple passive pre. just an input selector and volume pot really. can it be as easy as taking the signal from rca in to a selector switch, from there to a volume pot and out through an rca again?
the selector switch i'm looking at doesn't have a ground tap: www.hificollective.co.uk/switches/elma
how would i route the signal ground in an application like this?
also i noticed they list "make before break" and "break before make" switches. which one would be right for my application?
any other stuff to consider?
the selector switch i'm looking at doesn't have a ground tap: www.hificollective.co.uk/switches/elma
how would i route the signal ground in an application like this?
also i noticed they list "make before break" and "break before make" switches. which one would be right for my application?
any other stuff to consider?
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I think that is the definition of a passive preamp 🙂
It is not usual to switch grounds and so those switches should be fine. You want a break before make to avoid momentarily placing two source component outputs in parallel (although in 99.999% of cases nothing destructively bad would happen).
to avoid clicks and pops ( due to possible difference in potentials between inputs ) , make before brake is preferable for input switching
nothing wrong having two sources momentarily connected
though , without resorting to relay based selector , where unused inputs are grounded (separate route to main ground point !) , there will always be some amount of crosstalk between unused and used inputs
nothing wrong having two sources momentarily connected
though , without resorting to relay based selector , where unused inputs are grounded (separate route to main ground point !) , there will always be some amount of crosstalk between unused and used inputs
i guess you're right. but experience tells me that whenever i think something is really straightforward it turns out more complicated :d
so where do i take the ground from the rca in if not to the selector?
Think of one channel and you connect all the input grounds to a single point. So six inputs see six ground wires going to a single point. From that point you then run another ground wire to the output RCA socket.
Repeat for the other channel.
That keeps the left and right grounds separate (which tbh probably makes little difference here)
Repeat for the other channel.
That keeps the left and right grounds separate (which tbh probably makes little difference here)
both go to the same point where all the other grounds meet - left and right channel seperated ...?
You got it 🙂 for instance, if you're using coax, both screens, in and out of the pot go to the ground pin, that is the one on the left, with pins at the bottom, looking from the front of the pot. Oh I see what you mean, not quite, have you got it from my explanation?
Yes, but there are many different ways to implement it.
The picture has all the grounds connected together whereas I suggested keeping left and right separate. There are countless possibilities.
If you use a metal case for screening that should connect to the ground as well, but again you have options. You might find it better to loosely tie the case to ground via a low value resistor.
The picture has all the grounds connected together whereas I suggested keeping left and right separate. There are countless possibilities.
If you use a metal case for screening that should connect to the ground as well, but again you have options. You might find it better to loosely tie the case to ground via a low value resistor.
Mooly two low value resistor from RCA ground of each channgel to metal case?
What resistor value?
What resistor value?
see, i knew it wouldn't be THAT easy. it seems there are various opinions regarding grounding and even regarding shorting / non shortng selector switches.
now to make things easier i decided it could be convenient to put my phono pre including psu in the same chassis. now i'm wondering how that would make grounding more complicated...?
now to make things easier i decided it could be convenient to put my phono pre including psu in the same chassis. now i'm wondering how that would make grounding more complicated...?
There are no hard and fast rules, you have to build the preamp to suit your requirements 🙂
Typically something in the region of 4.7 to 10 ohm would be used. That ties the case to audio ground for shielding purposes. If you built a dual mono construction then tying both channels this way gives continued shielding even if only one channel is used, and the resistors still allow enough isolation to prevent any issues due to circulating currents.
Typically something in the region of 4.7 to 10 ohm would be used. That ties the case to audio ground for shielding purposes. If you built a dual mono construction then tying both channels this way gives continued shielding even if only one channel is used, and the resistors still allow enough isolation to prevent any issues due to circulating currents.
There are no hard and fast rules, you have to build the preamp to suit your requirements 🙂
Typically something in the region of 4.7 to 10 ohm would be used. That ties the case to audio ground for shielding purposes. If you built a dual mono construction then tying both channels this way gives continued shielding even if only one channel is used, and the resistors still allow enough isolation to prevent any issues due to circulating currents.
Typically something in the region of 4.7 to 10 ohm would be used. That ties the case to audio ground for shielding purposes. If you built a dual mono construction then tying both channels this way gives continued shielding even if only one channel is used, and the resistors still allow enough isolation to prevent any issues due to circulating currents.
I do as Mooly prefers and not as shown in the pic.
The input to the RCA socket is a two wire connection. The output from the RCA socket should also be a two wire connection.
Each RCA socket should use it's own two wire connection. A coaxial is suitable. Each coax (or twisted pair) must be connected at both ends. The signal current has to flow to the load and must return to the source.
Connect the signal returns from the multiple inputs only when they arrive at the selector switch/relays.
Do not take a common "ground" wire on some other route to a remote star. Doing that puts a large LOOP AREA into all the input wiring and that is a recipe for making the input sensitive to picking up interference.
The input to the RCA socket is a two wire connection. The output from the RCA socket should also be a two wire connection.
Each RCA socket should use it's own two wire connection. A coaxial is suitable. Each coax (or twisted pair) must be connected at both ends. The signal current has to flow to the load and must return to the source.
Connect the signal returns from the multiple inputs only when they arrive at the selector switch/relays.
Do not take a common "ground" wire on some other route to a remote star. Doing that puts a large LOOP AREA into all the input wiring and that is a recipe for making the input sensitive to picking up interference.
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