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 »

bassivus wrote: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?
The circuit works perfect for balanced and unbalanced signal and has enough gain range for even the lowest level signals. Make sure you feed the unbalanced signal into the +/- in and if runing on a floating power supply sometimes you may need to join -in to 0v. Remember a lot of cheap meters need a extra damping 100uF across there terminals.
Joe :-)
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bassivus
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Re: VU BUFFER KIT BUILD THREAD

Post by bassivus »

Thanks for the answer Joe!!! I'll try that when I find some time.

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Re: VU BUFFER KIT BUILD THREAD

Post by bassivus »

Still not working properly... this tells my story: http://www.youtube.com/watch?v=eKmfK9CEvKw

mylesgm
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Re: VU BUFFER KIT BUILD THREAD

Post by mylesgm »

Hi Joe,

What about a peak light? can that be added to this circuit?

M

kato
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Re: VU BUFFER KIT BUILD THREAD

Post by kato »

Bassivus, this may be an obvious suggestion, and pardon me if it is - but did you try adjusting the trim pot to a lower setting. It seems like you're maxing out your meter with an already hot, line-level signal, and then boosting it the buffer circuit. Or maybe the other way round - I just watched your video again and it looks like (hard to tell) the low level is at the right side of the meter and peak is at the left? Backwards from standard. Also, are you sure your meter doesn't already have rectifier diodes? You may be doubling that stage first on the PCB, then again in the VU meter. I'm not sure what effect this would have on a VU in real life, so I'm just throwing it out there.

Joe, I notice the values of R14, and R15 are changed from 3k3 in the original PDF to 47k in your redrawn schematic. Is this a mistake, or a purposeful design improvement?

I'm just wondering because I have enough extra 3k3 resistors to build it either way. I assume either will work - I'm just wondering about the advantages / disadvantages either way. Thanks for any guidance, Kato

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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

bassivus wrote:Still not working properly... this tells my story: http://www.youtube.com/watch?v=eKmfK9CEvKw
Video doesn't really tell me anything except that meter is way to fast and will need a 100uF cap across its meter terminals to make it more like a VU 300mS Attack and release.

If you reverse the meter wires do you get no meter movement?
Joe :-)
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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

mylesgm wrote:Hi Joe,

What about a peak light? can that be added to this circuit?

M
Yes but depends on the meter sensitivity.

1. Wire a 3 or 5mm led directly across the VU buffer meter terminals (long leg to +) and setting the Vu buffer trim pot so the peak led just lights up at the peak level you want.

2. Then add a trim pot in series with one of the wires going to the VU meter so its level can be then set to the needed 0VU level.

This led will have no attack and release slopes so may seem to flicker more then work as a normal peak led.

I may look at doing a small pcb with a real peak led circuit on it as well as the vu buffer circuit if there is enough interest.
Joe :-)
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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

kato wrote:Bassivus, this may be an obvious suggestion, and pardon me if it is - but did you try adjusting the trim pot to a lower setting. It seems like you're maxing out your meter with an already hot, line-level signal, and then boosting it the buffer circuit. Or maybe the other way round - I just watched your video again and it looks like (hard to tell) the low level is at the right side of the meter and peak is at the left? Backwards from standard. Also, are you sure your meter doesn't already have rectifier diodes? You may be doubling that stage first on the PCB, then again in the VU meter. I'm not sure what effect this would have on a VU in real life, so I'm just throwing it out there.

Joe, I notice the values of R14, and R15 are changed from 3k3 in the original PDF to 47k in your redrawn schematic. Is this a mistake, or a purposeful design improvement?

I'm just wondering because I have enough extra 3k3 resistors to build it either way. I assume either will work - I'm just wondering about the advantages / disadvantages either way. Thanks for any guidance, Kato
This is just to show that as long as the half voltage rail divider resistors R14 and R15 are the same value any value from 3k3 to 47k will work in there.
Joe :-)
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bassivus
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Re: VU BUFFER KIT BUILD THREAD

Post by bassivus »

kato wrote:Bassivus, this may be an obvious suggestion, and pardon me if it is - but did you try adjusting the trim pot to a lower setting. It seems like you're maxing out your meter with an already hot, line-level signal, and then boosting it the buffer circuit. Or maybe the other way round - I just watched your video again and it looks like (hard to tell) the low level is at the right side of the meter and peak is at the left? Backwards from standard. Also, are you sure your meter doesn't already have rectifier diodes? You may be doubling that stage first on the PCB, then again in the VU meter. I'm not sure what effect this would have on a VU in real life, so I'm just throwing it out there.

Joe, I notice the values of R14, and R15 are changed from 3k3 in the original PDF to 47k in your redrawn schematic. Is this a mistake, or a purposeful design improvement?

I'm just wondering because I have enough extra 3k3 resistors to build it either way. I assume either will work - I'm just wondering about the advantages / disadvantages either way. Thanks for any guidance, Kato
kato,

Thanks for getting into my problem. Of course I have tried all sorts of adjustments - trimming, adding the cap and also adding more resistance in various points... nothing helped. On my video VU meter is showing low level on right which is actually the bottom cause the VU is built vertically not horizontally. It does not have built in diodes and is the DC type

bassivus
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Re: VU BUFFER KIT BUILD THREAD

Post by bassivus »

Joe Malone wrote:
bassivus wrote:Still not working properly... this tells my story: http://www.youtube.com/watch?v=eKmfK9CEvKw
Video doesn't really tell me anything except that meter is way to fast and will need a 100uF cap across its meter terminals to make it more like a VU 300mS Attack and release.

If you reverse the meter wires do you get no meter movement?
Joe,

If you look the video again, I'm sure you can notice that nothing shows on the VU for first 7 seconds, even if the music/signal is fairly strong. The effect is like there is some strong threshold filter not letting anything under 40dB level to show. It is the same when I add cap - only slower... When I reverse the wires VU hits the bottom.

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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

bassivus wrote:
Joe Malone wrote:
bassivus wrote:Still not working properly... this tells my story: http://www.youtube.com/watch?v=eKmfK9CEvKw
Video doesn't really tell me anything except that meter is way to fast and will need a 100uF cap across its meter terminals to make it more like a VU 300mS Attack and release.

If you reverse the meter wires do you get no meter movement?
Joe,

If you look the video again, I'm sure you can notice that nothing shows on the VU for first 7 seconds, even if the music/signal is fairly strong. The effect is like there is some strong threshold filter not letting anything under 40dB level to show. It is the same when I add cap - only slower... When I reverse the wires VU hits the bottom.
There is definitely a mistake then in your veroboard circuit layout. As this is just a wide gain range amp with output rectifier and should have no time constant or threshold component to it except for power on settling which is almost instant with the 10uF cap values.

Maybe a VU buffer PCB would save you a lot of fault finding time. :wink:
Joe :-)
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bassivus
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Re: VU BUFFER KIT BUILD THREAD

Post by bassivus »

Joe Malone wrote:
There is definitely a mistake then in your veroboard circuit layout. As this is just a wide gain range amp with output rectifier and should have no time constant or threshold component to it except for power on settling which is almost instant with the 10uF cap values.

Maybe a VU buffer PCB would save you a lot of fault finding time. :wink:
Yes, you are probably right :D That was my first thought but I got confused when I got same result on both of my boards. I'm just afraid that the cause of problem is in the VU meters themselves...

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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

bassivus wrote:
Joe Malone wrote:
There is definitely a mistake then in your veroboard circuit layout. As this is just a wide gain range amp with output rectifier and should have no time constant or threshold component to it except for power on settling which is almost instant with the 10uF cap values.

Maybe a VU buffer PCB would save you a lot of fault finding time. :wink:
Yes, you are probably right :D That was my first thought but I got confused when I got same result on both of my boards. I'm just afraid that the cause of problem is in the VU meters themselves...
Have you got a large macro on well lit in focus photo of the top and bottom of the vero build as I may be able to spot the problem if it is neatly laid out. I do not think it is the meters.

Send them to my email address and I will have a look at them for you.
Joe :-)
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conleycd
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Re: VU BUFFER KIT BUILD THREAD

Post by conleycd »

Ok... a bit of an unusual question. Can I use this as a full or half-wave rectifier, buffer/gain for the front end of a LED VU meter? Would I just take the outputs from the meter output into the LED VU meter (either based on a typical LM339 or LM3916 circuit)?

Thanks.

CC

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Re: VU BUFFER KIT BUILD THREAD

Post by Joe Malone »

conleycd wrote:Ok... a bit of an unusual question. Can I use this as a full or half-wave rectifier, buffer/gain for the front end of a LED VU meter? Would I just take the outputs from the meter output into the LED VU meter (either based on a typical LM339 or LM3916 circuit)?

Thanks.

CC
The rectifying circuit on the VU buffer is a bridge made out of 2 diodes and 2 3k3 resitors and isn't ideally suited to interfacing to opamp input unless it is balanced. If it is balanced the meter output wires can go straight to the +/-in but you will need to add a 220uF to 330uF cap across the +/-in to get the correct attack and release for VU.
Joe :-)
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