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

[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

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LFO Sync R01--Magic Smoke Electronics.jpg
Description:	Sync Circuit for the Magic Smoke 8K LFO - works with most other LFOs too.
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This image has been reduced to fit the page. Click on it to enlarge.

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[feggster]

[oculus]

[diablojoy]

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]

[feggster]

[diablojoy]

[bubzy]

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.

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lfxsync.zip
Description:		Download (listen)
Filename:	lfxsync.zip
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Downloaded:	546 Time(s)

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[isak]

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.

[Tim Servo]

Hey Isak,

Yes, that Rev 02 schematic is the latest and greatest (the only change I've made so far is to update the value of R5).

Happy building!

Tim (born with a soldering iron in my hand... my Mom never let me forget that) Servo

[isak]

[Tim Servo]

Yeah, I may be a little confused on the changes, but the Rev 02 is definitely the latest one. And yes, the LFX is a hybrid of the TSQ and 2x TSW waveshapers. I highly recommend adding an LED monitor (with transistor or op-amp buffer) to get some idea of what the output is doing. Also, you have the sync circuit hooked up correctly. Looks like you've got some fun building ahead of you!

Tim (building an LFO is a lovely way to spend a weekend) Servo

[isak]

I will want to add a led indicator, I will come home later on and post the led scheme I have.

About the gate out to trigger ENV etc...is it possible to have?

cheers

[isak]

this is the led scheme i have from you..
i guess i need to put it at the output, the "problem" is there is not only one output, maybe use a 4pos rotary switch and from there to the led scheme?

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basic_led_driver_131.jpg
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[flab]

well, i think im really interesting to this as a vclfo ,with the sync part , same think you are looking for Isak , how are you going to apply a rate pot to it thought ?
cheers

[isak]

Well, I did few mods to the attached layout here with illustrator.
Didn't build this yet, the rate is like the original I guess Or maybe remove the fine tune? Don't know yet.
I changed the timing cap to 2 timing caps, dont remember the values, I think the values are 0.1uF and 0.001uF with a switch for high and low speed.
I'll upload the scheme and the modified board as soon as I can, not at home at the moment.
The mods are the add on led and 2 timing caps.

Cheers.

[flab]

I built that yesterday , beautiful
thank you Tim

cheers

[isak]

Hi flab.

Happy to hear you got this thing working
What did you eventually did with the fine tune/tune?
Did you used one of the layouts that attached to this post or directly from the scheme?

Cheers

[flab]

hiya,

well i kept both of them fine tune / tune ,
i added the sunc , a switch at R36
added three led indicators
also i think to place an 1M pot at the R1 so i can play with the tri offset ,
if am not mistaken, as long as is at my breadboard ,

[flab]

well what i said about R1 yesterday is all lies ,obviously is not working ,im sorry R1
also there is a think with the sync , can i change the 1n 914 diode with sth else ? like a equivalent one ? i think thats the think about my sync

[feggster]

hi there, just got round to trying a layout on stripboard for the sync, wondering if anyone cares to check it,
note: the 6.8k would go to a switch/jumper for v+ or v-

also as was asked, can the diode be subbed (1n4148?)
thanks.

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lfx sync.png
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[Alfredo]

Hello! So there´s any final pcb design with Waveshapers and Sync function?
Thanks!