VU BUFFER & PEAK LED KIT BUILD THREAD

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by Joe Malone »

bigboy wrote:
Sun Sep 19, 2021 12:44 am
I think the issue is I am sharing the power supply from the amplifier to power the buffer but don’t fully understand the wiring needed. I use a dc-dc buck converter to reduce the +35v amplifier rail to 12v which powers the buffer. I connect the amplifier input audio rca V+ to the V+ Of the buffer board and the rca V- to the V- of the buffer board. The 0v on the buffer is not connected to anything. Is this the correct wiring ? A sketch would help greatly.

Richard
Do you mean +in and -in for audio in ? As +V is power in? Best to attach some photos of the pcb buffer wiring to see if I can see the problem. As long as 0v from power supply is linked to the shield of the input it should be ok. The unused -in should also be wired to 0v.
Joe :-)
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bigboy
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by bigboy »

Hi Joe

Omg, I have spent 3 days trying to sort this out. One buffer board has fried an opamp, 2 1uf caps and a diode. I decided to desolder the lot and rebuild it and it seemed to fix the issue.... it seemed. Then the same meter stopped working all of a sudden. It turned out to be the solder connection at the rca input at the back of the amp. Joys of a hobbyist builder. Anyway it's working now, both VU meters are responding. Sorry to be a serial pest.

I ordered a prebuilt meter prior to finding the poor solder joint about 2 hrs ago. I don't suppose you could provide a refund as I won't need it anymore.

Regards

Richard

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by bigboy »

The saga continues :)

Fired up the amplifier this morning and there is no response from either VU meter. I must be wiring something incorrectly. I have attached my wiring diagram. Its as though the meters need to be "charged" or "awakened" some how. Any suggestions on the wiring appreciated.
Amp.png
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by Joe Malone »

bigboy wrote:
Thu Sep 23, 2021 12:32 pm
The saga continues :)

Fired up the amplifier this morning and there is no response from either VU meter. I must be wiring something incorrectly. I have attached my wiring diagram. Its as though the meters need to be "charged" or "awakened" some how. Any suggestions on the wiring appreciated.
Amp.png
From your diagram, you have the 12v dc going directly to the meter terminals which will kill the meters and buffer instantly if the meters are wired there as well???

You do not show any vu meter wiring at all?

Also the green and black wires are reversed on the input wiring.
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Joe :-)
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bigboy
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by bigboy »

Sorry, I have the 12V wired to the VU globe and not the meters, sketch was wrong.

So based on your sketch I just need to swap the black and green around ? I thought I had already tried that but I will give it a go and report back.

Final wiring as attached.
vu.png
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by bigboy »

Ok

Rewired as above

Adjusted meters and they do work...... but

After turning the amp off and on again they only way I can get them going again is to quickly wake them up by turning the volume up to almost 100% for a brief moment ? Progress I guess.

Richard

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by Joe Malone »

bigboy wrote:
Fri Sep 24, 2021 7:33 pm
Ok

Rewired as above

Adjusted meters and they do work...... but

After turning the amp off and on again they only way I can get them going again is to quickly wake them up by turning the volume up to almost 100% for a brief moment ? Progress I guess.

Richard
Have you checked the 12v voltages. What does it read on a dc volts meter?
Check to see how many ac millivolts noise it has on it if an 12v SMPS?
In an amp setup normally I would run from the output of the amp so buffer uses a lot less gain.
The buffer can actually run directly from the 35v rail also. The 12v could be used for the lamps only.
Best to attach actual photos of the buffer and wiring and top and bottom pcb photos so I can check them.
Maybe worth trying another TL072 encase this one has been damaged.
Joe :-)
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erhard58
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by erhard58 »

Hi,

I am using a TN-73-HS-9213H VU meter.
Measured internal DC resistance is 50 OHMS on a digital meter. It has no diodes or resistor inside.
Using +4dBm, which I equate to 1.0024V PP, I only get a max deflection between 3 and 2 on the VU meter.
Any advise would be appreciated, thank you.

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by Joe Malone »

erhard58 wrote:
Thu Oct 26, 2023 2:50 am
Hi,

I am using a TN-73-HS-9213H VU meter.
Measured internal DC resistance is 50 OHMS on a digital meter. It has no diodes or resistor inside.
Using +4dBm, which I equate to 1.0024V PP, I only get a max deflection between 3 and 2 on the VU meter.
Any advise would be appreciated, thank you.
Wow that resistance is very low for a meter. Can you cal +4dBu = +4dBm = (1.23vac RMS on multimeter) to correct 0VU?
and then if you put in +7dBu does the meter show +3 ?

If not let me know as the output 3k3 ressitor on the buffer will have to be made smaller in value.
Joe :-)
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erhard58
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by erhard58 »

thanks for the quick reply.
I think the confusion here is what is +4dBu/dBm in PP volts. I thought it was 1.0024VPP, but looking at it again it is 3.743VPP, is that the correct value, in that case, I should be able to calibrate 0dBVU at that signal level.
I will not be able to check that until later today.

erhard58
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by erhard58 »

so the saga continues!
This has been very frustrating.
In order to have more VU calibration, I changed the output buffer resistors, R11 & R12 from 3K3 to 1K, this has 'increased' the calibration sensitivity.
Now, this is the problem I am still facing.
I turn the VU driver on, calibrate it and the peak LED, no issues. I turn the VU driver off, then a short while later, turn it back on, no VU movement.
Nothing was changed during the off period.
The ONLY way I can get the VU meter to work again is to turn the level adjust trimmer right back, then turn it up again to its previous calibrated level. It almost seems like I have to 'kick start' the VU driver in order to make it work after power off.
This happens every time. Once I have the VU meter working again, I turn it off, then on again and nothing. I have to turn the level adjust trimmer down quite a way before the VU meter starts working again.
If I remove the signal source and back no issues, VU meter works. Only when I power it off, do I have to adjust the level trimmer down and then back up again.
I have tried different VU meters, same issue.
Would really appreciate to have this resolved, thank you.

erhard58
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by erhard58 »

further to my recent post, I tried the VU2 driver in the same preamp, I do not have the same issue as with the VU buffer & peak LED. I am wondering if it has something do to with the peak led driver section?

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by Joe Malone »

erhard58 wrote:
Fri Nov 17, 2023 4:58 am
so the saga continues!
This has been very frustrating.
In order to have more VU calibration, I changed the output buffer resistors, R11 & R12 from 3K3 to 1K, this has 'increased' the calibration sensitivity.
Now, this is the problem I am still facing.
I turn the VU driver on, calibrate it and the peak LED, no issues. I turn the VU driver off, then a short while later, turn it back on, no VU movement.
Nothing was changed during the off period.
The ONLY way I can get the VU meter to work again is to turn the level adjust trimmer right back, then turn it up again to its previous calibrated level. It almost seems like I have to 'kick start' the VU driver in order to make it work after power off.
This happens every time. Once I have the VU meter working again, I turn it off, then on again and nothing. I have to turn the level adjust trimmer down quite a way before the VU meter starts working again.
If I remove the signal source and back no issues, VU meter works. Only when I power it off, do I have to adjust the level trimmer down and then back up again.
I have tried different VU meters, same issue.
Would really appreciate to have this resolved, thank you.
If you are using lots of gain pot and lowering the output resistor you can end up with oscillation between the input and output of the circuit or latch-up of the TL072. It will depend on the wiring and power supply used and the TL072. Power up would be the time the circuit would trigger into latch-up or oscillation. Definitely swap the TL072 if you have any other from another kit encase it is damaged.

Basically, if you have to lower the output resistor and use full gain then something is wrong or the meter is too insensitive to be treated as a real VU meter. The circuit is designed to be used with the values stated on the PCB and with sensitive meters like 200uA to 500uA like VU meters. Modding outside of this is not for me to resolve. But if you give me clear info I can certainly try to help.

What power rail is the buffer running on? Volts & Amps?
Is it SMPS? Is the power supply running anything else?
Input reference level to the buffer? Balanced or unbalanced? If unbalanced have you tied -in to 0v?
What are the meter specs for the meters you have tried?
Is it wired in with other audio gear etc in the same case?
If so how are the power supplies wired? Photos are best for this.
Joe :-)
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by Joe Malone »

erhard58 wrote:
Fri Nov 17, 2023 7:07 am
further to my recent post, I tried the VU2 driver in the same preamp, I do not have the same issue as with the VU buffer & peak LED. I am wondering if it has something do to with the peak led driver section?
The buffer section is the same with a slightly different output bridge arrangement. The peak section should not do anything except draw more continuous current from the power supply. Answer the questions in the previous post as without real info it is hard workout why you need to mod and use so much gainpot
Joe :-)
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erhard58
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Post by erhard58 »

thank you for your quick reply, I appreciate it.
In this post, you mentioned that the 3K3 buffer resistor may need to be lowered, dated October 26, so I just started to experiment with a value and see what happens.
It was doing the same, ie no VU meter movement after power down and power up again with no resistor value changes, so lowering it to 1K, as far as I can see, has no effect on what it is doing when powered down and back up again.

I am using a TN-73-HS-9213H VU meter.
Measured internal DC resistance is 50 OHMS on a digital meter. It has no diodes or resistor inside.
Using +4dBm, I only get a max deflection between 3 and 2 on the VU meter.
Any advise would be appreciated, thank you.

Wow that resistance is very low for a meter. Can you cal +4dBu = +4dBm = (1.23vac RMS on multimeter) to correct 0VU?
and then if you put in +7dBu does the meter show +3 ?

If not let me know as the output 3k3 ressitor on the buffer will have to be made smaller in value.


To answer your question as follows:

What power rail is the buffer running on? Volts & Amps? 12VDC @ 1.5A
Is it SMPS? Is the power supply running anything else? It uses a 7812 regulator, well filtered and running nothing else, ie a dedicated VU driver power supply
Input reference level to the buffer? Balanced or unbalanced? If unbalanced have you tied -in to 0v? unbalanced and yes, I tried -in to 0V
What are the meter specs for the meters you have tried? see above
Is it wired in with other audio gear etc in the same case? The output of the preamp circuit goes to an EQ, then the output of the EQ goes to the VU driver input as well as to the main output of the preamp for external connections
If so how are the power supplies wired? Photos are best for this.

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