led vu meters

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little izzi
Posts: 10
Joined: Thu Oct 07, 2010 6:51 am

led vu meters

Post by little izzi »

Hi, I just brought a 1290 mono kit from JLMaudio and can't wait for it to arrive! (May take some time as I'm in London!) Anyway I have really big ideas for the presentation of this unit and really want to incorporate an all led variable vu meter as a backlight, possibly across the input or the output... Not sure yet? Just don't want it to be detrimental the the sound quality. does anybody have any ideas on how to do this possibly using a modified jlm vu buffer kit?? Any ideas would be greatly appreciated.
Thanks
izzi

little izzi
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Joined: Thu Oct 07, 2010 6:51 am

Re: led vu meters

Post by little izzi »

bump

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Joe Malone
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Re: led vu meters

Post by Joe Malone »

little izzi wrote:Hi, I just brought a 1290 mono kit from JLMaudio and can't wait for it to arrive! (May take some time as I'm in London!) Anyway I have really big ideas for the presentation of this unit and really want to incorporate an all led variable vu meter as a backlight, possibly across the input or the output... Not sure yet? Just don't want it to be detrimental the the sound quality. does anybody have any ideas on how to do this possibly using a modified jlm vu buffer kit?? Any ideas would be greatly appreciated.
Thanks
izzi
I am no sure exactly what you mean. But most led meters do not need a buffer as they are opamp input and make no distortion when connected across a input or output like our VUPPM40GR. If connecting across a input connect to the unbalanced secondary of the input transformer so to minimize noise injection into sensitive low level part of the preamp.
Joe :-)
JLM Audio
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little izzi
Posts: 10
Joined: Thu Oct 07, 2010 6:51 am

Re: led vu meters

Post by little izzi »

Hi Joe, thanks for your reply, I have a very good but now very distant understanding of electronics, so didn't know about the leds not needing the buffer, so that is a real bonus for me!
However I've since modified my needs, I am going to need the meter to be switchable between input and output and also stay on (half brightness) whilst the unit power is switched on, bearing in mind these LED's are going to be a main backlight for the unit, covering a fairly large area of the 2u rack front (maybe a 1/3rd of the face front will be backlit through frosted perspex, so it's kind of a one light does all) so these led's may need more power than the standard vu meters? It'll be so worth it when I post the pics of what I'm going to do to this beast!
Any circuit ideas welcome, trust me you'll love the design!!
Thanks
Brett

little izzi
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Joined: Thu Oct 07, 2010 6:51 am

Re: led vu meters

Post by little izzi »

bump

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Joe Malone
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Re: led vu meters

Post by Joe Malone »

little izzi wrote:Hi Joe, thanks for your reply, I have a very good but now very distant understanding of electronics, so didn't know about the leds not needing the buffer, so that is a real bonus for me!
However I've since modified my needs, I am going to need the meter to be switchable between input and output and also stay on (half brightness) whilst the unit power is switched on, bearing in mind these LED's are going to be a main backlight for the unit, covering a fairly large area of the 2u rack front (maybe a 1/3rd of the face front will be backlit through frosted perspex, so it's kind of a one light does all) so these led's may need more power than the standard vu meters? It'll be so worth it when I post the pics of what I'm going to do to this beast!
Any circuit ideas welcome, trust me you'll love the design!!
Thanks
Brett
I have never tried it but the LM3915 or better the LM3916 led meter chip may be able to have a large value resistors added to the cathode led legs to 0v so the led stays slightly lit without overriding the switching of the Led meter chip.

In our VUPPMGR40 led meter we can change the program to just turn on the leds slightly since it is CPU controlled.

You do not need to bump the threads as I get notified of the thread post but it will sometimes take me a few days to reply :D
Joe :-)
JLM Audio
Capturing Audio without Injury

little izzi
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Joined: Thu Oct 07, 2010 6:51 am

Re: led vu meters

Post by little izzi »

Thanks again Joe, sorry for the bumps :oops:
That sounds great, I may buy the VUPPMGR40 led meter for it, can the led's be changed for blue ones? bearing in mind the blue led's need a higher voltage I believe?
Thanks
Brett

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Joe Malone
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Re: led vu meters

Post by Joe Malone »

little izzi wrote:That sounds great, I may buy the VUPPMGR40 led meter for it, can the led's be changed for blue ones? bearing in mind the blue led's need a higher voltage I believe?
The VUPPMGR40 needs the special tricolor led bars which are not available in blue as far as I know.
Joe :-)
JLM Audio
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chrisp
Posts: 184
Joined: Sun Mar 04, 2007 11:46 am
Location: Sydney, Australia

Re: led vu meters

Post by chrisp »

Hey Izzi and Joe

I'va done a little 7 LED PPM meter circuit using the LM3915, and have built a 10 LED VU using the LM3916.

To be honest, the IC's are a little prone to oscillate so you need to be careful in layout etc, but with a bit of patience you do get there. The datasheets show circuits for peak, average and true VU.

The other thing is power and voltage. Re power, 10 leds drawing 10-20mA each needs to be factored in - make sure your supply is able to cope. The LM39XX chips also run at much lower voltages (especially the supply to the LED anodes) so you need to manage the heat budget carefully if you want to run (as in my case) a 48V supply to the preamps. A 42V drop at 200mA needs to shed warmth somewhere.
Chris P
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.

little izzi
Posts: 10
Joined: Thu Oct 07, 2010 6:51 am

Re: led vu meters

Post by little izzi »

Thanks for the replies! nice info, my needs have evolved yet again...
All I need now is 3 to 6 leds to come on when I switch the unit on, so I was thinking to wire this straight over the original on/off led with the new calculated resistance value (so running straight from the 48v supply) and then just maybe 3 to 6 red leds powered by the 48v supply but taking its signal from the unbalanced secondary of the input transformer as Joe said before ( I have a standard opamp based vu meter circuit that I can use ). I'm just wondering what sort of problems I may get from this setup? If any? Power draw??? Can the 48v supply cope or do I need another 12v supply??
Thanks for looking
izzi

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