# CDXL Response



## benny_profane

My CDXL build (corrected board) is having a number of issues.

With ‘Level’ maxed out, I get my clean signal with a fizz mixed in, but no autowah.
The response is sometimes extremely slow, and only kicks it on the decay of the note. This happens at various points of the sweeps.
The wah doesn’t fall smoothly. It peters out in a very wobbly (think super fast phaser) way.
Overall, it’s very weak (when it’s catching the input signal). Not at all as extreme as a wah sweep should be. 
I used the Xvive VTL5C4/2 from SBE. I’ve tried various values at R9 (i.e., 2k2, 4k7, and 6k8). 4k7 seemed to get the closest. I’ve also tried various dual op amps (i.e., TL07, TL062, and TL022). The TL072 has the worst response.

I’ve tested the circuit both with and without a buffer before it.

I’m wondering if others have had good luck with the Xvive reissues or not. I know there’s one successful build report, but that’s it. In any case, any ideas?


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## Chuck D. Bones

Would you like to show us a picture of the board?


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## benny_profane

Pictures attached. The socket is empty in the shots but various dual op amps have been used with correct readings. Pots are wired up with leads because I haven't drilled an enclosure or finished off-board wiring. I'm still working through the verification phase with a breadboard and testing rig. Thanks for taking a look.


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## Chuck D. Bones

Build quality looks good, no obvious shorts or bad solder joints.  You can see the board from different angles, so you have a better chance of finding a bad solder joint than we do.
SBE carries quality parts, so I doubt that the VTL5C4/2 is the cause.
Are all the caps the correct values?
Changing opamps should make little or no difference.
Can you verify that the opamp outputs (pins 1 & 7) are at 4.5V with no input signal present?


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## benny_profane

Thanks for the compliment about the build quality. Caps are indeed correct. I was pretty slow with this one to make sure I didn’t mix anything up accidentally. The Vc, Vref, and GND values are all good with the IC.

I’m a little concerned about the vactrol since it is a relatively new reissue. I don’t think SBE would’ve been at fault—just that the part may not be exact to the original part.

Beyond that, I’m not sure what to think here. Any other thoughts?


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## Chuck D. Bones

Do you have an oscilloscope?


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## benny_profane

Chuck D. Bones said:


> Do you have an oscilloscope?


Unfortunately, I do not.


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## Chuck D. Bones

Do you have any more VTL5C4/2's?  It would be pretty simple to bench test one so it can be ruled in or out as the culprit.  The most important device parameter in this circuit is the resistance tracking of the two LDRs inside.


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## benny_profane

I don’t, unfortunately. That’s my main reason for asking for others with successful builds to chime in. It’s a pretty expensive reissue part—and not one that’s used in too many projects. You’re right that the entire circuit depends on this part. I could remove it from the circuit this evening and test resistances. That’s probably the only step in order to move forward.


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## Chuck D. Bones

You can test the Vactrol in-circuit, no need to remove it.  Make sure IC1 is out of the socket.  Temp install a jumper across R10 and a 1K resistor across R11.  Set LEVEL to zero.  Apply power.  Record resistance pin 1 to 2 and 2 to 3 on the Vactrol.  Set LEVEL to 1 and repeat all the way up to 10.  If tracking is within ±20% you should be fine.  Some of the measurements at the low end of LEVEL will be more-or-less the same.

Can you better describe this "fizz"?  Are we talking about noise or distortion?

How are you powering this thing?

What is C5's voltage rating?


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## benny_profane

LEVEL Position (A100k)Vactrol 1 to 2Vactrol 2 to 30 – 5220k​220k​6151k​135k​78.7k​8.6k​82.15k​2.2k​9446R​465R​10288R​299R​


Earlier tests were powered via leads to breadboard rails powered from a wall wart. These tests were powered via leads to breadboard rails powered from a 9v battery.

C5's voltage rating is 35v.

The fizz is an underlying high timbre distortion of the guitar signal when the level is maxed out.


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## Chuck D. Bones

Those readings all look good.  I wanted to check C5's voltage rating because the rectifier that charges it (C4, D1 & D2) is a voltage doubler.  35V is plenty.

I'm out of ideas for the moment.


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## benny_profane

Chuck D. Bones said:


> Those readings all look good.  I wanted to check C5's voltage rating because the rectifier that charges it (C4, D1 & D2) is a voltage doubler.  35V is plenty.
> 
> I'm out of ideas for the moment.


Thanks for helping out. Let me know if you have any other thoughts here. I’m stumped too.


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## Bravin Neff

I'm having the exact same issues, using the replacement board. I bought (2) original boards, both turned out bad, got a couple replacement batch ones and while they "work," in some sense, the fizz/distortion you speak of is ever-present, the downward settling of the wah is stuttery and nonsmooth, the auto envelope opening is hyper sensitive to level and guitar dynamic control, and frankly... I'm just giving up. At some point the cost of one's time outweighs the rest.


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## music6000

Bravin, Did you use the same  Xvive VTL5C4/2 from SBE?


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## Bravin Neff

Yes, from small bear.


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## Chuck D. Bones

I've got another idea.  I recall troubleshooting a Mutron III a while back.  Turned out one of the opamps was oscillating at high freq.  If this board was on my bench, I'd put a 'scope on the opamp outputs.  Since you don't have one, let's see if some band-aids will fix things.  Tack solder a 470pF cap across R7 and another one across R5.  See if that makes any difference.  

There really should be a small resistor in series with C4, something around 100R would work.  I've seen this time and again.  Whenever D1 or D2 conduct, C4 and C5 load the opamp's output and that is a recipe for oscillation.  It's sloppy circuit design and completely avoidable with one resistor.  Before adding a resistor in series with C4, just remove C4 and see if you can tune the filter back & forth with the LEVEL control.  If the sound is good with C4 removed, then put it back in with 100R (or something close to that) in series.  You will have to get creative with how you accomplish that, but desperate times call for desperate measures.


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## benny_profane

Chuck D. Bones said:


> I've got another idea.  I recall troubleshooting a Mutron III a while back.  Turned out one of the opamps was oscillating at high freq.  If this board was on my bench, I'd put a 'scope on the opamp outputs.  Since you don't have one, let's see if some band-aids will fix things.  Tack solder a 470pF cap across R7 and another one across R5.  See if that makes any difference.
> 
> There really should be a small resistor in series with C4, something around 100R would work.  I've seen this time and again.  Whenever D1 or D2 conduct, C4 and C5 load the opamp's output and that is a recipe for oscillation.  It's sloppy circuit design and completely avoidable with one resistor.  Before adding a resistor in series with C4, just remove C4 and see if you can tune the filter back & forth with the LEVEL control.  If the sound is good with C4 removed, then put it back in with 100R (or something close to that) in series.  You will have to get creative with how you accomplish that, but desperate times call for desperate measures.


Cheers. I’ll give that a shot tonight and post my results.


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## music6000

Chuck, Should the 100r be in series with *-* side of C4 disconnected to right side of 1N4148's OR
*+* side of C4 disconnected to 2m2 & Pin 1 of Opamp


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## DGWVI

I'm having the same issues with mine. Will try Chuck's suggestions and report back


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## benny_profane

My CDXL build (corrected board) is having a number of issues.

With ‘Level’ maxed out, I get my clean signal with a fizz mixed in, but no autowah.
The response is sometimes extremely slow, and only kicks it on the decay of the note. This happens at various points of the sweeps.
The wah doesn’t fall smoothly. It peters out in a very wobbly (think super fast phaser) way.
Overall, it’s very weak (when it’s catching the input signal). Not at all as extreme as a wah sweep should be. 
I used the Xvive VTL5C4/2 from SBE. I’ve tried various values at R9 (i.e., 2k2, 4k7, and 6k8). 4k7 seemed to get the closest. I’ve also tried various dual op amps (i.e., TL07, TL062, and TL022). The TL072 has the worst response.

I’ve tested the circuit both with and without a buffer before it.

I’m wondering if others have had good luck with the Xvive reissues or not. I know there’s one successful build report, but that’s it. In any case, any ideas?


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## DGWVI

Chuck D. Bones said:


> I've got another idea.  I recall troubleshooting a Mutron III a while back.  Turned out one of the opamps was oscillating at high freq.  If this board was on my bench, I'd put a 'scope on the opamp outputs.  Since you don't have one, let's see if some band-aids will fix things.  Tack solder a 470pF cap across R7 and another one across R5.  See if that makes any difference.



Tried this. While it got rid of the fizz and wobbles, it killed the sweep. Basically just sounded like a wah stuck close to the heel down.



Chuck D. Bones said:


> There really should be a small resistor in series with C4, something around 100R would work.  I've seen this time and again.  Whenever D1 or D2 conduct, C4 and C5 load the opamp's output and that is a recipe for oscillation.  It's sloppy circuit design and completely avoidable with one resistor.  Before adding a resistor in series with C4, just remove C4 and see if you can tune the filter back & forth with the LEVEL control.  If the sound is good with C4 removed, then put it back in with 100R (or something close to that) in series.  You will have to get creative with how you accomplish that, but desperate times call for desperate measures.



I'll try this next. Does it matter if I replace C4 with a non-polarized cap?


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## benny_profane

I haven’t been able to try any of the mods yet, but looking forward to hearing how things fare. Hopefully you get it working @DGWVI


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## Chuck D. Bones

music6000 said:


> Chuck, Should the 100r be in series with *-* side of C4 disconnected to right side of 1N4148's OR
> *+* side of C4 disconnected to 2m2 & Pin 1 of Opamp



Either side, doesn't matter.  I can't promise that this will solve the problem, but it's a good idea regardless.  If it _does _solve the problem, then we got smarter. At least about this circuit.


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## Chuck D. Bones

DGWVI said:


> Tried this. While it got rid of the fizz and wobbles, it killed the sweep. Basically just sounded like a wah stuck close to the heel down.
> 
> 
> 
> I'll try this next. Does it matter if I replace C4 with a non-polarized cap?



Polar or non-polar, either are good.  If you install a polar cap, observe the correct orientation.


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## Chuck D. Bones

DGWVI said:


> Tried this. While it got rid of the fizz and wobbles, it killed the sweep. Basically just sounded like a wah stuck close to the heel down.



That should not be the case and indicates another symptom.  Are you sure you didn't get a solder bridge at IC1 pin 1 or 2?

As for the stuck waa sound, turning LEVEL should change the filter tuning.  Does it?


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## DGWVI

Chuck D. Bones said:


> That should not be the case and indicates another symptom.  Are you sure you didn't get a solder bridge at IC1 pin 1 or 2?
> 
> As for the stuck waa sound, turning LEVEL should change the filter tuning.  Does it?


Yes, the level changes the filter. With those caps installed, there was no (or, at least, seemingly no) sweep. With them removed, I get the fizzy, bubbly sweep as described by the OP, with no sweep if the Level pot is dimed.


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## benny_profane

Ah drag. I was hoping that this had been figured out! I still haven’t been able to get to my board, but I guess we’re back to finding new solutions. I’m out of my depth—I wish I could provide more constructive input. Thanks for your assistance thus far, @Chuck D. Bones


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## Chuck D. Bones

Then something else is wrong with the peak detector (IC1.1, the diodes, etc.).  Putting that cap on IC1.1 should not make it worse.


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## music6000

Chuck, Is this Correct orientation for the Vactrol ?


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## benny_profane

That’s correct. You can be sure by checking for continuity between the cathode pad and ground.


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## music6000

benny_profane said:


> That’s correct. You can be sure by checking for continuity between the cathode pad and ground.


I know yours is Correct, Not sure for the others!


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## Chuck D. Bones

Yes


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## music6000

Chuck D. Bones said:


> Yes


Chuck, Do you think by putting  temporary external Trimmers (Potentiometers) in place of resistors on the PCB would yield a better result in fine tuning this Build.
This is what I do where circuits have been finalized with Fixed resistors measured from an external Trimmer (Potentiometer).


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## benny_profane

Perhaps the 220k resistors should be a place to look? Also, that level taper probably should be linear. But, we’re a bit away from fine tuning this guy in that regard.


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## music6000

benny_profane said:


> Perhaps the 220k resistors should be a place to look? Also, that level taper probably should be linear. But, we’re a bit away from fine tuning this guy in that regard.


I plug an Original 1977 DOD 440 in last night & the Range knob only has a small window from CCW to just over halfway, after that I didn't notice any difference, The Sensitivity knob is in the same working zone as well & its at midway that it brightens up a bit like a tone control.
It has a TL022 in it.


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## Chuck D. Bones

Music6000, does your question about adding trimmers pertain to enhancing a working pedal or fixing one that doesn't work? 

How is more than 1/2 of the pot rotation a small window?  We can certainly adjust the pot ranges, but bear in mind that a good range for one guitar may not be a good range for another.


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## music6000

Chuck D. Bones said:


> Music6000, does your question about adding trimmers pertain to enhancing a working pedal or fixing one that doesn't work?
> 
> Adding temporary external pots to act as trimmers in a semi non working CDXL pedal in the critical areas that might better match the Xvive VTL5C4/2 which I believe might be the Issue.
> It's not the first time that Xvive reissues are causing problems with these old type circuits.
> 
> I also have a Tone Factor 442 (DOD 440 Clone) that works much the same as I described the Original.


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## music6000

If it was my Build, this is one of the many sites I would be looking at :
                  http://www.sierraic.com/VTL5C42


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## Chuck D. Bones

music6000 said:


> It's not the first time that Xvive reissues are causing problems with these old type circuits.



Can you be a little more specific?  Which pedals?  Describe the problem.  How do you know it was caused by the opto?


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## music6000

Searching the Web:



Incompatible response times from the Xvive vactrol could be the problem.


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## benny_profane

My CDXL build (corrected board) is having a number of issues.

With ‘Level’ maxed out, I get my clean signal with a fizz mixed in, but no autowah.
The response is sometimes extremely slow, and only kicks it on the decay of the note. This happens at various points of the sweeps.
The wah doesn’t fall smoothly. It peters out in a very wobbly (think super fast phaser) way.
Overall, it’s very weak (when it’s catching the input signal). Not at all as extreme as a wah sweep should be. 
I used the Xvive VTL5C4/2 from SBE. I’ve tried various values at R9 (i.e., 2k2, 4k7, and 6k8). 4k7 seemed to get the closest. I’ve also tried various dual op amps (i.e., TL07, TL062, and TL022). The TL072 has the worst response.

I’ve tested the circuit both with and without a buffer before it.

I’m wondering if others have had good luck with the Xvive reissues or not. I know there’s one successful build report, but that’s it. In any case, any ideas?


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## Chuck D. Bones

OK, but this does not describe the distortion that Benny is experiencing and Benny's test data shows that his opto spans the entire resistance range. Benny's data is static and doesn't tell us anything about time response, so it's possible that the problem lies there. 3rd-hand info gives me a headache. I'm not inclined to pursue that particular line of inquiry.

You can try swapping out the opto.  I suspect that if you had one, you'd have tried that already.

I don't like to advocate giving up, but in this case it might be more expedient to build one of the other auto-wah pedals on this site.


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## music6000

I believe that if you can find an Original VTL5C4/2, the issue would be solved :



 




Tone Factor 442



This uses a KA4558 Op Amp


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## benny_profane

No one is disputing that an original could solve the issue. Me and a few others in this thread have been trying to work through this problem with current production parts. If that’s not possible—which it seems like it is since we’re running out of ideas—the project may not be viable.

I’m not keen on the idea of giving up on a circuit, but I’m out of ideas and rather out of my area of knowledge trying to push forward. Perhaps if we break down the circuit into functional blocks, we could come to something.


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## Nostradoomus

Looks like I might have to buy one of these boards. I remembered I bought a 440 kit from GGG a decade or so ago (one of my first builds...it didn’t work). One genuine vactrol still attached!


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## music6000

Nostradoomus said:


> Looks like I might have to buy one of these boards. I remembered I bought a 440 kit from GGG a decade or so ago (one of my first builds...it didn’t work). One genuine vactrol still attached!
> View attachment 2800


Ha Ha , Try reflowing some of those pads, You can almost see through them. 
How much for that PRC vactrol ?


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## music6000

Here's another link, Located in Florida, Scroll to Bottom of page :





						Distributor Of Electronic, Military, Obsolete & Passive Components.
					

We are your distributor & supplier for electronic, military and   passive components, obsolete semiconductors, AMP connectors, integrated circuits, capacitors, transistors   & other discontinued parts. Purchase Electronic, Military, Obsolete & Passive Components at   summitelectronics.com.



					www.summitelectronics.com
				




*Update* : I just got a Quote of $85.00 each for a lot of 10, You read it right $850.00 for 10 only.


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## music6000

I’m not keen on the idea of giving up on a circuit, but I’m out of ideas and rather out of my area of knowledge trying to push forward. Perhaps if we break down the circuit into functional blocks, we could come to something.

Maybe try 2 A500k external pots as Trimmers in place of the 220k resistors, Set pots to 220k before connecting to PCB :


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## benny_profane

music6000 said:


> I’m not keen on the idea of giving up on a circuit, but I’m out of ideas and rather out of my area of knowledge trying to push forward. Perhaps if we break down the circuit into functional blocks, we could come to something.
> 
> Maybe try 2 A500k external pots as Trimmers in place of the 220k resistors, Set pots to 220k before connecting to PCB :
> View attachment 2814


I appreciate the time you took to make that graphic. However, I’m wondering if that’s part of this issue at all here? If we’re thinking this comes down to the response time of the vactrol, will adjusting these values significantly alter the response?


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## benny_profane

music6000 said:


> Here's another link, Located in Florida, Scroll to Bottom of page :
> 
> 
> 
> 
> 
> Distributor Of Electronic, Military, Obsolete & Passive Components.
> 
> 
> We are your distributor & supplier for electronic, military and   passive components, obsolete semiconductors, AMP connectors, integrated circuits, capacitors, transistors   & other discontinued parts. Purchase Electronic, Military, Obsolete & Passive Components at   summitelectronics.com.
> 
> 
> 
> www.summitelectronics.com
> 
> 
> 
> 
> 
> *Update* : I just got a Quote of $85.00 each for a lot of 10, You read it right $850.00 for 10 only.


Who do they think will buy that?


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## music6000

benny_profane said:


> I appreciate the time you took to make that graphic. However, I’m wondering if that’s part of this issue at all here? If we’re thinking this comes down to the response time of the vactrol, will adjusting these values significantly alter the response?


At the moment it's a Boat Anchor, what have you got to lose?

Other Option Below
Have you tried this Link :




__





						VTL5C42 | PerkinElmer Optoelectronics Distributor | Inventory
					

Current price and delivery information, Request Quote for VTL5C42 PerkinElmer Optoelectronics,  Photoconductive Cells and Analog Optoisolators (Vactrols)



					www.sierraic.com
				




or email  Sales@Sierraic.com


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## Chuck D. Bones

benny_profane said:


> Who do they think will buy that?



Government contractors buy stuff like that.  It's cheaper to build an old design that do a redesign.


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## music6000

music6000 said:


> Here's another link, Located in Florida, Scroll to Bottom of page :
> 
> 
> 
> 
> 
> Distributor Of Electronic, Military, Obsolete & Passive Components.
> 
> 
> We are your distributor & supplier for electronic, military and   passive components, obsolete semiconductors, AMP connectors, integrated circuits, capacitors, transistors   & other discontinued parts. Purchase Electronic, Military, Obsolete & Passive Components at   summitelectronics.com.
> 
> 
> 
> www.summitelectronics.com
> 
> 
> 
> 
> 
> *Update* : I just got a Quote of $85.00 each for a lot of 10, You read it right $850.00 for 10 only.


*Latest : Came back with a new Quote of $25.00 each for 10 Only.*


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## music6000

Got a Quote for 12 only @ $20.00 USD each, this does not include Shipping for Genuine NOS PerkinElmer VTL5C4/2.
Who would like to purchase, these will work!




__





						VTL5C42 | PerkinElmer Optoelectronics Distributor | Inventory
					

Current price and delivery information, Request Quote for VTL5C42 PerkinElmer Optoelectronics,  Photoconductive Cells and Analog Optoisolators (Vactrols)



					www.sierraic.com
				




*Update* : A  Builder in the USA is looking into it & will report back with his Results!


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## Chuck D. Bones

You're going on the assumption that these are the one and only problem.  Guess we'll see.


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## music6000

Chuck D. Bones said:


> You're going on the assumption that these are the one and only problem.  Guess we'll see.


 I have a Builder in the USA who is working on it & will report back when he has got the Parts & Build completed.


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## benny_profane

Bump to see if anyone has had success here? I’ve admittedly put it it pedal purgatory and haven’t worked on it further.


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## Chuck D. Bones

I found some real Vactech VTL5C/4 in my NOS stash.  No clue where or when I acquired them.  Must have been sometime in the previous century.  When I get around to it, I'll breadboard this circuit and report my findings.


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## benny_profane

Awesome, looking forward to that. 

And: Some?! I’d buy one off you if you’d be willing to sell.


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## music6000

benny_profane said:


> Bump to see if anyone has had success here? I’ve admittedly put it it pedal purgatory and haven’t worked on it further.


Yes, I'm waiting on the Builder to Report back!!!


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## Chuck D. Bones

benny_profane said:


> And: Some?! I’d buy one off you if you’d be willing to sell.



I've only got 4 of them, so I will not be selling any.  Sorry.


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## benny_profane

My CDXL build (corrected board) is having a number of issues.

With ‘Level’ maxed out, I get my clean signal with a fizz mixed in, but no autowah.
The response is sometimes extremely slow, and only kicks it on the decay of the note. This happens at various points of the sweeps.
The wah doesn’t fall smoothly. It peters out in a very wobbly (think super fast phaser) way.
Overall, it’s very weak (when it’s catching the input signal). Not at all as extreme as a wah sweep should be. 
I used the Xvive VTL5C4/2 from SBE. I’ve tried various values at R9 (i.e., 2k2, 4k7, and 6k8). 4k7 seemed to get the closest. I’ve also tried various dual op amps (i.e., TL07, TL062, and TL022). The TL072 has the worst response.

I’ve tested the circuit both with and without a buffer before it.

I’m wondering if others have had good luck with the Xvive reissues or not. I know there’s one successful build report, but that’s it. In any case, any ideas?


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## Chuck D. Bones

Haven't breadboarded it yet (got a PlimSoul mod going on the breadboard), but I did run some simulations.  Are you absolutely sure that C6 & C7 are the right values?  You can read them both?

Try this: temporarily install (tack solder) a resistor in parallel with R5.  Anything around 470K will work.  See if that makes any difference.  This test will at least prove or disprove that the filter Q is too high in your build.  I remain skeptical that there is anything wrong with the Xvive part.  Still possible, just no convincing evidence.


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## benny_profane

Chuck D. Bones said:


> I've only got 4 of them, so I will not be selling any.  Sorry.


No worries (worth a shot!). Thanks for the response. Still looking forward to your findings.


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## RajahMoore

Sorry to be resurrecting an old thread, but I really wanted to build a CDXL classic. After waiting a couple months and never getting notified for the pcb, I figured I'll make myself a PCB based on PedalPCB schematic and layout as a way to get familiar with EAGLE. At the time I didn't know people were having issues with this thing, so I went and got myself the xvive reissue vactrol from SBE. Had this same exact problem but after messing around, I actually ended up lowering the R9 to 870ohm, and swapped the C5 to 10uF. Not sure how well it performs compared to the original but it seems to be working for me.


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## daeg

Has anyone tried building this with dual LDR's and an LED?


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