VU rectifier

[Sleeper]

I've got some vu meters (of a sort, not true vu) that I'd like to use.
trolled the posts and tested them with a 10k resistor and 1.5v battery.
The needles move up w pos voltage and down with the battery turned around, so I'm pretty sure I need a bridge rectifier.

Three questions.

does the rectifer go before the 3.3k resistor?

And I hook up the rectifier as follows yes?
source + and - to ~ and ~ on the rectifier
and rectifier + to meter+ rectifier- to meter-

Just about any bridge rectifier should do right?
It is only getting a couple of volts tops... I have a bunch of 300piv rectifiers here.

Thanks
Kelly

 

[PRR]

Put the resistor before the rectifier. The rectifier connects directly to the meter. It may work the other way, but rectifier transients will zing the source: better to hide them behind the resistor.

Common Silicon diodes "work", except they have a 0.5-0.6V drop and you have two diodes in series, so low level signals won't move the meter at all. Better to find Germanium diodes: 1N34, 1N60 and modern replacements. If that fails, try the Schotkey rectifiers used in low-voltage switcher power supplies. What you really want is copper-oxide rectifiers, but they are hard to find. (If you can find a pure-analog needle multimeter rated like "20K/Volt", with an AC scale, it may have a copper-oxide rectifer inside, and such meters sell for $10.)

Another trick is to start wiring a 4-diode bridge rectifier, with diodes in the top, but 3K resistors replacing the bottom two diodes. This gives only one forward drop.

 

[dukasound]

[quote author="PRR"]Another trick is to start wiring a 4-diode bridge rectifier, with diodes in the top, but 3K resistors replacing the bottom two diodes. This gives only one forward drop.[/quote]
Hi PRR
Because my english is not good can you explain or draw.
Thanks

 

[Sleeper]

Hey thanks PRR.
I have a bag of IN34s here so I'm going to try this trick you mention.
I'[m with duka here a bit as I'm a little bit unsure what you mean
when you refer to the top and the bottom of the bridge rectifier.

Is this it?
.................................V+ -----------------.to meter+
.......................1n34........1n34
3.3k---------AC~ ......................AC~-----.0v
........................3k............3k
.................................V- -------------------meter-

Why do we call for a 3k in here?

Sleeper

 

[PRR]

Use the Germanium diodes. they will be fine.

Forget I mented a diode-resistor bridge: I now remember why we don't do it that way on passive meters.

 

[Sleeper]

:sam: :sam: :sam: :sam:
all ish compppleetely forgotteenn.
(foster brooks)

will use the germainuiums. thanksPRR
Sleeper

 

[bradzatitagain]

Hey Paul and all, what's your take on this Elliot Sound vu/ppm project?

http://sound.westhost.com/project55.htm

Does this become wildly complicated to modify if different valued meters are used, i.e. : 100ua, 200ua, etc?

rgrds,
Brad

 

[dukasound]

[quote author="Sleeper"]Hey thanks PRR.
I have a bag of IN34s here so I'm going to try this trick you mention.
I'[m with duka here a bit as I'm a little bit unsure what you mean
when you refer to the top and the bottom of the bridge rectifier.

Is this it?
.................................V+ -----------------.to meter+
.......................1n34........1n34
3.3k---------AC~ ......................AC~-----.0v
........................3k............3k
.................................V- -------------------meter-

Why do we call for a 3k in here?

Sleeper[/quote]

I tried with germanium AA series diode and I put one 10K trimer. To get same 0db on scale like on my Sifam I must conect about 5K.
I put this VU parallel to sifam.
Duka