CDXL Response

Chuck D. Bones

Well-known member
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.
 

music6000

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

DOD 440 Vactrol 1977.jpg DOD 440 Vactrol 1977 1.jpg


Tone Factor 442
Tone Factor.jpg
This uses a KA4558 Op Amp
 
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benny_profane

Well-known member
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.
 

Nostradoomus

Well-known member
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!
9A6D42C6-3061-4A17-BBBD-AB7CBEE6AC86.jpeg
 

music6000

Well-known member
Here's another link, Located in Florida, Scroll to Bottom of page :

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

Well-known member
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 :
CDXL External Trimmers.jpg
 

benny_profane

Well-known member
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?
 

benny_profane

Well-known member
Here's another link, Located in Florida, Scroll to Bottom of page :

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?
 

music6000

Well-known member
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 :

or email Sales@Sierraic.com
 

music6000

Well-known member
Here's another link, Located in Florida, Scroll to Bottom of page :

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.
 

music6000

Well-known member
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!

Update : A Builder in the USA is looking into it & will report back with his Results!
 
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Chuck D. Bones

Well-known member
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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