DIY Sig Gen/Amp unit for Chladni patterns

[pat foster]

Very slick! Much more elegant than the old stereo reciver/laptop setup.

For my speaker, I hang it from a spring so that it gets pulled down to use.

Pat

[yakka]

i down loaded a signal generator app to my phone and bluetooth it to a speaker my son uses and it seems to work well, NOT MY IDEA saw it on facebook. am i missing something.
regards
yakka

[Trevor Gore]

Been there, done that. Tried a phone as well as an iPad and a PC, wired link and Bluetooth link. Yes, we made all of those work, but the usability for demonstration/teaching purposes was not what I wanted, and it was after trying the PC/iPhone/iPad/Bluetooth idea that I decided to build the unit in this thread.

[dsutherland]

Hi Trevor,
I had a good read of this article and it was very interesting and I even imagined I might be able to replicate your design but unfortunately it is way outside of my skillset.

On the note of people blowing their speakers I was wondering if you think this Griffin signal generator with amplifier will work? I have purchased the same speaker you have.

https://www.fishersci.co.uk/shop/produc ... r/13119180

I made my first 5 guitars under Darrell Wheeler before setting up my own workshop. Now on number 12 and looking to get more measurable results with methods in the first book.

Kind regards,
Dave

[Trevor Gore]

On the note of people blowing their speakers I was wondering if you think this Griffin signal generator with amplifier will work?

Hard to say, Dave. The specs just say sig gen and amplifier. A bit like saying car with engine. See if you can get more detail out of Griffin, such as frequency range and RMS output power.

[dsutherland]

Hi Trevor,

Thanks so much for getting back to me.

I was able to find the following:

Signal Generator and Amplifier
IPC-4885-W
Introduction.
The IPC-4885-W is designed for use in the study of A.C. Circuits, Amplification
and General Electronics. Its uses include driving a Loudspeaker or Vibration
Generator as well as many other electronic based experiments.
Signal Generator Mode.
The IPC-4885-W can be set to provide Sine, Square or Triangle output
waveforms using the three-position ‘Waveform’ switch.
The output frequency ranges from 0.1Hz to 100kHz and is adjusted using both
the six-position ‘Range Hz’ switch and the multi-turn rotary ‘Frequency’ control.
The actual output frequency is continuously monitored and shown on the LED
Display.
The output amplitude of the waveform ranges from zero to a maximum of 10V
peak to peak using the rotary ‘Gain’ control.
The output signal can be taken between either the 4Ω or 600Ω white (4mm)
sockets and the common green (4mm) socket. The 600Ω signal output can be
attenuated by a factor of x1, x0.1 or x0.01 using the three-position ‘Attenuator’
switch. Note: the common green (4mm) socket is connected to the case earth
of the unit.
The maximum output signal power is 4W (rms) into a 4Ω load (using the 4Ω
output socket) and will drive loudspeakers or other low impedance devices of
4Ω to 15Ω.
Amplifier Mode.
The IPC-4885-W can also be used as a stand-alone Amplifier with a Voltage
Gain (Av) ranging from zero to 100 (+40dB) via the rotary ‘Gain’ control and a
frequency response of 1Hz to 100kHz (-3dB bandwidth). Note: the Amplifier
has an input impedance of 1MΩ and a maximum input voltage of 200mV peak
to peak (irrespective of the Gain setting).
To operate the IPC-4885-W in the Amplifier Mode simply turn the ‘Waveform’
switch to the -- position, confirmation of this mode will be indicated by the
LED Display showing 1 on the left-hand digit.
The amplifier’s input signal is connected between the blue (4mm) socket and
the common green (4mm) socket, while the output signal can be taken
between either the 4Ω or 600Ω white (4mm) sockets and the common green
(4mm) socket. Note: the amplifier output has all the same parameters and
functions as the Signal Generator Mode, as detailed above.


Really appreciate any feedback you have.

Hopefully this works otherwise back to the drawing board for my setup.

Thanks again,
Dave

[Trevor Gore]

With only 4 W RMS power, I don't think that's enough (c.f. 30 W RMS on the unit I built). You can probably get away with 15 W RMS. Modifying this unit for more power would require a new power supply and power amp module, or putting the output through a cheap stereo amp (e.g. like this or this).

[dsutherland]

Thanks for getting back to me Trevor. Shame the unit won't work. Back to the drawing board

[kiwigeo]

Ive got a Bradley unit with a 50 watt amp. I've found I need to have it turned up fairly high to get decent Chladni patterns with some tops.

[Trevor Gore]

I am re-visiting the DIY sig gen topic due to new hardware becoming available that looks very promising (having already tested it).

What I am seeking now is a sig gen app (preferable for free, but not necessarily so) that will run on a PC where the frequency is continuously adjustable using a mouse wheel. Good ole Visual Analyser will do this, but only with 2 or 3 Hz resolution via the mouse wheel in the low frequency range and an annoying click every time the frequency changes.

Rather than trying each of the hundreds of apps out there (I've tried a good few) does anyone know of a suitable app that satisfies the above criteria? (Continuously adjustable in 1 Hz increments or less via a mouse wheel (with no extraneous clicking sounds) over the frequency range 50Hz to 2kHz).

Thanks for your help!

[Trevor Gore]

OK, there weren't may suggestions there! But we'll move right along, anyway!

Those of you who wanted to get into Chladni patterns but were daunted by the build complexity of the kit shown above, rejoice! There is a much simpler solution, versions of which many of you will have adopted already, namely using a sig gen app and a Bluetooth speaker arrangement. The problem, though, has been in finding a Bluetooth speaker in the right configuration and with sufficient power (30+ watts RMS) and an app with the right usability.

The following Chladni kit can be configured in a few different ways (depending on how exotic you want to get and I'll hopefully show you some options later) but the basic config is pretty simple and can be used with good old Visual Analyser. The key component is this small stereo class D power amp, which can deliver ~ 40 watts RMS per channel if you power it with a large enough power supply. The switch mode power supply it comes with will get you into the 25+ watts RMS region, which will be sufficient in most cases. A student at the recent Modal Tuning Course in Denver demonstrated this little amp to us. The knob is for volume control.

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The amp can be sourced from here: https://www.amazon.com/dp/B09NN6TQLL?re ... _title_0_0

Similar amps can be found, all likely made in the same plant. It can be fed with a signal from your computer using one of the supplied cables or paired via Bluetooth. All you need to do is to pair it up, start your sig gen app (or any music app for test purposes) and plug in a speaker e.g. like the one featured above, and you’re ready to rock.

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The power input and speaker connections are on one side of the unit, the other side has an on/of switch, a USB input and a 3mm jack input (if you don't want to use the Bluetooth). When all is paired up, you get a solid blue light.

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The speaker is just the one shown in the original posts from 2017. What I didn’t show was how I cut down the speaker frame so it would fit over the 100mm PVC pipe…

…and how I cut the hole in the pipe cap, first roughed out with a jigsaw, then trimmed up to exactly the right diameter using a flush cut ½” router bit, where I had swapped the bearing to one from my binding cutter kit.

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If you're about to make a speaker unit, look for a 100mm/4" mid/bass unit that will handle the RMS power. In general, avoid the full range units as they frequently come with a phase plug which sticks out from the centre of the speaker. That helps with the high frequencies (2.5kHz and up, which are of little interest when making Chladni patterns) and are good if you're looking for hi-fi, but prevent you from putting the speaker face down on the bench. However, if you want some new computer speakers, this little amp and a couple of 4" full range drivers in PVC tubes will beat most of the stuff on the market!

The next thing is figuring out how best to set up Visual Anlyser, and I'll continue with that in another post.

[Dave M]

I love that little amp!

I think I have posted this before but thought it worth repeating. A simple wooden box works fine as an enclosure. As for speakers a pair of car speakers which can handle huge amounts of power can be had pretty cheaply - at least in the UK. I am still driving them with an ancient domestic stereo amp, but I don't have to cart the thing around.

You notice that i suspend the speaker on a bungee cord which makes it less likely that I drop it which would not be good!

[kiwigeo]

"Facmogu F900S 160W Bluetooth 5.0 Mini Amplifier..."

"Facmogu??!!!

[Trevor Gore]

According to Google translate, Facmogu means "Send out mushrooms"

This next part is about using the Sig Gen functions in Visual Analyser.

There are many versions of Visual Analyser and most of the time I use one of the earliest versions (v 9.0.6) because it does what I want with least hassle. However, the sig gen function (called Wave) produces an annoying click every time you change frequency, so I use Version 2019 (the still later versions have various downsides I won’t bother you with). Version 2019 has got rid of most of the clicks when changing frequency and I will go through how to set it up so you can change frequency using the mouse wheel. I suggest you keep both versions of VA (v. 9.0.6 and VA 2019), but to do that, when you load VA 2019 load it into a different folder. If you allow it to select the defaults it will likely overwrite any earlier version. Those of you who know how to use the Wave functions, skip ahead to the next section.

First, launch the “Wave” section of Visual Analyser. All you need to do is select the Wave tab on the front page of VA…(BTW, you can choose your own colour scheme for VA. I use this dark scheme for VA 2019).

Adjacent to the “Wave” tab is the “Frequency meter” tab, which we may use later. VA is quite capable, because it will run many functions simultaneously, e.g. Wave, Frequency meter, Scope and Spectrum.

The “Wave” function brings up the Main control tab (and there is a whole bunch of other tabs which default to sensible values and needn’t concern us)…

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The first thing to do is check that you can get sound from VA. Ensure that your computer speakers are on and set to a medium volume. Set the “Enable” check box, set the “Level” to ~50%, set the Wave Function to “Sine” (if it hasn’t already defaulted to that). Move the Left Channel frequency slider to 1kHz (click and slide with your mouse; frequencies below ~120Hz may be below the frequency range of your computer speakers) then hit the “On” button. On my Win 10 laptop the “Output Vol” slider does nothing, so I leave it set at 100%. You should hear a 1kHz sine wave through your left computer speaker. If not, check that you have your speakers on in Windows and then check the “Dev” (for Device) tab on the initial VA screen. On the “Dev” tab select an appropriate output device. Hopefully that will fix things.

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Now for some of the interesting features….
Any slider on the “Wave” page can be moved in numerous different ways:

1) Grab the slider with the mouse pointer and shift it
2) Having clicked on the slider, use the Page up and Page down buttons on the keyboard (which seem to work to opposite way to what I’d expect on my computer!)
3) Use the left and right arrows
4) Use the up and down arrows
5) Use the mouse wheel

They have varying degrees of sensitivity: some are very coarse adjustments, some are very fine. Play around with them and see how they work on your computer for the various sliders. The sliders we are most interested in are the frequency adjustment and the volume adjustment.

What I wanted to do was to make incremental frequency adjustments using the mouse wheel. The best way to do that (on my computer) is to first select the correct frequency range (see the drop down menu arrow) and select 100-1000 Hz. Then click on the frequency slider and roll the mouse wheel. One rotational click on the mouse wheel moves the frequency 1 Hz (on my computer) which is pretty much perfect for me.

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If I want a frequency below 100Hz I need to select another range, e.g. 10-100Hz. But now one wheel click gives me a 2-3 Hz frequency change, where I would have preferred 0.5 Hz change. However, selecting “Full range” on the frequency range section menu gives me 1 Hz shift for ~5 mouse wheel clicks, which is OK.

You can, in fact, stay on the “Full range” range and use the up and down arrows for coarse adjust, the page up and page down buttons for medium adjust and the mouse wheel for fine adjust.

The up and down buttons adjacent to the actual frequency window (above the Enable button) will always give you 1Hz up or down and if you require anything finer you can type the frequency required into the frequency window.

VA 2019 Wave options_5.jpg (46.95 KiB) Viewed 5115 times

So there are multiple ways of adjusting the frequency, just choose those that best suit your needs.

The Volume slider behaves in a similar fashion with the mouse wheel (and keyboard arrows) giving very fine adjustment and the page up/down buttons giving courser adjustment. Volume may also be adjusted using the Windows speaker icon in the tool tray (lower right of screen) using either your mouse or the keyboard arrows or (obviously) volume can be adjusted using the volume knob on the power amp.

Finally, if you want a large display of the frequency being generated, you can use the Frequency meter function that I mentioned earlier. However, there is a catch to this: the frequency meter in VA 2019 is now supposed to measure “spectrum peak value” but I have not been able to get it to measure anything! But the Frequency meter in v. 9.0.6 works fine and v 9.0.6 and VA 2019 will run together fine if you set them up initially in different folders.

I hope all that wasn't "teaching your grand mother..."

The next post will be of an alternative hardware arrangement using largely the same components.

[kiwigeo]

Thanks for the excellent tutorial Trevor....

[Dave M]

Yes thanks for that work Trevor. I have just acquired version 2019 and it works exactly as you describe.

Slightly surprising the mouse wheel and the page up and down work in the reverse way to what one would expect setting frequency but that's fine. (Actually you may have said that earlier).

I'm impressed that this chap is still putting effort into developing the software.

[Trevor Gore]

A minor clarification:

Where I said...

You should hear a 1kHz sine wave through your left computer speaker. If not, check that you have your speakers on in Windows and then check the “Dev” (for Device) tab on the initial VA screen. On the “Dev” tab select an appropriate output device. Hopefully that will fix things.

... the middle bit should read "and then check the “Dev” (for Device) tab on the Settings tab of the initial VA screen.

[Trevor Gore]

Because the Facmogu amp is so small, it will fit inside the speaker tube.

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It can be controlled via Bluetooth from VA on your PC, so access to the amp itself is not required. This installment shows you how to mount the amp in the speaker tube.

The only external “hard” connection required is the power supply. One way (of numerous possibilities) of making this connection is to mount a bulkhead barrel connector on the pvc pipe so that the Facmogu power supply plugs into it, and then make the connection to the amp.

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I happened to have a dead power supply with the correct size barrel connector in my electronics scrap bin, so I cut the connector off and wired it up.

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The speaker just wires up as you’d expect…

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… and the amp is stuck to the lid using hi-tack mounting tape. Set the volume control to ~80%.

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You now have a high power Bluetooth amp/speaker to use for Chladni patterns or any other use you may choose.

If you want to go completely wireless (not really needed for Chladni pattern use, but you may wish to use this unit for other purposes) you need a pretty large battery if you want to use the amp’s full capability. The amp is rated for a power supply ranging from 9-24 volts DC.

You likely already own suitable batteries – the ones on your cordless power tools. You just need a suitable adapter plate for the brand of tools you use, many of which are rated at 18v.

A wide selection of adaptor plates is available. https://www.yourtoolbox.com.au/collecti ... diy-range
Bolt the adapter plate to the lower pipe cap, and wire it to a barrel connector. Just make sure you get the polarities correct!!

The next installment (as I get around to it) is useful mainly for teaching/demo purposes. I’ve just got to finish building it…

[kiwigeo]

That's ended up as a nice little compact unit there Trevor.

[Trevor Gore]

I played around with the above kit to try and find a user friendly configuration for teaching purposes. I wasn’t altogether successful, but here’s what I did and some of you might figure out how to do things better (and let us all know about it!)

First, I wasn’t totally convinced about the security of the power connector to the speaker unit. I didn’t want it falling loose on someone else’s expensive guitar. I couldn’t find a handy mini screw connector (though I know they exist!) so I just re-wired the speaker with a trailing cable to a “male” (oddly) barrel connector to mate with the one on the power supply. I also added a wrist strap for even more security.

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The "big idea” was to have controls for frequency and volume on the speaker unit, but my implementation was not exactly elegant. For frequency control I used a Bluetooth mouse (as well as a wired mouse), so that the frequency control in VA could be high-lighted with the wired mouse and then the frequency adjusted with the Bluetooth mouse wheel (here, just taped to the side of the speaker unit). That worked fine, but wasn’t very ergonomic.

I had a few ideas for the volume control, but didn’t implement any of them. The volume control on the Facmogu amp is an encoder (rather than a pot), so if anyone can figure out how to dismantle the unit, I would think a suitable encoder could be fixed to the speaker case and wired up to replace the original encoder. Similarly, a Bluetooth mouse could be scavenged for parts with its encoder wheel mounted through the speaker case and the rest of the mouse entrails inside the pipe. So you would have a Vol wheel and a Frequency wheel on the speaker case, hopefully in some ergonomic layout to make them easy to use.

However, when using this unit, and having tried a few alternatives, I’ll probably go with a “free” second (Bluetooth) mouse (rigged for left-handed use) for Frequency and Volume rather than attaching it to the speaker as per the photo.

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Two versions of VA are running; v. 9.0.6 in “Floating Windows” mode with an expanded frequency display and VA 2019, also in “Floating Windows” mode running the Wave (Sig Gen) module. As an aside, the guitar being tested is the 2nd prototype falcate guitar which was tuned to a T(1,1)2 frequency of 170Hz in 2007. It has remained strung ever since and you can see the current T(1,1)2 frequency.

Over to you guys! If you have any ideas for a more user-friendly configuration, please let us all know!

My next piece will be on how to make guitars levitate.

[kiwigeo]

My next piece will be on how to make guitars levitate.

Should be a piece of piss for you Trevor