Wiring a VU meter

[Old Tele man]

...uh, just exactly WHAT do you want that meter to "show you"?

1) that something is happening inside?
2) that something is happening in the preamps?
3) that something is happening in the PI?
4) that something is happening in the power tubes?
5) that something is happening in the power supply?

...or what?

[danielzink]

...uh, just exactly WHAT do you want that meter to "show you"?

1) that something is happening inside?
2) that something is happening in the preamps?
3) that something is happening in the PI?
4) that something is happening in the power tubes?
5) that something is happening in the power supply?

...or what?

Okay - now realize - this is not a smart aleck answer but.....yes....

to simplify. Just for grins - I'd like a VU meter on the front of the amp - jumping around in realtion to something.

It's not for diagnostic purposes, it's not for anything - other than to have a big 'ol meter on the amp doing something.


Thanks for all the replies, Dan

[petemoore]

Here;'s what I'd do.
But I have free VU's laying around.
Can't hurt to try...
Connect guitar pickup to VU see what happens, probably little to nothing.
Then figure it's a 600ohm input, and that'll certainly dump signal, so use a buffer with low output impedance, I'd say try an LM386 which is able to drive a speaker, but that's probably overkill.
Use an active booster/buffer...breadboard.
Use a voltage divider [volume control], ease it up until the meter jumps.
I have pegged these things and they seem to take a good bit of current and still work.
Points being...You'll probably need a buffer to drive the VU, and will want one to drive a signal split anyway to prevent signal loading.
Guitar into buffer might make it jump.
Guitar into gain stage into buffer I think would do the trick.
I'd keep all the parts as opamps or discretes ...or...
try the slick trick described above which utilizes the voltage across the cathode resistor of a preamp stage to do the VU coil driving...only question I have is how much does a current draw influence cathode voltage, er...how much would that 'matter'...I think not much, seems like an elegant way to assign a VU to an 'already there' driver, haven't tried it to comment....I'd check/reread before building what I forgot about a voltage reducing divider between the tap and VU.

[bob p]

hey steve, i really like the red lettering on black. is that a lighting artifact, or is that the real color? it looks like you had 2 layer black on red plastic professionally engraved. or did you use some sort of lettering kit? looks good!

[Ampclutz]

Ok, Here we go,

I'm looking at an old tape recorder with a VU meter. This meter is wired between the speaker out jack's tip lug and ground. The meter has 10K resistance and no series or parallel resistors connected. It is really butt simple. I think the speaker is supposed to be 8 ohms.

This thread got my curiosity going so I just had to check and this is a modular recorder and I already have the amp out.

So, this is one way that will do something for sure.

Hope this helps,

AC

[petemoore]

I'm looking at an old tape recorder with a VU meter. This meter is wired between the speaker out jack's tip lug and ground. The meter has 10K resistance and no series or parallel resistors connected. It is really butt simple. I think the speaker is supposed to be 8 ohms.
I'd have half guessed connecting it directly to the speaker [well..'10k vs. 8k'] would bury the pegged needle.
So anyway it is like driving a speaker, tape player amp probably isn't as powerful as guitar amps, a series resistor would probably remedy that.
Looks 1/2 like an attenuator design I was dreamin' up..

[Ampclutz]

I'd have half guessed connecting it directly to the speaker [well..'10k vs. 8k'] would bury the pegged needle.
So anyway it is like driving a speaker, tape player amp probably isn't as powerful as guitar amps, a series resistor would probably remedy that.
Looks 1/2 like an attenuator design I was dreamin' up..

That may be a typo [well..'10k vs. 8k']... 10,000 vs. 8 ohms. or a 1250 to 1 ratio. This amp has a single end el84 output section for what... 5 watts output maybe. So a big amp could overdrive the meter. A trim pot would fix it probably

AC

[petemoore]

Looks 1/2 like an attenuator design I was dreamin' up..
Had about the same dream...lol.
And why not? wiggling inductor coil is something I dream up about too much...instead of all the speaker suspension stuff, all really needed is a coil alignment movement and some damping, that could all be done [aligned etc.] using a pendulum on a small bearing...instead of 'whole speaker style' [dual suspension/cone etc.] speaker attenuator, seems it'd be alot easier to mess with the damping and everything else if you could take it apart to mod it instead of having to glue together a whole new modified prototype dummy coil suspension system.

[CarlZ]

Leave it to me to throw a monkey in the wrench! But here's a thought...how bout on of those old "eye" tubes?! Don'e even ask me what the designator on the things are though. You used to see them in a lot of old reel to reel tape decks from the 60's as clipping indicators. Might be kinda cool with the little glow in the dark stripe bouncing all over the place as you play, especially if all you want is some sort of eye candy on the amp face. Would be a lot cheaper than buying a meter too.

-Carl

[petemoore]

We had a Sony with them.
Very eyecatching eye tubes, very cool tube mojo candy, and can be read quite easily from a distance. IIRC everyone who has ever seen them for the first time had numerous comments / questions.

[Steve Conner]

Hi guys,

Bob: It's clear plexiglass with the lettering laser engraved and edge-lit by red LEDs. It looks great in the dark. The laser can cut out all the holes too.

Magic eye tubes are cool. I used to have one wired to my speaker output so it would jump around in time to the music. The problem is that they have a relatively short life before they go dim, and aren't produced any more, so you'll have trouble finding good ones. And if you did, you might be better selling them to vintage radio enthusiasts...

A guitar pickup or PI output will not do anything to a VU meter. They just aren't sensitive enough, and with an impedance of only a few k Ohms, they would load the hell out of the signal. (The output impedance of your PI is maybe 100k plate-to-plate...) So the best idea is probably to hook it across the speaker terminals, with a 10k ohm series resistor and a small bridge rectifier, since all these meters want DC. 10k ohms is just a guess for the resistor value: you'll need to adjust it by trial and error depending on your meter, and the power output of your amp.

[bob p]

thanks!

[danielzink]

Hi guys,
the speaker terminals, with a 10k ohm series resistor and a small bridge rectifier, since all these meters want DC. 10k ohms is just a guess for the resistor value: you'll need to adjust it by trial and error depending on your meter, and the power output of your amp.

A rectifier like any of these ?

http://www.radioshack.com/sm-diodes-...8.2032230.html


Then I'll need guidance as far as wiring the rectifier 'eh ?
I can figure out how to bridge the speaker terminals with a 10k resistor

Thanks, Dan

[danielzink]

Anyone have a chance to look at those rectifiers ?


Thanks, Dan

[Old Tele man]

...yes, they'll work fine, but they're definitely "over-kill" current rating wise!