EASY VIBE Help please... (LFO problem using R.G. Keen's ramp up/down mod)

[R.G.]

I haven't forgotten this one, just had to tend to other things for a bit.

Sometimes, ticking and the more general crosstalk contamination can be maddeningly difficult to solve.

(Well, duh, R.G. )

I really think this one is caused by a few things:
(1) the nearness of the high impedance input to the LFO circuit on the board; as witness the change in impedance at the input changed it from a tick to a throb
(2) possibly some contribution of the input buffer being inside the same chip as one of the LFO circuits
(3) possibly some power decoupling or grounding issues. Haven't worked that out fully yet.

@orangetone:
The next thing I would do is to ground the input. Solid wire to ground right on the PCB. If that stops the throb and the tick, it's pretty definite that it's leakage into the input. If not, then there is at least one other place the throb/tick is getting in. If the grounded input makes it go away, you can then use your PCB if you'll make a little buffer circuit, just a gain-of-one opamp buffer, on a separate bit of perfboard, and connect its output to the input on the board. This should be placed out of the way of the LFO, and will force the input on the board to be essentially shorted, even with signal flowing.

If the short is not a complete fix, we need to dig deeper.

[orangetones]

The next thing I would do is to ground the input.  Solid wire to ground right on the PCB.

So essentially keep things the way they are now and jumper (short) the input pad to the ground of the board?  Am I reading this right?

If the grounded input makes it go away, you can then use your PCB if you'll make a little buffer circuit, just a gain-of-one opamp buffer, on a separate bit of perfboard, and connect its output to the input on the board.

Should I just duplicate the opamp buffer from the original schematic? Or do I need to make a different one.  Again, I understand what you are asking me to do, but I am not really an expert.  How would one construct a gain of one buffer like that?

This should be placed out of the way of the LFO, and will force the input on the board to be essentially shorted, even with signal flowing.

So when I connect the daughter board to the input of the original board, do I think keep the input pad shorted to ground as done above in this testing process?

I really appreciate the help on this one R. G.  I am also working on another layout for your modification that would have 4 dual opamps and hpoefully eliminate this issue.  Once I get this all done I think (as others mentioned in the thread) that I will finalize some off the values of the pots and such to allow them to have the most functionality.

Cheers! and thanks again for the help.

Steve

[R.G.]

So essentially keep things the way they are now and jumper (short) the input pad to the ground of the board?  Am I reading this right?

Yes, that is correct. Just to see if the "throb" goes away too. If it does, we know that the noise is getting in at that input, and we can work on that.

Should I just duplicate the opamp buffer from the original schematic? Or do I need to make a different one.  Again, I understand what you are asking me to do, but I am not really an expert.  How would one construct a gain of one buffer like that?

Just the one from the original schematic. What we're trying to do is just to get a very low impedance signal at that point on your board, and to have the very high impedance signal of the buffer input be a couple of inches away. The new added buffer lets  you physically move the high impedance point away, and it's output is very low impedance, suitable for connecting to the board.

So when I connect the daughter board to the input of the original board, do I think keep the input pad shorted to ground as done above in this testing process?

No, when you add the daughter board, remove the short we put there at first.

[orangetones]

R.G.,

Thanks again.

Just to be clear (I'm pretty sure, but)...  The input buffer consists of the two 10M, one 47k, and one 100k resistors and the 1nF cap, plus of course a single opamp.

As well, I simply connect the output of the opamp to the input pad on my board, with the short removed?  What happens then to the input buffer that is on the main board?  do I not have to bypass that?  Or did you mean that I would connect the output of the daughter board's buffer to where the first phase stage begins, thus replacing the main board input buffer.

Please forgive my ignorance on this matter.  And, as always, you help is very much appreciated!

Thanks again,

Steve

[orangetones]

oh, as well, I assume you want me to keep those paralell resistors and cap in place?  If I am correct on this one, I think I understand then that we are going in through the input pad, because we lowered the impedance by adding those resistors and cap in paralell.  Am I making sense?

[R.G.]

Yes, you're right. Lower impedance makes it much harder for anything to come through the stray capacitances.

[orangetones]

Great!  I will give this a try later on today and let you know what happens.

[solderman]

Hey there,

I have tried this mod and it works.  I even made a layout, however, we are experiencing some issues with my layout.  I am currently trying to solve it in conjunction with R.G.'s help, but I am also going to eventually design an alternate layour that will hopefully alleviate the problems I had with it.

As well, the pot values and such may need some tweaking to get the best gradation in speeds and ramp up/down speed. 

Check this thread for my progress.

http://www.diystompboxes.com/smfforum/index.php?topic=72395.0

Cheers,

Steve

Hi
I replay on this thread instead since both subjects are related.

Really nice layout there Steve. Is there any chance you might post the DIY file sins the PCB print from within the application is a the best way to get a properly scaled printout on a transparent folio. I always use the fotoresist method to etch my PCB:s

I haven't had any problem with motorboating or other LFO ticking or so on the Easy vibe. I built it from the original http://www.geofex.com/PCB_layouts/Layouts/easyvibe.pdf layout. On really high volume I can hear a little swooosching in LFO tempo when not playing, but not any thing loud enough to be concerned about. I have experienced this with othe LFO based tremolo circuits though. I have found that switching based cheap Wallvorts create tickin that can be filtered by a LM317. Only big E-lyt caps won't do it but I think everyone with this problem has tested with a fresh 9V battery to eliminate the power as a ticking source.

With the Easy Vibe I tested by disconnecting killing the LFO part but still have the rest functionally and hooking it up to my amp on full volume (15W practice amp but loud) then taking the thing in to my bathroom, putting out the light and flashing with a flashlight to simulate the LED:s. IT swooched at flashlight tempo with gave my the impression that the non wonted sound originates from the tonal part of the circuitry and not the LFO part. (i did this when I first hade the thing built on a breadboard so It was easier to tamper with tings then soldered on a PCB. The flashlight test was something I found useful when troubleshooting the 4ms Tremulus Lune with ticking problems. I did this to separate if the problem was cursed by the LFO or just a symptom of the LFO.

Looking forward to see yor progres with this one. I´m short on 4x Op-amps right now so I have to order some next week. Im getting back when I´v fiicshed the duild.

Cheers
//Solderman

[orangetones]

The thumping and ticking is gone when I use the daughter board.  Now about the tonal characteristics.  We have killed the tone by adding the 0.1uF and the resistors in paralell.  What do we do about getting that tone back?

[R.G.]

I think that pretty much nails down that it's layout related, then.

If you do a new layout, be sure to put the LFO as far away from the input as you can. The input is unique in that it has a very high impedance to keep all the treble in the guitar signal. But that also makes it susceptible to stray pickup.

It's even better if you can use an entire separate dual opamp for the LFO, so that can have a separate power supply and ground trace.

[orangetones]

R.G.  I sent you a link to a layout I was working on.  I was pretty sure that I needed to keep the LFO away from the input.  I didn't in my new layout, ubt I can easily move it. 

If I wanted to give it it's own powersupply and ground traces, would it still be powered off the same battery?  Or by powersupply, do you mean a separate battery and all?  I guess I am reading this as the LFO needs it's own ground, 9V+ and Vbias traces, but off the same battery.  Could you clear this up for me.

As well, in your layout on Geo, I think that the LFO is on half of 2 of the dual op amps.  Am I correct?  Why is there no issue there?  Is it because you have the LFO away from the input?  I would guess so.

Anyhow.  I shall try a new layout, as I really want to get your mods working and be able to share this with others.  In the meantime I am also working on building your NEOvibe as well.

Cheers,

Steve