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Old 12th May 2007, 04:57 PM   #1
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Unhappy Modutek VU Meters Installation Help!

Hello. I bought two (stereo) Modutek VU Meters to hook up to my JBL Pro pc amplified speakers. I purchased an all-purpose mounting box at a local electronics store as well as some wire, a strip containing two RCA female jacks and two 3.6K resistors. I drilled the holes in the box, mounted the VU Meters, cut and soldered an appropriate length of wire to connectors, soldered the resistors on one side (+) side, connected the wires to the meters. I then opened the front panel of the speakers, soldered two wires (blk [-], red [+]) to each wire leading from the speaker terminals; attached two RCA male plugs and plugged them into the VU Meter box. Result: nothing, nada, zilch! Meters do not budge! I'm obviously hooking them up wrong ! Can anyone help me? I don't think the meters need current to work, but maybe they do! Thanks!
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Old 12th May 2007, 05:22 PM   #2
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Are these Mechanical VU meters?? Not LED VU meters right??

What Balistic curcuit are you useing??? You can"t just connect the VU meters to your Speaker terminals and expect them to work correctly, ALL mechanical VU meters need a Driver curcuit called a "Balistic" to Drive the VU meters......


If you need a VU meter curcuit let me know and I can point you in the right direction.....


Cheers
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Old 14th May 2007, 01:07 AM   #3
radtech is offline radtech  United States
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I'm familiar with the brand, they would be mechanical meters.

I'll give a brief explanation of your problem...

These meters work by sensing DC current, your speakers work on AC current (the + and - markings on a speaker do not mean positive and negative in the same way a battery would be marked + and -, they're a reference for speaker phasing).

Hooking the meters directly to the speaker leads will give you no reading, as the AC audio signal will try to drive the needle roughly equally in both directions. To get a reading you need to convert the AC to DC by rectification, generally with diodes.

For a VU meter you need to have a circuit that not only rectifies the signal, but does so in a way that will display properly on the meter.
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Old 14th May 2007, 01:32 AM   #4
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Most of the VU meters I have seen had there own rectifier inside the Meter it"s self (Usually a silenium Bridge rectifier in the better ones)......

Here is a fairly simple curcuit that will drive your meters with a Fair amount of accuracy and it also shows how to connect a Diode Bridge to the meter if it doesn"t have one built in..........

http://sound.westhost.com/project55.htm
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Old 14th May 2007, 07:30 PM   #5
radtech is offline radtech  United States
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Maybe they do have rectifiers built in, I can't find any info on them though... I know Mouser sells them:

http://www.mouser.com/catalog/630/1750.PDF

but there's no mention of them on the Jewell/Modutec site.
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Old 18th July 2007, 07:43 PM   #6
scottso is offline scottso  United States
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I bought some modutec meters from here:

VU Meters


Specifically the (MTR) 810559-15DVU model on the right and I'm having a heck of a time getting them to work. I tried hooking them to my outputs on a preamp I built with a 3k6 resistor but the needle doesn't even start to move until the voltage hits about +/-5v! Shouldn't they be registering 0db at 0.775?

I also see the behavior where the audio signal tries to drive the meter in both directions. Do I need the aforemention ballistics driver for this? Is that the same thing as a buffer circuit or do I need both?

I was pretty sure these were AC VU meters and had rectifiers in them already as the back is a huge 1.5" diameter cylinder and protrudes the same distance back. In that case I thought I could just hook them up directly for now and worry about the buffer circuit later...

There is a small screw in the front of the VU meter which I assume is to calibrate it but I don't have my signal generator yet and I didn't want to mess with that until I could provide a known signal. If this is all thats wrong I will be relieved!

Sorry for the newbie sort of questions but I'm just a beginner. If anyone can clue me in I would be grateful! Thanks!
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Old 18th July 2007, 08:39 PM   #7
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Location: UK
Quote:
Originally posted by scottso
I bought some modutec meters from here:

VU Meters


Specifically the (MTR) 810559-15DVU model on the right and I'm having a heck of a time getting them to work. I tried hooking them to my outputs on a preamp I built with a 3k6 resistor but the needle doesn't even start to move until the voltage hits about +/-5v! Shouldn't they be registering 0db at 0.775?

I also see the behavior where the audio signal tries to drive the meter in both directions. Do I need the aforemention ballistics driver for this? Is that the same thing as a buffer circuit or do I need both?

I was pretty sure these were AC VU meters and had rectifiers in them already as the back is a huge 1.5" diameter cylinder and protrudes the same distance back. In that case I thought I could just hook them up directly for now and worry about the buffer circuit later...

There is a small screw in the front of the VU meter which I assume is to calibrate it but I don't have my signal generator yet and I didn't want to mess with that until I could provide a known signal. If this is all thats wrong I will be relieved!

Sorry for the newbie sort of questions but I'm just a beginner. If anyone can clue me in I would be grateful! Thanks!
Does one have to be SO old to understand analog meters?

The front panel adjustment screw is a mechanical adjustment of zero when everything is switched off.

This is a DC meter of 1mA full scale and needs a rectifying op-amp circuit to both get the levels right and protect it from overload.

Google VU meter circuit.

This place, vu meters is a good starting point.

I remember my old gran in about 1955 describing my analog meter as "the box with the moving arm."

Edited for crap typing.
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Old 18th July 2007, 09:30 PM   #8
scottso is offline scottso  United States
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Thanks for the response! You are the first person that could definitively tell me whether these were AC or DC meters! That place I bought them from is a surplus store so they have no information on them at all. I assumed since they were from a broadcast console they would be AC but alas.

Incidentally I've been googling vu meter all day. If you don't know what you are working with you don't know what applies and there are TONS of conflicting information. Like some people say 3k6 resistance for AC meters and then some people say 3k9 is what you need nowadays.

Why are these meters so huge in the back if they have no internal rectifier? Is it just because they are so old?
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Old 18th July 2007, 09:39 PM   #9
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Oh dear !

Quote:
Originally posted by scottso
Thanks for the response! You are the first person that could definitively tell me whether these were AC or DC meters! That place I bought them from is a surplus store so they have no information on them at all. I assumed since they were from a broadcast console they would be AC but alas.

Incidentally I've been googling vu meter all day. If you don't know what you are working with you don't know what applies and there are TONS of conflicting information. Like some people say 3k6 resistance for AC meters and then some people say 3k9 is what you need nowadays.

Why are these meters so huge in the back if they have no internal rectifier? Is it just because they are so old?
A meter works by passing a current through a coil in a magnetic field, thus producing movement. Good old Maxwell!

The big bit at the back is a MAGNET!

the difference between 3K6 and 3K9 is negligable.

You really do need to study a bit about volts, amps and ohms before getting into stuff like this.
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Old 18th July 2007, 10:08 PM   #10
scottso is offline scottso  United States
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That seems like an awfully large coil to move such a small needle. It didn't even occur to me the whole thing could be a coil just due to how big it was. Its bigger than a film canister. The needle must weigh 10 pounds.

The new DC meters I've looked at seem to get by without the huge magnet. I guess new is better than old.
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