Talkback Mic-Pre/Mixer
 

     The talkback system is one of the engineers most valuable tools and, as far as I know, there is not a mixer manufacture that has gotten it right.

     The Problem: You are adjusting a mix for the musicians headphone send; the send is soloed and you are listening to the nearfields. You need to know if the bass is loud enough so you press the talkback button to converse with the band and one of 2 things happens. Either you get feedback from the monitors (and the musicians are pissed at you already) or, if your mixer is so equipped, the headphone mix send is muted and you can't have a normal back and forth conversation.

     One Solution:  Instead of using a mixer channel or the built in talkback rig, mix the talkback mic and the headphone send(s) after the mixer. Now there is no way the talkback can get into the monitors and there is no need to mute the headphone send. Below is a schematic for a talkback mic pre and mixer
 


 

Amplifier Selector Switch
   

     Questions about amplifier selector methods often come up on the newsgroups and the usual answer is to use a DPDT switch. A problem is that the unselected amplifier is left with it's input open, often causing hum (especially with long connecting cables). The method shown below uses a DPDT switch and a few resistors. It has the advantage of grounding the inputs of the unselected amp. There is a very slight loss in level from the mixer to the amp. To make a balanced version you will need a 4PDT switch or you can use 2 DPDT switches (one for each channel). I mount them close together horizontally and glue a piece of wood between the 2 switch handles so they act as a single switch.
 


     

Microphone Cable
 

     This is a real gageteer's gadget - it was designed by John Bau (Spika Speakers). Not recommended for radio problematic environments. It is a length of 300-ohm foam cable (20 gage - low loss) with a loose wrapping of solid core wire to act as a ground/shield. (scoff if you must but it sounds great)
 



 

Mackie-ish Headphone Amp
 

     Below is a schematic for a headphone amp based on the circuit used in the Mackie mixers. It's simple and sounds good; with the right phones, there's enough volume for most drummers. One side is shown.
 


Basic Electronic Building Blocks
(That are handy for studio use)
 


 


Inside an AKG 451 -10db Pad
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