VU2 stereo VU buffer kit Build thread

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Joe Malone
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Re: VU2 stereo VU buffer kit Build thread

Post by Joe Malone »

Supablake wrote:
Wed May 26, 2021 5:55 am
Hi,

I’ve just finished the assembly of the VU2 kit,
Meter lights work, meters move very slightly on turn on,
But,
No response to input signal.
I’m using balanced inputs driven for testing with a Neutrik Minirator.

+4 DB gives nothing, I’ve adjusted the trim pots and still nothing.

Any suggestions on where to start trouble shooting?

Also what sort of voltage would I expect to measure from the meter outputs ?

Thanks,

Blake
What meters are you using with the VU2 kit?
Do you have diodes fitted to the VU2 or not?

Send me some photos of the VU2 top and bottom and wiring to the meters and 12v power to check for you.
Joe :-)
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Supablake
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Re: VU2 stereo VU buffer kit Build thread

Post by Supablake »

Not sure of the Meter Brand. eBay from China.

I have not added any diodes to the meter or between the meter and the VU2.

The meters have functioned with a couple of other brands of driver board,

But the Boards were unbalanced and introduced hum into the system.

The VU2 is powered from a regulated 12v board,
The lamps in the meters light up fine with the bypass resistor. They came supplied with their own to put in parallel with the meter lights.

I have several other meters I’ll try out.
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Supablake
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Re: VU2 stereo VU buffer kit Build thread

Post by Supablake »

Please disregard my posts.

User error.

I hadn’t adjusted the pots far enough.

I put a multimeter set to Mv and quickly saw that I just needed to keep turning the pots to get the readings I was looking for.

Thanks again!

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Re: VU2 stereo VU buffer kit Build thread

Post by Joe Malone »

Supablake wrote:
Thu May 27, 2021 7:42 am
Please disregard my posts.

User error.

I hadn’t adjusted the pots far enough.

I put a multimeter set to Mv and quickly saw that I just needed to keep turning the pots to get the readings I was looking for.

Thanks again!
Cool great to hear you got it working. Yes the 25 turn trim pots need lots of turns as they control a large gain range so it will work in any setup.
Joe :-)
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kmf123kmf
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Re: VU2 stereo VU buffer kit Build thread

Post by kmf123kmf »

Just got mine assembled and am having an issue. Possible user error as I didn't notice that R2R and R2L weren't installed before powering up. Both meter outputs showed around 0.2 DC volts regardless of input. Once I did notice the missing resistors and installed them, not much changed. Meter output voltage dropped in half is still basically invariable to input. I'm pretty sure I've turned the POTs enough and even tried replacing R7 with a lower value.

Did I damage the opamp or is there some other basic debug I should start with?

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Re: VU2 stereo VU buffer kit Build thread

Post by Joe Malone »

kmf123kmf wrote:
Wed Nov 24, 2021 1:06 am
Just got mine assembled and am having an issue. Possible user error as I didn't notice that R2R and R2L weren't installed before powering up. Both meter outputs showed around 0.2 DC volts regardless of input. Once I did notice the missing resistors and installed them, not much changed. Meter output voltage dropped in half is still basically invariable to input. I'm pretty sure I've turned the POTs enough and even tried replacing R7 with a lower value.

Did I damage the opamp or is there some other basic debug I should start with?
The buffer outputs have a cap so no dc can make it to the meter. Leaving those resistors out will not damage anything. Best first to send me some photos of the wiring and setup you have so I can see if I can spot the problem. Otherwise, as always top and bottom photos of the pcb helps to check for problems as well.
Joe :-)
JLM Audio
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kmf123kmf
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Re: VU2 stereo VU buffer kit Build thread

Post by kmf123kmf »

Joe Malone wrote:
Wed Nov 24, 2021 9:34 am
The buffer outputs have a cap so no dc can make it to the meter. Leaving those resistors out will not damage anything. Best first to send me some photos of the wiring and setup you have so I can see if I can spot the problem. Otherwise, as always top and bottom photos of the pcb helps to check for problems as well.
Top Side. Not using lamp power, so no RLAMP resistors.
Image

Bottom Side
Image

XLR's tied together on PCB. (Blue goes to red, white to white, sleeve to sleeve)
Image

Input end. Looks messy, but verified conductors are not shorted.
Image

Feeding -12/+12 from the aux of my SMPS
Image

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Re: VU2 stereo VU buffer kit Build thread

Post by Joe Malone »

kmf123kmf wrote:
Wed Nov 24, 2021 1:45 pm
Joe Malone wrote:
Wed Nov 24, 2021 9:34 am
The buffer outputs have a cap so no dc can make it to the meter. Leaving those resistors out will not damage anything. Best first to send me some photos of the wiring and setup you have so I can see if I can spot the problem. Otherwise, as always top and bottom photos of the pcb helps to check for problems as well.
Looks fine. Not sure if that 24v is tied to the same 0v as the power amp voltage. You should be able to measure the ohms across the gain pot on the buffer with the buffer off. Takes 25 full turns end to end.

What meters are you running as they may have an internal resistor and/or diode bridge?
Joe :-)
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kmf123kmf
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Re: VU2 stereo VU buffer kit Build thread

Post by kmf123kmf »

Joe Malone wrote:
Thu Nov 25, 2021 2:27 pm

Looks fine. Not sure if that 24v is tied to the same 0v as the power amp voltage. You should be able to measure the ohms across the gain pot on the buffer with the buffer off. Takes 25 full turns end to end.

What meters are you running as they may have an internal resistor and/or diode bridge?
I measured the pots and they are fully open, close to 0 ohms. I'm using some eBay Chinese 34mm round vu meters. I'm pretty sure these are all functionally the same?

I checked the other components on the board and they all seem to measure fine.

Please forgive my limited electronics knowledge, but at suggestion of Google I put the TL072 on a breadboard and put it in voltage follower mode. With VCC+ 12v and VCC- to ground I'm getting +12v output whether the non-inverting input is either 12v or ground. Is that the expected behavior? Is behaves the same on both sides of the IC.

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