Digging through a box I found some stuff I built years ago. Among them 2 phono preamps and one head amp (opamp based) and a power supply for them +-15vdc. All in separate enclosures, I used XLR to run the power to the devices.
Just for the heck of it I decided I want to put the head amp, one phono stage and the power supply in one enclosure. Put a switch on it so the input either goes to the head amp or the phono preamp, the heap amp will be connected to the phono stage internally. Basically I am putting an MM/MC phono stage together. BTW I make my own enclosures, here is a link to a video I made if anyone is interested:
The phono stage and head amp will be under power all of the time when the unit is on.
Attached is a crude drawing of what I intend to do. Of course there are 3 PSU wires, I only drew 2.
Question:
Should I run the signal grounds through a switch (as shown) or have them all common and just run the signal + through a switch?
On the MM connection the input signal will be injected at the phono preamp input, should that have a switch so there is no signal connection to the head amp when it is not needed?
Just for the heck of it I decided I want to put the head amp, one phono stage and the power supply in one enclosure. Put a switch on it so the input either goes to the head amp or the phono preamp, the heap amp will be connected to the phono stage internally. Basically I am putting an MM/MC phono stage together. BTW I make my own enclosures, here is a link to a video I made if anyone is interested:
The phono stage and head amp will be under power all of the time when the unit is on.
Attached is a crude drawing of what I intend to do. Of course there are 3 PSU wires, I only drew 2.
Question:
Should I run the signal grounds through a switch (as shown) or have them all common and just run the signal + through a switch?
On the MM connection the input signal will be injected at the phono preamp input, should that have a switch so there is no signal connection to the head amp when it is not needed?
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You will want to connect the phone cartridge to either the phone pre or the head amp. If not using the head amp you would need to disconnect it from phono pre and ground the head amp input for quiet op and prevent oscillation. One toggle switch that switches power to different small signal relays could be used to make the different connections.
Do I need to run the negative signal through a switch or just the positive?
If you are running balanced lines then both positive and negative signal should be switched. If single ended then the signal ground can be a common connection for all sections. Whether you turn off power to the head amp when not in use is your choice. It is probably very low power so not really neccessary.
It is single ended, I was planning to leave the ground as common if possible. The head amp and the phono pre are both opamp devices and draw very low power, I didn't think leaving the power to the head amp on would be a problem. Thanks for suggesting the relays and the suggestion of shorting the head amp input to ground when not in use, that did not cross my mind and is a perfect way to wire it.
You need independent rca sockets for MM and MC.
Than use one mini relay type RSM850 (+-11,6mA/12V) and switch (rocker/toggle etc). Relay between headamp and MM amp.
Relay should switch only signals, not ground.
Connection: relay is OFF plays MC; relay is ON plays MM.
I made that in my last little project.
You can 'steal' voltage from +15V.
Than use one mini relay type RSM850 (+-11,6mA/12V) and switch (rocker/toggle etc). Relay between headamp and MM amp.
Relay should switch only signals, not ground.
Connection: relay is OFF plays MC; relay is ON plays MM.
I made that in my last little project.
You can 'steal' voltage from +15V.
May I ask why? I have seen MM/MC phono preamps with a single set of RCA jacks and a switch.
I think it is easier to solve your problem. It is cheaper also. I used sockets Monacor T-740G/T-720 in my construction. This is convenient for me. I can connect two TT, one with MM and second with MC once without changing cables - but these were my assumptions.
With only one set stereo input socket you have to use two relays like johnhenryharris wrote.
Certeinly it's up to you what option you choose, maybe another one. Your money, your project, your work.
Electronics is the art of compromise. ;-)
I am a little confused. How can I disconnect the head amp output and ground the head amp input with one DPDT relay?
What I had in mind was three 13ma,12v DPDT relays. One for the input, one for the headamp to preamp connection and one to ground the headamp input. My power supply has a 25va transformer and 1.5A voltage regulators, should be more than adequate for three 13ma relays and two opamp devices.