Analogue signal generator (and maybe more related questions)

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Re: Analogue signal generator (and maybe more related questi

Post by woodrat » Thu Sep 15, 2011 11:27 pm

I downloaded the NHC tone generator but have had no issues...I use Firefox...not sure if that makes any odds.

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Re: Analogue signal generator (and maybe more related questi

Post by ChuckM » Thu Sep 15, 2011 11:40 pm

Hi Dom,
I believe you are correct in your assumptions as far as the monopole modes go. The back appears to have the major resonance at 362Hz (tapped in center of lower bout) When tapped in the upper bout a co-peak shows at 249Hz. The back is 3 piece American Cherry.

I guess it ends up being what you mean by "main top resonance". If you mean the T(1,1)3 then it didn't move. But it is no longer the dominant resonance. I agree that it didn't increase top stiffness. The bridge weighs 27g, so it is a bit heavy and should have dropped some resonance somewhere, but I don't see it either.

Since this thread is about generating Chladni patterns, it makes sense to show the results of such tests on this guitar. This photo is of my scribblings when I did Chladnis on this guitar with the round bridge attached. The upper part was speaker (air) activated and the lower part was activated by vibrating the bridge itself at those frequencies noted.
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Chladni patterns on round bridge guitar
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Re: Analogue signal generator (and maybe more related questi

Post by ChuckM » Thu Sep 15, 2011 11:58 pm

I figured a more complete set of data would be helpful. This is the back patterns. It's easy to see where the peak at 362Hz is coming from.
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Re: Analogue signal generator (and maybe more related questi

Post by J.F. Custom » Sun Sep 18, 2011 9:24 pm

Ok guys and girls.

I'm reading through the books (as many of us are) and the various threads with questions and answers. Now, having been wanting to set up for Chladni/Frequency testing for quite some time anyway, these publications have certainly pushed me over the edge to do so now. BUT, I am confused as to which way to go and am not sure if any general consensus has been achieved on the "best" option. So to briefly re-hash the options -

1 - Bradley Engineering dedicated unit including inbuilt amplifier @ $500 + $58.50 p&h (emailed for that latter info) + $ ?? speaker
2 - Digital PCB such as that Dom has purchased on eBay from China @ ~$40 + $ ?? Amplifier + $ ?? speaker
3 - Digital Signal Kit (Peter linked to by Silicon Chip) @ $150 + $ ?? amplifier + $ ?? Speaker
4 - Analogue Signal Generator on eBay @ $50-150 for either vintage quality units or more modern Chinese units + $ ?? Amplifier + $ ?? speaker
5 - Software Based Signal Generator @ $0-40 (depending on which software) + $ ?? amplifier + $ ?? speaker

I think this covers at least the most accessible options. Various comments have made me question the best way to go though. Now all units will require a speaker so that aside, the pro's and con's could be summarized in this way I think -

1: Pro's - Dedicated & assumably well engineered "all in one" unit; Con's - far more expensive than alternatives.
2: Pro's - Cheap and with digital readout; Con's - "unknown" factor of quality? accuracy? reliability? longevity? ease of use - construction required? enclosure? Time required for it. Requires a separate amp.
3: Pro's - Contained unit of a higher quality with digital readout, moderate price; Con's - "kit form" so requires some electronics/soldering experience/skill and presumably ample time, no "knobs" but seemingly operates by button control - ease of use?, still requires an amplifier.
4: Pro's - Older units are likely to be quality design and build, dial/knob sweep adjustments, on the cheaper to moderate end of the price scale; Con's - ease of use, analogue readout/accuracy requires a digital readout of some form, spare parts unlikely?, accuracy?, still requires an amplifier.
5: Pro's - Cheap; Con's - Output not high enough to drive all modes?, requires an amp?, not as user friendly with respect to adjusting frequency etc

Hence my confusion. I guess it depends somewhat on the budget available. The best choice if budget is not a consideration would certainly be option 1. However thereafter, it's more confusing. I believe Trevor said he uses an analogue unit - so option 4, but I'm not sure of his complete setup. Dom has suggested that software versions are not capable of the job, or at least are limited, due to the output power of the computer. He went down the "experimental" path of option 2, which may work out great and would be the cheapest option if so. I guess he doesn't stand to lose too much if it fails for any reason, except perhaps time. Matthew I think uses software so option 5, successfully? Does this depend on the type of frequencies needing to be generated or ?? Peter uses his own home design - sort of a cross between options 1 and 3, but this is not an option for most and I believe it was not cheap to set up either... Leading back to option 1. Markus chose option 4, but has since purchased extra's to suit including a digital readout, amplifier and protective switches etc.

I am tempted to just go the secure option of number 1. I have spent plenty more on other items in the workshop over the years so from that perspective, it could be seen as simply another quality addition to the tools I have at hand. Especially as it indeed will be purchased to further develop and improve my builds. The only hesitation is that I had not budgeted this much to set up for this job and to do so will put other plans on the back burner for a time.

So does anyone have any further comments or suggestions? What does anyone else use or possibly, what are you going to purchase in the near future? Is there anything I am not considering? Is anyone else trying to make the same decision currently?

Would love some more thoughts or conclusions (if such a thing exists) on this.

Cheers,

Jeremy.

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Re: Analogue signal generator (and maybe more related questi

Post by Kim » Sun Sep 18, 2011 9:32 pm

Good points all Jeremy, I wait with you for greater clarity.

Cheers

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Re: Analogue signal generator (and maybe more related questi

Post by matthew » Sun Sep 18, 2011 9:39 pm

i think you should spend as little as possible until you know that doing this sort of thing is for you.

you can do pretty much everything with free software, an old stereo amp, an old speaker and a camera.

if you get results, it makes sense to you, and you want to explore further, THEN spend your money.

:-)

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Re: Analogue signal generator (and maybe more related questi

Post by charangohabsburg » Sun Sep 18, 2011 9:59 pm

J.F. Custom wrote:Hence my confusion.
Now I am confused :lol: . Reading your post I believed you see it pretty clear.
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Re: Analogue signal generator (and maybe more related questi

Post by J.F. Custom » Sun Sep 18, 2011 10:06 pm

Kim wrote:Good points all Jeremy, I wait with you for greater clarity.

Cheers

Kim
Good! Well, at least that makes two of us. :)
matthew wrote:i think you should spend as little as possible until you know that doing this sort of thing is for you.

you can do pretty much everything with free software, an old stereo amp, an old speaker and a camera.

if you get results, it makes sense to you, and you want to explore further, THEN spend your money.

:-)
Yep - understand that Matthew. That's pretty much where I was at a while ago, knowing little of Chladni, but wanting to assess my instruments and try to repeat/improve on that in any - even vague way I could. Hence, why I had not budgeted much to set up for this.

However, with the release of these publications, in my opinion all that has changed. This is no longer random or simple pretty patterns on timber without comprehension. This is defining goals to aim for, frequencies to shoot for or experiment with or even avoid, specific to your design etc etc. So in a sense, your question/comment would now read - "Do I want to keep tapping on my timber and wondering why this one doesn't sound quite like the last and hope that in 30 more years I have a better grasp on that (as I have over the past 15yrs and do) or gather specific information on my builds, create targets and repeatably achieve or improve on those outcomes with each build." The answer to which for me, is a no brainer. Perhaps everyone does not want to take their builds to this level or in this direction preferring just the fine woodwork and the human ear... but I intend to try. :D

On the other hand, that does not rule out setting up on the cheap. What exactly is the setup you use as I do recall your images on the bass building thread. From memory it was software (but not sure which), a stereo amp? and a 12" subwoofer driver? If you don't mind, what watt capacity does the amp and speaker have? Do you have any problem generating enough power/volume as Dom alluded to?

Thanks.
charangohabsburg wrote:Now I am confused :lol: . Reading your post I believed you see it pretty clear.
:lol: Thanks for clearing that up Markus! 8)


Jeremy.

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Re: Analogue signal generator (and maybe more related questi

Post by woodrat » Sun Sep 18, 2011 10:35 pm

Jeremy, Thumbs Up for a couple of great posts... I dont know really what to do or which direction to go yet but I am slowly putting the parts of the puzzle together. I am very electronically challenged though.I have been looking at old school tone gens with nice big knobs on eBay but have not snagged one yet. I would love to go the No.1 option but really that is a bit out of reach with what I have allocated (not very much) to the whole thing. I was thinking of the aforementioned old school tone gen run through my old 1970's Pioneer hifi amplifier and checking it its accuracy with either Strobosoft or my Strobo Flip. Also the free Visual Analyzer has a frequency counter on it that I could use after I calibrated with the 440Hz output signal from the Stroboflip. So I could watch the counter on the laptop while I am turning the knob on my old school Tone Gen.... does this sound feasible...

Matthew...Thumbs Up for your post too...I dont want to splash cash to the wind on this one. I hope we all get it right...

...let me know if I am barking up the wrong tree. :wink:

John
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Re: Analogue signal generator (and maybe more related questi

Post by Trevor Gore » Mon Sep 19, 2011 12:13 am

My own kit is a BWD Minilab, from the 70’s as far as I can tell, rescued from a heap of derelict kit just before it hit the skip. It needed quite a bit of work to get it going again; trimming of the waveforms and setting up the power supply and amp sections. It works fine now, but needs a separate frequency meter (my computer). The sig. gen. part looks a bit like this:

http://uk.farnell.com/tenma/72-455a/aud ... dp/4261999

The latest incarnation of it is this:

http://www.mcvan.com/index.php?option=c ... &Itemid=11

No idea of the price, but probably not cheap.


The cheapest free-standing sig. gen. with analogue style controls that doesn’t need a frequency meter that I could find is this:

http://au.element14.com/tenma/72-7710/f ... /507450201

at $354.

There are a few other models that come in at a similar price, but many others in the $ thousands. The places to look are Farnell (now element 14 [!!??]) and RS Components. If you go for a cheaper one without a digital readout you’ll need to use either your computer or a phone app for frequency measurement.

For an amp, try Cash Converters and just about any “separates” unit ~20 watts RMS per side should do (typically called ~40 watts “music power”). Wire the sig. gen. into the CD or AUX input. A few years ago I bought a really great hi-fi amp from a CC in Melbourne for ~$30. I think it was cheap because if you selected "Speakers A" it didn't work, but if you selected "Speakers B" (different set of terminals) it did. It currently powers the sound system in my workshop. Or you could use a guitar amp. They’re pretty bullet proof!

For a speaker I use a 4” car speaker mounted in a piece of PVC pipe that was on my block when I moved in. The pipe is 140mm diameter – a weird size but perfect for the speaker I had. I got the speaker from Jaycar.

I think the speaker was 8 ohm, but otherwise similar to this:

http://www.jaycar.com.au/productView.as ... TID=1027#4

The speaker is rated to ~90Hz but I think you'll find plenty of sound down to ~ 60Hz, which is fine. Each is rated at 15 Watts, which is enough for guitar Chladni patterns. Price is ~$20 and you get a spare! (and I still have a spare!)

If you use a 4 ohm speaker, make sure the amp will live with that. It should say on the speaker terminals on the back of the amp.

When you set your gear up, make sure all the knobs you need to twiddle are close together.

Happy dumpster diving (or just call Don Bradley!)

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Re: Analogue signal generator (and maybe more related questi

Post by Dominic » Mon Sep 19, 2011 1:21 am

Jeremy and others, I have been having decent results using the NCH Tone generator but as Trevor mentioned, having the knobs close together is a big plus.

You could just hook up your computer with the NCH tone generator or similar to any stereo that you can plug your ipod into. I did this at first just to see what I could get. And I also tried a powered computer speaker straight to my laptop. All this worked OK but it was hard to hold the speaker and I had issues with power at lower frequencies. But i would suggest going a similar route until you know what you need and whether you enjoy it. Its like any luthier tool.
Start low tech, low cost and work up.

I now use this amp http://www.jaycar.com.au/productView.as ... TID=1009#4 I also got a discontinued 6 inch house speaker from them which I enclosed in a nice myrtle box with a handle on the top.
The amp needs a bit of wiring but it was easy. The hardest part was the power box which determines the power output. I had a power brick at home which was 15 volts and 5 amp which is perfect for max power. I would have preferred an old amp but I asked around and no one had one in their garage. Kind of thing that comes around but never when you need it. But this set up works fine and when the new digital unit comes it will be much easier to use because it has a knob to twist. It shouldn't be hard to enclose it in a box but at the moment I just have the components stuck on a board. Cost less than $100 so far.

Hope this helps.
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Re: Analogue signal generator (and maybe more related questi

Post by jeffhigh » Mon Sep 19, 2011 7:01 am

If you want a bit more omph out of you setup Dom, it may be worth looking into a better speaker.
Many of the jaycar speakers have a sensitiviy down around 87db whereas a decent Pa or guitar speaker is generally up around the 98-100 mark
Makes a huge difference in output, double for every 3db increase as I recall.

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Re: Analogue signal generator (and maybe more related questi

Post by Dominic » Mon Sep 19, 2011 9:50 am

Thanks Jeff, the one I got was pretty cheap=low quality and now I know what the numbers mean :D . I have to keep things down to half volume or it freaks out. So there is plenty of power coming out of the amp now. I'll keep fine tuning things as I go and get a better speaker when I see the right one but I was not ready to go and spend hundreds of dollars on a dedicated unit without trying to put something together myself and see if this is how I want to do things. Chladni is fun because you get to see the patterns but most can be done with spectral analysis it seems and for that I already have a decent microphone.
And I know that if I am patient people will start asking me if I want 1. an old orphan amp, and 2. a speaker.
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Re: Analogue signal generator (and maybe more related questi

Post by charangohabsburg » Wed Sep 21, 2011 11:43 pm

I'm still chewing on this one:
charangohabsburg wrote:I've been diving now a bit in the shallow waters of eBay and similar sites and found this polyswitch-calculator. :D

My next inevitable questions as an electronics noob are:
  • The wattage of the bass speaker I ordered is rated as 75 - 150 Watt max. (there's nothing written about RMS). I guess I have to calculate the polyswitch for the lower vale, 75 Watt. Is my assumption OK or do I miss something?
  • When searching on eBay for example for a 1.85 A polyswitch there's always mentioned also a maximum voltage, typically something like 30V, 60V, or 75V. That's also just OK I think. Or are these completely wrong items?
[...]
I figured out that the speaker rating 75-150 Watt must mean 75W RMS and 150W maximum peak allowed. But the speaker datasheet also mentions input impedance 4-8 Ohm. I am not sure what this range means. Do I have to calculate the polyswitch according to 4 or 8 Ohm?
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Re: Analogue signal generator (and maybe more related questi

Post by Dominic » Thu Sep 22, 2011 1:30 am

Hi Marcus, you want to match the impedance of the speaker with the same value for the amp. So for a 4ohm amp you should use a 4ohm speaker. It sounds like your speaker will operate at either value. So go with your amp value.
Here is an article on impedance. http://www.prestonelectronics.com/audio/Impedance.htm
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Re: Analogue signal generator (and maybe more related questi

Post by charangohabsburg » Thu Sep 22, 2011 8:23 am

Thanks Dom.

I finally found out (shoud have rembered or at least imagined) that the speaker impedance is frequency dependent:
Image
source: wikipedia.de
Dominic wrote:It sounds like your speaker will operate at either value. So go with your amp value.
The output impedance of the amp is 8 - 16 Ohm. The speaker impedance, as I interpret the data, depending on the frequency is from 4 to 8 Ohm. It seems that my ordered items (not yet arrived) do not match :?. Does it make sense to put a 4 Ohm resistor in series with the speaker or does this trick not work?
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Re: Analogue signal generator (and maybe more related questi

Post by Dominic » Thu Sep 22, 2011 9:35 am

Markus, Is there a switch on the amp? If not it probably adjusts to the speaker with a thing called active impedance matching. My amp is from 4ohms - 8ohms and I use an 8ohms speaker and everything is fine. I suspect the range on the speaker depends on how one or two speakers are connected together, in series or in parallel. 2 x 8ohm speakers in parallel would make 4ohms and in series would give you 16ohms. But without seeing it its hard to tell. I would read through the tech stuff for the speaker on their web site and work out if one speaker can run at 8ohms and if so you should be fine. If not, check the impendance of your car speaker before you start ripping that out. :wink: Cars systems are often 4ohms.

I know all this because I made the same mistake at first and the guy at jaycar sold me mis-matched amp and speaker and the output was really low. But I took it all back and swapped stuff until I got what worked. So I didn't waste any money.

I have not worried about polyswitches or other cut off devices. If I blow up my cheap speaker I'll look into it but we can run at lower sound levels to Peter and Matthew so I think the risk is lower. My little component amp has internal cut-off to protect the amp if it gets too hot or shorted. The sound is pretty annoying even with good ear muffs so I only keep it running for a short period.

Good luck
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Re: Analogue signal generator (and maybe more related questi

Post by matthew » Thu Sep 22, 2011 9:53 am

Dominic wrote: The sound is pretty annoying even with good ear muffs so I only keep it running for a short period.
I have wired a simple in-line light switch about a meter back from my speaker. This allows me to flick the sound on and off without touching the amp which is usually a few meters away. The neighbours appreciate this.

I also have an RCA-RCA junction on the speaker side of the switch. This allows me to change the speaker without effing around with the twisty wire and terminals on the back of the amp.

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Re: Analogue signal generator (and maybe more related questi

Post by peter.coombe » Thu Sep 22, 2011 10:34 am

Just a word of warning about this stuff. If you are going to go down this path, then to get the most out of it it does take time, and lots of it. Guitars are much better documented than mandolins so you do have a big head start over me. When I started I started from scratch because nothing had been published on mandolins so it took many many hours to figure out what the heck was going on. If you are not prepared to spend a fair bit of time to get the benefits then I would not bother. So, a token effort with el cheepo equipment is likely to be a complete waste of time because you will give up and go back to what you have always done. If you are serious and are prepared to put a big effort in terms of time, then go for something that will last the distance (e.g. option 1). Stuffing around with a computer and a mouse will drive you insane over a long period of time. Get the knobs, you won't regret it. Also, don't forget to document everything, and take pictures, and that also chews up time. Over the years all that documentation and pictures will give you insights you never dreamed of when you first started. Be serious, or don't bother is my advice.
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Re: Analogue signal generator (and maybe more related questi

Post by Kim » Fri Sep 23, 2011 3:05 pm

peter.coombe wrote: Be serious, or don't bother
That's exactly what my lecturer at clown school use to say Pete...guess its true, those that can do :lol:

Cheers

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Re: Analogue signal generator (and maybe more related questi

Post by charangohabsburg » Fri Sep 23, 2011 10:22 pm

Thanks for your advice Dom.
Dominic wrote: But without seeing it its hard to tell. I would read through the tech stuff for the speaker on their web site and work out if one speaker can run at 8ohms and if so you should be fine.
Yesterday I contacted the seller of the speaker and he meant that "... eeerm, well, yes I think that might be maybe just fine if your amp delivers 8 to 16 ohm" :shock: :roll: :lol:. So I gave it up and ordered another speaker - hoping to sell the first one at a profit. :lol:
Dominic wrote: If not, check the impendance of your car speaker before you start ripping that out. :wink: Cars systems are often 4ohms.
After thinking about the total value my car still might have, and the devaluation the loss of one speaker would mean to it in case I would want to sell it I just discarded this option. :mrgreen:

Once I have all the parts and (if) I get it working my neighbours will let you know. :shock:
Markus

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Re: Analogue signal generator (and maybe more related questi

Post by Dominic » Mon Sep 26, 2011 4:19 pm

OK, my little signal generator module turned up today. 2 wires in easy screw in sockets to connect to the amp and it was running. Its very cool. Nice clean signal and seems to generate much better/cleaner low frequency tones than I was getting from the computer.
It has a bunch of functions and generates a number of different wave forms. On the sin-wave function it has a resolution as low as 0.01Hz. It also has the all important knob to adjust the frequency with positive clicks that correspond to the frequency resolution. The resolution can be adjusted up to 1000Hz per click as you turn the knob.

The module is about the size of a pack of ciggies with a little screen. The amp is the size of a pack of tic-tacs so combined it is very small and I'll box it up at some stage but for now I just have the components screwed to a bit of mdf. All works perfectly.
If anyone is thinking of going down this route, of the ones for sale on ebay, some had a power supply and some didn't so check that when placing an order. Mine cost about $50 landed to my door.
Cheers
Dom
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Re: Analogue signal generator (and maybe more related questi

Post by Dominic » Mon Sep 26, 2011 6:03 pm

Here's a picture of the unit.
Dom
WB066-7f.jpg
WB066-7f.jpg (124.66 KiB) Viewed 24735 times
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Re: Analogue signal generator (and maybe more related questi

Post by colin north » Mon Sep 26, 2011 6:30 pm

Sorry, electronics Newb question.

I have a retired Panasonic hi-fi with speakers (about 40 W RMS/Channel ) and was thinking to try this (with Audacity as a SG) for Chandli testing.
I would "tube" one speaker for directionality.
Fine so far, but this would mean one channel output would be unused, and I am not sure if this would be good for the unused channel.
I seem to remember years ago someone saying it could be fried if the output was unconnected.

Any suggestions/comments?

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Re: Analogue signal generator (and maybe more related questi

Post by jeffhigh » Mon Sep 26, 2011 7:26 pm

I think it's only valve amplifiers that are vulnerable with no load (but my memory could be faulty)
Anyhow just turn the balance knob full to the chanel you are using.

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