8 channel rack mount VU meter bridge

[JeromeMason]

Does anyone know if there is a board or a schematic or, a kit for something like this? I'd like to have an 8 channel vu meter bridge I could rack mount over my summing mixer to see the levels going in. SM Audio makes one that is what I'm looking for, but I'm not so keen on trusting the quality of that company, especially since I've spent a lot of money on signal path and conversion. I would hate for a meter bridge to degrade my signal, but I trust the quality of what folks around here design.

What would be involved in making something like this?

Thanks!

 

[qmp audio]

some good reading here... Mr. Steiger's approach to this.

http://groupdiy.com/index.php?topic=45103.0

 

[JeromeMason]

some good reading here... Mr. Steiger's approach to this.

http://groupdiy.com/index.php?topic=45103.0

Yeah that's pretty cool...... but I'd really like to not go the 500 route, It would be nice to just but a simple cheap enclosure, decent meters, with a pure signal path in and out.

 

[sahib]

I have Sifam meters (mint condition) complete with driver circuitry mounted at the back. Bezels and mounting studs also included. All you have to do is to cut the case, stick them in and off you go. If interested PM me your e-mail for photographs.

 

[Rochey]

I have a board ready to go with a single channel with an SMD LED array for this exact purpose... It's in prototype, and simply needs motivation to get it finished. (I already have basic code working on a larger eval kit)

Picture should attach. wish me luck as I hit post.

 

[JohnRoberts]

I have been designing meters for decades and while old school mechanical VU meters have a certain legacy look, they are worthless IMO for managing peaks and headroom. They are also not easy to compare relative levels across any number of them  in a recording environment.

Of course the customer is always right so I offered a mechanical VU meter bridge option in my bigger consoles but my long time favorite a LED meter in a simple vertical array. I liked to simultaneously display peak and VU (peak as a dot floating above a VU bar). and even with tens of them in a row it is easy to scan across all of them to check for head room and relative loudness.

There are a bunch of different meter kits out there.

JR

@ Rochey, if I were you I'd tweak the software to deliver peak and VU... (my patent for this expired a long time ago so it is public domain and free to use. )

 

[JeromeMason]

I have been designing meters for decades and while old school mechanical VU meters have a certain legacy look, they are worthless IMO for managing peaks and headroom. They are also not easy to compare relative levels across any number of them  in a recording environment.

Of course the customer is always right so I offered a mechanical VU meter bridge option in my bigger consoles but my long time favorite a LED meter in a simple vertical array. I liked to simultaneously display peak and VU (peak as a dot floating above a VU bar). and even with tens of them in a row it is easy to scan across all of them to check for head room and relative loudness.

There are a bunch of different meter kits out there.

JR

@ Rochey, if I were you I'd tweak the software to deliver peak and VU... (my patent for this expired a long time ago so it is public domain and free to use. )

John,

I'd really like an 8-10 channel meter section that will go into a single 1u 19 rack. I'd like to be able to monitor the input going into the inputs on my summing mixer, and then the other two meters to monitor the output of the summing mixer. If I wanted to build this could you recommend a simple PCB for each meter? I want something that doesn't compromise my input and output signal in anyway.

I could buy a blank 1u case and just customize it for all my meters. Also, could I go external for the PSU instead of onboard so I wouldn't have to worry about any interference from onboard PSU? Seems like it could be done for a pretty good price to rival some really expensive designs and I could pick whatever meters I want.

Any help would really be appreciated.

Thanks!!

 

[bruce0]

The best way to minimize effects on the signal is to have a high impedance meter interface, and balanced impedance to ground (maintain CMRR of balanced signals).

I just got delivery of some meter cards.  Each set is a pair of small PCB's that mate together, and will fit in a 1u case vertically (8 pairs of them would fit no problem.).

One board is a board that holds 8 led's and 2 LM339 comparators and a resistor network to set the indicator levels (so you can do any scale you want.)

The other is a board that has a balanced line receiver circuit (with precisely balanced input impedance based upon figure 4 in this article http://waltjung.org/PDFs/Op_Amps_in_Line_Driver_and_Receiver_Circuits_P2.pdf) it can run at very high impedance. 

Board 2 has adjustable meter dynamics (you can set the rise time and fall time separately).  This works for both mechanical meters or LED arrays, so you can make them act like VU or PPM (if the mechanical meter is fast enough).  This works surprisingly well making cheap meters like the ones in the SM Audio unit)

Board 2 can drive board 1, or it can drive an actual meter.

Board 2 can support an LED peak/clip indicator, and has clip hold functionality/reset funtionality.

The boards can be daisy chained using ribon cable for power, voltage reference, clip reset/hold, so they would be easy to wire up.

This is the second revision of the cards, just got them the other day so they are untested as yet.

You could make better version of the SM Audio unit with 8 board 2's, and some of the meters they use (ebay $7.50 in small volume). That plus  some TL074's and a few transistors and caps.

 

[JeromeMason]

Could I use something like this??

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=190&added=1

 

[pucho812]

paul wolf and tonelux make a meter bridge, dsub connections.

 

[bruce0]

Yes.  I have used them in a project, and I have tested them.

I think not evenly balanced impedance to ground or very high impedance for that matter (I think 25K like the SM-Audio).  But they work fine. Take a balanced input, and response to both positive and negative peaks (minus a bat85 diode drop I think). You can trim the amp on the board.  It is fine for driving cheap meters.

However meter dynamics (rising and falling) are not separately adjustable (just a cap across the meter to damp it) and there is no peak indicator or peak hold capability. 

Here is a very simplistic writeup of the JLM meter buffer and meter buffer's in general.  Schematic is shown.http://www.audiotechnology.com.au/PDF/TUTORIALS/AT51_DIY_VU.pdf

I do need someone to test the new board revision, are you going to build this soon?  Do you have a meter you want to use?

 

[JeromeMason]

Yes.  I have used them in a project, and I have tested them.

They are not precisely balanced impedance to ground or very high impedance (I think 25K like the SM-Audio).  They work fine. It takes a balanced input, and response to both positive and negative peaks (minus a bat85 diode drop I think). You can trim the amp on the board.  It is fine for driving cheap meters.

However meter dynamics (rising and falling) are not separately adjustable - just a cap across the meter, and there is no peak indicator or peak hold capability). 

Here is a very simplistic writeup of the JLM meter buffer and meter buffer's in general.  Schematic is shown.http://www.audiotechnology.com.au/PDF/TUTORIALS/AT51_DIY_VU.pdf

I do need someone to test the new board revision, are you going to build this soon?  Do you have a meter you want to use?

Sure, I can test an 8045 VU Meter from hairball that I have. Just need a bom and a board.

 

[bruce0]

PM me and I will drop one in the mail.

Bom varies, and is smaller if you just want meters and no peak hold.

 

[JeromeMason]

PM me and I will drop one in the mail.

Bom varies, and is smaller if you just want meters and no peak hold.

I really don't have any use for the peak hold. I just want VU's on my inputs and a stereo Pair on my final output.

 

[bruce0]

PM me and I will drop one in the mail.

Bom varies, and is smaller if you just want meters and no peak hold.

I really don't have any use for the peak hold. I just want VU's on my inputs and a stereo Pair on my final output.

Schematic Attached.  BOM to follow (one file per post limit).
bb

 

[bruce0]

BOM

No peak hold
Meter dynamics adjusted with R6 and R7, see note in BOM
(Note I specify a couple of wire jumpers to keep the unused amp happy.)

+/-15V works fine allows you to meter up to +22dB approx.  Single supply should work too but you will need a single supply quad amp.

Let me know if you need help, will mail you the card tomorrow.

bb

\

 

[JohnRoberts]

Could I use something like this??

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=190&added=1

That looks like the electronics to drive a mechanical meter... standard VU meters won't fit in 1U.

I am not a fan of horizontal LED meters, while you could squeeze some closely spaced vertical LED meters in a 1U chassis.

You don't need peak? Are you recording to digital?

JR

 

[bruce0]

I think the OP wants to build something like this

Maybe using those little Taiwan Nissei meters you can get on ebay or from hairball/jlm etc.

http://www.ebay.com/itm/2pcs-VU-Panel-Meter-500-A-Warm-Back-Light-LED-Recording-Audio-Level-Amp-35x35mm-/251288477282?pt=LH_DefaultDomain_0&hash=item3a81f5de62

 

[JeromeMason]

Could I use something like this??

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=190&added=1

That looks like the electronics to drive a mechanical meter... standard VU meters won't fit in 1U.

I am not a fan of horizontal LED meters, while you could squeeze some closely spaced vertical LED meters in a 1U chassis.

You don't need peak? Are you recording to digital?

JR

Yeah that's exactly what I want to build, I've already got one of those meters here, the LED inside is burnt out, but it's functional for testing. But what I want to build is exactly what bruce posted, with those small VU's. It's tight, but they'll work, all I should need is the buffer circuit and a blank case with 8 of those meters and I'll be in business. Ideally, Id love to have 10, so I could see my final output, but i'll just have to build myself a set of larger meters that are separate for that. Unless I could find like a mini stereo pair of VU meters, I havn't searched, they just about anything these days.

 

[bruce0]

They are 35 mm wide  10 should fit