Three Input Passive Microphone Mixer

[ruffrecords]

I quickly built this prototype of a very simple 3 input passive mix pre-mixer similar to the sort of thing used at Abbey Road in the days of the Beatles.

Schematic:




Top view:



Connectors:



This was the project on which I was trying out low cost methods of applying legend. In the end I used vinyl printable paper. Reasonably satisfactory but not very durable.

The MK2 version will have:

Metal enclosure
Four inputs
Combo input sockets
Phase switch on at least one input
Phantom defeat switch for use with delicate ribbon mics
PCBs for the connectors and controls

Cheers

ian

 

[k brown]

What (if any) effect does this have on phantom power (especially with transformerless mics)?

What resistor values would you change if only two inputs?

 

[Rob Flinn]

I've used the vinyl printable paper on a couple of things that are now maybe 3 or 4 years old. They are still ok, but maybe a little faded in comparison to new. I guess one gets what on paid for. I'm currently building a small analog synth for a bit of a change. I have gone an even cheaper method with that which is printing on to thin card & then laminating the card. I will probably use a bit of contact adhesive spray to secure it on the panel.

 

[k brown]

I've used the vinyl printable paper on a couple of things that are now maybe 3 or 4 years old. They are still ok, but maybe a little faded in comparison to new. I guess one gets what on paid for. I'm currently building a small analog synth for a bit of a change. I have gone an even cheaper method with that which is printing on to thin card & then laminating the card. I will probably use a bit of contact adhesive spray to secure it on the panel.

Just need to have lightfast inks in the printer; run of the mill home printer inks are not.

 

[ruffrecords]

I've used the vinyl printable paper on a couple of things that are now maybe 3 or 4 years old. They are still ok, but maybe a little faded in comparison to new. I guess one gets what on paid for. I'm currently building a small analog synth for a bit of a change. I have gone an even cheaper method with that which is printing on to thin card & then laminating the card. I will probably use a bit of contact adhesive spray to secure it on the panel.

We recently had some work done on our front path. We could not use it for a day so I put a No Entry notice on the front gate. I only have an ink jet printer so I used some HP photograph inkjet paper to print the notice. It is about as thick as thin card. I fully expected the ink to fade in the sun or run from the rain but it was both sunny and it rained that day and the print was in pristine condition when I took it down. So this might be a similar way of creating front panel legends.

Cheers

Ian

 

[ruffrecords]

Just need to have lightfast inks in the printer; run of the mill home printer inks are not.

Can you get those in cartridge form for HP printers for example?

Cheers

Ian

 

[ruffrecords]

What (if any) effect does this have on phantom power (especially with transformerless mics)?

It effectively adds between 2K2 and 3K2 in series with the phantom supply to each mic input. It is not really meant to be used with phantom powered mics. The amount of phantom power will vary with the level control position. Also you would have dc flowing though the pot which is never a good idea. You might power one phantom mic through it but more than one might be a problem.

Back in the day they would have used dynamics or mains powered tube condenser mics so it would not have been an issue

What resistor values would you change if only two inputs?

Change the 360 ohm resistor to 300 ohms and you are done.

Cheers

Ian

 

[ruffrecords]

I just came across this little gem. Only £20 plus tax and that includes the battery. I am very tempted to buy one just for the enclosure.

https://cpc.farnell.com/qtx/mm41/4-channel-mini-mic-mixer/dp/DP35486

Cheers

Ian