1176 VU Meter Substitution Question

[Echo North]

Hi,

Novice to intermediate user here and I apologize if this has been covered.

I starting the process of collecting info/parts to build the Gyraf 1776 using the mnats boards. I know that standard VU meter of choice is the Sifam AL29WF. I have several (6) VU meters from a yamaha pm-1000 board sitting around (pictured below). They are labeled "Hiaki R-55" and the meter is almost identical in dimension to the AL29.

Obviously it mounts a little different and will have the extra plastic exposed below the meter...however, is this an ok substitute for the AL29? Would there be any problems with using this meter? Or should I just shell out the $ for the AL29 and avoid potential headaches. Keep in mind I know NOTHING about VU meters.

Thanks!

Mike

 

[Arrigotti]

That meter is probably fine.

To test it, you could run .775 volts through it and see if the needle swings to 0.

 

[keefaz]

Or run an audio output through it with a 3.9k resistor in serie

 

[Bluzzi]

Mike, that meter is fine. I used old Simpson VU meters on my 2 LA2As and they work great.

Don't worry about a thing.

jim

 

[Echo North]

Thanks for the replies! I do have a question about checking the meters.

Keep in mind this is my first time with VU's so sorry if this ends up being a stupid question.

I want to check to see if the .775 volts would generate a "0". Not having an Oscillator I decided to use "Tone Generator" inside of protools. So I set it to a 1000hz RMS sine wave at 0db and it went off the chart (above +3db).

The output I was using was a +4db output, is that adding 4db's to the .775 sine wave?

I had to set it to 1000hz at -20db to get the meeter to "0".

Does this make sense? I am only using the top terminals on the meeter.

Thanks again,

Mike

 

[Echo North]

Just an update on this.

I attached a multimeter (very cheap crappy one) to the protools output with the settings 1khz RMS 0 db. This was showing an AC voltage of 1.5v. I'm assuming something is getting messed up int the D/A converter.

My terrible multimeter only shows AC voltage to one decimal point so I lowered the db's on my tone generator until I got .7v. This still peaked the VU meter.

When I lowered the db's to about -22db I got the VU meter at 0 and the multimeter showed .5v AC.

Should I just assume this is fine and blame it on a cheap multimeter not even designed to show AC current this low?

Thanks again,

Mike

 

[Arrigotti]

You're just fine with that meter. The 1176 has a Zero Adjust, so you can fine tune the meter at the end anyway.

Start reading up on your build. Read through MNATS webpage a few times, and print out the wiring guide, put it in a folder, and have it handy as you are wiring it up.

Also, the info on the gyraf.dk site is very helpful when wiring things up, and cross-referencing part placements.

I love the 1176 project. I've built 5 myself.

 

[Echo North]

Will do!

Thanks again for the help guys!

Mike

 

[skipwave]

Regarding the test signal coming from ProTools: That actually sounds correct. 0dbVU should be down around -18 to -20dbFS. Two different scales that overlap at a point determined by the manufacturer, and there has been a lot of discussion around here about folks recording too hot signals to their DAWs, because they don't realize this or because the damn manufacturers recommend recording as close to 0dbFS as possible.

Just thought I would offer that. Hope it's helpful.

 

[Bryson]

As long as it looks good: that's all a GR meter is for anyway.

 

[3nity]

Guys do you know if we need to change any resistors for this Vu meter to work fine in here?

Thanks.

 

[SSLtech]

IF that ProTools test was performed with NO 3.6kΩ-3.9kΩ resistor in series, then it would peg/over-read quite seriously.

Also your voltmeter may not be reading true RMS... cheap ones are more likely to be a little bit 'approximate' in that regard, but it shouldn't be colossally wrong.

Keith

 

[Echo North]

3nity,

Are you talking about the PM1000 VU you got from me?

The test I preformed above did NOT have a resistor in series.

I have like 7 PM1000 meters from 2 different units. I've done a newer test (since the protools test) with a signal generator and a Fluke TRUE RMS meter.

All of them showed +2 (or so) VU at .775v RMS.

Any thoughts Keith? Here is an image:

Seems like the meter "0" on the G1176 should easily make up for this. Mine swings my SIFAM VU from peg to peg.

Mike

 

[3nity]

mine goes to 3dB!!!

 

[SSLtech]

Well, it's a rectifying meter -which is good- and it seems to have a little excess deflection -which is much easier to fix than not enough deflection. :wink:

I say just throw a little resistance in there until 0.775V reads 0VU. -Best set it with a potentiometer/variable resistance, then read the resistance and go with the nearest E12/E24 standard value.

Try a 0-5kΩ pot or trimpot and let everyone know what value seems to be needed.

Keith

 

[Echo North]

Unfortunately, I do not have a reasonable valued pot laying around.

Fortunately, I have a ton of 1% tolerance resistors and patience.

1K got it a hair below 0.

910 or 820 ohms should be spot on...although to meters 0 adjust should make any of them fine.

Thanks again Keith!

Mike

 

[SSLtech]

[quote author="Echo North"]...although to meters 0 adjust should make any of them fine.[/quote]
Whoah there... hold on a minute...

That screw is NOT there to adjust zero VU... It's there to adjust "minus-infinity VU". -If you turn it so that the leedle moves 5° clockwise to sit at 0VU with the right signal present, then it will read as if it sees a small signal when there is silence.

It is the REST POSITION ADJUSTMENT and nothing else. -You always adjust it BEFORE setting the zero VU position.

If you need to furkle with a resistance somewhere between 910 and 1000 ohms, try the 1000 ohms with a 3.3kΩ resistor in parallel... or a 2kΩ. -Now large steps in resistance produce very small overall parallel resistance changes, and therefore allow for VERY fine tuning... even with 20% resistors!

But make sure that you understand that rest-position adjustment screw.... it sounds like you might not.

Keith

Keith

 

[3nity]

1K sine wave goes to +4db.......if i engage the pad i reach 10db????
I dont know...

 

[Echo North]

[quote author="SSLtech"]But make sure that you understand that rest-position adjustment screw.... it sounds like you might not.[/quote]

I think I do now. Thanks Keith!

Luckily I did not touch the screw.

3nity do you mean the 10db pad pushes it -10db on the meter?

Mike

 

[3nity]

yes!

Does a 1k sine wave means .775V?
if so the meter goes past the +3dB.
If i do the pad -30dB on the generator needle goes to -10dB.??

Thanks.

edited: the 1K didnt do nothing at all!??