The LFX experimental LFO (8K LFO and Weird Waveshapers)

marvkaye · Joined: Mar 14, 2011 Posts: 225 Location: Fla

Great ideas, Tim. I've suffixed the LFX with an "r1" and added it and the date to the silkscreen. I've already placed a MiniBoard Pro order for these, should see them on Monday. I'll put up photos as soon I get one populated.

If you'd be so kind to post the LED driver addition I'll bet it could be added to the existing board without growing its size. Personally, I don't have a problem adding a little daughterboard (if necessary) to add functionality.

<marv>

bubzy · Posted: Sat Aug 27, 2011 12:08 am Post subject:

added the text and transistor to my layout, have etched the board just now, gotta wait for my wife to wake up before i drill it though :p results later .........

bubzy · Posted: Sat Aug 27, 2011 10:23 am Post subject:

working

pcb layout confirmed :p

marvkaye · Joined: Mar 14, 2011 Posts: 225 Location: Fla

v-un-v · Posted: Sat Aug 27, 2011 11:59 am Post subject:

Dougster · Joined: Sep 20, 2005 Posts: 272 Location: Tucson, AZ, USA

/me posts obligatory complaint about software not being available under Linux...

(Which is why I use Eagle...)

Tim Servo

Hey Everyone,

One small change to note. R5 should be 220 Ohms, not 470 Ohms as I originally listed. I've updated the schematic on the first page, so that is correct now. With R5 at 470 Ohms, you'll only get a range of 4,200:1, but with R5 at 220 Ohms, you'll get the full range (about 8,800:1). Sorry for the error, and thanks again to Ian Fritz for letting me know. If you've already installed R5 and don't want to pull it out, you could just install another 470 Ohm resistor in parallel. The resulting resistance will be roughly 230 Ohms, which is definitely close enough.

Cheers,

Tim (one small change) Servo

marvkaye · Joined: Mar 14, 2011 Posts: 225 Location: Fla

I received my MiniBoard Pro order from ExpressPCB today... can't say enough nice things about them. Here's a picture of the component side of one of their boards complete with solder mask, component screens, the works. Were I to cut the boards in half, the laid in cost from them for this level of service came to about $14/module including shipping. I didn't make any allowances on the boards for mounting so will probably use Thomas Henry's method of glued angles (courtesy of his "Build a synth" DVD, thank you TH!) BTW, the price could have been around $10 per module by ordering the PCBs without solder masks or screens. It's a great deal either way if you ask me.

<marv>

ExpressPCB_LFX^2.jpg

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Nice stuff from ExpressPCB

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Tim Servo

Hey Marv,

Looks nice! A couple of thoughts on PCBs (these are just some things I do on my own / Magic Smoke PCBs)

1) Include the board name, and a date or revision number so you know what the board is and what schemo you used for it.

2) On the part designators (R1, U3, etc.), I always try to move them off to one side so that they're still visible when the part is in place. Makes troubleshooting or modding quicker and easier. You can't always do this on really cramped boards, but one most of mine I've been able to do it.

3) If possible, try to keep all similar parts pointing in the same direction. In other words, all ICs should point the same direction. I also try to keep all resistors in the same orientation. It generally makes assembly easier and makes the board look cleaner. This is a must for boards that are going to be automated, although that's something I've never had to worry about (although I do have a project coming up ...)

4) Whenever possible, traces on one side of the board should be at a right angle to traces on the other side. This minimizes interference, and even though that's not going to be a problem on an LFO board, it is a good habbit to get into.

For layout software, I've had really good luck with KiCAD (and it's free / open source).

Let us know how the LFX boards work out!

Cheers,

Tim (has plenty of bad habbits too) Servo

marvkaye · Joined: Mar 14, 2011 Posts: 225 Location: Fla

HI Tim,

Thanks for all the great pointers. If I ever manage to actually come up with my own PCB design I'll try to keep them in mind. It was actually bubzy who did all the heavy lifting with this one, I just made a few very minor changes and sent ExpressPCB money Rolling Eyes

I'll probably cut small stencils for them and airbrush the name of the board and revision down the center... I figured I'd keep them together and layout a MOTM style front panel that accommodates the pair.

Did you ever come up with the LED driver for this? MFOS Ray has a simple one that takes a couple resistors and a 2n3904 (on his Synth DIY page under the "Hot tips" menu item) but I don't know if it's appropriate to this application or even where it would tie into the circuit. Just curious....

<marv>

Tim Servo

Hi Marv,

For marking the boards, you might want to also consider a fine-tip permanent marker, or even a paint marker (don't know if those come in a fine tip).

As far as an LED driver, the transistor driver on Ray's site is an excellent, and very simple solution. I have some slight enhancements on that, but that original design is the simplest. You can hook it up to any of the waveform outputs - the buffer will pull very little current from the output, so the output can still drive lots of mod inputs.

Tim (the original, and the simplest) Servo

bubzy · Posted: Mon Aug 29, 2011 11:39 pm Post subject:

sorry its been such a while, been very busy. marv, the transistor driver is quite simple. try this https://homepages.westminster.org.uk/electronics/images/vot3.gif

in the meantime, ive added it to the circuit board and done a little shuffling of components to try and fit a shrouded header onto the power pins. something i overlooked in the original design.
***this now includes the pdfs of the indiviual layers***

LFX PCBv2.zip

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LFX PCBv2.zip

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marvkaye · Joined: Mar 14, 2011 Posts: 225 Location: Fla

Tim Servo

Hi All,

I just posted a handul of different LED driver circuits at
http://www.electro-music.com/forum/topic-49449.html

I'll post more as I have time, but there are a few there to get you started. I use the "Bipolar Driver with Adjustable Bias" for the output of my LFX and it really works nicely. Smile

Tim (head towards the blinky light) Servo

oculus · Joined: Oct 30, 2011 Posts: 35 Location: Iceland, Reykjavik

Congrats and thanks for sharing this Tim
this LFO sounds very interesting,
i´ll definetly try this one out.

this would be amazing with a retrigger option,
to be able to kind of sync it to the tempo of the song one would be working on.

do you think this could be possible by using a fet transistor ? or some other way?

Tim Servo

Hi Oc,

Yes, it's pretty easy to set up sync on this (or most other) LFOs by using an FET or an analog switch to change the charge on the timing cap. You can set up the circuit to pull the cap up to V+ or down to V-. In most triangle core oscillators, the integrator is inverting, so this means that pulling the timing cap up to V+ means the output triangle will be reset to V-. By the same token, pulling the cap down to V- means that the output wave will reset to its positive peak. It just depends on what behavior you prefer (or you could even put in a switch). The circuit below has already been posted on the Magic Smoke Facebook page (that's the place to go if you want to see this stuff a little sooner).

Tim (peaky!) Servo

LFO Sync R01--Magic Smoke Electronics.jpg

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Sync Circuit for the Magic Smoke 8K LFO - works with most other LFOs too.

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feggster · Joined: Sep 12, 2011 Posts: 52 Location: uk

oculus · Joined: Oct 30, 2011 Posts: 35 Location: Iceland, Reykjavik

diablojoy · Posted: Wed Jul 24, 2013 7:27 pm Post subject:

Tim is there a reason for not pulling the intergrator cap to 0V ?
instead of the negative or positive rail
resetting the wave to 0V seems more intuitive to me

Tim Servo

Hey DJ,

In this design, you can reset the cap to 0V by connecting the 6.8K resistor to 0V. However, if you pull the cap to 0V, the output won't consistently reset. If the LFO wave was on the down slope, a reset to 0V will make the output start at 0V and head negative. On the other hand, if the LFO wave was on an upward slope, the reset will set the output to 0 and the it will start up. Resetting the LFO wave to the negative (or positive) peak means that the output behaves exactly the same way on every reset, regardless of where the LFO wave was when the sync pulse hits.

Tim (resetting it to 0K?) Servo

bubzy · Posted: Thu Jul 25, 2013 4:11 am Post subject:

feggster · Joined: Sep 12, 2011 Posts: 52 Location: uk

diablojoy · Posted: Thu Jul 25, 2013 3:29 pm Post subject:

bubzy · Posted: Fri Jul 26, 2013 6:21 am Post subject:

haven't made a pcb for some time, so this might not work, I haven't tested it (or done a huge amount of error checking :p)

this is the original board, but with the sync section added.

hope it works, let me know if it doesn't and ill fix it.

lfxsync.zip

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isak · Posted: Thu Sep 26, 2013 10:13 am Post subject:

Hi Tim and Guys.

just wanted to make sure that the scheme that open this post is the last updated scheme of the 8k LFO, i'm asking cause i seen few schemes of the 8k in the forum

cheers,
Isak E.