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Replacing LED's in a VT Deluxe

#21
line6man said:
I'm not sure what you're trying to argue. Of course you adjust the resistance based on the brightness you want, but you can choose a resistance based on a basic equation for the specs that are given. A lot of aftermarket LEDs come with a table on the back of the packaging, which indicates the resistance to choose for various supply voltages. The OP can go with that, as well.
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I may have misunderstood your post then. It sounded like you were describing picking the current limiting resistor like you would instead for a voltage divider and your statement "Current is not an issue" then seemed odd (to me) becuase current is usually exactly what you want to dial in for the LED via the current limiting resistor. My apologies if that's not what you meant.
 
#22
wlater said:
I may have misunderstood your post then. It sounded like you were describing picking the current limiting resistor like you would instead for a voltage divider and your statement "Current is not an issue" then seemed odd (to me) becuase current is usually exactly what you want to dial in for the LED via the current limiting resistor. My apologies if that's not what you meant.
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I said that current is not an issue, because you don't need to worry about whether or not the power supply can supply what you need. There is a low risk of drawing more than it can safely supply, as long as you are not using ridiculously power-hungry LEDs.

The only current spec that you need to know about is the rating of the LED at its specified voltage. With that, you can get a value for your resistor, and an idea of what wattage you will need. If that value turns out to be too dim, then decrease it.
 
#23
OK. I guess we're saying the same thing in just different ways. But since LEDs are current devices, I usually would work with them and describe them in terms of current. And since the light output is (almost) directly proportional to the current, a design often needs to balance power consumption with light intensity by adjusting the current. The voltage across the LED is going to stay pretty much the same.
 
#24
And for JimmyM:
JimmyM said:
Oh geez, now I have a headache! This turned out to be more than I bargained for. I think I'll just put my hand over the LED's when I switch it ;)
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Now you know how I feel when reading some of the music theory threads. :confused:

It's actually not so bad as it sounds. Much simpler with real numbers. Let's say the VT Deluxe has a 9V power supply. Using the suggested 3V typical LED voltage drop yields 6 volts across the current limiting resistor. Assuming 20ma through the diode will produce a nice bright light, you get 6V / 0.20A = 300 ohms for the current limiting resistor. Easy peasy.
 
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#26
JimmyM said:
OK, so all I need to do is find 5 mm LED's that work at 9v and I'm good without replacing resistors or doing math?
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If you are looking for red LEDs, just try one that is designed for 40-50mA and the right size (like the two I linked, assuming it does measure out as 5mm on yours), and you should probably be fine. I would forget about the voltage drop / resistor selection stuff for now unless you find that it is too dim. If that is so, then you could also try replacing the resistor at that time.


wlater said:
[...] It's actually not so bad as it sounds. Much simpler with real numbers. Let's say the VT Deluxe has a 9V power supply. Using the suggested 3V typical LED voltage drop yields 6 volts across the current limiting resistor. [...]
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The thing is though, the resistor may be dropping from a 9V supply rail, or it may be dropping from a 5V logic level, etc. -- the "digital recall" functionality suggests that the VT deluxe has some sort of small microcontroller in there and thus also a 5V or 3.3V supply, not just 9V levels. You will not necessarily know what resistor to select until you can see the schematic, or you could try to use a multimeter to measure the voltage drop and current over the existing resistor and calculate it from there. I just wouldn't worry about it unless you found that you had to. Since most red LEDs have similar voltage drops and a 50mA LED will run fine at 20mA it's probably not worth the effort at this time to really figure it out unless he is unsatisfied with the result.
 
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#27
Nope,J, you need to find brighter LEDs that draw same current with whatever nominal voltage is spec'd in the VTD.

Or more likely, some resistors to match the new brighter LED nominal voltage drop. I thought they were spec.d to voltage but I'm not sure since someone else says otherwise.
 
#29
LOL! Yeah, in this day and age, it only makes sense to use brighter LED's but it's a great pedal so I won't bust balls. Thought Chris might chime in on it, but if I don't hear from him by middle of next week, I'll PM him. Can't do anything until then anyway. Road trip.
 
#30
Downunderwonder said:
[...]I thought they were spec.d to voltage but I'm not sure since someone else says otherwise.
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They are spec'd to maximum current, but as a semiconductor have a nonlinear knee-like voltage drop curve. In and around its operating range this usually means for example that a red LED will drop a little less than 2V from anode to cathode (or in the high 3V range or more for blue, etc.). The voltage drop is related to the semiconductor composition.

You generally design the power for the LED around the current it wants (for a given brightness); somewhere under the maximum current. The LED itself handles maintaining a happy voltage drop at that point. So while the LED does have a voltage based parameter (forward voltage drop), you don't want to just provide it that voltage with an unlimited current capacity -- you design to limit current and let the voltage across the part sort itself out. If you are just using a resistor for this purpose, as opposed to a constant current supply or something like that, then what you want to do is to select the resistor based on the current draw and voltage drop.

It's just a basic Ohm's Law exercise: Vs - Vf = If * R, so R = (Vs - Vf) / If
Or, in other words the resistor would be the supply voltage minus the forward voltage drop of the LED, divided by the current you want to flow across it.

Anyways the consequence of this is that the further the supply voltage is from the voltage drop, the less changing the value of the resistor will matter for swapping an LED even if it has a slightly different voltage drop. For example if we had a 9V supply voltage and a 20mA max / 1.7V drop LED originally (which seems to be typical of "regular" red LEDs), you would have a 360 Ohm resistor in there. If you were to replace that LED with a 50 mA max / 1.9V drop LED (typical of "high brightness" red LEDs), then it would have 19.7mA flowing through it, about a 2.7% drop in current. If you had a 5V supply voltage originally, you'd have a 160 Ohm resistor in there for the same LED and putting the replacement 1.9V drop LED in there would be a 6% drop in current. This will continue to get bigger and bigger as the supply and drop voltages converge.

"High Brightness" LEDs -- I believe -- produce more lumens per watt within their operating range and if you look at the spec sheets the 40 and 50mA ones linked are happy to operate around 20mA. So even if they are not pushed to their maximum current I would think they would be brighter than the standard LEDs.

Given that and the illustration of current differences above this is basically a long winded way of showing that swapping the regular red LED with a high brightness red LED will probably be fine without worrying about much else. If JimmyM is worried about having to deal with resistor calculations, etc. I would just perform the swap, see what it looks like, and only worry about anything further as necessary. It's hard to make any further assumptions about what would be necessary without either seeing the schematic or opening it up and taking measurements.

Anyways that's enough of LED 101 out of me -- plenty of other (and better) resources than me on the subject if anyone feels inclined to look into it.

For JimmyM, I think the thing to worry about most at this point is developing reliable soldering skills :)
 
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#32
I have suffered similarly with my VT Deluxe, day time outdoor gig couldn't see s**t!! made for nervous moments when switching from boost patch to effects loop etc. I am fairly confident with my electronics skills i might just swap out my LEDs and let you know how i get on, i think i might just change the color to green or a brighter spec red, the only things i would really be worried about is the forward volt drop and that the current draw was in the ball park of the originals i have about 50 to choose from @ my place of work lol ( so figure finding some that work wont be a problem ) and as was mentioned before developing soldering skills is a must! if you want to attempt removing parts with out doing any damage.
 
#33
_Elf said:
For JimmyM, I think the thing to worry about most at this point is developing reliable soldering skills :)
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+1
JimmyM, if you don't know already, PCBs are much more fragile wrt soldering than pots and the like. Make sure you have a proper wattage iron and proper solder removing tools (I prefer braided wick but some prefer "snot" suckers). And LEDs are almost always soldered flush to the circuit board which means you can't really work to remove one lead at a time like you can with some other components, you have to wick away the solder on both leads/pads enough to remove the LED. Soldering the new one in should be easier.
Oh, and I'm sure you know but just in case, even a company as good as Tech21 is unlikely to honor your warranty after such a mod.
 
#38
Yeah, it is expensive. That's the new model, but if you are looking for something cheaper, this one replaces their older 808 model and you can find some really good deals on them on ebay sometimes.

Once it warms up, it literally takes a second for each thing you desolder.
 
#39
I spoke with our tech here and he said it would be best to send the unit in as it requires a good deal of soldering. The LEDS we use currently are brighter than the older ones and are spec'd for that unit. You could drop in those super bright Blue LEDs but if they draw more current the phantom power may not function as well and the battery life may be diminished. I know, it's always something. On the flip side the pedals that are bright enough for outdoor use can be blinding on an indoor gig where its dark and you bend over to adjust them. My Durham Sex Drive boost pedal is ridiculously bright.
 
#40
tech21nyc said:
I spoke with our tech here and he said it would be best to send the unit in as it requires a good deal of soldering. The LEDS we use currently are brighter than the older ones and are spec'd for that unit. You could drop in those super bright Blue LEDs but if they draw more current the phantom power may not function as well and the battery life may be diminished. I know, it's always something. On the flip side the pedals that are bright enough for outdoor use can be blinding on an indoor gig where its dark and you bend over to adjust them. My Durham Sex Drive boost pedal is ridiculously bright.
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Thx Chris, I will be PMing you about that later tonight or tomorrow. I agree with your tech that it's the safest route, and probably the cheapest, as if I screw it up then I have to buy another VTD, and as assed up as I got over being able to solder in a new battery clip for my wireless, an LED changeout would introduce ten extra opportunities for me to screw up ;)
 

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