Questions on Lola Phase BOM

[Kevin Mitchell]

I had just used their contact link and afterwards seen that it may not be best to use for build or troubleshoot questions. So I guess I should have copied my inquiry to post here 
These are really questions that could be answered by anyone who has already built the thing.
Build doc here

Are the PCB mount rotary switches Alpha type like this;
https://www.taydaelectronics.com/rotary-switch-4-pole-3-position-alpha-sr2612f.html

Are all of the trimpots the vertical 3296W type?

Are the two 1000uF caps 5mm lead spacing and 12.5mm diameter?

How many of each should I purchase for matching? The matching methods are listed in the build doc but not how many would be ideal to do so.
LDRs (need 12)
LEDs (need 2)
Transistors (need 2)

Thanks for any help! Looking forward to working on the beast 
-KM

[danfrank]

Hi,
I bought 12 of the LEDs which is overkill but I had to buy them from Newark and they came in from Great Britain, so basically I bought like $10 worth.
The LDRs are a different story. They're cheap but their values are all over the place. I bought 50 of them, that way several closely matched sets can be made.
Yes, those are the rotary switches needed.
3296 or 3299 will work, the 3299 are a bit thicker.
If those are the 2 big caps by the regulators, that size should work. They are supposed to lay down horizontally, IIRC... Leads bent 90 degree angle

Self promotion mode: Did you check out my ADA TZF several posts down? Lol!

[Kevin Mitchell]

Thanks for the reply! Glad I was on the right track.

Dino had emailed me. I'll share here for the record.

• Yes for the rotary
• Yes on the pots
• 5mm spacing for the two 1000u caps.
• Except for one exception, all our trimmers are 3296 type. Generally, if we use a different type, we will specify as such.
• LED's - 6, LDR's - 36, transistors - 12. You should be able to get close enough sets with those quantities.

Yes I had looked at your post briefly. I'll comment in a moment.

-KM

[Kevin Mitchell]

I've got another question on this. It could probably use it's own thread but here will do.

For the two single vactrols it's suggested to use a VLT5C1 or 5C3. I do what I can to not use up my optos as they aren't getting any cheaper!

Can someone suggest a photocell that is close in value to these optos? The build guide suggests a device with <1k LIGHT and >2M DARK - so I guess the dark resistance doesn't have to be that exact as the VTL5Vx varies between 10M and 50M. I've looked around but haven't found anything that looks promising enough or perhaps I'm interpreting the datasheets incorrectly - but it's pretty straight forward.

There's another clone out there that presumably used LDRs all around that are rated at 300ohm LIGHT and 3M DARK, but no mention of what type and the link is dead.


-KM

[danfrank]

Someone please correct me if I'm wrong but the important thing about these vactrols is that they react fast to light, there is little latency in their reaction time. Most LDRs have a certain latency when they react to light, it's not just the light/dark resistance they have that's important.  Do the homework by reading up on their (vactrols and LDR) respective data sheets.
The vactrols can be home brewed but the 5C series are of a known spec and therefore standardized for certain parameters.
BTW, Xvive makes a (relatively) cheap 5C3 vactrol.
One more thing... The main purpose of the vactrols in the LOLA is to turn on or off each phaser (A & B) output. Probably not that critical of a part but the 2 vactrols/LDRs should be well matched in parameters. Also, use LDRs with the least amount of latency you can find.

Good luck.

[Kevin Mitchell]

I've made a coupler of optos using two matched GL6615 LDRs and also matched a couple 3mm red diffused LEDs. If it doesn't work out I'll just have to use a couple of 5C3s from my stash.

One confusing part of the calibration in the "Phaser matching procedure", why would you need a splitter cable for the inputs if we're shorting the inputs of each channel together through the channel B input rotary and in doing so, input jack B is disconnected anyways. That does not make any sense  Am I missing something?

On page 12 of the doc
Input schematic is on page 20

[digi2t]

One confusing part of the calibration in the "Phaser matching procedure", why would you need a splitter cable for the inputs if we're shorting the inputs of each channel together through the channel B input rotary and in doing so, input jack B is disconnected anyways. That does not many sense  Am I missing something?

Nope, you're right. I over thought it. My bad. Ditch the Y splitter. I'll pull that out of the procedure when I find a minute.

[Govmnt_Lacky]

I've made a coupler of optos using two matched GL6615 LDRs and also matched a couple 3mm red diffused LEDs. If it doesn't work out I'll just have to use a couple of 5C3s from my stash.

Check the specs of the LDRs to see what wavelength they respond best to. Most LDRs tend to respond best to Green wavelength. 495-570 nm.

[Kevin Mitchell]

Ah thanks! I thought I was going mad there trying to make sense of it 

And thank you, Govmnt_Lacky. I'll check out the specs of the LDRs and see what color gives the LDR's the widest range. I tend to forget that bit when I roll my own optos 

[Kevin Mitchell]

Trying to wrap my head around pairing LDRs and LEDs... A little difficult without knowing the exact LEDs that I have but at least we can get an idea.

Here's the spectrum graph for the GL5516 LDRs.


Around 550 nanometers seems to be the peak of the spectrum to get the full response of the LDR. Guessing around what LEDs a vendor like Tayda supplies, a green diffused 3mm LED has a peak wavelength of 565Pnm. A red diffused has 660Pnm

So for the GL5516, the green diffused one is the better choice of the two.

That wasn't too bad 

[danfrank]

I don't know if your post has a question but here is a link to the original that it called for in the docs:

https://www.newark.com/kingbright/l-1553gdt/led-green-5mm-x-5mm-5mcd-565nm/dp/20M7462

It's a pretty dim LED. Most green diffused LEDs are 550mn wavelength, I doubt 15mn will make much of a difference. You will have to adjust the distance between the LED and LDRs once built to get the response you want out of the LOLA

[Kevin Mitchell]

There wasn't a question but rather my findings that I'm open for folks to validate, correct or learn from. I'm talking about substituting the two VTL5C3 optos. The research for pairing LDRs and LEDs is something I've been neglecting for a long time until now.

[PRR]

Trying to wrap my head around pairing LDRs and LEDs... ....

It's not just color. Red is historically MUCH more light/mA so being off-color really does not matter.

Also all modern LEDs will make much more light than a photoresistor needs, so it does not matter.

Green is not "wrong". I just don't think it is worth the walk to get green if red is in the house.

[Rob Strand]

Unfortunately stuff to do with light is all or nothing.   Lots of details.    If you want to maximize transfer just fix the LED current, and the separation distance between the LED and sensor then pic the one with lowest LDR resistance.

The numbers given for LEDs are mcd (milli-candlla).   That's the units for *luminous* intensity.  When you see the word  luminous it means the numbers have been adjusted to compensate for the eye's sensitivity.

Things other than light use the term *radiant* intensity and they have nothing to do with eye.   You would use those for anything that's not light.  Like a radiation from the microwave oven.

So here's where you need to avoid double counting,

Here's the spectrum graph for the GL5516 LDRs.

IFAIK, that graph is the sensitivity for *radiation* at different frequencies.

For the LEDs you linked,

Green:  20 mcd  @ 10mA  ; 565 nm

Red:     65 mcd @ 20mA   ; 660 nm
             so at 10mA, we get 32.5 mcd

So to the eye the Red LED would be expected to be perceived brighter for the same current.   We do that by comparing the mcd values.
 
So assuming the LDR is in radiation units we need to undo the luminous adjustment factors in the LED mcd number to make them radiation.   That allows us to measure what the sensor sees.

Here's a nice graph of the eye response, the numbers at the top are the inverse values,


It's from this thread, which is actually quite good,
https://electronics.stackexchange.com/questions/208523/human-perceived-relative-brightness-of-indicator-leds#216757

The adjustment for the green LED is pretty much 1.0.
However the adjustment for the red LED is 15.0.   Notice if we are off a bit in color it could be only 3.4.   ie. the color has an enormous effect on the numbers.

So the adjusted "units" are green = 20 "units" and red is 15 * 32.5 = 490 "units".   So red produced about 25 times more radiation than green.

On the LDR response the sensitivity to red is only 60% of green which is dwarfed by the difference in radiation.  So you would expect red to clearly win.

Some caveats:
- I've noticed some LED datasheets quote CIE "mcd" values which are about 1/3 the value of a supposedly "non" CIE value - whatever the hell that could mean.   Using the lower value would mean the 25 times would drop to about 8 times.   It still implies red is better.
- The LED color isn't a single color is a spectrum and that messes with the simple calculations I've made.   For example, the low amount of green from a red LED counts 25 times more to the mcd value than the red.
- LED specs vary all over the map.  So applying the calculations to other LEDs could be way off.
- The ultimate test comparing two LEDs is measurement.

[Kevin Mitchell]

Wow thanks, Rob! That's very informative. Looks like there's quite a bit more to it than I had gathered.

So last night I wasted effort dissecting the pairs I had already made.
I was comparing a couple of VTL5C3 optos with my hand-made options. I have a variety of LEDs so I can play around and see what comes close.

PRR is totally right about modern LEDs. I knows these NOS VTLs have old red LEDs in them and the resistance shows much higher than new ones (I also have dissected VTLs due to brunt out LEDs) - so I can verify the differences.

Looking at the Lola schematic we're really just going for the lowest ON resistance - total DARK will be over 1M ohms no matter as the LED is totally disconnected from it's power supply with the channel switch. So in this case, red is indeed the favorable choice. But in the case of using the LDR in a phase shift, the wider resistance sweep from a green LED is probably more favorable.

Now to put them back together 

[Kevin Mitchell]

Another question;

If I'm understanding the schematic correctly does that mean both channels will be off until the pedal switch is grounded? So without shorting that connection on the PCB or bypassing the LDR, there will not be any output without a remote switch?

Edit - ah yeah. Per the original Owners Manual "The Phasor circuits will not operate unless the foot switch unit or the optional footpedal/foot switch is plugged in via the back panel connector".

Good thing I was already working on the remote 

[Rob Strand]

The best way to handle different LED brightness is to change the LED drive current.   If you change the current to make the light output the same then the LDR won't know much different.     In order to do that  you have to know what the LEDs in some reference circuit were doing, which info that's rarely available.

The other way is knowing  the range of resistances you want for the LDRs and just tweak the LED current so it matches that range.   The LDR's won't all agree so I'd probably err on matching the mid to lower *frequency* points on a log scale, freq_middle = sqrt(freq_lo * freq_hi).    That's going to be the higher resistance and the middle resistance R_middle  = sqrt(resistance_lo * resistance_hi).