jlm vu buffer
« on: February 02, 2007, 03:09:23 PM »
link here

Just saw this while browsing the site...  whats the deal with all this stuff?  looks kind of cool for low price type stuff.  36 bucks i guess is a bit of a saving over more expensive meters, but are these dc type vu meters crap to begin with?

dunno...  worth a note i thought.


NewYorkDave

jlm vu buffer
« Reply #1 on: February 02, 2007, 03:26:25 PM »
A buffer amplifier and rectifier won't turn a cheap DC microammeter into a real VU meter. A true VU meter has a defined ballistic characteristic--a certain "response", for want of a better word. The kit turns a DC meter into a usable (in the relative sense) indicator, but it still won't behave like a real VU meter.

A buffer is not a bad idea even if you're using a real VU meter. You can make a buffer amplifier yourself with an op-amp IC and a handful of other components.

jlm vu buffer
« Reply #2 on: February 02, 2007, 03:36:38 PM »
hey dave!

yeah i've still got your 'superbal' drawing somewhere, and i've breadboarded it and it works very well, but i have no (good) place to put it yet ;]  i like it especially because it can be powered on single ended or bipolar...  handy tool.

I was thinking about a good way to cheap out on a vu meter, but man, i've learned my lesson about cheaping out.  rarely worth it for me.....

i did see some nice backlit sifam vu's on ebay for 11$ (!!) the other day.  should've bought some.  probably still there, actually.

good to see you around again dave!

astrovic

jlm vu buffer
« Reply #3 on: February 02, 2007, 08:23:56 PM »
Joe's board was part of a recent dialogue on Vu meters in Audio Technology magazine here in Australia in the last couple of months.  Rob Squire designed the circuit, and published it in the magaizne and Joe made the PCB for it.

There was a lot of debate in the metters section of the mag about use and worth of Vu meters in modern studios - some swear by them, others think they add nothing.  To each their own, I suppose.

I reckon Dave summarised Rob's and Joes' comments about the circuit pretty nicely.   :grin: I've grabbed a couple of boards of Joe - I don't know whether I'll use them to buffer a couple of Sifam meters, or to "rectify" some cheapie meters.  It'll depend on application and purpose, I suppose. I thought about whipping up the circuit on breadboard or veroboard, but Joe's PCB's are so nice (and tiny!) that I couldn't refuse.

jlm vu buffer
« Reply #4 on: February 02, 2007, 08:36:31 PM »
man, nice and tiny they are ;]

i think i'm about to order me up some 99v's and some Baby animals pretty soon.

with variable ip transformer loading, i'd imagine they'd end up being some veyr handy preamps for me.

but no.  finish other projects.  finish other projects.  finish other projects. finis

chrissugar

jlm vu buffer
« Reply #5 on: February 03, 2007, 02:23:54 AM »
It is a good idea to use a buffer before a real VU meter.
The distortion introduced by a VU meter connected unbuffered to audio, was documented by Stephen Paul at his now not existing forum. He said that some hearable distortions on Beatles albums were generated by the meters.

chrissugar
Christian Mike Sugar
        CMS-LAB

okgb

jlm vu buffer
« Reply #6 on: February 03, 2007, 11:59:37 AM »
And note you should be able to use cheap I.C.s  since you don't hear
audio through them .................741s anyone ?
GKB Audio / Greg Boboski

JohnRoberts

jlm vu buffer
« Reply #7 on: February 03, 2007, 12:17:56 PM »
The importance (and cost) of a true VU meter ballistics is IMO archaic for modern recording and signal processing. Strict VU ballistics were used by recording engineers to apply "windage" based on their experience for sundry individual instrument crest factors. For example record heavily compressed bass tracks hotter than dynamic close mic'd snare hits on the same VU scale.

Now peak reading meters are IMO more useful to prevent digital or solid state paths from OL since we no longer have X dB of graceful tape compression or vacuum tube OL to mitigate too hot signals.

When I used simple mechanical meters I typically targeted a 200 Ms averaging time constant with a peak LED nearby to indicate headroom issues. Another tidbit when designing buffer/drive electronics for a mechanical true VU type meter, yes you can cut corners on S/N or slew rate but be careful buffer doesn't run out of headroom as that can cause meter to under report with loud transients.  

JR
It's nice to be nice....

okgb

jlm vu buffer
« Reply #8 on: February 03, 2007, 12:48:18 PM »
good point about the headroom ,

seems to have fallen out of favor  [ or fashion ]but the V.U. meter Peak l.e.d. seemed a good idea .
GKB Audio / Greg Boboski

 

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