Simpson VU Ballistics Variation

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MrG

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Hey All,

I recently purchased an amazing set of vintage Simpson extra large VUs (I believe called Wide-Vue), and I hooked them up to a VU box that I bought from someone who modeled it from the SSL 9k desk circuit. Looking at it, I believe it's +/- 15v. Everything seems healthy within the VU buffer circuit and the previous meters that were hooked up to that seemed fairly symmetrical/matched.

My question is, these meters seem to track differently - perhaps one of them is moving a bit more freely than the other - and I'm just not seeing something that looks like a correlated stereo program from the meters. Now admittedly, I am not well-versed in the theory here, however, I'm wondering if these are actual real VU meters, and thus they are showing a very intricate amount of organic differences between the channels, or if by chance one of them is broken or needs some adjustment.

When I run a 1k tone at +4dbm to them they align nicely, and similarly at other frequencies and levels. It's more the ballistic travel that seems sort of dull on one of them. Not dramatically but it's visible.

I did have to adjust the zero rest position on one of them when they arrived to me, as one needle was at like -20, and the other was bottomed out entirely. But after the adjustment to the front zero screw, they are lining up fine.

Thanks in advance for any insights!

Best,
MG
 

DaftFader

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Typically, 'dc' meter movements are magnetically damped so are slower than those used in proper VU meters , they will both correctly read 1mA but as you've noticed the ballistics will be completely wrong . I have a couple of 'vu' meters here with the same problem , someone has replaced the movement.
 
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MrG

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Typically, 'dc' meter movements are magnetically damped so are slower than those used in proper VU meters , then wil both correctly read 1mA but as you've noticed the ballistics will be completely wrong . I have a couple of 'vu' meters here with the same problem , someone has replaced the movement.
Thanks for this. So are you saying that perhaps between these two meters, someone modified the electronics of one of them?

I’ve read other threads here about determining if a meter is AC or DC, but I need to revisit to see the most direct test. Do you happen to have a solid method you use?

The meters looked really solid and untouched, so this is a bit of a bummer if they can’t be used.

Best,
MG
 

JohnRoberts

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True VU meters expect a specific drive circuit to deliver specified meter movement ballistics. Drive circuits for "looks like a VU meter" may behave differently driving true VU meters.

For the record, I do not find any extra value in slow responding mechanical meters. Back when mechanical meter were the only option, tightly controlled ballistics was useful. Now they serve mainly as eye candy.

Of course opinions vary. YMMV

JR
 

MrG

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True VU meters expect a specific drive circuit to deliver specified meter movement ballistics. Drive circuits for "looks like a VU meter" may behave differently driving true VU meters.

For the record, I do not find any extra value in slow responding mechanical meters. Back when mechanical meter were the only option, tightly controlled ballistics was useful. Now they serve mainly as eye candy.

Of course opinions vary. YMMV

JR
Thanks for this, John. I do hear you and I’ve read your opinions, which I appreciate. Just for clarity I use many precise meters in mixing and mastering, and these are to serve a specific purpose.

Regarding the circuit, this was built by someone I don’t know personally, but it looks quite robust and perhaps overbuilt. I’m not capable of tracing the circuit and diagraming it, but would it be helpful in determining somewhat if I uploaded a quality photo?

With that said, is there an agreed upon schematic for a true VU drive circuit? Lastly, just noting that whatever’s going on seems to only be affecting one of the two meters. The one meter seems to be snappy and responsive from very low to very high levels, where as the other seems sort of doped in the highest and lowest regions.

Best,
 

DaftFader

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True VU meters expect a specific drive circuit to deliver specified meter movement ballistics. Drive circuits for "looks like a VU meter" may behave differently driving true VU meters.


VU meters are very simple they only require a resister (to give 0dBvu @ 0.775vrms =1mAfsd) in series with the source (you may be thinking of PPMs )
 

JohnRoberts

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wiki said:
The original VU meter is a passive electromechanical device, namely a 200 µA DC d'Arsonval movement ammeter fed from a full-wave copper-oxide rectifier mounted within the meter case. The mass of the needle causes a relatively slow response, which in effect integrates or smooths the signal, with a rise time of 300 ms.
The true VU meter was designed to interface with a 600 ohm network.

Since the customer is always right, I offered mechanical VU meters in large consoles last century. I did not use "true VU" meters because I'm cheap and so were my customers. I used simple op amp drivers.

JR
 

MrG

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VU meters are very simple they only require a resister (to give 0dBvu @ 0.775vrms =1mAfsd) in series with the source (you may be thinking of PPMs )
Interesting. The guy I bought these from was a console tech I believe, and proud of his efforts in creating the SSL 9k VU meter circuit.

Just to clarify, are you all saying that if these are true VUs (I think these old Simpson’s typically are yes?) then I literally only need some resistors in place to have them fully functioning? I am running a powered circuit which I saw has opamps, so I’m beginning to think I’m running a PPM circuit without knowing it, unless I’m mistaken.

I have another mastering friend who runs true VUs, and I always thought I just didn’t see his PSU, but now I’m thinking I wasn’t realizing he didn’t need one.

Please forgive my lack of knowledge and thank you all for enlightening me.

Thanks!
Mark
 

MrG

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To add to that and cut to the chase, I’m wanting 0dBVU to be calibratable, so I can make -7dbm (I think m, maybe u?) at 0 VU. Would I use a potentiometer? Any specifics would be really appreciated.

Thanks all!
Mark
 

DaftFader

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As correctly quoted by John above (my memory is erm, well I've forgotten exactly what it is but , definitely not what it used to be) the VU movement requires 200uA fsd which would be 1v (0.775 =0vu) so a 5kohm series resister (commonly 4k7) was used .

You could probably get away with a lower value resistance (or a pot) to get your -7dB to 0vu . There's a slight danger that the meter is designed to expect a certain source impedance so reducing it may change the ballistics slightly (but then again they're only bloody waggling needles so why worry :cool:)

Suck it and see. If the meters don't seem to 'fit' the music , try finding an amplified source (headphone output?) and use a 5k resistor

For what it's worth, my good friend Pete Reynolds (mastering - look him up , hundreds of discs to his credit) swears by his VU box (that I made for him) , says it give a far better idea of visual level than any of the (many) digital meters he has (including the one I made).
 

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MrG

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As correctly quoted by John above (my memory is erm, well I've forgotten exactly what it is but , definitely not what it used to be) the VU movement requires 200uA fsd which would be 1v (0.775 =0vu) so a 5kohm series resister (commonly 4k7) was used .

You could probably get away with a lower value resistance (or a pot) to get your -7dB to 0vu . There's a slight danger that the meter is designed to expect a certain source impedance so reducing it may change the ballistics slightly (but then again they're only bloody waggling needles so why worry :cool:)

Suck it and see. If the meters don't seem to 'fit' the music , try finding an amplified source (headphone output?) and use a 5k resistor

For what it's worth, my good friend Pete Reynolds (mastering - look him up , hundreds of discs to his credit) swears by his VU box (that I made for him) , says it give a far better idea of visual level than any of the (many) digital meters he has (including the one I made).
Thanks so much for this - and that's exactly what I think regarding mastering. Awesome to hear you did that work for him!

So did you do it in the way we're talking here if you don't mind me asking? Completely passive with a 4k7 resistor?

Also one more question - if it's in series, does that mean it only has to be in series on one leg of the VU? Or do I need a resistor or a potentiometer on either leg?

Best,
MG
 

MrG

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Thank you so much DaftFader! That is very cool and generous of you.

Good news! I wired my line out directly to a 10k potentiometer dialed to 4k7 and into the VU and it tracked really beautifully. I haven't compared the two, but I don't know why they would track differently if calibrated similarly.

Is it possible/likely to have two meters of the same brand broken or dissimilar in function, or was that likely the fault of the way I was hooking a VU meter up through all of those excess electronics do you think?

The box with the meters is attached - super simple which I love.

Best,
MG
 

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emrr

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A Weston is the only 'true' to spec VU meter. Many other old ones are very close. Two of the same type should track the same. Many have oxidation on internal mechanical parts, even if NOS, which acts like a brake shoe creating drag, changing the ballistics. Many have bad sections of the internal diode bridge and may read low.
 

MrG

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A Weston is the only 'true' to spec VU meter. Many other old ones are very close. Two of the same type should track the same. Many have oxidation on internal mechanical parts, even if NOS, which acts like a brake shoe creating drag, changing the ballistics. Many have bad sections of the internal diode bridge and may read low.
Thanks, Doug! Just for my understanding, you do feel that what I posted a picture of is an actual VU meter (can work via this resistor-only method), it's just not true to definitive spec?

And thanks for those notes. I plan to mount the jacks and trim pots on this box and if these don't track well maybe I can find replacements later. I doubt the kind of things you mentioned can be repaired easily or at all, yes?
 

emrr

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Sure, a Simpson is an obvious old school VU, more VU than a Sifam VU. It's stuff like TEAC and Yamaha meters that really aren't VU's.
 

MrG

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Sure, a Simpson is an obvious old school VU, more VU than a Sifam VU. It's stuff like TEAC and Yamaha meters that really aren't VU's.

Ah, ok I see what you're meaning. Thanks again and sorry for being pedantic!

Best,
MG
 

DaftFader

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Is it possible/likely to have two meters of the same brand broken or dissimilar in function, or was that likely the fault of the way I was hooking a VU meter up through all of those excess electronics do you think?
As I alluded to above:

What can happen is (and I have examples here) ; the meter breaks (needle falling off is common) , user seeks new meter is shocked that it cost so much , and while browsing notices he can buy a 200uA meter of the same size and shape for a third of the price : "Aha I'm being ripped off" so proceeds to buy dc movement and transplant it into a VU ; It sets-up just fine and measures levels OK , but does not track , because the "dc" movements are different , they are damped (usually by shorted turn in the magnetic field )

Back in the early days of electronically transmitted sound (aka Radio) it became essentially to get the modulation level correct (or at least consistent) . Various solutions were devised , 'magic-eye' valves etc. The simplest was a sensitive dc (moving coil) meter with a full wave rectifier . It later acquired a logarythmic 'Bel' scale (divided by ten to give a more sensible deci-bel or dB scale) so the Volume Unit meter was born . The VU 'spec' was created from these early meters to give some level of standardisation.

Later , broadcasters (BBC?) developed a meter that better fitted the need of the transmitter that was quasi-peak reading ( with a completely stupid scale on the BBC one ) called a PPM - peak programme meter. (Aha , of course there's a wiki page - Peak programme meter - Wikipedia)

If a meter meets the specification it IS a VU meter but, as suggested above, many (most?) that are marked 'VU' simply do not meet the spec. (I remember being puzzled by my Nakamichi TT1000 until I found that the meters were actually peak reading - in fairness ,if I'd have looked close enough , it did say so on the meter :))
 

MrG

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As I alluded to above:

What can happen is (and I have examples here) ; the meter breaks (needle falling off is common) , user seeks new meter is shocked that it cost so much , and while browsing notices he can buy a 200uA meter of the same size and shape for a third of the price : "Aha I'm being ripped off" so proceeds to buy dc movement and transplant it into a VU ; It sets-up just fine and measures levels OK , but does not track , because the "dc" movements are different , they are damped (usually by shorted turn in the magnetic field )

Back in the early days of electronically transmitted sound (aka Radio) it became essentially to get the modulation level correct (or at least consistent) . Various solutions were devised , 'magic-eye' valves etc. The simplest was a sensitive dc (moving coil) meter with a full wave rectifier . It later acquired a logarythmic 'Bel' scale (divided by ten to give a more sensible deci-bel or dB scale) so the Volume Unit meter was born . The VU 'spec' was created from these early meters to give some level of standardisation.

Later , broadcasters (BBC?) developed a meter that better fitted the need of the transmitter that was quasi-peak reading ( with a completely stupid scale on the BBC one ) called a PPM - peak programme meter. (Aha , of course there's a wiki page - Peak programme meter - Wikipedia)

If a meter meets the specification it IS a VU meter but, as suggested above, many (most?) that are marked 'VU' simply do not meet the spec. (I remember being puzzled by my Nakamichi TT1000 until I found that the meters were actually peak reading - in fairness ,if I'd have looked close enough , it did say so on the meter :))
That’s all very interesting - thank you again! So when did the switch from DC to AC meter occur then - when it switched to logarithmic behavior?

Update: I wired both with a potentiometer at a 4k7 value and they’re tracking beautifully and matched. It seems to me that they’re functioning extremely well, with no signs of damage or aging. The previous supply must have been providing slightly different voltages or resistances across the different channels I guess?

I’m thinking I may switch from a potentiometer to a resistor network switch to give more precision, but this seems to be case closed. Thank you all very much!

Best,
Mark
 
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