summing speaker/power signals, help !

[isophase]

thanks sodderboy,
Well what we do at the studio is mainly "rock and roll" type bands with drums, guitars, synths... and usually record the basic tracks live so we do need good headphone monitoring system. Usually, i'll do just one mono mix for all musicians and its fine, very seldom i will do two mixes or a stereo mix, but the other guys seem to have their own habits (but i think they are more afraid to make choices and be content with it) the studio is too small to record a full orchestra so its almost always 4 musicians maximum tracking live but you never know, thats why i added an extra headphone plug to the box just in case.
One single robust on-on-on switch would be nice, but would have to add an extra switch for mono listening/monitoring from a stereo mix (same problem with the 3x4 rotary switch on the plan) not essential, but a nice feature.
i'm familiar with the furman 6channel headphone mixer system and the 8 channel HEARback system, they're nice but they cost a bit, and the CAT5 connector is quite sh... in terms of solidity speakon wins !
also i realised it would be a better idea to split the input of the amplifier (or use Y cables) in order to send the same mix to both tracking spaces, as opposed to loading one amp with 4 boxes for example. i know this is not good and if i'm not mistaken, this system could only take a maximum of two boxes per amp in order to work within its limits, thats why the speakon patchbay is mabe a bit risky because it lets you the possibility of doing so... mabe this is getting too complicated/compromising to have too much options.

 

[audiomixer]

If you design the resulting impedance of your boxes high enough you can add almost any number of boxes to an amp channel. if you get 32 ohm per box and leg you can run eight boxes and you will get 4 ohm nominal load on the amp, no problemo. design as per your need, do not adjust your need as per someones design...

you can think of it as your local water supply: an amp would be like the main reservoir water conduit feeding little drip irrigation systems. 100W for the amp, 0.1W four your headphones. so in theory you could (matching impedance of course) supply 1k headphones...... order of magnitude wise, your numbers might vary.....

- Michael

 

[joaquins]

I would use a 4 position rotary switch, no switching negative outputs from the amp, in fact you aren't in your design, you always have at least one to ground, one position have both, so it's the same for practical pruposes.

In the 4 position now you have all what you said and the mono with both signals summed but with the same switch.

The other option is to make a couple of lo Z passive mixer for the 8 power signals you have and use the headphones directly from there, so you won't have to buy little mixers, just 8 (or 16 pots for stereo) for each amp, and anybody could make his own mix. With this you can use any option also, but you need to take all 8 signals to every place of the studio, chose the connector you like with at least 9 pins.

 

[sodderboy]

One single robust on-on-on switch would be nice, but would have to add an extra switch for mono listening/monitoring from a stereo mix (same problem with the 3x4 rotary switch on the plan) not essential, but a nice feature.

No you do not.  Draw the connections as I described.  It is a three position toggle switch so you get three choices- Stereo, L mono, or R mono.  The other way to make mono mixes is with the actual cable from panel to box.  With boxes like the Little Red Cue Box with no choice I would wire and label cables for "L mono", "R mono", or "Stereo", or simply have a splitter at the wall.  It really simplifies the design to lose the switch!

And you do not have to use Speakons.  They are rated for way more power than you are pulling with headphones.  They get a bit bulky on the actual boxes where they are heavier than delicate headphone cables and the boxes need to be taped-down.  You can use nickel XLR's and mic cables.  They have worked well in cue boxes for decades.  When I make a load of new mic cables for a studio the old ones get checked and used for CUE.  You run heavier 3-conductor cable from amps to your panels, and then small cable to boxes.

As designed you can put 4-8 boxes on one amp.  That's the point of a distributed cue system.  You need to increase volume with more boxes, but that's it.  Whatever you design make sure that the gain structure is proper- you want headphone volumes at 3-4 o'clock when in use, and unused volume knobs should always be full ON.

Mike

 

[isophase]

thanks,
yes, now i see with switching only the positive pole and tie the negative together... yes a 4 channel passive mixer system would be nice but a bit more expenssive, and then there is the need to make choices for stereo monitoring: two seperate knobs for Left and Right? or two mono and one stereo with one knob? or 4 knobs + a switch to convert ch 1 and 2 (or 2 and 3) to an additionnal stereo pot, lots of options...
it would be a good idea to mabe add another speakon plug on each box in order to chain them in parrallel, determine the total number of chainable boxes , and make a few little "fictive loads" with a pair of resistors soldered inside a speakon connector to terminate the boxes, in the case only one box is needed so that you don't have to always have all the boxes plugged together.
i will see with my friends at the studio what they want to do... i will report back when/if we decide to build it.
thanks to everyone for your help !!! greatly apreciated !
respect,
jon