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Old 11th April 2013, 05:20 PM   #1
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Default Adding a db VU meter to an existing tube mic pre

I would like to add a 600ohm VU meter on the output of my one bottle pre. Tried to hook it up and got very little response from meter unless Im slamming it hard. Any tips for how to do this. Im just connecting off of OT. I have seen some schematics that use resistors and diodes. Just wondering if anyone has some tips to keep it a passive installation.
And if not, how about a circuit to drive the meter.
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Old 12th April 2013, 05:47 AM   #2
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Vu Meter Driver PCB Board Stereo for Two Vu Meters New | eBay
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Old 12th April 2013, 08:48 AM   #3
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A tube mic pre with transformer output should have no trouble driving a true VU meter which makes me suspect your meter. A true VU meter includes a bridge rectifier and a series resistance of over 3K so it presents a minimal load to anything capable of driving a 600 ohm load. You can find out if you meter really is a VU meter with a simple test. Connect the meter to a battery or low voltage power supply via a 10K resistor. Then reverse the polarity of the battery/supply. If it is a real VU meter it will indicate normally no matter what the polarity of the supply. If it is not then it will indicate normally with one polarity and try to move the needle backwards with the other.

Cheers

Ian

Last edited by ruffrecords; 12th April 2013 at 08:49 AM. Reason: typos
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Old 12th April 2013, 09:58 AM   #4
Tesla88 is offline Tesla88  Italy
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I've recently build a pair of 1176 compressors clone , the vu meter is connected directly to output XLR and with only a limit resistor , so if you are using an AC vu meter , assuming sensibility is ok , you don't need nothing more than a resistor to adjust reading.
If you are using a simple DC micro-amperometer you need a circuit to drive the thing , simple approach i used on a studio preamp with a 100uA DC meter is a GERMANIUM diode to rectify the output with a series 3300 ohm resistor and one 1n4001 directly connected to the meter coil to limit voltage across meter avoiding damage from loud signals and made a "log" display...
A more scientific approach is to use op-amps to made a full-wave IDEAL rectifier followed by a log-amp - this is what McIntosh Amps use tu "move" power meters.
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