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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Inductors for output shaping?
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droffset



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PostPosted: Wed Aug 22, 2012 2:15 pm    Post subject: Inductors for output shaping? Reply with quote  Mark this post and the followings unread

just watched this video:
http://www.youtube.com/watch?v=NgwXkUt3XxQ&feature=plcp

I'm going to try just placing different inductors that I have salvaged in series with the output of some lunetta stuff to see if the square waves become a little more interesting. Has anyone tried this kind of thing?

For example

Lunetta---->MelodyGenerator----->inductor----->mixer

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Uncle Krunkus
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PostPosted: Wed Aug 22, 2012 2:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sounds like a great idea to me. It should roll off that digital "sparkle" really well. If you've got two outputs, why not try putting them each through an "air core" inductor with a nice lump of soft iron coupling the core of the two inductors? Might create some nice softening of both. Very analogue.
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tjookum



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PostPosted: Thu Aug 23, 2012 2:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Some time ago I was looking at different filters and I came across the same video. I did try to make a inductor/capacitor or LC filter but I never really got any interesting results. But I was just jamming in random inductors in random places, a little more care and thought might give some great results.
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nathanxl



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PostPosted: Thu Aug 23, 2012 3:39 am    Post subject: Reply with quote  Mark this post and the followings unread

I would be very interested in seeing the results you get out of this...
Love the idea.
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Cynosure
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PostPosted: Thu Aug 23, 2012 5:54 am    Post subject: Reply with quote  Mark this post and the followings unread

I used inductors a couple of time because I got a bunch from an old EQ I salvaged for parts.

I used it in my UM-TSS drum machine bass just passing the kick sound through it in order to soften the sound a bit.

I also used it going to ground with a pot for a lowpass filter in a delay circuit. The sound goes through a PT2399 wired up in the echo method in the datasheet, and then the passive low pass inductor circuit warms the output sound a bit. I find that it lowers the volume level less then when I use a capacitor.
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nathanxl



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PostPosted: Thu Aug 23, 2012 6:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Cynosure wrote:

I also used it going to ground with a pot for a lowpass filter in a delay circuit. The sound goes through a PT2399 wired up in the echo method in the datasheet, and then the passive low pass inductor circuit warms the output sound a bit. I find that it lowers the volume level less then when I use a capacitor.


Wow. Any chance of sound grabs, pics, vids or schemes of this Cyno? Love to see/hear how the inductor changes the output.
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Cynosure
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PostPosted: Thu Aug 23, 2012 6:14 am    Post subject: Reply with quote  Mark this post and the followings unread

I can do a quick demo tonight with the reverb unit. The drum sound goes through a bunch of filters, so it will be difficult to hear the changes for just the inductor.
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jcintheus



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PostPosted: Thu Aug 23, 2012 8:37 am    Post subject: Reply with quote  Mark this post and the followings unread

I've had luck with this:http://www.geofex.com/article_folders/wahpedl/wahped.htm
I used a 600mH inductor, a 5v supply, and 2N2222 for the transistors.
You can "modulate" it, with the output of an r-2r, at the node connecting the inductor, 3 resistors, and cap.
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Cynosure
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PostPosted: Thu Aug 23, 2012 4:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think I followed the schem on this site but used a pot for the resistor:

http://www.opamp-electronics.com/tutorials/low_pass_filters_2_08_02.htm

It doesn't provide a lot of filtering with the value i used, but i just wanted to roll off some of the high frequency resonance from the delay loop.

Here is what happens in the mp3:

0-16sec: Clean sound
16sec: reverb with no filtering
26sec: Start to slowly turn down the pot for the inductor to increase filtering
36sec: start to turn up the aux send to the reverb on my mixer to compensate for the inductor lowering the volume


So if you listen to 16sec and then skip to 40sec you can hear that the latter has a nice warm reverb.


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droffset



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PostPosted: Thu Aug 23, 2012 5:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

My first attempts last night didn't sound very different,
Unfortunately my scope doesn't want to power up, maybe it blew a fuse. Will need to hook up to the soundcard.

Here's a pic of most of the ones I found. Some of them are variable, which got me excited, but I think they're all too low values, in the uH, where something in mH is needed...maybe, I don't know.

One is a crystal just for fun, i guess it isn't really an inductor but a resonator?

Posted Image, might have been reduced in size. Click Image to view fullscreen.

I just placed the inductor in series with the output, I'll try some filter designs next I guess.

This PDF might help:
http://www.jaycar.com.au/images_uploaded/crossovr.pdf

edit:
just placing some resources here for safe keeping:

http://www.deephaven.co.uk/lc.html

http://obiaudio.com/wp-content/uploads/2010/07/frequency_chart_lg.gif
http://www.loopblog.net/wp-content/uploads/2010/11/podcomplex-frequency-overview-chart.gif
http://www.independentrecording.net/irn/resources/freqchart/main_display.htm
www.deepsonic.ch/deep/freeload/audio_frequency_chart.pdf

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Cynosure
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PostPosted: Thu Aug 23, 2012 6:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think I used 3mH and it doesn't filter a lot. You will need high or have it rigged another way to more it work better. I think they can be used with opamps because the EQ had a bunch of opamp chips too.
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Draal



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PostPosted: Fri Aug 24, 2012 4:57 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm a guitar and amp freak so I'll give ya all I know regarding inductors (which ain't much Laughing ):

I have used them in wah circuits, modded wahs and fixed Q wahs. The Fasel inductor is sort of a Holy Grail for some; that inductor runs at a optimal 500mH for it's trademark sweep. Inductor based wah pedals have more resonance, beef, warmth, mojo, etc. than twin T filters to some of us gear snobs.

A lot of debate regarding which inductor gives the best tone because we all hear a bit different. Also, the inductor wah circuit as a whole is more important than just which brand of inductor is used. Again, lots of forum fights over this Holy Grail of tone stuff.

Anyways, back to our needs. Yes, as jcintheus eluded to: you should try something way bigger than those little guys.

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PostPosted: Sat Aug 25, 2012 8:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

I checked mine, and it is actually 3.2H

Not mH.
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droffset



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PostPosted: Sun Aug 26, 2012 1:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Something interesting also is the relationship between the inductor and the size of the capacitor. If you look at that deephaven link there's a calculator for figuring out what values you need to filter at a certain frequency. Maybe a big cap will compensate for a small inductor.

Haven't had a chance to play with it again but will this week.

And thanks for the input everyone.

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RingMad



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PostPosted: Sun Aug 26, 2012 4:41 am    Post subject: Reply with quote  Mark this post and the followings unread

I have nothing to contribute to this thread, but just saying that I'm keeping my eye on it... I also salvaged a whole bunch of inductors from various things I was ripping apart... not sure why... they are fascinating and come in so many shapes and sizes.
They are one of the simplest components... a coil of wire, essentially... but somehow quite magical. They seem to have little place in the Lunetta / logic chip world, so I'd be really curious as to what you folks come up with.

James.
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Uncle Krunkus
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PostPosted: Sun Aug 26, 2012 4:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've always been fascinated by inductors of all kinds.
Next time you've got something breadboarded up, and I mean anything.
Replace part of a resistor at the start of the circuit with one coil off a small audio transformer. Then replace part of a resistor at the end of the circuit with the other side of the transformer. Whether it's a filter or a fuzz circuit, you can get some very subtle anomalies happening.
BTW I think inductors are very much allowed in a Lunetta. I'm not sure why? Maybe because it is, in effect, just a long wire! Laughing

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Uncle Krunkus
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PostPosted: Sun Aug 26, 2012 4:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Also because so much of a Lunetta sound is often very sharp square waves, and it sometimes needs this harsh, "brilliance" toned down to some extent. Cool
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Uncle Krunkus
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PostPosted: Sun Aug 26, 2012 4:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Some early organs I've seen take the square waves straight off the TOG and dividers and then straight into an enormous board covered with inductors (some are aircore bobbins up to 40mm across) and capacitors.
So the timbre changes produced by different footages are not just from emphasizing certain harmonics of the squarewave, but also by attenuating everything else, through the use of these LC networks.

So, I'd definitley be looking at the larger inductor values. Anything smaller than a 1.5cm cube is probably only going to effect Radio Frequencies. I actually made that mistake when I first bought them. I got the uH types which are about the size of a 1/2W resistor. They seemed to have absolutely no effect on the workings of a fuzz box! Confused ........ Idea Then I went back to the books, and found that I needed upper mH range through to whole Hs. Laughing

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RingMad



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PostPosted: Sun Aug 26, 2012 7:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

BTW, when I said inductors seem to have little place in Lunetta's, I meant that I hadn't seen any circuits involving them, not that they should or shouldn't be used.

Hmmm, I'll have to look up how to determine the values of some of these I've salvaged... my multimeter doesn't do that. I also ripped out of some VCR or something a metal box filled with air coils.

I agree that sometimes the harshness of these square waves can be toned down, but I guess I went the glide and triangle waveshaper route rather than the frequency-filtering one. Although recently I was thinking it would be nice to do a bit of that to emphasize certain interesting sounds.

Hmmm #2: If there's an LC like there's an RC, is there an L/2L like there's an R/2R? Smile

James.
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elektrouwe



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PostPosted: Mon Aug 27, 2012 5:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus is right : we talk about "Henrys" for filters in the audio range. All Ls you can see on the posted picture and what you can savage from todays electronic waste is uH or best case mH - forget it....but : small 50/60Hz transformers eg from (older) wallplug PS show "Henrys" on the primary side. They also have a remarkable winding capacitance, so the have resonance frequencies in the range of 1k..20kHz without additional components ! Paralleling C's brings them down to the base range. Secondary windings are also useful: a DC current can drive the iron core towards saturation. This will reduce primary inductance and rise res.freq. and also cause signal distortion.
I attached a circuit that I started experimenting with years ago. Try different transformers ( 1..2.5VA range) and add Rs (series) and Cs (to GND) to bend frequency response. BTW : CV input is not CMOS compatible; needs low impedance drive (small power amp or lab power supply for DC control)


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droffset



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PostPosted: Tue Aug 28, 2012 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Awesome info, thanks, there's a lot to learn about this stuff.
Sorry if it's getting too far away from CMOS, the original idea was to just stick an inductor in there but now I guess I'm on this Wah research line.

Found this link, might help:
http://www.jensen-transformers.com/an/Audio%20Transformers%20Chapter.pdf

Currently looking for info on those little 3ohm-3ohm audio coupling transformers from radio shack and jaycar, the vendors don't list henries, just impedances, but they do list frequency responses sometimes.

http://www.jaycar.co.nz/products_uploaded/MM2534.pdf

http://www.jaycar.co.nz/products_uploaded/MA1510.pdf

Update:
Oooh, big find using said transformers in a Wah circuit!
http://members.shaw.ca/roma/wah-two.html
Good explanation here:
http://www.geofex.com/article_folders/wahpedl/wahped.htm

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Tomoroh Hidari



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PostPosted: Sat Sep 01, 2012 4:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

well, this looks interesting. I have an old wahwah (disassembled since it didn't filter well, but made much noise) with a 500mH inductor lying around somewhere... was thinking of maybe, once I know my way around well enough, i might repair it or whether it might be smarter to just use all the useable parts and (re-)build a filter with that...
i'll keep watching what you come up with to see what i'll do!
... still a lot to learn and try and time has been sparse this last weeks...

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PostPosted: Fri Sep 14, 2012 8:50 am    Post subject: Reply with quote  Mark this post and the followings unread

I like this thread! It's fun to see the range of experience that everyone has from wtf is an inductor to talk of transformer parasitic capacitances resonating with the core, nice! I could chime in on several topics here but I'll mention just one to be careful about when using inductors: ShOcKiNg CiRcUiTs!

If you pump some DC for a while into an inductor you build up it's magnetic field to some value, then if you open circuit the connection, say with an analog switch like a CD4052 (?) or CD4051 (?) or similar, then the current cannot change instantaneously and the collapsing magnetic field produces a giganourmous voltage spike. ZAP! goes the chip! In fact, it would be fun to have a thread where we designed the circuits that self-destruct in this way in the most audio-spectacular sound, hahahhaha!

So be careful with those inductors, don't yank em around or you'll blow stuff up!

Les

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Uncle Krunkus
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PostPosted: Fri Sep 14, 2012 6:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Tell what you think of this idea. Smile

With a classic 40106 oscillator you have the output feed back to a charging cap to ground right?
Well, I'm very interested in the "starve a whole 40106" oscillator bank idea, and I was trying to work out a way to make it sound better. I've settled on just three oscillators per chip, however, that leaves three inverters wasted.
What if we add two inverters to the standard oscillator, so the output of the first inverter goes to a second, then a third which is the right phase to feedback to the first. The first needs the cap and resistor, but what if the second one is coupled with a small inductor? (uH->40mH?)
I reason that this could create a low pass filter which will force the second inverter to be slightly delayed from the first. If we take the delayed out and mix it with two standard 1 inverter oscillators on the same chip, it should add some nice lower frequencies and force the first two to stay out of sync with the third.
Does this make sense?
Is it feasible?
I'll be finding out real soon, no doubt. Laughing

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