VU BUFFER KIT BUILD THREAD

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Joe Malone
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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

bernbrue wrote:Hi Joe,
I've got a few of your vu buffer pcbs stuffed and use them with Sifam R28 VU meters. Since they have built in rectifiers I bypassed the rectifiers on the pcb. Unfortunately I don't get enough gain to set the meters to 0dbu. I tried various resistor value changes but that didn't help. Could you help me to make them work properly?
Regards
Bernd
Should not need any changes to get heaps of gain for Sifam Meters.

1.Bypass rectifier on VU buffer PCB.

2.Attached sifam meter direct to buffer (do NOT use a 3k9 resistor in series with meter as there is a 3k3 one on the buffer PCB already.)

3.Make sure you fitted the trim pot the correct way around for your overlay so clockwise is gain increase (other anti clockwise will be gain increase)

If you still have problems after checking the 3 notes above attach a top and bottom VU Buffer PCB photo and photo of your wiring.
Joe :-)
JLM Audio
Capturing Audio without Injury

bernbrue
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Re: VU BUFFER KIT BUILD THREAD

Post by bernbrue »

Arrrrgh, mea culpa. The board supposed to get 24V from the mixing desk but for some reason there were only 12V that went down to 3V with the buffer connected. With a stable 24V the buffer works as it should with plenty of gain. Thanks a lot for your help.
Regards
Bernd

Pullmanite
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Re: VU BUFFER KIT BUILD THREAD

Post by Pullmanite »

Sorry, folks. Complete noob alert here.

I've wired together a VU kit with JLM's 34mm analog meter here: http://www.jlmaudio.com/shop/index.php? ... oductId=20
I can't seem to get the circuit to work and I'm hoping it's a simple glaring issue.

I wired according to this particular schematic and wondering if it is appropriate for this particular VU meter: Image

Here are a couple pics of my wiring job... shaky old hands make for good vibrato ;) but not for the best soldering.

Image

Image

I'm applying 12V and 100mA. The VU lights up but no needle movement. Audio in is wired as tip/sleeve from a 1/8" TRS.

Thanks for your help.

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Joe Malone
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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

Pullmanite wrote:Sorry, folks. Complete noob alert here.

I've wired together a VU kit with JLM's 34mm analog meter here: http://www.jlmaudio.com/shop/index.php? ... oductId=20
I can't seem to get the circuit to work and I'm hoping it's a simple glaring issue.

I wired according to this particular schematic and wondering if it is appropriate for this particular VU meter: Image

Here are a couple pics of my wiring job... shaky old hands make for good vibrato ;) but not for the best soldering.

Image

Image

I'm applying 12V and 100mA. The VU lights up but no needle movement. Audio in is wired as tip/sleeve from a 1/8" TRS.

Thanks for your help.
You are using 12vdc (not 12vac) and wired the correct way around to the terminals?

Also you have fitted the trim pot the reverse way around so to turn up the gain you will have to turn the trim pot counterclock wise up to 25 turns to increase the meter movement?

Otherwise the build looks correct.
Joe :-)
JLM Audio
Capturing Audio without Injury

Pullmanite
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Re: VU BUFFER KIT BUILD THREAD

Post by Pullmanite »

Yes, applying 12VDC, not AC.

Reversed the trim pot as advised; thank you. That did the trick.

lonesomerobots
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Re: VU BUFFER KIT BUILD THREAD

Post by lonesomerobots »

Hello and thank you in advance for the clarity of answers and schematics in the thread.
I am planning to build a VU meter using your circuit with Sifam Al29 VU meters.
I have already incorporated the diode and resistor modifications of the circuit for the AC meters as well as a DPDT switch and extra trimpot for HI/LOW switching.
I also want to use their lightbox for illumination. I cannot find exact numbers but it seems that the bulbs are 12V 5W festoon incadescents.
I was planning to use a 12V power source. I wanted to ask whether adding the load of the lamps prior to the rest of the circuit will affect the circuit in any way. Also should i consider something in the power source to accomodate these lamps along with the boards? I was thinking of using a 12V power brick and in the circuit i connect each lamp just prior to the diode.
Thank you very much again, this thread helped me immensely with my project.

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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

lonesomerobots wrote:
Mon Jun 29, 2020 7:35 pm
Hello and thank you in advance for the clarity of answers and schematics in the thread.
I am planning to build a VU meter using your circuit with Sifam Al29 VU meters.
I have already incorporated the diode and resistor modifications of the circuit for the AC meters as well as a DPDT switch and extra trimpot for HI/LOW switching.
I also want to use their lightbox for illumination. I cannot find exact numbers but it seems that the bulbs are 12V 5W festoon incadescents.
I was planning to use a 12V power source. I wanted to ask whether adding the load of the lamps prior to the rest of the circuit will affect the circuit in any way. Also should i consider something in the power source to accomodate these lamps along with the boards? I was thinking of using a 12V power brick and in the circuit i connect each lamp just prior to the diode.
Thank you very much again, this thread helped me immensely with my project.
Our exact sifam clones have led backlighting so 680R series resistor on 12v works perfectly
Joe :-)
JLM Audio
Capturing Audio without Injury

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