LFO on sk

Chicken Poc · February 09, 2009, 07:27:24 PM

I'm trying to add an LFO to my sk1, I want to build one using the ltc1799 chip.

I'm just confused, about numbers 3 and 4. Does 3 just mean to add a 1meg Pot? and does 4 mean just to add a toggle?

the_zombiest · February 11, 2009, 05:29:07 PM

right, I have limited understanding on this but here goes...

Pin 4 is a divider pin. you connect to either ground, open or V+. this will give you added depth allowing for a deeper pitch range. The divider may not need to be used at all, but I like to keep my options open and run it both open and to ground.

Pin 1 goes to V+ and to the right lug of your pot.
pin 3 goes to the middle lug.

use a trim pot in line with the pot as you would when replacing any timing component.

Also try feeding the output into the original timer, I didn't try this with my SK, but it worked well on the coiled vtech stuff

You'll have to use a multimeter to find a 5V connection to hook this up to otherwise you'll fry it with the 7.5v the casio uses. I built a voltage regulator for mine, but that was pretty pointless as you can find a 5v in a few minutes of probing.

It's good to have an alternate power switch for this n' your sk as it will consume battery power even if your sk is off.

Also hook up the original timing componant so you can switch between the two. I found it crashed mine out occasionally, especially when batteries are running a bit low. but it's nice to be able to return to the original pitch.

Are you planning on making the board from scratch?
I'd seriously consider just buying them premade from getlofi. I really wouldn't fancy soldering to something that's smaller than a gnats cock.

There's some useful info about the ltc1799 on both Getlofi and on Sailormouth if you haven't already checked it out.

hope I've helped.
Luke

Chicken Poc · February 11, 2009, 08:10:10 PM

thank you thank you thank you! really helpful information. Yes, I have seen them already made on getlofi, but i am planning on building it myself, since the parts are so cheap, it will be much cheaper. you can actually get free samples of the chip from the manufacturer (i think) website. i ordered a few, so when they get here i'll get to experimenting and see what happens

Chicken Poc · February 26, 2009, 06:59:33 AM

i managed to pull this off, and so i tried it, and it worked great at first! but only after 1 minute it started to quiet down and the batteries were draining fast.. anyone have idea why so? does this oscillator drink batteries fast or something?

Gordonjcp · February 26, 2009, 11:06:00 AM

Quote from: Chicken Poc on February 26, 2009, 06:59:33 AM
i managed to pull this off, and so i tried it, and it worked great at first! but only after 1 minute it started to quiet down and the batteries were draining fast.. anyone have idea why so? does this oscillator drink batteries fast or something?

Can you measure the current that the oscillator draws?

the_zombiest · February 26, 2009, 03:03:41 PM

I've not know mine to drain batteries that quickly.
How have you set up the divider?
Are you running it at 5v?
Were you using fresh or old batteries?

If your divider is set to +v, I imagine it would sap your batteries much faster than if it's set to ground... but I'm not overly sure on that one.

Chicken Poc · February 26, 2009, 08:07:30 PM

here are some pictures of how i set it up, can you tell if i did anything wrong? i think the v+ is set at 5v but i cant be positive since my multimeter is not working. does it really matter if the v+ is on the center lug or side lug of a pot? i dont think thats the issue, because it did work fine the very first time i fired up the sk1 and it worked awesome. i am using fresh brand new batteries and it turns on very weak, the lights dim,and there is just subtlle noise, the keyboard doesnt work itself though. i even tried a 7.5 ac adapter and it doesnt work either, it just makes a buzz sound sort of. the picture shows if i set up a divider or not, im not sure if i did, i probably did

Gordonjcp · February 26, 2009, 09:20:10 PM

That's very, very neat. Lovely job.

Can you measure how much current the oscillator module is drawing?

Chicken Poc · February 26, 2009, 09:30:07 PM

thanks!

i cant at the moment since my multimeter doesnt work..

im starting to think its the original crystal, maybe its damaged?

the_zombiest · February 26, 2009, 11:53:34 PM

Hmmm... You seem to be wired up right. Your divider is unused, so that's not a factor. What I didn't notice was whether you had trimmed the pot at the top end. I think a 47k trim pot is enough to stop it crashing out.

Of course, you may have wired it's power to two incompatible points seeing as your multimeter is on the blink. I guess one way to find out is to backtrack, Try again with fresh batteries, check all your connections, make sure your pot/switch/osc/coil are all actually working as they should.

Good luck with it all though.

pneaveill · April 07, 2009, 02:51:31 AM

This sounds like a very interesting project. Would like to follow the progress please.

Thanks in advance