MM/MC Switching

[JRKO]

i can't figure out my MM/MC switching

I'm using the boozhound labs MC phono stage and their MM stage board. The MM stage is just a booster circuit and must feed back through the MC pre. They will be running from one shared power supply.

Ideally I want one set of phono sockets on the back of the preamp (one deck, one arm and but several cartrages) and the switching to be done on the one 'input' rotary switch

Possible

 

[DF96]

More likely that the MC is a booster before the MM preamp.

You will need at least 4 poles in your switching, as you need to switch the inputs to both MC and MM.

 

[JRKO]

Thanks DF96. Mea culpa! Proof given of my idiocy

Yes MM with MC booster

Was hoping to use a 4 input relay selector module I already have. In which case I guess a DPDT on-on switch would be the simplest option ie. select MM/MC via the switch and then select phono through the relay input selector.

Do I have that straight?

 

[DF96]

You have up to 4 cartridges, which are a mix of MC and MM?

To switch an extra preamp in and out of a circuit require 2 switch poles per channel, so 4 for stereo. This is because you need to switch both input and output. This is in addition to any source selection, although sometimes it may be possible to partially combine the two switches (e.g. if you have only one MC cartridge then you don't need to switch the MC preamp input, and the MC preamp output can be switched via the source selector).

 

[JRKO]

I'm really sorry. I'm being a right plonker

The 4 input selector is for everything, pc, radio, blue ray & vinyl.

I'd like to be able to switch between mm/mc (using the single input) as I use a technics 1200 with hot swap headshells, but don't want to swap cables about as they will be buried at the back.


Would the DPDT work?

 

[AndrewT]

the MC stage may allow you to simply bypass it to invoke the MM input.

If that works then you need a relay with two poles, one to each channel and those poles can be single way/throw.

when the relay is open the MC booster operates. When the relay closes the MC is bypassed.

dpst relay

Now does the RIAA handle impedance changes between MM & MC?

 

[DF96]

You need to switch the input and output of the MC preamp, unless you can be sure that it presents a high impedance at both places when unpowered. Unless the circuit was specifically designed to do this you should not assume it. As I said, this requires 4 poles for stereo.

 

[JRKO]

This is the preamp I am currently using JFET Phono/RIAA Preamplifier kit – Boozhound Laboratories

This is the MC step up that I want to use with the above JFET Moving Coil Pre-Preamp kit – Boozhound Laboratories

 

[jan.didden]

I think what DF96 means is the following.

You have two outputs from a cartridge, two channels. You must select between two cartridges, that's a DPDT.

Then you need to switch whatever cartridge you selected, to either the MM input or the MC input. Another DPDT.

If you connect the selected cart to the MC input you must also connect the MC output to the MM input. Another DPDT

This has nothing to do with the source selection at your preamp.

Jan

 

[DF96]

Ask Boozhound what impedance their MC preamp presents at input and output when it is unpowered. A high and linear impedance could be left in place when you are using MM, so then you will only need 2 poles of switching.