Passive Control Center

[dintymoore]

I put this box together. I'm hesitant to call it a passive preamp because it doesn't preamp anything. It goes right before my studio speaker amplifier and does this:
* has stereo inputs from my mixer to hear the audio and MIDI tracks and another pair from the soundcards L/R outs for the final mix. That allows me to monitor recording then listen to playback without switching anything. The final stereo tracks go straight to the amp and don't go through the mixer. I fought with that problem for years.
* has two toggles on the front - one turns the sunwoofer off and on and the other kills everything.
* has L/R sends to my speaker amp, a headphone amp and a subwwoofer system. I haven't used the headphone outs.
* large detented Noble 100KΩ volume pot which is numbered and makes it simple to return to the same playback volume. It was scavenged from a 70's Mitsubishi receiver/small boat anchor.

The enclosure started life as a Digitrex 12 bit effects unit, probably the worst of all time, it has 1988 stamped inside of it. You can see I added flat aluminum to the front and back to cover up the old holes. There's a metal cover that goes on top.

I used 10KΩ summing resistors on the inputs.

The one numbered "9 + 10" is the final L/R mix, the one labeled "MAIN" is from my mixer:

This is a working mock up. I'm not... er... too happy with the aesthetics. I hope to rebuild it sometime and maybe combine it with an ugly working mock up speaker selector I made. I would use a wood cabinet next time.

But technically, this box solved a lot of problems that drove me nuts before... like switching to hear playback vs monitoring recording and also the basic question "how loud is it?".

 

[Chili]

Looks good. It's very similar to what I want to do. I might get started in a couple of weeks. I've got an old Digitech rack mount delay that no longer works. I'll use that chassis. I want to add a couple of headphone amps in case I ever get a guest in my tiny studio.

Thanks for sharing.

 

[pezking]

Nice looks good.

How did you wire up the mute switch, to you find that it creates clicks/pops when switching?

 

[dintymoore]

Nice looks good.

How did you wire up the mute switch, to you find that it creates clicks/pops when switching?

I mocked up this whole thing with a pack of alligator clip wires from Radio Shack to see what worked.

The mute switch is just bozo simple: it's a DPDT (from Ace Hardware) that just cuts the input L & R from my mixer. Just cuts it off cold and there's no capacitors or nothing and it's dead silent - never so much as a click or pop even once.

I was surprised that it worked... I expected a click or pop too, like when you pull a plug out of a guitar jack input... not sure why it doesn't. That's an example of why you should mock it up in place with alligator clips because a) what works here at my house might not work for you and b) if you ask people they will tell you all this complicated theoretical stuff that's true but not for sure what you need. You need the minimum that works.

If you don't know what I mean let me know and I'll explain better.

 

[pezking]

Cool.

Thanks for your info - it's helping me to make decisions about my controller I wish to build - I have a thread going here too...

I will try using the basic switching which you have employed. I hope it works well! But like you said a quick mock-up first will help me get the correct results.

As an aside - pulling out a jack is slightly different to flicking the switch because when you pull a jack out, there is a short circuit as the tip/ring catch the wrong connectors in the socket.