LM3916 Inline VU Meter

[karbomusic]

Anyone interested in this? I designed it over the weekend and worked most of the kinks out yesterday. A little too big to work into an existing circuit in most cases but I designed it as an inline piece for my pedal board (and as a driver for a LED meter tower). I've noticed the occasional post asking about similar so I thought I'd share if there were an interest:

Basic features:

- Buffered input/output channel so it can be inserted into a signal chain.

- Gain switch for either line/inst. When in inst mode the buffer gain is adjustable, otherwise is a unity buffer. This buffer gain is for VU only, not the buffered pass through signal. Translation = You can plug a guitar directly into it.

- Meter gain trimmer (to calibrate VU range)

- Mode switch for bar/dot modes.

Obviously the LED bar is not required. One can just omit that and solder individual LEDs or wires leading to LEDs directly instead of the bar.

[vigilante397]

Very cool. I did something similar a while back with the 3916, very cool chip. Mine isn't quite as tidy on the inside though

[karbomusic]

Hey that's pretty neat. How did you power two rows? Did you use one or two 3916s?

[lion]

I'm interested - got a schem to share?

Erik

[vigilante397]

Hey that's pretty neat. How did you power two rows? Did you use one or two 3916s?

I used two 3916's. I have a buffered splitter, one output from the buffer goes straight to the output jack and the other just splits (nobody cares about tone-sucking when there's no output) to the two inputs for the 3916's. I do think the bar LEDs look super slick though, and I like how you've got the switch between bar and dot modes. One of those things that people will continually ask "Yes, but what does it actually do for your sound??

[duck_arse]

Hey that's pretty neat. How did you power two rows? Did you use one or two 3916s?

One of those things that people will continually ask "Yes, but what does it actually do for your sound??

..... has anyone done the obvious answer for this in another thread? something about brighter sound? or getting their coat?

a double row of leds (and two sources) could probably be done with a 7555, a 4066, and maybe a pair of npn's.

[karbomusic]

Hey that's pretty neat. How did you power two rows? Did you use one or two 3916s?

One of those things that people will continually ask "Yes, but what does it actually do for your sound??

..... has anyone done the obvious answer for this in another thread? something about brighter sound? or getting their coat?

a double row of leds (and two sources) could probably be done with a 7555, a 4066, and maybe a pair of npn's.

Don't know, I just wanted one that didn't muck with my tone and designed one to do that (as well as a base design for other uses); and I wanted to use the 3916 for its True Peak/AVG/VU capabilities but I did not add that feature to this design, that's next week's playtime.   Where is the other thread?

[karbomusic]

I'm interested - got a schem to share?

Erik

I'll try to post tonight or tomorrow when I'm home.

[Luke51411]

Hey that's pretty neat. How did you power two rows? Did you use one or two 3916s?

One of those things that people will continually ask "Yes, but what does it actually do for your sound??

..... has anyone done the obvious answer for this in another thread? something about brighter sound? or getting their coat?

a double row of leds (and two sources) could probably be done with a 7555, a 4066, and maybe a pair of npn's.

What about if they ask if it colors your tone? 

[tubegeek]

Anyone interested in this?

Yes!

I would be curious to see how you did it - did the app note help you out or did you go freestyle or....?

If I'm not mistaken (a big if) I think you can double these chips up so you can get a higher-resolution display if you want it (twice as many lights/half as large a signal difference between lights.) Or maybe doubling it just allows you to have a smaller "quiet" range at the bottom of the display, I forget.

Always been curious as to how hard these babies are to get working usefully, I'd love to know what you did, thanks!

[karbomusic]

Anyone interested in this?

Yes!

I would be curious to see how you did it - did the app note help you out or did you go freestyle or....?

If I'm not mistaken (a big if) I think you can double these chips up so you can get a higher-resolution display if you want it (twice as many lights/half as large a signal difference between lights.) Or maybe doubling it just allows you to have a smaller "quiet" range at the bottom of the display, I forget.

Always been curious as to how hard these babies are to get working usefully, I'd love to know what you did, thanks!

I used the datasheet then added a dual non-inverting buffer in front (TL072 etc). The buffer splits over to the 2nd channel for the thru, 1st goes to the meter. I also added gain to the meter buffer then just added a switch that just cuts R2 of the NFB out of the circuit in order to turn the gain portion off (hope that's legal LOL). Pretty much a caveman approach since I'm not doing any rectification (yet) which is required for true avg/peak IIRC. TBH, other than a backwards electro cap leaking DC into the meter causing the first two LEDs to mysteriously turn on, it was very easy. Swapped that and fixed.

Yes, you can chain these guys. 1 chip = 10 LEDs = 20 DB so for more of range you'd want two (datasheet has examples). This one was (or rather is still being) designed as multipurpose. I can plug a guitar into it, I can throw it on the pedal board at the end of the chain, I can send it a line level signal from other gear... I did that because I build stomp boxes but I also record a lot and I'm dying to make one of these for my Studio except sideways and with 0 VU touching for L/R, that way it visually gives stereo spread as well as VU.

I'll get the schemo posted tonight, just remember it's still in prototype phase and likely a part or three that need values changed or even removed due to troubleshooting I was doing on the BB (and being a newb).  I'm not sure dot mode is working properly so I need to debug that me thinks.

[woody alien]

I'm also interested. At the moment I have LM3914, which needs 0-5V DC for its input. Therefore it needs an audio rectifier, which again, needs split power supply.

Karbomusic's device seems to be a lot better option to make an envelope 'Slice-o-Matic', that I'm after. 

[Tony Forestiere]

That is really cool looking. 

[Kipper4]

Great Job. I'm intrested.

[karbomusic]

Here's the schematic that goes with the video in the first post. I did insert an A/B switch when auditioning earlier using my guitar and the buffering is working fine aka no tone suck.



And a PCB; beware that things could change if I find a problem but the below does work...

http://www.wallsonic.com/public/posts/VueMeterPCB.pdf

http://www.wallsonic.com/public/posts/VueMeterLayout.pdf

[karbomusic]

That is really cool looking.  

Yea, I found those when searching for info on the 3916 and makes me want to build one.

[karbomusic]

The above PCB in a box... My first need/attempt at square holes...

[vigilante397]

The above PCB in a box... My first need/attempt at square holes...

That looks amazing! I stuck with round LEDs because I wasn't ready to try square holes, but you nailed it

[karbomusic]

That looks amazing! I stuck with round LEDs because I wasn't ready to try square holes, but you nailed it

LOL thanks! I had no idea but drilled out the middle, dremeled to within a pretty close distance then filed the rest. I have a set of mini files which just happened to work out well. Now I know what all those different shapes for file are meant for. 

[lion]

Here's the schematic that goes with the video in the first post. I did insert an A/B switch when auditioning earlier using my guitar and the buffering is working fine aka no tone suck.

Thanks for sharing the schem and layout details. Appreciated!

Erik