Roll Your Own Vactrol

[Lizard King]

I'm building a tremulous project from the TonePad site.  It calls for a Vactrol VTL5C2.  I found them for $4.50 on eBay. 

I can get a KE-10720  LDR for 25 cents.  If I heat shrink that with a red LED will I get the same result as a VTL? 

Thanks.

[nocentelli]

I made a tremulus lune with a cheapy LDR and LED and it worked fine - I don't think the circuit ius that picky.

[Lizard King]

I made a tremulus lune with a cheapy LDR and LED and it worked fine - I don't think the circuit ius that picky.

Sweet...thanks.  I'll give it a try.  No sense spending $4.50 when a 25 cent LED will do....

[crane]

My tremulus lune also works with DIY vactrol. Might be that it has a little different charecter but
1) I don't have one with VTL5C2 to do A/B tests
2) Even if it differs - that can be corrected with controls.

[digi2t]

Dann Green recommended this as a good replacement for the Mouser ones that aren't available anymore;

http://www.goldmine-elec-products.com/prodinfo.asp?number=G15177&variation=&aitem=1&mitem=1

[lonewolf]

I've been wondering if a H11F1/NTE 3085 photo FET would work in this circuit..anybody tried that?

[EATyourGuitar]

if you have one VTL5C2, you can do some testing to see what the on and off resistance would be in circuit for the lune. then you have some data to work towards when you tweak the power going to the LED (your DIY vactrol) with some resistor changes.

I purchased these http://www.goldmine-elec-products.com/prodinfo.asp?number=G17898 super cheap. they all have resistance marked on the package but they are all different. one of them says 403 for example (40k). they all have a white dot probably indicating they did not pass factory quality control. the leads are only 7mm long on one side. I did not have time to build a test circuit yet.

VTL5C2 should be going way way up in price very soon. the company was purchased by another company who made an announcement that the price will jump from $7 to $9. if you found a VTL5C2 on ebay for $5.50 shipped, it could be fake! do not buy directly from honk kong on ebay unless you know the seller or you know where it is manufactured.

[smallbearelec]

The VTL series has become unreasonably expensive. I got a Chinese manufacturer to clone several of them:

http://www.smallbearelec.com/servlet/Detail?no=1255

and they have been vetted by a guy who is known to the residents here. At less than six bucks each in small quantities, they are decent value for something that is preassembled and known to work consistently. If you want to go the economy route, these photocells:

http://www.smallbearelec.com/servlet/Detail?no=711

cost less than a buck each, and you will know what you are getting. The high dark-resistance types like 9200 and 9203 should make you happy with a high-brightness red or grenn LED.

[armdnrdy]

they all have a white dot probably indicating they did not pass factory quality control.

The "white dot" is the polarity marking.

[Mustachio]

I've tried a buncha different led's and ldr's and I really like the KE10720 when its used with this LED

http://www.mouser.com/ProductDetail/Lumex/SSL-LX433GD/?qs=sGAEpiMZZMs4quMj8r4lmjaw8B5qKY8aX7D4mSD%252b5KI%3d

I was able to use 2 of the KE10720's with one of those lumex leds that have a fresnel lens and a low value limiting resistor to the LED (8.1K) in a neutron and it turned out spectacular! I think the large viewing angle helps flood the ldr's evenly and the intensity of the light is more suited for the application. Give it a try its cheap if it doesn't work out for you. In the tremulous lune I think the led intensity is controlled by the depth pot and a few other resistors but I could be wrong. You may want to play with those values to fine tune the led.

Good luck. The smallbear vactrol substitutes are nice! Id give em a try as well its worth a couple of bucks to A/B test them. I always use sockets for the opto section so I can test a few out.

[digi2t]

I've tried a buncha different led's and ldr's and I really like the KE10720 when its used with this LED

++1 on the KE10720. These are what I use for my custom rolled Mutron vactrols, in combination with white 5mm LED from Mammoth, http://www.mammothelectronics.com/4SLED-WP7113QWC-D-p/1000-102-wh.htm . If anyone is interested in how I put them together, the build process is here; http://www.diystompboxes.com/smfforum/index.php?topic=95269.0

The KE10720's are also very good for the EH Talking Pedal "dual pot to dual LED/LDR" conversion. Take that to the bank.

[Lizard King]

Nice detail on your build but wouldn't heat shrink work nearly as well?

[digi2t]

Nice detail on your build but wouldn't heat shrink work nearly as well?

The Mutron vactrol has two LDR's, side by side arrangement, and a single LED. It would be really tough to align the two LDR's with each other, and the LED, with heatshrink, and get good (equal) performance out of the whole assembly. Not to mention that a heatshrink arrangement opens up the possibility of mechanical misalignment, i.e. dropping the pedal, etc. Encapsulation allows you to align everything just right, and is a lot more "bulletproof" in the long run. Just my 2 bits.

[Lizard King]

Ahh...I read the dual LDR but it didn't register.  For my purposes I assume heat shrink will work.  I could swear I bought a commercial unit a few years ago that was just heat shrinked....thanks!

[midwayfair]

Rather than start my own thread ... does anyone know a discrete LDR with dark resistance more like 50M? I have to snag some 9203s to see if they work, but I'm trying to find a sub for the VTL5C1.

(I know I can use a photochip for this, but they just aren't as good.)

[smallbearelec]

Rather than start my own thread ... does anyone know a discrete LDR with dark resistance more like 50M? (I know I can use a photochip for this, but they just aren't as good.)

http://www.smallbearelec.com/servlet/Detail?no=1296

[PRR]

> LDR with dark resistance more like 50M?

Why?

Any damp day, the PCB leakage will approach 50Meg.

For audio, any slight stray capacitance will clobber all the audio that will fit in 50Meg.

Unless the LDR is hermetically sealed (metal can), there is a fair chance it might do 50Meg today but not next year after summer damp creeps in.

And "many" LDRs do go over 50Meg.... after an hour in UTTER darkness. But you can't get rich selling parts that take an hour to test. Dark is usually specified as a few seconds, something you can do in mass production.

[midwayfair]

Thanks, Steve. Not sure how I missed those. Are they brand new? [Edit: Oh, they're listed separately from the other three.)

> LDR with dark resistance more like 50M?

Why?

Because in this design:
https://dl.dropbox.com/u/9878279/Jon%20Patton%27s%20layouts/Nonmini%20builds/Blue%20Warbler%20Schematic.png

Apparently I can't get tremolo with any photocell except the VTL5C1. Anything with lower dark resistance (e.g. 5C3) just doesn't work.

Maybe there's some other reason, but I do know that the only things that work besides a 5C1 are things like the H11F1, and the common thread I can see is extremely high dark resistance.

[PRR]

In that plan, the LDR works against the 100K output load.

Put a 1Meg or 5Meg pot where the LDR goes. Diddle it. I'm suspecting the action-point (obvious tremolo) is 200K-1Meg.

We could reduce that with a smaller load. Say 10K. Whoops, the Q1 impedance is near 4.7K, a 10K load is significant.

Might still be worth trying with 22K or 33K in shunt with the Level pot.