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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 6:59 am
by srgny
A few really dumb questions:
To Setup VU Buffer and Peak LED pcb.
1. Connect dc power you are using. VU buffer and peak led can run on +12 to +36vdc @ 30mA so main current draw will usually be the VU meter light.

I am using 12 volts-seems to work fine.

2. Send 1kHz tone in at the reference level you want for the VU meter like +4dBM for example.

Exactly what reference level do I want? What should a +4dBM signal show on a VU meter? Supposing I choose +4dBM, how will I know the signal is +4dBM? What's a dBM anyway?? What is +4dBM equal to in VU (if anything)?

3. Adjust Trimpot marked VU for correct 0VU level for your system.

What level of 0VU do I want? On my current system, 0VU is fairly loud, generally louder than I play the system.

4. Send 1kHz tone in at the reference level you want for the Peak LED meter like +18dBM for example.

Same question: how do I know the signal is +18dBM? I have no specialized equipment.

5. Then adjust trimpot marked LED until the LED just lights.

The LED is supposed to light at the highest level or just at the peak of any interval?

Note to set high peak levels than +18dBM or +18dBu a power rail of more than +12vdc will be needed.[/b][/u]

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 12:17 pm
by Joe Malone
srgny wrote:A few really dumb questions:
To Setup VU Buffer and Peak LED pcb.
1. Connect dc power you are using. VU buffer and peak led can run on +12 to +36vdc @ 30mA so main current draw will usually be the VU meter light.

I am using 12 volts-seems to work fine.

2. Send 1kHz tone in at the reference level you want for the VU meter like +4dBM for example.

Exactly what reference level do I want? What should a +4dBM signal show on a VU meter? Supposing I choose +4dBM, how will I know the signal is +4dBM? What's a dBM anyway?? What is +4dBM equal to in VU (if anything)?
In most systems +4dBM shows = 0VU on the meter = 1.23v rms on a multimeter. But any level is correct if it works you in your system.
3. Adjust Trimpot marked VU for correct 0VU level for your system.

What level of 0VU do I want? On my current system, 0VU is fairly loud, generally louder than I play the system.
VU meters are usually running before any output volume control so they stay calabrated no matter what level you are listening too.
4. Send 1kHz tone in at the reference level you want for the Peak LED meter like +18dBM for example.

Same question: how do I know the signal is +18dBM? I have no specialized equipment.
Turn up your A/D or D/A until either the digital screen meter shows clip and then turn back so clip just turns off and cal peak led to come on then. To reach +18dBM you will need to run the buffer on higher voltage like 24vdc. What /D/A or A/D are you using and when level do they clip out? Spec page in the A/DD/A manual will tell you this. As I have idea what you are trying to use the meter for?
5. Then adjust trimpot marked LED until the LED just lights.

The LED is supposed to light at the highest level or just at the peak of any interval?

Note to set high peak levels than +18dBM or +18dBu a power rail of more than +12vdc will be needed.[/b][/u]
The led will light above the level you set.

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 2:13 pm
by srgny
Thanks for your replies.
I think this is all a little beyond me. Basically, I use the VUs for their look as they remind me of older, simpler times.
I have the VU meters connected to the outputs of my amplifiers. Turning up the volume on the amp causes more deflection in the VU meters.
How do I measure 1.23v rms on a multimeter? As I said, I have a simple multimeter, but nothing more sophisticated. I don't think my multimeter will measure rms.
I don't have a dedicated A/D or D/A unit. I am running simple 4-20 watt amps with inputs from my computer, radio or iPod. Clipping is not generally a problem as I don't turn the volume up that far.

On another front, I find that if I turn off the power to the VU meter after adjusting the "VU pot", when I turn it back on, it needs to be readjusted to show deflection. Any reason for this?

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 2:25 pm
by Joe Malone
srgny wrote:Thanks for your replies.
I think this is all a little beyond me. Basically, I use the VUs for their look as they remind me of older, simpler times.
I have the VU meters connected to the outputs of my amplifiers. Turning up the volume on the amp causes more deflection in the VU meters.
How do I measure 1.23v rms on a multimeter? As I said, I have a simple multimeter, but nothing more sophisticated. I don't think my multimeter will measure rms.
I don't have a dedicated A/D or D/A unit. I am running simple 4-20 watt amps with inputs from my computer, radio or iPod. Clipping is not generally a problem as I don't turn the volume up that far.

On another front, I find that if I turn off the power to the VU meter after adjusting the "VU pot", when I turn it back on, it needs to be readjusted to show deflection. Any reason for this?
Does you amp have a preamp output or tape out on it as these are before the volume output ?

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 2:29 pm
by srgny
No, no output before the mains (very simple home made amps).

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 2:36 pm
by Joe Malone
srgny wrote:No, no output before the mains (very simple home made amps).
OK since they are home made if you could get to the wire going into the volume pot this would be the ideal for the VU meters. The +in would connect to the top of the pot and the -in to the 0v fully off side of the pot. Do you have a schematic of the amp at all?

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 2:57 pm
by srgny
amp-sch.jpg
What about the change in gain with power off?

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 4:20 pm
by Joe Malone
srgny wrote:amp-sch.jpg
What about the change in gain with power off?
Not sure as I am not sure how you have wired it to the amp output so may have gain trimpot fully turned up.

Best is to wire it across the input to the amp.
+in to 2 and -in & 0v to 1 on each amp input that way it can be set and meters will be aligned always

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 8:39 pm
by srgny
Hooking the VU directly to the amp input (iPod output, for example) causes no deflection in the meter needle. "VU pot" turned all the way clockwise.

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 8:45 pm
by Joe Malone
srgny wrote:Hooking the VU directly to the amp input (iPod output, for example) causes no deflection in the meter needle. "VU pot" turned all the way clockwise.
With the ipod running half to full output there should be heaps of gain in the buffer. Need to see wiring and pcb build as something is not right. What meters are you using with the buffer? Photos would help.

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 8:53 pm
by srgny
You're right. Turning up the iPod volume causes the VU to work.

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 9:15 pm
by Joe Malone
srgny wrote:You're right. Turning up the iPod volume causes the VU to work.
Can you get the meter to 0VU with the ipod playing?

What power supply does the amp run on?

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 9:20 pm
by srgny
With iPod at maximal volume, VU registers about 3 to 2. !2volt power to VU buffer.

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 9:26 pm
by Joe Malone
srgny wrote:With iPod at maximal volume, VU registers about 3 to 2. !2volt power to VU buffer.
Do you have the input to the buffer wired so -in and 0v wire together and to 0v ground on input of amp?

+2 or +3dB in the red section?

If your amplifier runs on a 24v to 36v power supply it could run the buffer as well with the meter lamps in series with resistor so you wouldn't need the 12vdc supply.

Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Posted: Mon Sep 17, 2018 9:37 pm
by srgny
No, it measures 3 to 2 in the black region. I have the yellow wire hooked up to power supply ground. Black is hooked up to input - and red is hooked up to input +.
Amplifier runs on 12 volts. Separate supply from VU.