# CDXL test … and a question for anyone building it -



## I Love Music (Oct 27, 2019)

I put a red led in place of the vactrol to see how sensitive the input is on the CDXL circuit. 

Well, the answer seems to be "zero" - no LED flashes at all. The LED dimmed with the "range" knob, but never flashed. I removed the 4.7 uF  cap from the board, and measured - pin one of the tl072 is slammed to the positive rail at all times. Of course I switched tl072 chips, no difference. 

Now ... the cool part .... I switched pins 2 and 3 of the tl072 , and bingo - pin 1 of TL072 follows the 4volt input from the op amp divider, and the LED sitting in the vactrol holes flashes as it should.

Can anyone verify that their CDXL board works without switching pins 2 and 3 of TL072 ?


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## Robert (Oct 28, 2019)

The first prototype batch of these was drawn from an Beavis schematic with an error.

They were supposed to have been trashed but it sounds like a few made it into the bins...   

Let me check to be sure, but in the meantime assume this is the case.   

I'll send replacement corrected boards to anyone affected, so if you haven't started the build yet contact me for a replacement just to be safe.


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## I Love Music (Oct 28, 2019)

Robert said:


> I'll send replacement corrected boards to anyone affected, so if you haven't started the build yet contact me for a replacement just to be safe.





*** Is there an easy way to determine if these are indeed the earlier boards ? ***



If so, I bought two of 'em, and would enjoy having the corrected boards sent to me :

Order #27399 was placed on October 9, 2019 and is currently Completed.

If you want to throw in a couple of Arachnid boards for my time troubleshooting this problem, I won't argue with you.   

thanks, 

  Bill


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## Jovi Bon Kenobi (Oct 28, 2019)

Not sure of the batch I got so thanks for this offer.


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## Robert (Oct 28, 2019)

If you haven't started assembly yet just consider them all bad. Shoot me a message and I'll get you set up for a replacement.


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## Kelmark1 (Oct 29, 2019)

I ordered one, I’ll be placing another order soon , I’ll remind you about this when I do and you can send mine when I do

Ray




Robert said:


> If you haven't started assembly yet just consider them all bad. Shoot me a message and I'll get you set up for a replacement.


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## Bravin Neff (Oct 29, 2019)

Aw man. I assembled mine already, but haven't fully finished the jacks... so I haven't tested it yet, but its 90% done. Are you saying you are sure its bad?


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## Betty Wont (Oct 31, 2019)

Bravin Neff said:


> Aw man. I assembled mine already, but haven't fully finished the jacks... so I haven't tested it yet, but its 90% done. Are you saying you are sure its bad?View attachment 2075


I believe your vactrol is installed upside down.


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## Nostradoomus (Oct 31, 2019)

Torgoslayer said:


> I believe your vactrol is installed upside down.



No that’s correct. It’s a hard one to bugger up as one side has 3 legs and the other has 2.


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## Betty Wont (Oct 31, 2019)

Nostradoomus said:


> No that’s correct. It’s a hard one to bugger up as one side has 3 legs and the other has 2.


upside down, not backwards.


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## Robert (Oct 31, 2019)

Bravin Neff said:


> Aw man. I assembled mine already, but haven't fully finished the jacks... so I haven't tested it yet, but its 90% done. Are you saying you are sure its bad?



Not all of the boards that shipped were bad, no.

It's not a complicated fix if yours is one of the affected boards... 

Lift pins 2 and 3 of the opamp, use short jumper wires to connect them to the opposite pads. (Pin 2 to Pad 3,  Pin 3 to Pad 2)

I'll still send you a credit towards another board, use can use it for another (correct) CDXL or a different PCB if you'd prefer.

EDIT: just realized we've already talked via email,  same offer applies to anyone who ordered a CDXL PCB prior to Oct 30, 2019.


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## Nostradoomus (Oct 31, 2019)

Torgoslayer said:


> upside down, not backwards.



oh, no it’s in there the right way. Cathode to square pad.


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## phi1 (Oct 31, 2019)

On the pcb rendered image on the product page, the round hole is connected to ground (led cathode to ground on dod 440 schematics I’ve seen). So the anode should be in the square pad, and the cathode in the circle pad. This has been discussed at length in another thread in the troubleshooting section, although it has yet to be confirmed by @PedalPCB. Seems there should be more clear indication silkscreened on the pcb.


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## Nostradoomus (Oct 31, 2019)

Ahhh


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## Robert (Oct 31, 2019)

I will check and confirm this afternoon.


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## Robert (Nov 1, 2019)

Square pad is anode on current version.      This will be marked on the PCB from now on.


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## I Love Music (Nov 21, 2019)

OK … so I have the new CDXL "rev.2" board.  

I built it with exact value components, wired it into a case, and … nope. It passes audio thru the tl072 just fine, but no quack. So, I replaced the tl072 and xvibe with spares, and went again. Still no quack. I put a red LED in place of the xvibe, and it flashes with guitar input just fine - perfect.  I shorted across the xvibe output, the side with 3 wires, and immediate change in tone … so the filter circuit works. I can watch the voltage drop at the input when I reattach the xvibe, so the xvibe internal LED is working.

All this brings me to ask …. was an xvibe brand component used for in-house testing when this board was designed ? 

I'm using an "Xvive Audio VTL5C3/2 Dual Element Opto-Coupler" … is this the correct one to use ?

I seem to have an impedance mismatch from the optocoupler output to the filter. 

Anyone else built this rev.2 board yet  ?


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## Robert (Nov 21, 2019)

I'll have to see if i still have the prototype so I can see which vactrol was used.

It was robbed from a much older project though so I don't think it was the Xvive reissue.


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## I Love Music (Dec 4, 2019)

ok - quick summary of the xvibe part :  1 mA (low light) into the LED allows ~5k ohms … at 40 mA (bright light)  into the LED brings the resistance to 1.5 ohms.    Zero light from the LED is ~10 megohms resistance.  This is my fault, for assuming the xvibe part had the correct values internally; it does not.

I'd like to hear from anyone who found a currently-available optocoupler that works with the cdxl ?


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## I Love Music (Dec 4, 2019)

To say this plainly, this needs a part that uses 90% of it's resistive scale values between 100K and 1Meg ohms.  The xvibe has 90% of it's usable scale between  1 and 5000 ohms … not helpful when in parallel with a 220K resistor.


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## I Love Music (Oct 27, 2019)

I put a red led in place of the vactrol to see how sensitive the input is on the CDXL circuit. 

Well, the answer seems to be "zero" - no LED flashes at all. The LED dimmed with the "range" knob, but never flashed. I removed the 4.7 uF  cap from the board, and measured - pin one of the tl072 is slammed to the positive rail at all times. Of course I switched tl072 chips, no difference. 

Now ... the cool part .... I switched pins 2 and 3 of the tl072 , and bingo - pin 1 of TL072 follows the 4volt input from the op amp divider, and the LED sitting in the vactrol holes flashes as it should.

Can anyone verify that their CDXL board works without switching pins 2 and 3 of TL072 ?


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## benny_profane (Dec 4, 2019)

You should be using a VTL5C4/2 I believe. Also see here.


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