implementing sync

[Luka]

hey yall

i want to find a cool quad lfo design with sync or implement sync on this schematic. i was wondering if you guys could help me make this happen.
i kind of understand how to do it but not sure if my theory is correct or not.

i thought that perhaps you could just send a pulse into the caps (c1 - c2) that it would sync. so is this correct? what sort of components would i need to chuck in to make this work (if it will work)

---

quadlfo.jpg
Description:	digisound 80-23 quad lfo schem
Filesize:	33.98 KB
Viewed:	8016 Time(s)

---

[bubblechamber]

the problem i've had in getting a sync to work with LFOs is the waves tend to get cut off when the oscillator resets. With audio rate oscillators this is hard to hear and even adds a little to the overall sound, but with LFOs i've found the result can be a little more unpredictable than i would like.
ian fritz has had some sucess using FETs, but i'm still not completely convinced that it's not truncating waves...
hopefully you'll get more helpful responses from people that actually know what they are doing, just wanted to throw my 2¢ in here

[urbanscallywag]

I think the ARP Odyssey has sync on the LFO (I think it syncs on key press). You might take a look there.

[ericcoleridge]

The Odyssey LFO will 'reset' from key gate. It doesn't sync.

I also want to have sync (or at least reset) on my LFOs. I like VC for controlling rate with a pedal controller, etc, but really, sync would be most useful in many applications. It's definitely great to be able to reset to keybrd gate, tap tempo switch, clock syncing, etc. But on the designs I've seen, I find that it's one or the other.

The Oakley Micro LFO has sync I believe (but no VC).

[bubblechamber]

i've been thinking about LFO resetting lately, too.
I think it could be done really easily by putting a momentary switch to interrupt the timing cap and ground it. it seems to me that this would achieve a reset when the switch is released. for me this would probably suit my needs.
or i could be completely wrong. i wish i had the time right now to sit down and try this out.
david

[urbanscallywag]

What's the difference between sync and reset?

[blue hell]

I think sync is a broader term? It could also mean phase reversal, at least for audio rate oscillators. But in the context presented here it would be the same thing I guess ...

Re. resetting LFOs this would always give jumps, these might be small jumps when the LFOs run at nearly the same speed (and once synced). When syncing to the onset of a note this jump doesn't have to be a problem, as it will likely be masked by an envelope being at zero value at that time.

Anyway, those are the two situation I use LFO reset. To (1) maintain a phase relation between two LFOs where one runs at a speed that is (nearly) an integer multiple of the syncing one and (2) to start a modulation at the onset of a sound in a predictable way.

[ericcoleridge]

[urbanscallywag]

I see. I understand that definition of LFO sync, but I guess my first thought (and I imagine other people's also) is sync like oscillator sync.

I imagine you'll need a counter or frequency and phase lock loop to get LFOs to run at the same (or multiple of) rate.

[Luka]

do you know of any examples of phase lock loop that i can check out?

[urbanscallywag]

Sorry I only know a little bit about digital PLLs.

I think if you could come up with a good "synching" LFO (I don't know exactly what to call it) you could sell many of them.

Now that I think about it maybe a counter might be a better solution than PLL since rates can go so low.

[ericcoleridge]

[ian-s]

[bubblechamber]

[loss1234]

bubblechamber-

where is the IAN fritz lfo with sync (using fets) that you mentioned?

also anyone know where is that lfo at the top of the topic from?

thanks

[Luka]

i guess i do hehe

it is the digisound80-23 module
quad lfo

http://www.digisound80.co.uk/digisound/modules/80-23/80-23.htm

[bubblechamber]

i've been going nuts trying to find the oscilloscope pics of an osc. resetting. it's looking like i might have seen them in a dream...

[frijitz]

[bugbrand]

Ian had kindly replied to a question I'd had about adding sync to a LM13700 osc --- I never managed to make it work well, so.....

Here's the thread that maybe caused the confusion??!!

May be worth checking this Fonik thread too??

[frijitz]

[bugbrand]

Sounds similar to what I suggested for an alternate XR2206 sync:

http://electro-music.com/forum/viewtopic.php?highlight=sync&t=28182

-- Now, given a couple of months, I've had *some* success using this approach.. but sometimes not.

I've been using, for example, the XR2209 and this required a stronger reset pulse - so I replaced the tranny with an opamp comparator.
And on some other things I just used the tranny and diode (no JFET)

I'd say --- do up a test LFO and then take wires out to a breadboard on which to try various syncing ideas. Check with an oscope, listen with the ears!

[Luka]

will do, just about to order some jfets

thanks genta

[BOB-SNARE]

[bugbrand]

Hi
No - I've been making use of the XR2209 - simple 8pin VCO chip (not so easy to locate... kind of like the NE566 but still in production). Much of it behaves similar to the 2206, but without all the extra features. Just Tri/Sqr output..

I'll have to check on a scope.. I'd kind of presume that the direction would always be the same on resetting if you're shorting the cap out?? .....

[frijitz]