0-9V LFO voltage swing

[WhenBoredomPeaks]

Can anyone link any simple op amp lfo-s which can swing between 0V and 9V from a normal 9V supply? Using rail-to-rail opamps and of course it will be still a few peren weaker than 9V.

Basically any op-amp LFO can do that with the right chip? For example here is Rick's LFO from the clari(not) topic



Will this put out a powerful rail-to-rail waveform if i  gonna swap the opamps to rail-to-rail opamps? I don't care if it will destroy the LED because i won't use it with a led.

[PRR]

[Jaicen_solo]

Why not just use the LFO to turn a FET on and off? That way you can have more or less full voltage swing and current at all speeds, and without a rail to rail swing.

[WhenBoredomPeaks]

Why not just use the LFO to turn a FET on and off? That way you can have more or less full voltage swing and current at all speeds, and without a rail to rail swing.

Because i don't know what are you talking about (=i am not smart enough)
But i designed a few stuff before so if you could tell me in a few words that how should i connect a FET to this circuit i could probably understand it. (something like "connect collector to 9V, drain to opamp output etc.")

Thanks! So with a proper opamp this gonna give me pretty much full voltage swing?

BTW are there certain effects i can "destroy" by "attacking" them with a hefty 9V LFO? I am mainly thinking about vintage ICs here. Like what if i "swap" the LFO for example in an EHX Small Clone with my LFO, could it destroy the MN3007?

[slacker]

Yeah with an opamp that can swing its output near to the rails you'll get pretty much 0 - 9 volts out.

What are you trying to achieve with this?

[WhenBoredomPeaks]

Yeah with an opamp that can swing its output near to the rails you'll get pretty much 0 - 9 volts out.

What are you trying to achieve with this?

I wanna make a standalone über-LFO unit with tap tempo, different waveforms etc. It will have 1 or two extra op amp LFOs and a sequencer too. Then there will be a mixer at the output to blend those waveforms creating custom waveforms.

Then i will mod my existing pedals to be able to host external LFOs. And then hopefully, there will be magic.

[deadastronaut]

blowing the dust off this..

i need a  0-9v lfo also...to use as CV in to the Q&D vcf to get the full filter range

tried the mods above to ricks one but only getting 2.7 to 7.3 v.... (tl072)

[samhay]

Just replied to your filter thread, but bottom line is that if you want an op-amp based LFO, then you will need a rail-to-rail op-amp.

[deadastronaut]

cheers sam.... nothings easy is it..

[merlinb]

cheers sam.... nothings easy is it..

Even a rail-to-rail opamp won't go truly all the way to the rails. It might get within 0.5V of them, so you might get a swing from 0.5V to 8.5V.

The alternative is to bootstrap the rails (e.g. see the Glassblower), in which case you really can get rail-to-rail swing, and beyond!

[deadastronaut]

cheers merlin, i had a look at the glassblower..

but its a bit beyond my understanding ...

you wouldn't have a rail to rail lfo example would you?..

[merlinb]

cheers merlin, i had a look at the glassblower..
but its a bit beyond my understanding ...
you wouldn't have a rail to rail lfo example would you?..

You would build the LFO circuit however you like- choose your favourite LFO. But instead of powering the opamp directly from the rails, you insert the circuitry in red.
The section in black is just the opamp, which you treat perfectly normally.

[deadastronaut]

brilliant, cheers man,

3906/3904 be ok in that then?..

[merlinb]

3906/3904 be ok in that then?..

Possibly not. I think you'll need some transistors with higher continuous current rating, like 500mA or more.

[samhay]

The Glassblower uses a very cool trick. I guess if you want to go down a similar road, then you could also try using a transformer instead.

[R.G.]

I'm reminded of the old joke about a man going to see his doctor. He tells the doctor "Doc, it really hurts when I do this", moving his arm to a very funny position. The doctor replies "Then don't do that."  

It is possible to do almost anything that's not strictly forbidden by some natural law at least once if you want to try hard enough. The questions then become whether it is worth the price you paid to do that again.

Here's the question I would ask: is 0-9V really, really necessary, or would 0-5V work as well as 0-9V?

As you note, you can always get 0-9V_almost by multiplying by 9/5 on the 0-5V waveform. You are planning to modify your pedals to work on the 0-9V already. Why not just modify them to accept 0-5V (or other voltage you pick) instead?

I do understand the concept of setting a standard and going with it. The problem with the 9V standard is that there aren't many (if any!) really 9.000V pedal supplies. Batteries start at about 9.5-9.6V for a fresh alkaline, and sag to about 7V when exhausted. Most pedal power supplies are not 9.0V. Even the popular fixed voltage 7809 based regulators are rated for +/-5%. So the question then becomes can all your pedals cope properly with 0-9V for an LFO?

The underlying issue with LFOs is that the thing they're modulating may not like the voltage and/or current you're feeding it. Synthesizers solved this problem by saying "The control voltages in these things will now and forever be 0 to ____Volts". They then subbed in usually 10.0V, but sometimes 5.0, and a few of them other values. The individual module that was to be controlled was made responsible for accepting 0-10V (or whatever).

A diode modulator needs a control voltage of about 0.45-0.6V per diode. An OTA needs about the same, and an LED about the same, unfortunately all with different base values for the diodes. The real problem with these is that they are linear(ish) with current fed through them, and exponential(ish) with voltage across them. They are only approximately linear and offset if you feed them through a resistor a voltage starting from 0 and going to some value. JFETs need a voltage of 0V to minus(!) Vgsoff to change from rdson to open circuit. When linearized by feedback, they need 0V to minus 2*Vgsoff. And Vgsoff is different per every JFET, even within the same type number.

Usually everything you want to LFO-modulate needs a different value/kind of control. It makes sense to set a standard for the controller, but then expect to have to modify each thing being modulated to take that standard.

This is the reasoning that went into my saying that you can pick another standard. You're probably going to do about the same amount of work to get your pedals to eat a consistent LFO, so make the LFO generation easy, at least. SOMETHING ought to be easy, for heaven't sake!  

[Mark Hammer]

A Texan using a Henny Youngman joke to make a point about electronic design?  Now I've seen everything. 

Carry on. 

[R.G.]

Henny was an honorary Texan in many ways. 

[deadastronaut]

a peanut walks into a pub with a pedal power supply that supplies 9.10 volts

the barman asks '' can i get you a drink''

the peanut replies '' no thanks i'm sorted'' ..(salted),( but with a london accent)



@merlin: so i will use that circuit on my q&d vcf filter then, not the lfo.?...excuse my dumbness

[samhay]

@merlin: so i will use that circuit on my q&d vcf filter then, not the lfo.?...excuse my dumbness

I think he was suggesting you bootstrap your LFO power supply (well it's the gain stage that really matters), not your filter's.