Remote potentiometer?

[imloggedin]

I really dont wanna explain the whole project and what im trying to do so i just have a simple question. How would i go about controlling a pot from 100 ft away? Ive read a little about digital pots but i dont really understand how they work. Before anyone cries 'SEARCH' i did and i could find anything or i was using the wrong keywords. Thanks.

 

[jdbakker]

Searching for 'digital pots' (verbatim from your post) yields a few interesting threads:

http://www.groupdiy.com/index.php?topic=24223 (recent)
http://www.groupdiy.com/index.php?topic=655 (somewhat longer ago)
http://www.groupdiy.com/index.php?topic=2148 (ditto)

[quote author="imloggedin"]I really dont wanna explain the whole project and what im trying to do[/quote]
That's a pity, as sharing thoughts/plans is what makes this forum particularly worthwhile.

JDB.

 

[imloggedin]

ill elaborate then. i just didnt feel like typing it all out cause it may just be a stupid idea.

im trying to come up with a way to not spend $1000 on a HEARBACK system. i want to have individual headphone mixes for each member (3 of us) of my band live and at practice and i want each person to have control of their own mix. well i think the HEARBACK system does this by using some converter to put ADAT on CAT5 send it digitally and then all the little mixers convert it back to audio. i was thinking of just having a box near the main mixer that you bring 6-8 lines into and it will do everyones mixing locally via remote pots. so it would be like having 3 little mixers in a box and all the pots would be controlled remotely. then each persons mix is sent out to their headphones.

might sound dumb but i cant think of any simpler way without spending lots of $$$$. i thought about just splitting the lines into 3 and sending it over a snake cable to each person, then doing the mixing locally. but then youre looking at alot of balun transformers, cause i wouldnt want to get out on a stage and have loads of noise.

hummph

 

[JohnRoberts]

The common solution for that application is to do the local mix at the listener position with real pots. Sending line level balanced feeds should give adequate noise rejection, without transformers.

YMMV

JR

 

[Martin B. Kantola]

Know exactly what you are talking about, been thinkin along the same lines for my studio setup! Thumbs up for sharing!

You could use digital pots, or VCA's or Vactrols or FET's or really any type of voltage controlled attenuator...

The cool thing (unless it's obvious) is that there is only one stereo feed going out to each musician instead of a bunch of lines. Cable work is no fun.

Martin

 

[jdbakker]

I would second John's suggestion. A cheap Behringer mixer would likely suffice at each listening point, at a cost much lower than any DIY if you factor in the case + PSU. You don't need ultra-high fidelity here, you just need audio cues without so much distortion that it gets distracting.

[quote author="Martin B. Kantola"]Cable work is no fun.[/quote]
True, but if you want to run eight balanced line-level signals over ~100ft and you don't care overly much about crosstalk or hum pickup you can do a lot worse than running them over a pair of CAT-3/4/5 cables. Assign each balanced signal to one of the twisted pairs and you should be good. Tape them together to get an ultra-cheap snake.

Yes, you can build a triple-bus remote mixer with relays, digital pots or VCAs, but you'll be spending a lot more time and money, and I doubt you'll be laying less cable even if you use RS-485 or other fancy schemes to multiplex the control signals onto one pair of wires.

JD 'KISS' B.

 

[imloggedin]

then i would need 8 balun transformers & instead of CAT5 probably a snake cable that has 24 wires (from redco or something), so i wouldnt have to run 3x CAT5 cables for 8 channels of balanced audio. also i would need an 8 channel line mixer with preferably headphone control (some kind of amp since im splitting the signal in 3 on each channel) (so far i cant find a cheap line mixer with a headphone jack, so i dont know if they have enough output), and more cable to chain them together, and all kinds of TRS ends.

The cool thing (unless it's obvious) is that there is only one stereo feed going out to each musician instead of a bunch of lines. Cable work is no fun.

I agree.

 

[jdbakker]

[quote author="imloggedin"]then i would need 8 balun transformers[/quote]
Not at all. If your mixer doesn't have balanced inputs, just use 8x THAT 1246 (upgrade to THAT 1206 if you feel you really need transformer-like performance). Both are available from Mouser in qty1 ($3.78 for the former, $6.66 for the latter) and come in DIP-8 packages so they're easy enough to solder.

[quote author="imloggedin"] & instead of CAT5 probably a snake cable that has 24 wires[/quote]
Why do you need 24 wires for 8 balanced lines? If you go from one driver (your FOH mixer) to one receiver (on-stage) and don't need crosstalk attenuation better than -40..-60dB, a single shield is fine. 16 wires in 8 pairs (or the dual CAT-5 that was mentioned upthread) will do.

If you want to DIY your mixer/head amp, it can be as simple as eight 1246/1206 chips, eight pots and an op-amp to drive the cans.

JDB.

 

[imloggedin]

thanks for the transformer/chip suggestions. the problem i have with unbalanced lines is since they are more susceptible to noise and there could be dozens of venues we could possibly play at. i would really like to have the balanced lines running from FOH mixer to our units. i dont wanna get on the stage and go. CRAP WHATS THE HORRIBLE BUZZ, oh well cant do anything about it now.

thanks

 

[sodderboy]

[quote author="imloggedin"]i dont wanna get on the stage and go. CRAP WHATS THE HORRIBLE BUZZ, oh well cant do anything about it now.
[/quote]

That situation can happen with one active stereo pair just as easily as with 4. I have yet to use any kind of active/trafoless splitter, booster or distributor that was 100% reliable in ANY live venue. Quality trafos in the right places will behave better than active in a remote or local mixer situation. Look at the best touring systems and there is always transformer isolation- on audio and power.

If asked to design this, I would go with local mixers/quality cabling/trafos and avoid the science project. I would not entertain the possible wierdness involved with multiplexed control lines, banks of digital pots and audio taped together in solid-wire CAT5 bundles, used in a live situation.

And what about someone being a monitor engineer? Personal mixing in a live sitch seems self-indulgent, unless y'all are all lead guitarists :wink:

Mike
PS: if a hot-chick band just HAD to have a remote controlled mixer system, I would design around the DS 1669 digital pot. I think fletcher picked the part number.

 

[walter]

I use a behringer ha4700 headphone amp. It has room for four headphones. each channel has an aux in. You can run the main mix to all headphones, and with each players signal going to their own aux in, they can boost themselves as much as needed. To remotely control each players aux, a separate volume pot (line out?)for the signal going to the aux jack. Or what about MIDI?

 

[PRR]

> How would i go about controlling a pot from 100 ft away?

Ten 10-foot poles lashed together?

Use a bigger stone to kill more birds.

WHY do you want many amplifiers all over the stage? They need power. Batteries are a drag. Plug 'em in, now you have a lot of 200-foot ground loops between 120V power cords and low-level audio cables. And then you need fancy-tricks to kill the buzz and CB radio. And the small amps are custom-DIY or Banjo Centre junkboxes.

Get a bunch of 100W amps. Maybe your old monitor amps. Put them at FOH. Maybe they are already there.

Be sure they are Common Ground, because we are gonna tie all the black terminals togther. Put 1 ohm 10W resistors on all terminals to give something cheap to chew on when wires short. Feed each with an instrument or submix.

Each performer gets a box of 1K pots and 270 mix resistors and headphone jack. No electronics, no power except what comes in the audio signal.

One CAT5 cable will carry 7 signal wires and one common ground. Yes, unbalanced! Speaker wires don't collect crap, because the far end floats, the signal level is 20V, and the source impedance is 2 ohms.

7 signals might even be enough for a 3-man band. Bigger acts will use multiple CAT5 cables: a set of red green grey black CAT5 (24 signals total and two grounds in each cable) is far cheaper than any shielded pair snake.

I show daisy-chain, but for larger acts you should probably have a splitter (CAT5 punchdown panel and jumper links) so only a few performers are on each run.

 

[PRR]

> You could use digital pots, or VCA's or Vactrols ... The cool thing ..is that there is only one stereo feed going out to each musician instead of a bunch of lines. Cable work is no fun.

Agreed; but how does the pot position get back to the head-box? Bogen remote-control mixers ran a ground, a bias voltage, and a line for each knob. If he wants 6 sources, that's 6 pot-wires, plus a common reference, and unless you get clever, probably a +5V rail (Bogen ran +200V). And your headphone wires. 9 to 11 wires. 6 twisted-pair under common shield is only 13 wires, not a big increase over remote-pot.

Up past 8 sources and half a dozen performers, it does get cheaper to time-multiplex with a 4051 CMOS "rotary switch". I did that way too many years ago. It didn't work well because I didn't understand how much charge had to go into the line; someone else did it better and commercialized it around that time, with little market take-up. If you are doing hand-turn pot-signals instead of audio, the rate is much slower, and CMOS will do it.

There is a model airplane system to TDM 6 or 8 analog voltages on one 27MHz carrier and back to push rudder servos around. It's just ugly signals on AM, and you can probably bypass the radio bits. Or keep them. (And how cool-looking are those model airplane controllers?)

Next year, WiFi and pocket computers will be so cheap we'll just spray 8 channels over the aether and mix-down in the CPU. Savvy bootleggers will get custom mixes. Not there yet.

 

[Martin B. Kantola]

[quote author="PRR"]Agreed; but how does the pot position get back to the head-box?[/quote]

Here's what I had planned: MUX and digitize the pot positions, with 8 or more bits resolution. Feed the data into a standard AES/EBU transmitter (plenty of bandwith there). Run one standard balanced cable pair to head-box.

So, each musician's box needs:

- power line (+24V)
- two balanced audio feeds
- one balanced control data send (AES/EBU)

Minimum number of needed wires 7 + GND/SHIELD? Cheapest solution 9-pin D-connector/cable?

Martin

 

[JohnRoberts]

I recall looking at this decades ago as a commercial product in the context of individual monitor mixes for recording studio use, and found that too many had already built their own because it was so simple. This product also had some headwind because many muso's were not trusted to roll their own mix.

Since then the boom in low cost recording gear has given even entry level musicians some familiarity with basic mixing.

It might be cheaper to just buy a handful of small Uli-mixers and move on. If this is for the big show (serious touring) perhaps spec a high end digital console for monitor world that can be controlled from wireless tablet or your I-phone and just let the muso's mix themselves wirelessly. They may even be able to share one controller if they don't all need to change mixes at the same time.

Any way it seems this might be reinventing some wheel.

JR

 

[Martin B. Kantola]

Good point about musicians being able or not to create a mix that makes any sense. My plan was to do a general cue mix for them on the console, then split it up/assign to maybe 4, 6 or even 8 stereo groups, which they can then blend as they like. In this case, 4-8 pots in a neat row would be much better than a cheap mixer that contains a crappy headphone amp...

At least for headphone cue mixes, I'm personally not too excited about anything digital, the latency can be very annoying. Yes, even simple converter latency. Call me nuts if you like

Martin

 

[bcarso]

You are not nuts! Latency is a plague, another place where naive bitheads get their comeuppance :razz:

 

[JohnRoberts]

Latency can be more of an issue with cans than speaks for monitors due to bone conduction path.

JR

 

[bcarso]

Of course not all data converters have so much latency. It's the near-universal use now of sigma-delta ones that creates a lot of the problems.

 

[Martin B. Kantola]

[quote author="JohnRoberts"]Latency can be more of an issue with cans than speaks for monitors due to bone conduction path.[/quote]

Sounds like a very reasonable explanation!

Now, with a 9-pin connector there would be one pin free (please see previous post). That one could be a talkback bus. An electret capsule + a push-to-talk button on each headphone box. Talkback bus with the usual limiting of course.

Martin