Master Section Controller

[dmp]

Currently I have a simple monitor controller with meters, input selection, Level, and output selection. The level control is a nice goldpoint switch.

I'm expanding this to a nice master section controller with talkback and other features. All the signal switching will be done with relays.

Going from left to right on the front, this will have:
- three input options, one of which is a unbalanced TRS on the front for ipod type devices to plug into.
- Talkback control. The talkback can be turned on to the output (labeled playback on the back) in multiple ways. The switch on front, a remote control, or a 1/4" jack on back for a footswitch. When engaged, the master is dimmed (-12 dB) or muted, based on the rear panel switch . When the switch on front is put down, the master audio is routed to the talkback output for playback (playing the mix to the live room). The switch in middle position has talkback and playback off.
- Each meter has an adjustment for calibration (coming off the JLM VU buffers)
- mute switch
- dim switch (-12dB)
- Left / right only switch: three position switch to hear left only, right only, or normal (middle position). This means if the switch is to the left, the left side audio signal will play through both speakers.
- Mono switch: sums the left and right to mono using a passive resistor summing (475 ohm / 20k / 475 ohm) Found this little circuit on the forum. A simple way to have mono without too much trouble.
- Subwoofer out: sums the left and right with the same passive resistor summing to a single sub output. This will create some crosstalk in the L/R, but I'm OK with that. I don't use a sub much.
- 6 output options with the last position being a internal headphone amp (JLM Headamp)

From back of the envelope drawings I think this can be done with about 11 relays.

Comments / suggestions?

 

[druu]

Looks interesting. Are you able to share the schem on mono and dim features?

 

[kante1603]

Very nice!
I'd add a phase reverse switch for one side at least,so you can check stereo signals for mono compatibility.
Also (if you haven't done it already) a booster for the iPod input.Most of them are on the lowish side levelwise.The e.g. Regurgitator from Joe will do the trick,you'll need two for stereo of course.
For metering I like to see peak values too,not unimportant with all that digital stuff nowadays.
For the output selector you should run the phones line in parallel prior to the switch.In case you want to listen via phones while a client listens to your mix on the main monitors you know.Otherwise the switch would kill "his"  monitors.So position 6 is not necessary I think.

Just my 2 ct,best regards,

Udo.

 

[dmp]

I'd add a phase reverse switch for one side at least,so you can check stereo signals for mono compatibility.

Great idea! Added.

Also (if you haven't done it already) a booster for the iPod input.

Good idea. I think I could get by without it but it would be easily added.

For metering I like to see peak values too,not unimportant with all that digital stuff nowadays.

Good idea, but I think I can get by without that since the DAW shows it. It would be nice if the JLM VU buffer had a peak LED - if it were that easy I would add it.

For the output selector you should run the phones line in parallel prior to the switch

I have to think about this. I think I agree with you.


I haven't made up the schematic yet, but I will once the plan is finalized.

 

[dmp]

I also added a foldback input on the back to send the performer backing mix (click track, etc) out to the live room. A switch on front to monitor the foldback on the monitors.
Then the playback option switches the monitor mix for the foldback going out to the live room.

 

[kante1603]

Cool idea!
And for the peak led,

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=189

Go to the build thread,there's a schematic already.Might be useful for you.

Best,

Udo.

 

[dmp]

Working on a PCB for this now, but here is a signal flow diagram.

 

[dmp]

Update as I've made a lot of progress recently (after no progress for 6 years!). Used the same relay boards as shown in this thread by bjosephs.
I used two boards with 8 relays on each: one for right and one for left. The right side has a phase and the corresponding relay on the left side is used for the talkback unmute. The relays are activated with a +5v signal.
Currently trying it out before labeling the front panel and it is mostly working well.
I have 8 dB measured loss at max level. (20k mix resistors ahead of the 20k goldpoint stepped switch).
The unbalanced converters on alt1 and alt2 are working great. I have a TRS input that goes to DRV134 balancing boards, with the output going to the switched side of TRS balanced inputs (so inserting balanced inputs on back, disconnects the balancing board output).
Level is a lot lower for the phone unbal input, but still there is plenty of gain in hand.
The listening features are working great (phase, mono, L-St-R)
I used the JLM Amp Head for the headphone amp. I have two parallel outputs - one on the front panel (with the HP level) and one on the backpanel.
I added diffuse warm white LEDs to the Weston meters. These are great sealed meters. I always wanted illumination in them so took them apart to add LEDs inside (shock). But

 

[dmp]

Block diagram and for context a workflow diagram.
This is pretty customized to work when mixing in the DAW.
The foldback mix generally goes to the stereo cue mix, but the master section has the option to send the main mix instead (to let the performs hear the full mix).
Likewise the main mix or the foldback can be heard in the monitors.
And because I also want to be able to record directly sitting in front of the monitor controller, the cue mix can go to the headphone amp instead of the main mix.

 

[dmp]

I'm having a problem with the talkback unmute switching. The frontpanel TB / dim switching is working correctly.
The TB unmute activates 3 relays (TB, dim-L, dim-R) and the dim can be independently switched, cutting off the TB switch. Relays are activated with a +5v signal (that draws 0.4mA)
I made up a transistor circuit to allow a footswitch to plug into a TS jack, where the TB unmute is activated by the tip connected to sleeve / ground. I don't want to send 5v through the footswitch.
Problem is the transistor inverting circuit I am using is thrown off by the current draw of the relay board so the +5V drops to about 4V and the relays flicker, due to voltage drop over the 1k resistor. In this schematic the 4.2k resistor is the equivalent resistance of the three relays (TB, dimL, dimR).

 

[dmp]

How it's built on lug terminal strip

 

[ruffrecords]

I'm having a problem with the talkback unmute switching. The frontpanel TB / dim switching is working correctly.
The TB unmute activates 3 relays (TB, dim-L, dim-R) and the dim can be independently switched, cutting off the TB switch. Relays are activated with a +5v signal (that draws 0.4mA)
I made up a transistor circuit to allow a footswitch to plug into a TS jack, where the TB unmute is activated by the tip connected to sleeve / ground. I don't want to send 5v through the footswitch.
Problem is the transistor inverting circuit I am using is thrown off by the current draw of the relay board so the +5V drops to about 4V and the relays flicker, due to voltage drop over the 1k resistor. In this schematic the 4.2k resistor is the equivalent resistance of the three relays (TB, dimL, dimR).

Something is wrong. If the footswitch is open and the FP is closed the transistor turns on right across the supply. Bad news.

Cheers

 

[FIX]

Also, remember that the emitter is grounded, but through a junction, so it's really a little above ground, and when you ground the base, it's also above the ground a bit, so you may not have good shut off, take a diode and put it from the emitter to ground, that lifts the device 2 diode drops above ground, and when you ground the base, it's now below ground.

 

[dmp]

Yeah it's a bad design. I didn't think of that. Adding a diode is needed to prevent the reverse voltage from the FP switch, but increases the voltage drop making the 'on' voltage to the relay board even lower and not reach the voltage threshold at all.
Basically I need a +5v signal to the relay board when a footswitch is engaged, and 0v to the relay board when the footswitch is open. I think there should be an easy way to do this, but the transistor switch doesn't seem to cut it

 

[dmp]

Also, remember that the emitter is grounded, but through a junction, so it's really a little above ground, and when you ground the base, it's also above the ground a bit, so you may not have good shut off, take a diode and put it from the emitter to ground, that lifts the device 2 diode drops above ground, and when you ground the base, it's now below ground.

I don't understand how something that is directly grounded can be a little above ground? If the base is grounded and the emitter is grounded, i_b = 0, so the transistor is off, yes?

 

[ruffrecords]

I think you need to diode OR the transistor output and the FP switch output. So each sends its output through a diode and the two cathodes get wired together to feed the relay board Which will need a pull down resistor at the input.

Cheers

Ian

 

[dmp]

I think you need to diode OR the transistor output and the FP switch output. So each sends its output through a diode and the two cathodes get wired together to feed the relay board Which will need a pull down resistor at the input.

I don't think the control voltage to the relay will be high enough. The main problem is I need to send ~5V to the relay which draws 1.2 mA. If the 5V is through a resistor and diode there is too much voltage drop before the relay.

 

[dmp]

Added a second 2n3904 as a buffer. The control voltage is down a diode drop across the transitor (~4.3v) but is above the 'high' required by the relay board. This also prevents the FP switch from causing any problems.
It's working well.

 

[ruffrecords]

So is one end of the relay tied to 0V?

Cheers

Ian

 

[dmp]

There is a control circuit on the relay board and the board gets 5v and ground separately.