Flintlock Flanger (A/DA Flanger) Debug

[Dasher]

I'm a bit stuck trying to work out a problem that I'm having with a Flintlock Flanger (A/DA Flanger) that I recently put together. I'm hoping someone here might be kind enough to offer a few ideas to help me resolve it.

Schematic and build document here: http://lectric-fx.com/wp-content/uploads/2015/07/FlintlockFlangerV1.2.pdf

Description of the problem: The flanger works as expected for the most part. However, there is a loud knocking/popping noise at the extreme ends of the flanger's sweep. The knocking noise can be sped up or slowed down with the "Speed" pot. The noise can be regenerated with the "Enhance" pot. The "Threshold", "Range" and "Manual" pots do not affect the noise.

Any parts substitutions: I used a 470pf cap and a 33pf cap in parallel for C16 instead of a 510pf cap. I also used two resistors in series for R17 instead of a 1.3M resistor. I don't think either of these substitutions would be a problem.

What I've done so far:
•   I calibrated the flanger to sweep from 69.6kHz to 2.6mHz.
•   I've tried using a TL062, LM358 and LM1458 for IC4 (the LFO one). The knocking noise is there with each IC.
•   I've double checked the values of all capacitors and resistors. There's still a chance that I missed something though...those tiny colour bands are hard to read!
•   I've checked for iffy looking solder joints but didn't notice any. Unfortunately, some of the solder side of the PCB is hidden beneath the board mounted pots, so I'm not able to check there yet; I don't want to go about removing the pots unless I absolutely need to. I did ensure that the pot casings are not shorting out against the PCB (I used those plastic guard things that come on Tayda's pots).
•   I've tried removing the LFO IC (IC4) to see if the noise would go away; it did! I also checked to see if I could trigger the knocking noise at the extreme ends of the sweep with the manual pot; I wasn't able to.

My investigation so far leads me to believe that the problem lies somewhere in the LFO section of the circuit (or its power supply). Does that sound reasonable?

And now for the long list of IC voltages. The voltages associated with the LFO are wobbly, as expected...please excuse the rough measurements on those:

IC1 – 4558
1: 7.13
2: 7.13
3: 6.25
4: 0
5: 8.66
6: 8.77
7: 8.68
8: 14.23

IC2 – 4558
1: 4.8
2: 4.8
3: 4.78
4: 0
5: 7.1
6: 7.1
7: 7.1
8: 14.24

IC3 – 4558
1: 7.12
2: 7.1
3: 7.04
4: 0
5: 7.1
6: 7.1
7: 7.1
8: 14.62

IC4 – LM1458
1: ~2V varies
2: 7.2
3: varies
4: 0
5: 7.1
6: 7.1
7: varies
8: 14.75

IC4 – 4007
1: ~60mV varies
2: ~60mV varies
3: 0
4: ~100mV varies
5: ~100mV varies
6: 0
7: 0
8: ~100mV varies
9: ~100mV varies
10: 0
11: 7.95
12: varies
13: 15
14: 15

IC6 – 4047
1: ~14.8 varies
2: varies
3: Varies
4: 15
5: 15
6: 15
7: 0
8: 0
9: 0
10: 7.48
11: 7.51
12: 0
13: ~14 varies
14: 15

IC7 – 78L15
I: 7.12
G: 0
O: 15.01

IC8 - 4558
1: 7.83
2: 3.93
3: 3.92
4: 0
5: 6
6: 6
7: 5V – 6V (varies)
8: 14.60

IC9 – 4049
1: 14.91
2: 7.49
3: 7.50
4: 7.50
5: 7.50
6: 7.50
7: 7.48
8: 0
9: 7.52
10: 7.49
11: 7.50
12: 7.48
13: 0
14: 7.51
15: 7.49
16: 0

IC10 – MN3007
1: 14.85
2: 7.51
3: 6.89
4: 1.03
5: 0
6: 7.50
7: ~5V varies
8: ~5V varies

IC11 – LT1054
1: 1.38
2: 5.04
3: 0
4: 15mV
5: 0
6: 2.5
7: 1.4
8: 9.18

IC12 – 4558
1: 7.1
2: 7.1
3: 7.1
4: 0
5: 7.1
6: 7.1
7: 7.1
8: 14.23

IC13 – 4558
1: 7.28
2: 7.2
3: 7.1
4: 0
5: 7
6: 7.1
7: 7.1
8: 14.23

Q1 – 2N5457
D: 7.1
G: 7.06
S: 7.1

Thanks in advance for any help.
Scott

[Scruffie]

Can you post some photos up? Also where did you source your parts from? (I don't trust those Tayda 'Chong' electrolytics for filtering jobs).

If you have a spare electrolytic (10-47uF) try tack soldering it on the LFO Op Amp, positive to pin 8, negative to ground and see if that helps.

There is a 100nF cap (C25) that forms a low pass filter for the for the control voltage, if that had a poor connection it could cause your problem too.

[ElectricDruid]

Do you know whether you get the noise at *both* ends of the LFO sweep or only one end?

At a guess, it sounds like the LFO is pushing the clock beyond what it (or the BBD) can cope with and the signal is dropping out. This is usually at the fast end (at the slow end, you just get progressively more clock noise and sampling effects but nothing stops working). So if you've trimmed it to 2.6MHz at the top, I'd try trimming it down to 2.3MHz or 2.2MHz or 2MHz or whatever until the noise disappears.

HTH,
Tom

[Scruffie]

Do you know whether you get the noise at *both* ends of the LFO sweep or only one end?

At a guess, it sounds like the LFO is pushing the clock beyond what it (or the BBD) can cope with and the signal is dropping out. This is usually at the fast end (at the slow end, you just get progressively more clock noise and sampling effects but nothing stops working). So if you've trimmed it to 2.6MHz at the top, I'd try trimming it down to 2.3MHz or 2.2MHz or 2MHz or whatever until the noise disappears.

HTH,
Tom

The circuit can definitely cope with it and has been built plenty of times by others so I'd be more inclined to say there's a problem with the build than the circuit.

[Dasher]

Thanks for the ideas so far.

I put together a quick youtube to help demonstrate the problem I'm having: https://www.youtube.com/watch?v=_9JZDDUck9A&app=desktop
I just noticed something while watching the video. I turn the "Threshold" pot at the end of the video. The sound changes from something like a, "Tick....Tock" to a "no noise....Tock". I hope my explanation makes sense .

Here are a few photos of my board: https://postimg.cc/gallery/2h3ikzwnw/
I'm aware that IC4 is empty . I had taken it out for testing when I took the pictures.

To answer some of the questions:

1. Where did I source parts from? - My resistors and caps were mostly whatever I had in my parts bins and from various sources. I can't say for sure where the electrolytics came from...but I know that I've never had a problem with one in the past. My ICs were from smallbear.

2. Can I tack on an electrolytic cap between IC4 pin 8 and ground? - I tried tacking on a 33uf cap with no change.

3. Do you know whether you get the noise at *both* ends of the LFO sweep or only one end? - Hmmm I think it's both ends. Does the video posted above help clarify this? The guitar playing in the video is somewhat hard to hear because it's much quieter than the knocking sound.

I also had some time tonight and reflowed the solder on all parts that I could access without removing the pots; this didn't help. I'm guessing that I used the wrong part somewhere... now I just need to find it!

[ElectricDruid]

Do you know whether you get the noise at *both* ends of the LFO sweep or only one end?

At a guess, it sounds like the LFO is pushing the clock beyond what it (or the BBD) can cope with and the signal is dropping out. This is usually at the fast end (at the slow end, you just get progressively more clock noise and sampling effects but nothing stops working). So if you've trimmed it to 2.6MHz at the top, I'd try trimming it down to 2.3MHz or 2.2MHz or 2MHz or whatever until the noise disappears.

HTH,
Tom

The circuit can definitely cope with it and has been built plenty of times by others so I'd be more inclined to say there's a problem with the build than the circuit.

I agree. But if it were possible to trim the noise out as I suggested, that tells you a lot about where the noise is coming from and why, so it's a debugging tactic rather than an ultimate solution.

[StephenGiles]

Do you know whether you get the noise at *both* ends of the LFO sweep or only one end?

At a guess, it sounds like the LFO is pushing the clock beyond what it (or the BBD) can cope with and the signal is dropping out. This is usually at the fast end (at the slow end, you just get progressively more clock noise and sampling effects but nothing stops working). So if you've trimmed it to 2.6MHz at the top, I'd try trimming it down to 2.3MHz or 2.2MHz or 2MHz or whatever until the noise disappears.

HTH,
Tom

The circuit can definitely cope with it and has been built plenty of times by others so I'd be more inclined to say there's a problem with the build than the circuit.

Thoroughly agreed, I built 2 SAD1024 versions on veroboard - no ticking at all.

[ElectricDruid]

Ok, here's some things to try.

If you put the range control all the way to one end, you should get just the Manual control with no LFO. If you twiddle the Manual control in this position, does the flanger "drop off the end" at either end of the pot's travel?

If you put the range control all the way over to the other end, you presumably get the periodising ticktocking that we've heard from the video, right?

It still looks/sounds like the VCO is being pushed out of range. That could be because the LFO bias is wrong, or it could be something messed up in the circuit that controls the VCO (IC8.2/IC5).

One thing I don't understand though - if you've checked the clock frequencies and they're within range (as everyone says) why is this happening? What did you use to measure the clock frequency?

[Scruffie]

Do you know whether you get the noise at *both* ends of the LFO sweep or only one end?

At a guess, it sounds like the LFO is pushing the clock beyond what it (or the BBD) can cope with and the signal is dropping out. This is usually at the fast end (at the slow end, you just get progressively more clock noise and sampling effects but nothing stops working). So if you've trimmed it to 2.6MHz at the top, I'd try trimming it down to 2.3MHz or 2.2MHz or 2MHz or whatever until the noise disappears.

HTH,
Tom

The circuit can definitely cope with it and has been built plenty of times by others so I'd be more inclined to say there's a problem with the build than the circuit.

I agree. But if it were possible to trim the noise out as I suggested, that tells you a lot about where the noise is coming from and why, so it's a debugging tactic rather than an ultimate solution.

Oh I seeeee and as you've said in your new post, that can be achieved by changing the width/manual controls so re-trimming isn't needed, unless the biasing is wrong.

Ok, here's some things to try.

If you put the range control all the way to one end, you should get just the Manual control with no LFO. If you twiddle the Manual control in this position, does the flanger "drop off the end" at either end of the pot's travel?

He mentions trying that in the first post, it is possible that the LFO biasing trim is off though and therefore isn't matching up to the manual frequencies once it's 'automatic' so it could be worth twiddling the "Auto" trim.

I agree though, it doesn't sound much like LFO tick in the demo and more like VCO tick.

[Scruffie]

On your voltages pin 10 of the 4007 is 0V, double check that.

[Dasher]

If you put the range control all the way to one end, you should get just the Manual control with no LFO. If you twiddle the Manual control in this position, does the flanger "drop off the end" at either end of the pot's travel?

If you put the range control all the way over to the other end, you presumably get the periodising ticktocking that we've heard from the video, right?

I still get the noise when I put the range control fully CCW. It doesn't sound like the flanger drops off at either end of the Manual pot's travel. However, it's a bit difficult to say for certain because the flanger sound is most noticeable when the Manual pot is moving and you can't move past the end of the pot's range.

One thing I don't understand though - if you've checked the clock frequencies and they're within range (as everyone says) why is this happening? What did you use to measure the clock frequency?

I used the frequency setting on a DMM that I bought at a hardware store. It's no Fluke, but I don't have a reason to believe that the readings it's giving me are incorrect.

He mentions trying that in the first post, it is possible that the LFO biasing trim is off though and therefore isn't matching up to the manual frequencies once it's 'automatic' so it could be worth twiddling the "Auto" trim.

I've adjusted the "Auto" trim for a sweep between 69.6kHz and 2.6mHz when the range control is fully CW. It didn't take much of an adjustment to the Auto trimpot...slightly counter-clockwise I believe.

On your voltages pin 10 of the 4007 is 0V, double check that.

Good catch! That was an incorrect measurement on my part. I doubled check it and it's actually 5.81V. I figured it'd probably be a good idea to go and double check all my IC voltages...so here they are again. Note that I'll only list the ICs where at least one pin had a voltage that differed significantly from those I posted above. I also made sure to set all my pots fully CW before measuring this time.

IC3 - 4558
1: ~7.1V varies
2: 7.1
3: 7.04
4: 0
5: 7.1
6: 7.1
7: 7.1V varies
8: 14.62

IC4 - 1458
1: 6V varies
2: 7.2
3: 6V varies
4: 0
5: 7.1
6: 7.1
7: 7V varies
8: 14.75

IC5 - 4007
1: 1.12
2: 1.12
3: 0
4: 1.18
5: 1.18
6: 0
7: 0
8: 1.32
9: 0.14
10: 5.81
11: 7.95
12: 0.79
13: 15
14: 15

IC6 - 4047
1: 14.8 varies
2: 0.8 varies
3: 8.07
4: 15
5: 15
6: 15
7: 0
8: 0
9: 0
10: 7.48
11: 7.51
12: 0
13: 14 varies
14: 15

IC8 - 4558
1: 11.41  --> this seems high
2: 3.93
3: 3.92
4: 0
5: 6
6: 6
7: ~5V varies
8: 14.60

IC10 - MN3007
1: 14.85
2: 7.51
3: 8.76
4: 1.03
5: 0
6: 7.50
7: ~7 varies
8: ~7 varies

IC13 - 4558
1: 5.71
2: 7.2
3: 7.1
4: 0
5: 7
6: 7.1
7: 7.1
8: 14.23

[StephenGiles]

I don't trust the power supply at all. I suggest you disconnect it completely from the 15v regulator and connect up two 9v batteries instead - see if the noise goes away.

[Scruffie]

I checked all the values and orientations I could see and they all check out, watching your video again, I do find it odd the way the threshold control affects the cut off points of the ticking, I wonder if your little 1M3 resistor Teepee is working as an antenna, there is an enormous amount of gain in that circuit section and it does share a power line with the VCO and turning up the threshold control reduces the gain there. I've always just used a 1M2 in that section and never had a problem with the gates function.

Grasping at straws after that would be a static damaged CD40XX chip that is working but on its way out. Failing that I think it has to be a short or bad joint.

I don't think the charge pump is the problem, your voltages look fine and the behaviour is not what I'd expect for a bad supply.

[Dasher]

Thanks again for the suggestions. I'm going to remove the pots so that I can see the entire solder side of the board. I think that I trimmed some of my component leads a little long after installing them so I wouldn't be too surprised if there was a short somewhere. I'll swap out my 1.3M resistor at that point as well, just in case.

[StephenGiles]

Ah, I also never bothered with the threshold control so didn't have any potential problems associated with that!

[Scruffie]

Ah, I also never bothered with the threshold control so didn't have any potential problems associated with that!

You're missing out Stephen! It can be quite effective for some interesting envelope controlled flanging rather than simple noise control.

[Aph]

Ah, I also never bothered with the threshold control so didn't have any potential problems associated with that!

You're missing out Stephen! It can be quite effective for some interesting envelope controlled flanging rather than simple noise control.

I agree. Turning the control down and vamping lightly on some chords and then hitting a chord here and there a little bit harder sounds extremely cool.

[Dasher]

Scruffie and Aph. You're teasing me here! I want some of those cool sounds too .

[StephenGiles]

Ah, I also never bothered with the threshold control so didn't have any potential problems associated with that!

You're missing out Stephen! It can be quite effective for some interesting envelope controlled flanging rather than simple noise control.

I agree. Turning the control down and vamping lightly on some chords and then hitting a chord here and there a little bit harder sounds extremely cool.

Possibly if you are giving a demo to your girlfriend in your bedroom (!!!!!!!!!!!!) but I'd wager that in a band situation it's a hinderance .

[Dasher]

I replaced my "2 resistors in series" 1.3M resistor with a single 1.5M resistor and the noise is still there. I was also able to bend the pot terminals enough to get at the solder side of the pcb beneath them but there's nothing that looks suspicious there.

I think it's time that I put this project aside for awhile and work on something else. Maybe coming back to the flanger in a couple of weeks with some fresh eyes will help.

Thanks for everyone's help!