Crying time non madbean ( fixed sort of)

[Matt]

I just built a crying time lfo wah and I'm having one small issue.  I am getting a ticking sound in about the last quarter of the depth control.  I used a 100uf cap for the lfo filter cap instead of the 47uf listed in Jon's layout, so I don't think that's the cause.

The only thing I can think is that the transistor or that the external rate led and/or the vactrol led are causing the problem.  But that's just a wild uneducated guess.  Anyone know what it could be and how to fix it?

Thanks in advance.

[RobA]

You can file this in the might be related category. I've been finishing up a design for a microcontroller based tremolo that uses a vactrol. Because I set the level of the output voltage to the vactrol with the microcontroller, I've got really tight control on the values. What I've noticed is that if I get the current at just the point where the LED(s) don't ever turn completely off, then I can eliminate all clicks/ticking. Using the depth control when the LED's do turn off, I can mask most of the tick, but then I can't get the complete drop to zero volume that I want. Also, I put a trim pot on the path to ground for the vactrol's LED and this lets me control the current level as well. Getting it set just before the shutoff point for the LED seems to be the key to getting full range and no tick/pop/click.

Maybe you could try socketing the current control resistor to the LEDs and try moving its value up in small increments and see if you can eliminate the tick that way.

[midwayfair]

I just built a crying time lfo wah and I'm having one small issue.  I am getting a ticking sound in about the last quarter of the depth control.  I used a 100uf cap for the lfo filter cap instead of the 47uf listed in Jon's layout, so I don't think that's the cause.

The only thing I can think is that the transistor or that the external rate led and/or the vactrol led are causing the problem.  But that's just a wild uneducated guess.  Anyone know what it could be and how to fix it?

Thanks in advance.

Describe the ticking in more detail. Is it a thump, woosh, CLICK, etc.? The reason I ask is because people often use the term 'ticking' (which is an actual LFO issue) when it's really just line noise being affected by the LFO at idle.

In any case, if it really IS a clicking noise, I'll try to think of some things that can be done -- you can also check the original Light Wah thread non DIYSB -- I know early on some people had LFO ticking, but this LFO is usually pretty well behaved.

You could try flipping the transistor, too.

[Matt]

I messed with it a bit more today and here is what I found.  I set the rate to the slowest setting and determined that the "tick" is happening at the high side of the sweep when the led is the brightest.  It is also present in stuck wah mode when the led doesn't light up so I'm guessing that isn't it. 

The "tick" is also present when the effect is bypassed.  I found that out by putting a distortion pedal after it.  I couldn't here it until then.

I just built a crying time lfo wah and I'm having one small issue.  I am getting a ticking sound in about the last quarter of the depth control.  I used a 100uf cap for the lfo filter cap instead of the 47uf listed in Jon's layout, so I don't think that's the cause.

The only thing I can think is that the transistor or that the external rate led and/or the vactrol led are causing the problem.  But that's just a wild uneducated guess.  Anyone know what it could be and how to fix it?

Thanks in advance.

Describe the ticking in more detail. Is it a thump, woosh, CLICK, etc.? The reason I ask is because people often use the term 'ticking' (which is an actual LFO issue) when it's really just line noise being affected by the LFO at idle.

In any case, if it really IS a clicking noise, I'll try to think of some things that can be done -- you can also check the original Light Wah thread non DIYSB -- I know early on some people had LFO ticking, but this LFO is usually pretty well behaved.

You could try flipping the transistor, too.

The best way I can describe the noise is a click or tick, definitely not a thump or whoosh.  Do you think it's the transistor switching?

Could a cap from the transistor base to gnd help or would that mess with the way the lfo operates?

[midwayfair]

The transistor softens the triangle wave. It's probably not causing the issue.

I wish I had a way to help. Unfortunately it sounds like the LFO bleeding into ground. You might try a different power supply (I had not trouble with a one spot), or ask advice over on the DIYSB thread.

[Matt]

Cool ill check it out thanks

[Matt]

Ok, so tried flipping the transistor.  That didn't work.  Tried some of Mark Hammers ideas I found online, a LM358 in place of the jrc4558 and tried a higher value CLR between the supply and the power pin of the LFO IC.  Those didn't work either. 

Then I remembered some thing I read in another thread about someone with a similar issue being told to use a pedal with a buffer in front of the problem pedal.  No ticking!

[Cortexturizer]

Ok, so tried flipping the transistor.  That didn't work.  Tried some of Mark Hammers ideas I found online, a LM358 in place of the jrc4558 and tried a higher value CLR between the supply and the power pin of the LFO IC.  Those didn't work either.  

Then I remembered some thing I read in another thread about someone with a similar issue being told to use a pedal with a buffer in front of the problem pedal.  No ticking!

I made an EHX Pulsar couple years ago and no matter what I did I couldn't make the ticking go away. The only way to make it silent was to put a highly buffered pedal in front of it. For example, two millenium bypass pedals in front of it made the ticking disappear. But my Ibanez HD1000 rack processor in front of it made it completely noiseless. The more the buffering I guess, the less ticking there is. I'd like to hear an explanation of this if someone cares to chime in...thanks.

[midwayfair]

I'd like to hear an explanation of this if someone cares to chime in...thanks.

Me too.

Yet another reason I'm thinking of switching to buffered bypass ...

DC10: You might be able to make a source-follower input buffer fit in the 1590A with this. You only need a couple components: the FET, a 10K source to ground, a 470nF input cap, and a 2.2M gate to ground.

[Matt]

Ok, so tried flipping the transistor.  That didn't work.  Tried some of Mark Hammers ideas I found online, a LM358 in place of the jrc4558 and tried a higher value CLR between the supply and the power pin of the LFO IC.  Those didn't work either. 

Then I remembered some thing I read in another thread about someone with a similar issue being told to use a pedal with a buffer in front of the problem pedal.  No ticking!

I made an EHX Pulsar couple years ago and no matter what I did I couldn't make the ticking go away. The only way to make it silent was to put a highly buffered pedal in front of it. For example, two millenium bypass pedals in front of it made the ticking disappear. But my Ibanez HD1000 rack processor in front of it made it completely noiseless. The more the buffering I guess, the less ticking there is. I'd like to hear an explanation of this if someone cares to chime in...thanks.

I'd like to hear an explanation of this if someone cares to chime in...thanks.

Me too.

Yet another reason I'm thinking of switching to buffered bypass ...

DC10: You might be able to make a source-follower input buffer fit in the 1590A with this. You only need a couple components: the FET, a 10K source to ground, a 470nF input cap, and a 2.2M gate to ground.

Me 3!  I'd love to understand the reasoning behind this.

Luckily I will have plenty of room for a buffer.  I built this in a 4s125.   

Anyway, when I get back into town, I'll try that buffer out.  It'll be a good opportunity to revisit the amz page on buffers as well.  I'll breadboard a few, until I find the one I like best.  I wish I didn't have to use a buffer, this peal sounds so much better without it.  It really reminds me of a Hendrix / Trower wah tone.  (but an lfo wah version of course)

[Cortexturizer]

http://i.imgur.com/ySe8i.gif

Here's what people suggested to me when I was trying to work out the ticking issue with the Pulsar. Just insert this buffer they said...well it did not work for although some of them were positive that this is THE solution.
Not for me.

[RobA]

It could be that the tick comes from the movement in the power supply caused by the power draw of the LFO through the LED's. The buffer would mean that you would have a higher impedance input and the output of the buffer would be better able to feed the input of the effect even though the power supply to the op amp is moving/pulsing. I'd think that this would tend to be a bigger issue in effects with BJT or inverting op amp input stages.

If that's the cause of the problem, trying different op amps for the audio op amp might help some. I've noticed that some are more susceptible to ticking/thunking than others. Also, putting a 100nF ceramic cap from the Vcc of the op amp to ground can help. The cap should be as close to pin 8 as you can get it in the layout.

It would be interesting to get some measure of the current fluctuation on the power supply into the pedal and see if the tick corresponds to when the current draw hits one of the turn around points.

[RobA]

So, I put this circuit on the breadboard last night. First let me say that it sounds great and is fun to play with.

I've been trying everything I can think of to make it tick or thunk or anything and it just won't do it. I've used a bunch of different op amps in both positions, different LED's, multiple different vactrols and LDR's, different transistors, etc. I've tried putting in the junkiest caps I've got. But, nothing will make it tick. I'm running straight from the guitar into the wah and using a complete garbage cable to get the worst connection reasonable into the input and this still doesn't cause ticking.

So, I was wondering what op amps, LED's, LDR, and transistor you were using. I'd really like to get this to tick so that I can try to understand what is happening.

[Cortexturizer]

I'll just say that you are a real ace Rob for doing this, kudos to you man!

[RobA]

Thanks. It's become an interesting puzzle so it's actually kinda fun to try and figure out. Besides that, I'm working on a couple of fairly closely related circuits that do some nutty LFO type things and it will help me to characterize this problem.

I'm kinda stuck for now until I can figure out something else to look at. I've got it sitting on a breadboard though so I can stare at it and see if any enlightenment happens  . I have noticed that the circuit is sensitive to power supply voltage. I've got one unregulated supply that puts out about 10 to 11 volts instead of 9 and when I use it the wah sweep is reduced a bunch. So, maybe a power supply that is under voltage would contribute to the tick. I'll rig up a sag type circuit to power it with when I get back to it and see what happens.

I'll report back if I figure anything out.