D.I.Y External VU - clarification needed.

[nightcat23]

This probably has been asked before, but I can't find any hard information on a D.I.Y. project I am wanting to do. I basically want to create an external Analog VU meter for my setup. I'm not looking for something accurate, just a visualization so to speak. Anyways, I'm no electrical engineer but I understand you can't just hook up a VU meter directly to speaker terminals and expect anything to happen. You need a driver board or some kind of electronic components to go between the meter and the output. I have seen a few driver boards on ebay such as these:

https://www.ebay.ca/itm/VU-Meter-Dr...463403?hash=item27fba29f6b:g:iZsAAOSwUuFW2A3B

https://www.ebay.ca/itm/DIY-KIT-Ana...888733?hash=item33d18b231d:g:hbkAAOSwvjdZUPpp

https://www.ebay.ca/itm/1x-NEW-VU-m...254565?hash=item2ca1641fe5:g:eFAAAOSwLqFV77SL

From what I can gather, I need a power supply to power this, as well as the wires to hook it all up. However I have a few questions on other aspects that I cannot figure out.

First of all, how do i know what type of power supply I would need? I figure this runs off dc so would need a transformer.

Second, how can you connect it to the output of the receiver/amp? It looks like these things have common ground, which seems kinda dangerous to hook up to the speaker out. Is there a possibility of hooking it up to a record output via rca? Since that's line level it makes more sense and won't be like the output meters I have on my yamaha amp.

My third and (hopefully) final question is regarding what actual meters I can use. Can re-purpose some vu meters from a tape deck or something, or do I need to purchase the ones that are sold on ebay as a kit? I find those are a little too small and would prefer to salvage some from an old tape deck or something.

Also, I really don't know how those driver boards differ and if one is better than the rest. Probably need to look around for a hobby enclosure box, but can't really do that until I know the size of parts I am working with.

Anyways, hopefully someone can help me out with this.


Thanks

 

[deltalight]

It appears as though the circuit in the 3rd link was resigned to replace the obsolete TA7318P VU Meter driver IC. Since the offered assys are low cost, just buy one, say, the Dual one in the 3rd link. Look at the accompanying schematic which should spell out whether you need a split supply or a single supply. Contact the seller and ask them what supply is needed. You then need to secure two VU meters. Perhaps one of the PC assys will indeed allow a direct connection to the speaker terminals if they allowed for an onboard resistive voltage divider. I see one of those assys has provisions for an LED backlight, nice!

 

[soundmotor]

@nightcat23 of the ones shown, I like the 2nd one. It was designed by the seller and he seems open to queries on how to set it up. However, it is a kit and you must assemble it yourself. Not tough but if you've not soldered onto a PCB before there is a bit of a learning curve. It is made with through-hole components though and those are easier for first timers to assemble if you proceed carefully.

That said, all the boards seem roughly equivalent. The main thing missing from their descriptions is what the uA spec and internal resistance spec the meters need to be? Perhaps it does not matter with the active boards but my thinking is it will be the easiest to get one working correctly if you use the same meter spec the board was designed around. I'd shoot PMs to each of the sellers and see what they say. That answer may legitimately be "Don't worry about it, just make sure both meters are the same. Adjust the trimmers until they read correctly." -

As far as getting it to run properly off the speaker outputs, you will need to make a voltage divider to drop the level to that which the board can receive. This is connected in parallel to the speakers and is essentially invisible to them when in use. You could connect it at your amp or receiver from the same terminals the speakers are powered from -

http://vesselyn.com/c3BlYWtlci10by1saW5lLWxldmVsLWNvbnZlcnRlci1zY2hlbWF0aWM/

 

[TerryS]

Like you, I want a power meter just to watch the needles bounce.
I found that a VU meter is not a good choice for a bouncy power level meter. The problem is the range isn't right. A VU meter only has 23dB of range. They are scaled from -20dB to +3dB. If you look at the meters on amplifiers, they will have a much wider range (like -50dB to +6dB or more). With a VU meter it is very difficult to get it set so the level is in a range that makes the meter do much. It is different when they are used to set record levels (like they are intended to be used) where you actually set the level into the range of the meter.
I am working on a speaker power level meter based on this design:
http://www.tronola.com/Audio_Level_Meter_Article.pdf
I built a stereo version of it, but am not happy with the ranges, so I am working on a modified version with a different meter range. Currently the meter has 3 ranges with VU (-20 to +3) response, and a full log range of -90 to +10dB. But the VU ranges are too small to get much meter activity, and the log range is too wide and not expanded. They just don't have the 'bounce' I'm looking for. I looked at the meters on several amplifiers, and they all have a wider range that is expanded at the top. There doesn't seem to be any standard range, but they are all similar to what is known as the PPM (Peak Programme Meter) standard:
https://www.soundonsound.com/sound-advice/q-whats-difference-between-ppm-and-vu-meters
Here is an old design for a PPM meter. I am working on an upgraded version of it to replace the VU scales on the meter design from tronola.com.

The bottom line is that a VU meter isn't going to bounce like the typical power level meters you see on amplifiers. The range just isn't right.

Now cue the people who will feel compelled to point out that a power level meter doesn't really measure the power

Terry

 

[nightcat23]

It appears as though the circuit in the 3rd link was resigned to replace the obsolete TA7318P VU Meter driver IC. Since the offered assys are low cost, just buy one, say, the Dual one in the 3rd link. Look at the accompanying schematic which should spell out whether you need a split supply or a single supply. Contact the seller and ask them what supply is needed. You then need to secure two VU meters. Perhaps one of the PC assys will indeed allow a direct connection to the speaker terminals if they allowed for an onboard resistive voltage divider. I see one of those assys has provisions for an LED backlight, nice!

I'm not really sure what you mean by onboard resistive voltage divider. is that something I would have to create by myself and connect into the circuit board? Again i'm not an electrical engineer or anything so I am not actually totally sure what you mean. Regarding the power supply, the first one says AC 220 V to AC 9-15 V. So i assume this would mean the whole circuit will be AC powered, or is this simply a typo? Anyways, I am going to ask the seller some questions about this and see if they can help me out. I don't want to end up frying my system or anything.

@nightcat23 of the ones shown, I like the 2nd one. It was designed by the seller and he seems open to queries on how to set it up. However, it is a kit and you must assemble it yourself. Not tough but if you've not soldered onto a PCB before there is a bit of a learning curve. It is made with through-hole components though and those are easier for first timers to assemble if you proceed carefully.

That said, all the boards seem roughly equivalent. The main thing missing from their descriptions is what the uA spec and internal resistance spec the meters need to be? Perhaps it does not matter with the active boards but my thinking is it will be the easiest to get one working correctly if you use the same meter spec the board was designed around. I'd shoot PMs to each of the sellers and see what they say. That answer may legitimately be "Don't worry about it, just make sure both meters are the same. Adjust the trimmers until they read correctly." -

As far as getting it to run properly off the speaker outputs, you will need to make a voltage divider to drop the level to that which the board can receive. This is connected in parallel to the speakers and is essentially invisible to them when in use. You could connect it at your amp or receiver from the same terminals the speakers are powered from -

http://vesselyn.com/c3BlYWtlci10by1saW5lLWxldmVsLWNvbnZlcnRlci1zY2hlbWF0aWM/

soldering isn't too big of a deal but it honestly is just more work than I am willing to go through. I assume the resistance of the meters dictates the sensitivity of the display? I think these all do have trim pots though to adjust. I need a voltage divider if connecting to the speaker inputs? I would really prefer to use RCA as I can get the line-out into it and the meters will be the same regardless of the volume. What is this schematic for that you linked?

 

[soundmotor]

soldering isn't too big of a deal but it honestly is just more work than I am willing to go through. I assume the resistance of the meters dictates the sensitivity of the display? I think these all do have trim pots though to adjust. I need a voltage divider if connecting to the speaker inputs? I would really prefer to use RCA as I can get the line-out into it and the meters will be the same regardless of the volume. What is this schematic for that you linked?

The voltage divider schematic as well as many others are at the link I posted in my reply.

If you aren't connecting to speaker outputs just run source out from your preamp or receiver directly into the VU meter board as shown in your 1st ebay link -

 

[Dingman]

This one is good looking - not very functional but that's not the goal.

 

[ConradH]

All this is way too complicated for me. I just feed the speaker output to a diode or bridge of diodes, then through a pot to the meter. Job done. It's a good idea to have a limit resistor in series so you can't set the pot too high and blow the meter.

 

[nightcat23]

The voltage divider schematic as well as many others are at the link I posted in my reply.

If you aren't connecting to speaker outputs just run source out from your preamp or receiver directly into the VU meter board as shown in your 1st ebay link -

So to get this straight. That schematic is for hooking up to speaker terminals? And if I want to hook it up to rca rec out, I can just cut one end of an audio rca cable off and connect it to those terminals? I assume the middle black one is for ground? Would It be smart to ground this to something? Like something metal? Also, when people refer to "trim pots" to adjust the output to the meters, are those the blue and grey things in the middle of the board? With my basic understanding I think it is just an adjustable resistor?

 

[stoN_Cold]

I am working on a speaker power level meter based on this design:
http://www.tronola.com/Audio_Level_Meter_Article.pdf

Nice.

 

[soundmotor]

So to get this straight. That schematic is for hooking up to speaker terminals? And if I want to hook it up to rca rec out, I can just cut one end of an audio rca cable off and connect it to those terminals? I assume the middle black one is for ground? Would It be smart to ground this to something? Like something metal? Also, when people refer to "trim pots" to adjust the output to the meters, are those the blue and grey things in the middle of the board? With my basic understanding I think it is just an adjustable resistor?

Yes to the first 3, your ground is through the audio ground of your source R & L to the VU board, and yes & yes.

I'd also consider starting your electronics ref library w/ this, there is a whole series and they are very useful -

 

[nightcat23]

Yes to the first 3, your ground is through the audio ground of your source R & L to the VU board, and yes & yes.

I'd also consider starting your electronics ref library w/ this, there is a whole series and they are very useful -

Interesting, thanks for the book suggestion. It would be nice to be able to understand some of this stuff myself haha. And by audio ground of source, do you mean like connect it to the phono ground? I do have a turntable hooked up though which might change things.

 

[soundmotor]

Interesting, thanks for the book suggestion. It would be nice to be able to understand some of this stuff myself haha. And by audio ground of source, do you mean like connect it to the phono ground? I do have a turntable hooked up though which might change things.

No, the RCA shield is ground. (I reference that book series all the time, good stuff.)