Let's design a portable audio test set

NewYorkDave

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I'm thinking of something like the Whirlwind Q-Box, but bigger (still portable) and much more versatile. Let's begin with the wish-list:

Small amplifier and speaker, with headphone output and variable gain and level.

Signal level/VU meter with selectable reference level, switchable to monitor signal input or output.

White-noise generator and selectable-frequency tone generator with two outputs and adjustable level.

Some sort of channel ID on one of the generator outputs (e.g., signal gated at regular intervals).

Powered from readily-available batteries.

XLR, 1/4" TRS and RCA I/O connectors.

Some nice-to-haves, not really essential:

Selectable load impedance on inputs.

Selectable source impedance on outputs.

Calibrated attenuator(s) for "gain set" type measurements. (Old broadcast guys know what I'm talking about :wink:).

Built-in iso xfmr with input and output connectors.

WECo longframe and TT bantam connectors in addition to connectors listed earlier.

Phantom power check circuit.
 

Samuel Groner

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Cool--I'm working on something similar (though simpler) for a friend. Two ideas:
* chargeable with phantom power
* generator output(s) switchable to common mode

Samuel
 
G

Guest

Guest
wow, I missed this earlier... this is a really cool idea, i espicially like the VU meter thought.
 
G

Guest

Guest
Good idea!

I have thaught about putting something similar together.
As a Livesound engineer i sometimes need to check the speakersystems
to see if all speakers are "alive".
Most of the times you need to get an amprack and cables, etc etc, just to get some sound out of the speaker.

I thought it might be possible to add a 4-pole and one 8-pole speakon that is connected
to the amp NYDave suggested.
Maybe a switch for selection between internal and ext speaker and one rot-switch for selection of pins in the speakon.

/Hampus

EDIT: Some spelling
 

pucho812

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Dave as long as were doing noise wouldn't pink noise be better instead of white noise? Maybe both pink and white :? Is your choice of white a broadcast thing :? Also being able to send test tones at set calibrated levels would be nice. For example 1K, 10K, 100 HZ, 440 @ +4DBM/U, 0 DBM/U and -10 DBM/U maybe a phase checker for the various connections as well. Often time at work i get a this cable is broken when in actuality it got repaired incorrectly and flips pin2 pin 3 at one end.
 

Scodiddly

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This might knock it out of the pure DIY approach, but I'd love to see some small tone generator where you just download .wav or .mp3 files of whatever the heck you want.

Aside from that... yes, like a Q-box, but without the excessive noise. I don't know if having every possible connector is necessary - that seems like something that would be better implemented as a "box 'o adaptoids".
 

Scodiddly

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[quote author="mediatechnology"]
This might knock it out of the pure DIY approach, but I'd love to see some small tone generator where you just download .wav or .mp3 files of whatever the heck you want.

Oh, you mean like an iPod? With a line-driver interface.[/quote]

It's been a "would like to have" item for some time now - but not in the form of a delicate consumer item, but in the form of one of those "XLR test tone plug" things. Something you could plug into a mic line for a line check, since tone or noise doesn't tend to be very useful for checking line quality in a live concert situation (ie straining to hear how it sounds over a pair of headphones).
 

NewYorkDave

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White noise...

Yeah, that was just a typo. I had white noise on the brain when I wrote that, probably because minutes before I had been pondering an easy way to generate pink noise--which usually means starting with white noise and filtering it.

The "Ipod" idea is cool but way beyond the scope of the kind of instrument I have in mind. Anything that involves a μProcessor and RAM would bring (IMHO, of course) too much complexity and circuit density to the project.

The Kelvin (four-wire) load-compensating idea is also a cool one, but then you'd have to add a whole ALC system to implement it. (But maybe there's a low-distortion, single-chip ALC available. I dunno, I don't keep up with the latest ASICs). But really, is turning a knob and reading a meter all that much of a hassle? Flip the meter to "output", ref. level to "+4", tweak the pot till it reaches zero. 3-5 seconds of work. If the tone generator is well-designed, the output level won't change as you switch frequencies.

I don't want to seem like a naysayer, but I do wanna keep things manageable (and keep the package about the size of, say, a jewelry box, and powered off a couple of 9V batteries at worst). The crazier/fancier the concept becomes, the less likely it is that it'll ever get built.

I am very intrigued by that Chipcorder idea--for many possible applications, even if not for this particular project. Does it require a lot of support circuitry, μP and all that?
 

NewYorkDave

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I was thinking the Kelvin could be done with some feedback after the build-out R like many line out stages. Just having accurate trimpot calibrated preset ref levels would be good.

Ah, that's reasonable. A line-out stage like that would be easy enough for me to breadboard during a lunch break. Maybe I'll even do it tomorrow.
 

Kev

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every time I make one of these things it gets borrowed (stolen) and I never see ity again

I used LM833 and SSM2143 and 2142 ... cos I do

and the headphone thing is often a problem cos the unit is single channel so a simple single ear high impedance ear piece is good enough and you can plug it into straight line outputs etc ... even the 2142 will make some noise into high impedance

I also had one with an MP3 player inside for various tone and typical program sounds ... ranging from control room output to directors talk back

bears-toy04.jpg

this unit above is a mains powered one but it was born from various dual 9 volt portable units
cut and paste on Protel and the above was the result

battery life can be an issue

the Shure portable headphone and line tester thingy is a cool unit and the batteries last for ever

none of my stuff does ... LM833 and 2143 2142 and not good for power saving
 

Rob Flinn

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battery life can be an issue

Would there be any margin in perhaps making the unit so that you could switch of power hungry sections that weren't being used.

Also battery & mains power would be useful.
 

NewYorkDave

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Hmmm... I just thought of a problem with the "load compensating" output arrangement. I mentioned earlier that I'd like selectable output impedance, say "low Z", 150 ohms and 600 ohms. If I wanted to check the frequency response of a mic amp from a 150-ohm source, the load compensating output would tend to null out a droop in load impedance at the mic amp input (from, say, the primary inductance of the mic amp's input transformer) and give a misleading result. It would do the same when checking, say, the response of a dry-pair STL: as you swept to higher frequencies, it would increase its output in response to the falling impedance of the line, giving a "false flat" result.
 

Kev

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[quote author="mediatechnology"]You Your test box is a nice piece of work. Nice construction and a very full case.
...Do you have a front panel shot?[/quote]
all a bit messy inside as it was one of those quick projects that started and ended all in less than a day

I didn't post a front panel cos I was trying to save on forum noise
but
here 'tis

bears-toy01.jpg


there is duplicate and other back panel connections as well
no picture for that ( don't know why ... didn't think to take one )
 

enthalpystudios

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man... i need something like this in a big way. i feel like not having a proper signal is really holding things back for me as far as testing is concerned.
 

walter

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I like the sweep control on the tone generator for finding LF Buzzz in speakers and cabs. I suppose an O-scope display is beyond the scope of this project, but it would be cool to have a little sine wave on an LCD. Is that even possible? perhaps a couple jacks to connect a digital multi meter. I have been interested in building something similar to this, but with a dummy load, and sig gen.
 

Kev

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[quote author="mediatechnology"]You built this in a day? Must not have kids...[/quote]
no Kids ... but it was a work thing

the Boss arrived through the workshop door and said

" Right !! ... move ... I wanted to do a job at home on the weekend and couldn't "

it turned into " Foreigner Day "

Foreigner Day is when no work gets done and we all concentrated on private projects.
... often the private projects were work based anyway

I'm sure I got a few PCB's made for my future projects that day
and to tell the truth ... Bear's test rig above got start a couple of times that day as he changed his mind along the way.

:cool:
those were the days
 

pucho812

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[quote author="walter"]I like the sweep control on the tone generator for finding LF Buzzz in speakers and cabs. I suppose an O-scope display is beyond the scope of this project, but it would be cool to have a little sine wave on an LCD. Is that even possible? perhaps a couple jacks to connect a digital multi meter. I have been interested in building something similar to this, but with a dummy load, and sig gen.[/quote]

why not just have the outputs mult and one be for a scope. then plug in your scope
 

NewYorkDave

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"Foreigner day." I like that!

I used to work for a real micro-managing hardass. He had been a tech himself, so he always second-guessed and criticized everything we did. God forbid I let him see me with a personal project on my bench, even on my own time (during lunch break or whatever). We'd get the lecture about how we shouldn't use the resources--bench space, solder, the ten cents' worth of electricity to run the soldering iron and 'scope for an hour--for non work-related projects. Of course, that didn't stop the old hypocrite from borrowing some tools or a bench and working on his own stuff when he saw fit.

Then there was a big reorganization at the job. The one good thing that came out of that is that now we have a new boss, a nontechnical person who's very laid-back, works in a completely different part of the building and leaves us alone most of the time. We don't really need supervision because we know what we're doing and we're conscientious about getting the job done and keeping the place running. But now and then, when things are slow, we do get to enjoy a "foreigner day"--which is fortunate for me, because I don't have any space to work on stuff at home.
 

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