Vumeter wiring to output

[Deepdark]

Hi there.

I just finished an la2a nd took this vumeter on ebay: http://www.ebay.ca/itm/321236001999?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

It's rated 500mcroamp. I strap it as the schematic without caring of the rating of the vu meter. I can adjust the gain reduction 0 withing ghe 1M trimmer, but output +4 and +10 don't sit to 0 when injected signal, even a really strong one, it will move a little and if i exeed, in exemple, +4db, then the needle became crazy.

What ut tells me us that the meter may not be to read 1.228v at 600ohm through an external 3k6 resistor. Am i right? I guess i would have to test different external resistors value to get 0 at 1.228v? My output is terminated with an 680r across pin 2 and 3.

Thanks guys

 

[ruffrecords]

This is because it is not a true VU meter. It lacks the diode bridge that is normally in a VU meter. As their eBay listing says, it is intended to work with their VU meter driver board which will have the rectifiers built in. Most true VUs have a germanium bridge rectifier built in. Simplest solution is to wire 4 x 1N4148 diodes as a bridge. Connect dc output meter and ac in via 3K6 resistor and try again.

Good Luck

Ian

 

[Deepdark]

Damn, you're right. I didn't think about the fact it may not have the rectifier inside. Glad i have some germanium diode here. Thanks Ian

 

[PRR]

> Most true VUs have a germanium bridge rectifier built in.

True VU is a copper-oxide rectifier. (Consistent CuOx production was one of the key technology developments which led to the VU standard.)

Germanium would be a sign of a less-than-VU meter, some Japanese tape-deck decoration.

FWIW: "Jim's" driver board *appears* to use an IC, and there were several stock ICs to drive audio level meters.

IAC, unless you only hang across broadcast high-level outputs (telco lines or recording busses), you usually do not want a true-passive level meter. The diode switching distorts the audio, and much audio is (or should be) way-far down-scale on a linear meter. (Which is one reason why log-scale meters including BBC PPM are useful.)

Since VU meter accuracy was marginal for 1938 and lame in this 21st century, Ge or those Schottkey things is fine for needle-dancing.

A set of "identical" VU meters *was* useful in early US networks. If NYC and Tulsa and L.A. all saw about the same levels in the same parts of the program, there was no major level-error in the long-long lines and hundreds of boosters. Off-air, tone-tests could get a closer reading (but you don't need a VU meter for tone-testing).

 

[Brian Roth]

> Most true VUs have a germanium bridge rectifier built in.

A set of "identical" VU meters *was* useful in early US networks. If NYC and Tulsa and L.A. all saw about the same levels in the same parts of the program, there was no major level-error in the long-long lines and hundreds of boosters. Off-air, tone-tests could get a closer reading (but you don't need a VU meter for tone-testing).

Back in 1972, I worked at a radio station in OKC.  On Sundays, we ran a 11:00 AM live church service which was fed to us via Ma Bell.  I **think** the remote line was an actual copper pair that was patched through several central ofices

Around 10:30, a Bell tech would call our control "hot line" from the remote site.  I'd pot up the remote in the Audition channel and watch the levels on the CCA console's VU meters.  The tech would start with a 1 K tone, then higher and lower frequencies.  I'd relay the VU readings on the studio end, and he'd tweak the EQ.  Nowadays, I would bet there was a Pultec EQ on the remote end!


Bri