JLM AUDIO

Posted: **Thu Aug 20, 2009 8:59 am**

Hey,
Does anyone know the voltage required for the little led's inside the small round 34mm VU's that Joe sells??? http://www.jlmaudio.com/VU%20Buffer.htm

I have bought two of them, but cant find the answer to this question anywhere.

Also, can you open them up to replace or change the LED? I wanted to put yellow ones in to give them a more 'vintage' glow.

Assuming the voltage of the LED's, I have a 30volt rail and am planning on using both meters and two 56k resistors all in series.....will this work?? (should give about 4volts)...

cheers,
Mac.

Posted: **Thu Aug 20, 2009 9:23 am**

JLM VU Buffer Kit Thread wrote:LED
If you want to run the LED on more than 12volts you will need to add a series resistor.
Use this formula R = (V - 12) / 0.02.
So if you have a supply of say 24v regulated the blue LED would need a resistor =
R = (24 - 12) / 0.02 = 600ohm. So use 620ohm or 680ohm standard value resistor.
Will need to be a half watt type. [/color]

LAMP
If you want to run the Orange / Green Lamp on more than 12volts you will need to add a series resistor.
Use this formula R = (V - 12) / 0.08.
So if you have a supply of say 24v regulated the blue LED would need a resistor =
R = (24 - 12) / 0.02 = 200ohm. So use 220ohm standard value resistor.
Will need to be 1watt type or better use 100ohm 1watt in each wire to the lamp to spread the wasted heat better.

So (30 - 12) / 0.02 = 900 ohms for the series resistor based on a 30V supply

Of course you can open up the VU meter. But can you put it back together again, that is the question .....

Posted: **Thu Aug 20, 2009 10:16 am**

Thanks Chris,
So do you know that the led in the 34mm VU is 12volt, or are you assuming it is?

I used the online calculator at http://led.linear1.org/1led.wiz and assumed the values, ahead of actually finding out what i was dealing with.

regards,
Mac

Posted: **Thu Aug 20, 2009 10:20 am**

also,
I had planned to connect both in a string, since i have so much input voltage at my disposal.

Mac

Posted: **Thu Aug 20, 2009 2:24 pm**

Mac wrote:So do you know that the led in the 34mm VU is 12volt, or are you assuming it is?

Sorry - I should have checked that you are using the JLM VU buffer PCB. But Joe's thread quoted above does seem to indicate that it is 12V.

Mac wrote:I had planned to connect both in a string, since i have so much input voltage at my disposal.

I'd suggest connecting them in parallel to your supply, rather than in series. If one goes down for whatever reason, the other will still work. In series, one goes down they'll both go down.

Posted: **Thu Aug 20, 2009 5:18 pm**

I'd suggest connecting them in parallel to your supply, rather than in series.

Yeah, thanks Chris. I thought about that after I posted. But I figure if one goes down I will open the unit anyway

I might email Joe and find out from the horses mouth what the voltage and draw of these things are. I tested with 6v this morning very briefly and they sure looked pretty bright at 6v - so I am hesitant to give em 12...

Mac.

Posted: **Fri Aug 21, 2009 11:42 am**

DO NOT connect the LED in the 34mm meter directly across a 12v supply as there is only 1 x white LED in the 34mm small VU meter which is 2v so you will need a series resistor to run it on any voltage. If using 2 meters run them in series to get a 4v LED and run one resistor. Only the large VU meters with the four x 3v blue leds or JLM large AL29 meter with lamp can run on 12v.

Series Resistor value = (Power rail voltage - Led voltage {2v or 4v}) / o.o1

The face of the 34mm meter with support backet unclips from the back of the meter and the scale just slides out so the LED can be changed fairly easily

Posted: **Tue Aug 25, 2009 3:43 pm**

Thanks Joe,

Series Resistor value = (Power rail voltage - Led voltage {2v or 4v}) / o.o1
30v rail - 4v/0.01= 2600 (one 2.6K resistor)

Shouldnt I use two resistors to spread the heat??

Mac.

Posted: **Tue Aug 25, 2009 9:08 pm**

Series Resistor value = (Power rail voltage - Led voltage {2v or 4v}) / o.o1
(30v rail - 4v)/0.01= 2600 (one 2.6K resistor)

Shouldnt I use two resistors to spread the heat??

You can if you want but you don't need to.

Wattage = (Power rail voltage - Led voltage {2v or 4v}) * o.o1
(30v rail - 4v) * 0.01 = 0.26W (0.5watt resistor)

So for 2k7 a 0.5watt normal resistor will be fine.

If you need a brighter backlight you can go up to 20mA, So 0.02 instead 0.01.

Series Resistor value = (Power rail voltage - Led voltage {2v or 4v}) / o.o2
(30v rail - 4v)/0.02 = 1k3

Wattage = (Power rail voltage - Led voltage {2v or 4v}) * o.o2
(30v rail - 4v) * 0.02 = 0.52W (1watt resistor)

Posted: **Tue Aug 25, 2009 9:14 pm**

Cool,
thanks heaps Joe. And thanks for taking the time on such a simple noob question...

cheers,
Mac.

P.S. how far away are your new tube kits I have been hearing about?? I might hold off on building a Gyraf G9 if I know you might have something available in the next few months...
DONT WORRY - just saw your responses here for thread - Valve Preamp & Compressor Kits- AT Interview.

JLM AUDIO

JLM small 34mm VU - QUESTION

JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION

Re: JLM small 34mm VU - QUESTION