Flanger LFO Cutting Out

[Scruffie]

I'm in the process of designing a flanger akin to the Hollis Ultra Flanger in simplicity but to my own preferences at the moment, i've got a 4047 clock with a 4049 buffer, everything works great except for one problem, the LFO (it's not the one from the Hollis design) I can't get it to drive the clock hard enough to produce a good sweep.

At the moment, I have it connected up like in a small clone via a diode, with the timing cap however, the only way I can get it to work without cutting in and out is to use a 33k Resistor across pins 2 & 3 of the 4047 (it has to be that value) at which point, I only get milder flanging, if I put my fingers on that resistor, I can hear the sound I want, remove it though and it's back to drop outs.

I've tried everyway I can think of to hook the LFO up to the 4047, I tried a FET as a Variable resistor, the Diode, some stuff that just came about through trial and error, i've added a buffer to the LFO which just didn't work at all and i'm at a bit of a loss because it's almost there...

Obviously... schematics, I would post it, however i've used up my internet allowance untill next months billing (in a few days) so I can't upload them, however the LFO i'm using is simmilar to this http://www.piclist.com/images/www/hobby_elec/e_ckt16.htm with a 10k off the output and the 8.2k is connected to a B1M Pot for Rate and it's running off V.Ref and the cap is two back to back 22uFs (I tried the A/DA Flanger LFO aswell, no better) and the clock is a standard 4047 into 4049 buffer.

Any ideas? I know without schematics it's guess work but I just wanna get this bug nailed out, another way of connecting the LFO up to the Clock perhaps? Although while keeping it simple preferably, no 4007s...

One other bit of info, I tried using an LED in place of the diode for a visual idea of what was going on and noticed if I swapped it round, I got the other half of the sweep before it cut out so one position was the top part, other the bottom end of the sweep... seems like there could be something there.

Maybe i'm just expecting too much from the sweep though... but it seems like it should be able to put out a little more.

[Dave W]

How high/low are you trying to clock the BBD?
What BBD are you planning to use?

[Scruffie]

How high/low are you trying to clock the BBD?
What BBD are you planning to use?

V3207 (I tried a MN3206 as well, which is only 128 stages) and no idea of Frequency, none of that equipment availabe at the moment, but not amazingly high, as much as a 4047/4049 can put out, the LFO is the issue, not the clock (well the combination)

I compared it to my Electric Mistress and it's wayy off, it's not getting a shorter delay... a fuller one? The sound is there, I just can't get to it... As I said, when I put my fingers to that resistor, I hear the sound I want so the clock can cope, it's the LFO that can't or how i'm joining the two atleast.

I'm gunna try one more LFO and see if it helps but i'm certain the problem lies in the connection between the LFO & Clock... the LFO Bottoms out and I can hear it charge, add a buffer though and it wont take to the clock, however I am trying to make this an incredibly simple flanger so obviously there is only so much I can do with a small parts count.

Also on the clocking front, on my Electric Mistress when I clocked it too high I just got a dead spot at the top of the flange, this isn't a dead spot it's half a missing sweep and the fact it takes a 33k resistor and nothing else to make it work is raising eye brows.

Really wish I could post the schematic lol.

But I will say, simple as it is, the basic design can put out more than i'm getting from this LFO and i'm sure of it.

[Fender3D]

This may be a good starting point: http://www.diystompboxes.com/smfforum/index.php?topic=18529.msg109521#msg109521

[Scruffie]

This may be a good starting point: http://www.diystompboxes.com/smfforum/index.php?topic=18529.msg109521#msg109521

Bingo! Too much voltage, never even crossed my mind, glad that's sorted.