Audio amp UI design: Creativity vs. usability

9/22/2011 1:22 PM EDT

I believe that you could have a panel the is creative and stylish but at the same time, is functional and user friendly. All great designs take both into consideration -- yin and yang in harmony. :)

9/22/2011 6:06 PM EDT

Front panel design can be quite a task because there is also the consideration of what is behind the panel. Clear labeling is valuable, and a reasonably convenient user interface, but don't get too creative in coming up with new names for standard functions such as power on/off and volume control, and possibly input select. Contrast ratio for labels can be a problem as it can make them very hard to read. But there shoulkd be room for a lot of creativity anyway. My best source of panel labels was Kinko's, printed on adhesive backed vinyl with a lexan film overlay, $19 per square foot, with very little limitation in colors. Anything that you can create in a drawing file they could produce. Th at was great for some industrial machines, cheaper and faster than traditional, and much better looking.

9/26/2011 5:18 AM EDT

My first consideration would be ergonomics and AFAICS the present layout has controls and cable jumbled close together, making access to the controls fiddly.

On/Off between two cables?

If it were me, I'd swap the On/Off and input, and drop the cables below the PCB & controls, to give more room for fingers.

It sounds a bit, though, like that observation may be too late.

I like the funky diagional symbols, but if I can't reasonably understand them without an explanation, I think they're not doing their job properly. For yourself and friends, I guess you'd understand them OK, for 750 customers, I'm not so sure.

9/26/2011 5:19 AM EDT

Sorry, On/Off and Headphone.

Thats due to a combination of misreading the funky graphics and being dumb :-(

9/27/2011 11:56 AM EDT

Hello Rich, hope all is well. Good to see your delving into some DIY... nothing teaches us more than a smoking board, and the investigation into why things didn't work first time! :)
Your post intrigues me. My first thought is that you’re putting a lot of controls on a front panel, all with equal importance and real estate.
There are two things that I'd be tempted to do if I was in your shoes.

Firstly, I would be try to differentiate controls between things that users are changing on a near constant basis and things that don't change all that often.
Secondly, look for controls that you could "automate" by understanding other things in the system.

An example of differentiating between controls would like looking at the volume control. Users are constantly fiddling with the volume knob; therefore your volume control should be front and center, with plenty of room for those of us with chubby fingers.

In contrast, most users will use their headphone amp with the same piece of hardware (maybe it'll be repeatedly connected to their MP3 player or PC etc). In which case, the gain switch is more like a "set and forget" switch. It sounds like it'll be a switch between a real 2VRMS line in (therefore "low gain") and a media player 1VRMS output (therefore "high gain"). My temptation would be to throw this control on a dip switch mounted on the back of the case, or something similar that users have to make a determined effort to switch. (however, it might be tempting to throw a "signal detect" LED on the front panel, so users know if they are driving the system with a 1VRMS or a 2VRMS signal and an LED to show which is connected.

9/27/2011 11:56 AM EDT

From the second consideration, i.e. controls that can be automated....

There are some tricks that audio connectors can do to help our system design.
One of the tricks I've seen in guitar pedals over the years is where the device is only powered up when the cables are connected in the system. That means that the guitar pedal has a battery inside, doing nothing, not burning any power, until input and output cables are connected. Cool stuff. If you had the same functionality in your headphone amp, you could even remove the power-on switch.

However, if your paranoid about users leaving things plugged in, walking away and the system still being powered on, you may want to add a small input detector circuit that could power up the rest of the system.

This could be as simple as a small comparator that constantly monitors the input, whose output is connected to some power switches (FET's? Relays?). When you have no content running in your system, the comparator outputs a "0", which cuts power to the rest of the power circuitry. The only device being powered then is your comparator. (That’s a very small amount of current - nA of current if you use a TLV3401).
When you have signal, the comparator outputs a "1", which drives power through to the headphone amp and the rest of the circuit.

You'll need some hysteresis and some delay on power down in this circuit, but that's nothing that a cup of tea, a logic selection guide and a notepad and pen can't get around.

You've now reduced your front panel to 2x 1/8" jacks and a volume knob. The back panel has a DC jack and a recessed gain switch, while your power switch is now automated to work only when you have both input and output connected, AND have signal flowing into your amplifier.

My fee will be in the post *kidding*

Take care, and don't forget to update us when your design is complete -- we all love PCB pictures ;)

Best Regards

Dafydd Roche
Audio Semiconductor Systems Engineer
Texas Instruments

9/29/2011 2:54 PM EDT

Hi Dafydd, good to hear from you. I agree with virtually all your points in general. In this case the amplifier (which was designed by "NwAvGuy" and described at http://nwavguy.blogspot.com/2011/08/o2-details.html) was designed with some very specific size, cost and performance goals, and its front panel layout has been pretty much dictated by these considerations (including restrictions resulting from the optimized-for-performance pc-board layout).

These restrictions/trade-offs were considered acceptable for this version of the amp, which is meant to be usable for both portable and desktop applications. However, a desktop-only version of the amplifier is also planned, which may well address some of these issues and perhaps include enhanced functionality. I believe the amp's designer reads this blog, so I'm sure he'll see your suggestions and take them into consideration.

As for pc-board pictures, I'll see what I can do. :)

11/12/2011 5:12 PM EST

There is a serious angle to this; if you are using this as a learning project or selling it openly, then you MUST use the standard form of symbols for power at least, and make sure any 'creative' symbols cannot be confused with any safety-related symbols. This protects any casual user from accidents, and shows that you have considered such risks. Boring, yes, but you wouldn't want to be in court explaining why someone has tried to connect AC power to your DC unit. Exercise your creativity on the look and feel of the thing, plus the usability that has been discussed already.