A/DA Flanger does TZF?

[Dan N]

Charlie, any thoughts as to which trims would be best as multi-turn and which ones are fine as single turn?

[powerplayj]

About ready to fire mine up............

LFO section: Based on the info I have for Rev 04, a 2.2uf is needed for C24 and I can jumper to the speed pot bypassing C25 (unpopulated).  Correct???

[markusw]

Should be fine.
Good luck with firing up! 

Markus

[moosapotamus]

Just a reminder; the "dry" signal at the output mixing resistors is only completely "dry" when the regen is "off".

Right. I realized that after I posted. Need to get the dry signal from either pad A or B.

Did you build a version 2, or did you do additional mods?

I built it stock on a Ver.1 board. But, I plan to build a few more, possibly with some of the mods.

Charlie, any thoughts as to which trims would be best as multi-turn and which ones are fine as single turn?

T4 and T5 could be mult-turn, but it's not really a big deal. Single-turns are fine.

BTW, here's a little info on setting up the trimmers, based on my experience...

I used the frequency counter on my DMM, positive lead on the test point (TP) and common lead to ground. But, I think you could definately do this by ear, too.

Threshold 100%, Manual 0%, Range 100%, Speed 50%, Enhance 50%, all trimmers at 50%.

Plug in a noise maker, theremin, looper/sampler, keyboard, whatever... Something that makes a continuous sound, as opposed to having to keep strumming your guitar, for example. If you use a theremin or keyboard or something that doesn't have a lot of harmonics, try putting it through some kind of fuzz/dist/od pedal so you'll be able to hear the sweep more prominently.

Adjust TR1 bias until you hear the effect sweeping. Then turn Range to 0%. You should now be able to sweep the effect manually by twisting the Manual knob.

Now, set the low and high points of the sweep, keeping Range at 0%...
With Manual at 0%, adjust TR4 to set the low point, ~35kHz. Turn Manual up to 100% and adjust TR5 to set the high point of the sweep, ~1.3MHz. TR4 and TR5 interact with each other, so you need to go back and forth (set Manual 0% adj TR4, set Manual 100% adj TR5, repeat) until you get the low and high sweep points set where you want.

I left TR3 set at 50%. It does seem to alter the range, but I couldn't hear it doing much of anything else.

I also left TR6 at 50%. I'm not hearing any appreciable bad noise. It quiets down very nicely when not playing.

I'm still deciding where I want to leave TR2... to self-oscillate or not to self-oscillate... that is the question.

Actually, here's the question I have...

Is it possible to tweak the symmetry of the LFO?

To my ears, it seems to sweep much more slowly through the low end than it does through the high point. I'd like to try to make the sweep more "even" if possible.

Thanks!
~ Charlie

[Joe Kramer]

Hey Charlie,

About the LFO symmetry: seems like lots of flangers suffer from a lop-sided sounding sweep.  One solution to that is to use a hypertriangular wave form--half the wave is sine-shaped, the other half is triangle-shaped.  The asymmetry of the actual waveform makes the sweep sound symmetrical.   Here's one approach--about midway down the page, there's a schemo and an o-scope shot (with thanks to Scott Stites):

http://mypeoplepc.com/members/scottnoanh/birthofasynth/id19.html

There is another sine-shaper out there that uses an FET and a pair of diodes, and gives you a hyper wave if you omit one of the diodes.  I can't seem to find it right now, but it was in an issue of Polyphony magazine. 

BTW, hope you are going to be making some more A/DA PCBs someday.  I seem to have missed the boat on the first go round. . . .

Regards,
Joe

[powerplayj]

Should be fine.
Good luck with firing up! 

Markus

Checked a few voltages, inserted IC's except for the $AD and played through it with guitar to make sure I had a clean signal, added SAD and I now have a flanger!  Charlies "scopeless" tutorial above is right on time until I get access to a scope and signal generator.  What LFO cap values and polarities is everyone else using?  I started with a single 33uf polar I had on hand and will try a few others once I tune.  Seems like oldschoolanalog recommended non-polars here.....

[moosapotamus]

What LFO cap values and polarities is everyone else using?  I started with a single 33uf polar I had on hand and will try a few others once I tune.

I'm using a 33uF polar, too... positive leg toward IC4b pin 7. The speed range seems pretty good to me.

About the LFO symmetry...

Yeah, that's exactly how the sweep sounds to me, only more so. Like this...



...so, I think the LFO is already more "hyper" than it needs to be. Making it more hyper-triangular would make it sound like it was moving even more slowly through the low point, right? But, the way I hear it now, I think it needs to go faster through the low point. And I guess, rather than grafting in an entirely different LFO circuit,  I thought there might be some part of the existing LFO section that could be tweaked to change the duty cycle such that the sweep was less hyper-triangular and more triangular... maybe?

Thanks
~ Charlie

[oldschoolanalog]

Yes, I recommended NP caps here for 2 reasons. Both of the "personal choice" nature.
1: Its easier. (I'm lazy)
2: I had a wide variety of NPs to play around with. (The "use what ya' got" thing...)
I settled on 33uf (C24) and C250k (P5). I found C500k a bit too slow for my taste. Also the response of the 500k got a bit too "bunched up" (too sensitive) at the fast (cw) part of the rotation.
Play around until your ears are happy  .
Oh. BTW, the Polyphony article on hypertriangular LFOs are at Mark Hammers wonderful ( ) site.

osa

[Joe Kramer]

Hey Charlie,

I could be mistaken about this, but it may be that the o-scope shot is showing what you want, but upside down.  In the case of the A/DA, I assume the LFO puts out a sine wave, which sounds fine during the up-sweep (shorter delay region), but warpy or lop-sided on the down-sweep (longer delay region).  In that case, you would want the sharp side of the hyper wave to point south, which is a simple matter as far as tweaking the sine-shaper is concerned.  Anyway, regardless whether it points up or down visually, the idea is to have the triangular half of the wave affecting the longer delay, down-sweep region. . . .

As far as ideas for tweaking the symmetry of the stock A/DA LFO, I  have a Ross flanger that has the same lop-sided problem and have been considering adding an external modulation input to override the internal LFO with a hyper wave.  Besides that, I don't know of any way to tweak the existing symmetry enough to make a difference. . .

Thank OSA for pointing to that Polyphony article on Hammer's site. . . .

Joe

[oldschoolanalog]

A/DA LFO = Triangle wave.  UTSF, "LFO tutorial". 3rd post down. RG does a real nice job of explaining this.

[Joe Kramer]

Hey OSA,

Thanks for the UTSF advice, but I didn't really need it this time, since I've been posting to that "LFO Tutorial" thread all week. 

I don't see where RG says the A/DA LFO outputs a triangle wave.  I assumed it was a sine because the circuit looks very similar to my Ross flanger LFO.  I just looked at the output of its LFO on a scope last week, and it's a sine wave, so there's not much that can be done to tweak it.  But with the A/DA being a triangle, it would be all the easier to add that sine-shaper and get a hyper wave.

Joe

[puretube]

rectified sine looks a lot like hyperbolic... (see octave-doublers)
just a matter of correct mirror-axis (DC)...

[Joe Kramer]

Now that's making lemons into lemonade!  All you'd need a xstr phase-splitter, a pair of diodes, and an LFO that runs verrry ssslowly. . . . 

[puretube]

worx with xformer, tube, (opamp-)inverter..., too
BUT: like said: watch the mirror-axis (DC-base-line)

nuff said... 

[oldschoolanalog]

Hey OSA,

Thanks for the UTSF advice, but I didn't really need it this time, since I've been posting to that "LFO Tutorial" thread all week. 

I don't see where RG says the A/DA LFO outputs a triangle wave.  I assumed it was a sine because the circuit looks very similar to my Ross flanger LFO.  I just looked at the output of its LFO on a scope last week, and it's a sine wave, so there's not much that can be done to tweak it.  But with the A/DA being a triangle, it would be all the easier to add that sine-shaper and get a hyper wave.

Joe

Sorry about that Joe  .
RG didn't  mention the A/DA in that thread. I was referring to his explanation of the Schmitt Trigger/Integrator LFO. I thought it was mentioned much earlier in this thread that was the type of LFO used. I just assumed (bad idea) that was a foregone conclusion. My bad. Apologies to all if I created any confusion .

osa

[Dave_B]

rectified sine looks a lot like hyperbolic... (see octave-doublers)
just a matter of correct mirror-axis (DC)...

Thanks to Mark Hammer for preserving this: http://hammer.ampage.org/files/hypertriangleclock.gif

[powerplayj]

A few component / mod questions....

LFO caps: do these have any affect on tone or are they primarily related to oscillation/speed.  Differences with higher vs. lower values?  My optimal speed range is bunched up at 3/4 turn of the pot.  I might try a few resistors across the pot to spread out the range and lower the max speed. 

1458 Dual Opamp: Is this used in the circuit in such fashion that substitutions here will change the tone or is the goal here just to get one that has the lowest noise?  I have quite a few on hand which is why I ask....

Anyone modded theirs for use with a voltage control pedal (Manual override)

[Joe Kramer]

Hey OSA,

It's all good, friend.    Analog rules!

Joe

[sfr]

I've been playing mine for a while, at some point I'll open it back up again and get it tweaked now that I have a scope again - I've noticed the same thing that others have posted, about the speed control being bunched up in one end - for me it seems to be an artifact of the slow speeds being so glacially slow - it's harder to notice the difference between "slow" and "slower" than between "fast" and "faster".

But I'm just wondering - we timed my unit on the slowest speeds the other day at band practice - with the manual knob fully off, running feedback into the flange at it's slowest speed, we counted 15 seconds up and 15 seconds down.  A 30 second sweep.  Anyone elses going this long?  I've had bands where I could finish a song in that time!  Full speed is into pitch-bending madness.

[Dave_B]

...with the manual knob fully off, ... we counted 15 seconds up and 15 seconds down.  A 30 second sweep.  Anyone elses going this long? 

According to one of A/DA's advertisements, the unit features "An automatic sweep that varies between 0.1 to 25 seconds for a complete sweep cycle."  So yours sounds about right.