8ch 1U VU meter rack?!? Difficult to build?

Hi All,

Ive really been interested in an 8ch VU meter rack. I found one manufactured in Japan, but its over $2k. Is there really that much to it?

The link to the one Ive seen is here:

http://www.crnt.co.jp/en/csp158a.html

Is there anyone who could put 1 (or 3) together cheaper?

Any tips or places in the USA that Im just out aware of?  The only other one Ive seen is from SM Pro Audio and goes for  $300. Looking for something more like the Japanese design.

Have a look for "meter bridge" on eBay.
There's often loads from old consoles.
e.g
http://www.ebay.co.uk/itm/Crest-Audio-VU-Meter-Bridge-for-X-VCA-Mixing-Console-/171302914622?hash=item27e2730a3e:g:VHIAAOxyBvZTTwn9

You may want to build a buffer circuit for interfacing  Vu's to your outputs tho as they will add  distortion if connected directly.

+1 To Clunk's advice re: distortion. It tends to be high order, odd harmonic and quite ugly.  Also, note that some of the schemes to rectify the signal can be very crude, giving a highly non-linear response (I once built a circuit used by a fairly respected console oem, with the same meter they used, and found 10dB = 20dB). Breadboard the circuit first if you go the diy option. All drivers are not the same.

I'm very interested in this as i want to build a meter bridge for my line mixer. So i will need 8 vu meter buffers as well. Anyone suggest any? I know jlm has them. Is there a cheaper solution for those of us stateside?
Are those Chinese vu meter buffers on ebay decent? I'm thinking an external 1u or 2u that sits on top of a 3u mixer. Maybe connected via dsub.

Rod Elliot has a page on buffers http://sound.westhost.com/project55.htm

http://diy-tubes.com/vu-buffer-diy-kit.html

3 or more $8.00

Rocinante said:

I'm very interested in this as i want to build a meter bridge for my line mixer. So i will need 8 vu meter buffers as well. Anyone suggest any? I know jlm has them. Is there a cheaper solution for those of us stateside?
Are those Chinese vu meter buffers on ebay decent? I'm thinking an external 1u or 2u that sits on top of a 3u mixer. Maybe connected via dsub.

Click to expand...

Hello,

I have tried the Chinese VU buffers and was not impressed. I found mine acted very weirdly.

I've been following your Neve summing mixer build thread.

I noticed you are designing your own backpane. Why not include your own VU buffers into the backpane PCB circuit? You could use 2 TL074 IC's(total of 8 opamps) as the buffers, you already have the power source ready to go(provided its -+18v or lower, I don't think you mentioned it, or maybe I missed it).

Something to consider if you are going to the efforts to create the backpane.

Thanks for the links fellas.  Of course diy tubes has some.

Too late as the backplane arrived yesterday but its a good idea. I was gonna have the vu meters in a seperate enclosure but i also see no reason why the buffers need ti be next to the vu meters anyway.  Something to keep in mind. 

thermionic said:

It tends to be high order, odd harmonic and quite ugly. 

Click to expand...

I have a few old Akai M9 Vu meters on the way and I am going to be running a test on how noisy they are in use with no buffers. If the noise is actually that bad I may be hopping on the buffer train. The output impedence seems to play a critical role on the noise added by the Vu meter. The style of Vu meter seems to also matter.
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This thread has some good info:
http://groupdiy.com/index.php?topic=2763.0

If you have transformers on your outputs here's a simple buffer scheme. [Just the circuit on top]
It's a mod for Ampex MM1200 VUs.

The transistors listed are obsolete but they're nothing special.
One day i'll make  some smt boards to fix straight on the back of our MM1200 VUs.
Never made an smt pcb before, so will be fun!

What about the simple solutions:

http://www.banggood.com/AC-12V-Stereo-VU-Meter-Driver-Board-Amplifier-DB-Audio-Level-Input-Backlit-p-1045528.html

and

http://www.banggood.com/2pcs-500VU-Panel-VU-Meter-Audio-Level-Meter-6-12V-Audio-Level-with-Warm-BackLight-p-1014725.html


or:

http://www.banggood.com/2Pcs-VU-Meter-Warm-Back-Light-Recording-Audio-Level-Amp-With-Driver-Board-p-1031012.html

Jakob E.
(no, I don't get commision  - I'm just impressed about chinese pricing..)

How are those cheap Chinese VU meters? Anyone tried the actual meters?  I wouldn't expect too much in terms of accuracy but it could be cool in terms of visual aesthetics.

They're decent enough, I think class 2.5 or better - and specially the small version movements has ballistics in the right range (when comparing to e.g. Sifam AL-29).

Nowadays, very few engineers depends on precision and exact ballistics of analogue meter movements, so I wouldn't shy away from these for precision reasons..

Jakob E.

buildafriend said:

The output impedence seems to play a critical role on the noise added by the Vu meter.

Click to expand...

Indeed; it is directly related. Distortion introduced by VU-meters is due to non-linear loading. The higher the source impedance, the higher the effects of load non-linearity. [/quote] The style of Vu meter seems to also matter.
[/quote] What do you mean by "style"? There are some meters that are not really VU-meters; a real VU-meter is supposed to have definite electrical characteristics. In particular they are designed to present an effective impedance of 7.5k when fed with a +4dBu signal, including a built-in 3.9k series resistor. The historic rectifier was a metal-oxide trype, which has been replaced with Ge diodes first, but I suspect now they are replaced with Si diodes that have sharper characteristics and may introduce harsher distortion.
The nominal sensitivity of the galvanometer movement is 200uA, but I know some cheap meters have movements of up to 1mA; they introduce about 5 times more distortion than a true VU-meter.

abbey road d enfer said:

The historic rectifier was a metal-oxide type, which has been replaced with Ge diodes first, but I suspect now they are replaced with Si diodes that have sharper characteristics and may introduce harsher distortion.

Click to expand...

Quick question here, not to derail the topic, are those copper(?)-oxide rectifiers still available in any shape or form? I do remember back then, that they were the way to go for low forward voltage loss, and a really soft, minimal-distortion-producing knee in the transition curve. And often found driving audio meters with no buffer. The Simpson 260 analogue meter used something like this for the AC volt ranges, because of the very low forward voltage loss.

Gene

It seems the low-power metal rectifier manufacturing is definitely extinct. There seems to be some current manufacturing of low-voltage high-current metal rectifiers for electroplating and aluminium production.

> are those copper(?)-oxide rectifiers still available in any shape or form?

200 pound racks for, as Abbey says, electroplating and other extreme low-V high-I work.

Yes, I've looked for copper-oxide rectifiers and found them virtually impossible to source.  Best bet seems to be robbing from an old meter with a dead movement, unfortunately. 

A thought I have is to use the meters out of a junker 8-track like a Teac 80-8/Tascam 38, they look small enough for a 1U rack, but glancing online it looks like the prices of those machines are going back up (!).

PRR said:

> are those copper(?)-oxide rectifiers still available in any shape or form?

200 pound racks for, as Abbey says, electroplating and other extreme low-V high-I work.

Click to expand...

I suppose even those are replaced by Schottky rectifiers or mosfets used as synchronous rectifiers thesedays.

I can't imagine a copper-oxide rectifier used for anything other than a True Museum Piece, or to measure its characteristics to be reproduced with "modern" parts such as 1N4148s, already-mention TL074s and a few passive parts. Without too much work, you can buffer the meter from the signal source AND get the Official VU Response you want.

Wasn't there some recent thread where someone was doing this with an 8-bit microcontroller? (probably driving LEDs and not a physical meter movement, but it's pretty much the same) With an ARM Cortex M (and a Small Amount Of of Programming) you can surely do 8 channels at once and have a bunch of different switchable meter responses.