VU BUFFER KIT BUILD THREAD

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Joe Malone
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VU BUFFER KIT BUILD THREAD

Postby Joe Malone » Sun Jun 14, 2009 8:37 pm

VU buffer kit parts
Image
47k = Yellow Violet Black red
3k3 = Orange Orange Black Brown
100R = Brown Black Black Black

Install resistors and diodes with there white or black stripes to the left
Top Diode can be any type 1N4001,2,4,7 or BAT85 or 1N5819 as it is only to stop reverse power wiring from damaging the opamp.
Bottom 2 diodes need to be Schottky BAT85 1N5819 etc or Germanium OA47, OA91 etc type for the meter to track correctly at low levels.
Image

Note 1. When using a meter with internal rectifiers like our Nissei AL29 do the mod shown below to disable the VU buffer recitifier.
Image
VU buffer PCB measures 1.45" (36.8mm) x 1.5" (38mm)

Note 2. Since the VU buffer runs on a single power rail it will have a power on voltage jump which will show as a large deflection on the meters pointer.
The size of the pointer deflection varies depending on meter type, voltage used, gain setting. This can be greatly reduced by slowing the rise of the half rail voltage on the VU buffer PCB.
This can be done by either changing the two 3k3 resistors shown below both to 47k or 100k. Or change the 10uF cap shown below to 100uF to 220uF 16v. Or doing Both changes. (VU buffer kits will have 2 extra 47k from Feb 2012)
ImageImage

Install IC socket semi circle cut out to the top as shown
Image

Install Terminals now if not soldering wires directly to Power and In pads
Image

Fit Capacitors (Note they all face in the same direction)
Image

Fit Trim pot as PCB overlay shows and TL071 IC into socket as shown with pin 1 in the top left corner
(Note new PCB's have the trim pot with the screw in the bottom right corner and pot should be fitted as marked on the New PCB which is opposite to photo below)
Image

The PCB uses the bottom edge to mount on to the VU meter + and - terminals.
Use any hole on the left for + and any hole on the right for -.
(If your meter has solder tags you can solder on directly or if there are 2 bolts use 2 cut off component legs to solder to the PCB and then wrap around the VU meter bolts.)
Image

Fold PCB back behind VU meter
(Note 100uF cap mounted across SEW / FLASHSTAR meter to slow its response down to normal VU response)
Image

If using the 12v regulated supply the Lamp or Blue led kit can be wired straight to the power for the VU buffer.
(Also the VU Buffer is protected against reverse voltage by the third diode at the top of the PCB)
Image
When connecting to a unbalanced signal +in goes to the signal and -in to the audio shield.
(A TRS socket will automatically do this when a TS unbalanced plug is plugged in to the TRS socket.)

BLUE LED
If you want to run the LED on more than 12volts you will need to add a series resistor.
Use this formula R = (V - 12) / 0.02.
So if you have a supply of say 24v regulated the blue LED would need a resistor =
R = (24 - 12) / 0.02 = 600ohm. So use 620ohm or 680ohm standard value resistor.
Will need to be a half watt type. [/color]

ORANGE / GREEN LAMP
If you want to run the Orange / Green Lamp on more than 12volts you will need to add a series resistor.
Use this formula R = (V - 12) / 0.08.

So if you have a supply of say 24v regulated the blue LED would need a resistor =
R = (24 - 12) / 0.02 = 200ohm. So use 220ohm standard value resistor.
Will need to be 1watt type or better use 100ohm 1watt in each wire to the lamp to spread the wasted heat better.

Audio Test Generator and Meters Great free Tone Generator and Meter software setup up your VU buffers and meters.
http://www.minorshill.co.uk/PC/Meters/Setup%20Audio%20Test.zipjpg[/img]

Fit Capacitors (Note they all face in the same direction)
[img]httpcom/VU/VU%20BUFFER%20PCB%20low%20thump%201
Joe :-)
JLM Audio
Capturing Audio without Injury

chrisp
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Re: VU BUFFER KIT BUILD THREAD

Postby chrisp » Mon Jun 15, 2009 9:40 am

For clarity........

Joe sells 2 types of Nissei meter.

The 1U size 34mm small round VU Meter from Joe is NOT an AL29, and needs the two rectifier diodes at the bottom of the board.

The AL29 is a larger rectangular meter and will not fit in a 1U case. This is the one with internal rectification where you should omit the PCB diodes.
Chris P
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I do lots of things. I believe eclectic skills are best.

conleycd
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Re: VU BUFFER KIT BUILD THREAD

Postby conleycd » Tue Sep 08, 2009 11:05 am

Just wondering. With the VU meter buffer board - would I simply through this on an output? Would my main output sound be messed with if I did that? Or should I have say a high impedance input unity gain opamp buffer first and then into the VU board?

Anyone?

CC

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Re: VU BUFFER KIT BUILD THREAD

Postby Joe Malone » Tue Sep 08, 2009 11:19 am

Just wondering. With the VU meter buffer board - would I simply through this on an output? Would my main output sound be messed with if I did that? Or should I have say a high impedance input unity gain opamp buffer first and then into the VU board?

Anyone?


Yes connect the VU buffer across the output and it will isolate the VU from the output and give you a att/gain trim to cal the meter. It is the isolating buffer so nothing else is needed between it and the output.
Joe :-)

JLM Audio

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mylesgm
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Re: VU BUFFER KIT BUILD THREAD

Postby mylesgm » Sat Sep 12, 2009 5:05 pm

What kind of meters will this board drive? I've a range of old meters that though they wont have full vu ballistics would certainly look good and thats what I'm thinking of for a particular project. Anyway what kind of rating should the meter have?
M

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Re: VU BUFFER KIT BUILD THREAD

Postby Joe Malone » Wed Sep 16, 2009 11:19 pm

mylesgm wrote:What kind of meters will this board drive? I've a range of old meters that though they wont have full vu ballistics would certainly look good and thats what I'm thinking of for a particular project. Anyway what kind of rating should the meter have?
M

The VU buffer will drive basically any AC or DC meter movement from 50uA up to a few mA.
Joe :-)

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rocksure
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Re: VU BUFFER KIT BUILD THREAD

Postby rocksure » Wed Oct 07, 2009 9:52 pm

I have been building a summing mixer round a pair of old Ward Beck summing amps. I assembled an AC/DC and world transformer kit and it's working great to power up the 25 volts DC I needed. So I have the mixer up and running. I have a couple of old Tascam tape machine VU meters that I want to run straight from the input busses to monitor the input signal. As I am not using the +48 V rail in the AC/DC, could I use this to drive a pair of these VU meters? Also the Tascam VU metes have already got a circuit board on the back of them so I can't put these buffer kits on in the manner you describe...I would have to run wires from them to the existing +- terminals on the circuit boards fixed to the meters. Would this work for me? Any advice is greatly appreciated and if this could work I will buy a pair of the buffer kits.

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Re: VU BUFFER KIT BUILD THREAD

Postby Joe Malone » Thu Oct 08, 2009 8:06 am

rocksure wrote:I have been building a summing mixer round a pair of old Ward Beck summing amps. I assembled an AC/DC and world transformer kit and it's working great to power up the 25 volts DC I needed. So I have the mixer up and running. I have a couple of old Tascam tape machine VU meters that I want to run straight from the input busses to monitor the input signal. As I am not using the +48 V rail in the AC/DC, could I use this to drive a pair of these VU meters? Also the Tascam VU metes have already got a circuit board on the back of them so I can't put these buffer kits on in the manner you describe...I would have to run wires from them to the existing +- terminals on the circuit boards fixed to the meters. Would this work for me? Any advice is greatly appreciated and if this could work I will buy a pair of the buffer kits.

Yes you could turn the 48v rail down to 24 to 30v for the buffer to run on. If you want to run lamps it might be best to disable the pump charge on the 48v altogether and set 12v etc or what ever voltage the lamps are. But first you would need to be able to get direct to the meter wires if you have no info on the PCB attached to the meter which could be a buffer already. Without seeing photos of the PCB on the back of the meters it is hard to say what it does and if it will work with our buffers. Our buffer just wants to connect straight to the meter movement tags.
Joe :-)

JLM Audio

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rocksure
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Re: VU BUFFER KIT BUILD THREAD

Postby rocksure » Thu Oct 08, 2009 8:17 pm

The circuit board on the back of the VU meters is I think very basic with routing for a peak light and all power and signal wires are attached to it. I don't think it has buffering circuitry and there is certainly no op amp on it. I think they ran on 24v and the bulbs are missing but would have been fuse type 8v bulbs.

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Re: VU BUFFER KIT BUILD THREAD

Postby Joe Malone » Thu Oct 08, 2009 9:24 pm

rocksure wrote:The circuit board on the back of the VU meters is I think very basic with routing for a peak light and all power and signal wires are attached to it. I don't think it has buffering circuitry and there is certainly no op amp on it. I think they ran on 24v and the bulbs are missing but would have been fuse type 8v bulbs.

As long as you can get to the meter movement directly then it will work fine. If the lamps are 8v then 16v would run them in series and run the VU buffers as well.
Joe :-)

JLM Audio

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conleycd
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Re: VU BUFFER KIT BUILD THREAD

Postby conleycd » Wed Dec 02, 2009 3:22 pm

Joe,

Which of your VU's that you are selling will fit in a 1 rack enclosure? Does just the JLM 34mm fit?

Thanks.

CC

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Re: VU BUFFER KIT BUILD THREAD

Postby Joe Malone » Wed Dec 02, 2009 6:23 pm

conleycd wrote:Joe,

Which of your VU's that you are selling will fit in a 1 rack enclosure? Does just the JLM 34mm fit?

Thanks.

CC


Yes only the 34mm one.
Joe :-)

JLM Audio

Capturing Audio without Injury

conleycd
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Re: VU BUFFER KIT BUILD THREAD

Postby conleycd » Sun Dec 27, 2009 4:39 pm

So... potentially silly question... Can (with maybe some modifications) the buffer board be used to drive an LED instead of a VU. Could an LED be installed to show clipping or general signal presence?

Any thoughts on this?

Thanks.

CC

chrisp
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Re: VU BUFFER KIT BUILD THREAD

Postby chrisp » Sun Dec 27, 2009 9:54 pm

In theory, yes, but in practice its probably not necessary. Depends on how you implement the LED drivers. However, there's a few IC LED drivers out there that already buffer the input and have schematics for rectification and VU timing/scaling (all of which is what this circuit does), you probably won't need this as well as the LED driver PCB. Remember that LED arrays can be power hogs, and that a meter can take up as much power as the BA pre itself.

I'm working on a 7 LED peak meter for my super-BAs as we speak! It was 10 LEDs but I'm working to both a power and space budget, and 7 is plenty to show me what's happening. Grab the datasheet on the lm3915 and lm3916 ICs.
Chris P

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I do lots of things. I believe eclectic skills are best.

bassivus
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Re: VU BUFFER KIT BUILD THREAD

Postby bassivus » Fri Jul 02, 2010 2:12 am

Hi,

first I would like to thank you for the nice VU buffer schematics. I saw it searching for something that I could use on home preamp with some old Grundig VU meters from tape machine. I have test build it on the piece of proto board. It works, but since I don't use it on balanced signal I can not adjust it to show useful levels of signal. The VU needle jumps like crazy. Can you give me some hints?

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