Ad VU meter api 312
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Rybow
Well-known member
When I did mine I used the 34mm VU meter and VU buffer kits from JLM audio. Easy peasy lemon squeezy.
djmiggymigz
Well-known member
we're back!! I Love reactivating old threads lol.
Working on the same thing here. Just want to confirm, are the 2 unused output transformer leads (Vio/Gry) what would be routed to the VU meter inputs? I'm currently looking at the JLM 34mm VU as well as their buffer circuit.
Working on the same thing here. Just want to confirm, are the 2 unused output transformer leads (Vio/Gry) what would be routed to the VU meter inputs? I'm currently looking at the JLM 34mm VU as well as their buffer circuit.
Walrus
Well-known member
Yes, you can use that spare winding, but as the transformer is a 1:1:1:1 ratio and you are joining 2 of the windings in series for the output (1:2 step up),
the spare Violet Gray winding will only show half the level of the actual output.
I've not looked, can the JLM buffer board be adjusted enough to correct for this?
the spare Violet Gray winding will only show half the level of the actual output.
I've not looked, can the JLM buffer board be adjusted enough to correct for this?
djmiggymigz
Well-known member
Hmm okay cool Yeah I'll look into that and see. I'm not sure if the buffer is just isolating the power supply to the VU or if its actually adding some gain as well. There is a TL072 in the circuit so maybe that's configured to amplify the input signal?
You don't need a vu buffer amp. API consoles did not have vu buffer amps, and neither did most consoles pre 1980, and at least half of 1980 to 1985 consoles still had no vu buffer amps.
A true vu meter will read 0vu when driven by a +4db signal through a 3.6kohm resistor. The 3.6kohm resistor buffers the signal just enough that few will notice the tiny added distortion and actually distortion from a vu meter fed by 3.6kohm resistor makes for better sound for all forms of rock and pop music but probably not legit traditional classical or jazz. It may be that the improvement in sound will only happen if the signal path is Output tyranny>>3.6kohm resistor>>vu meter. Historically the move away from true vu meters to toy meters driven by buffer (beginning around 1980) probably contributed to the apparent thinning sound (as compared to vintage gear) but it was often experienced cuz a lot of vintage consoles built correctly were still in use. As the SSL and Neve V series pushed a lot of or most of the vintage consoles out of top rated studios the sound of pop and rock music thinned out across the board and yet there were still some fat sounding recordings for various reasons such as tracked at a "B" studio that had a vintage console even though mixed at an "A" studio on SSL console.
Even though with some difficulty one can find cheap (made in china) vu meters that require the 3.6kohm resistor they may still be toys in that they will not have correct ballistics...typically the needle response will be too fast, and so distortion signature might not be the right flavor.
I'm just guessing...but if you look at this recording session (look at the gear, use of protocols) I suspect a lack of vu meter distortion....so sad in a way...japanese rockers wowed by Ed Sheeran's succe$$ (even though different genre) and they ended up with a sound of only average excitement and only faux angst compared to, from similar genre, "In the End" by Linkin' Park.
"In the end" was recorded at NRG studios in North Hollywood, Ca, circa 2000. I think they had a Neve console.
A true vu meter will read 0vu when driven by a +4db signal through a 3.6kohm resistor. The 3.6kohm resistor buffers the signal just enough that few will notice the tiny added distortion and actually distortion from a vu meter fed by 3.6kohm resistor makes for better sound for all forms of rock and pop music but probably not legit traditional classical or jazz. It may be that the improvement in sound will only happen if the signal path is Output tyranny>>3.6kohm resistor>>vu meter. Historically the move away from true vu meters to toy meters driven by buffer (beginning around 1980) probably contributed to the apparent thinning sound (as compared to vintage gear) but it was often experienced cuz a lot of vintage consoles built correctly were still in use. As the SSL and Neve V series pushed a lot of or most of the vintage consoles out of top rated studios the sound of pop and rock music thinned out across the board and yet there were still some fat sounding recordings for various reasons such as tracked at a "B" studio that had a vintage console even though mixed at an "A" studio on SSL console.
Even though with some difficulty one can find cheap (made in china) vu meters that require the 3.6kohm resistor they may still be toys in that they will not have correct ballistics...typically the needle response will be too fast, and so distortion signature might not be the right flavor.
I'm just guessing...but if you look at this recording session (look at the gear, use of protocols) I suspect a lack of vu meter distortion....so sad in a way...japanese rockers wowed by Ed Sheeran's succe$$ (even though different genre) and they ended up with a sound of only average excitement and only faux angst compared to, from similar genre, "In the End" by Linkin' Park.
"In the end" was recorded at NRG studios in North Hollywood, Ca, circa 2000. I think they had a Neve console.
djmiggymigz
Well-known member
Hmmm interesting!! How does the VU meter affect the sound of the pre? For example, where my current design/pcb layout is at, the vio/gry output tx leads are just unconnected. So how would the sound of the pre vary between that and having those leads connected to a good VU/a cheap VU??
Edit: Re-reading your post, so the VU meter itself adds some level of distortion that also makes it to the output of the preamp via the output transformer? Is the function of the VU buffer to fully isolate it then so that none of that distortion is present at the output? I suppose that could be a fun thing to experiment with! Could potentially be cool to figure out how to get some medium-heavy-ish distortion out of the VU and then have a switch to swap between the buffer/clean and no buffer/dirty! (Tho that may be too much to even fit in a 500 series build!!)
Edit: Re-reading your post, so the VU meter itself adds some level of distortion that also makes it to the output of the preamp via the output transformer? Is the function of the VU buffer to fully isolate it then so that none of that distortion is present at the output? I suppose that could be a fun thing to experiment with! Could potentially be cool to figure out how to get some medium-heavy-ish distortion out of the VU and then have a switch to swap between the buffer/clean and no buffer/dirty! (Tho that may be too much to even fit in a 500 series build!!)
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djmiggymigz
Well-known member
Okay so I've found that there's "real" VU's and then tons of cheap "not real" vu's around these days. So If I got a cheap vu from say Aliexpress, I would certainly need a buffer circuit for it to work. However if I got something like the Sifam AL15 meter (linked is the data sheet) then I wouldn't need a buffer circuit and coould run this straight from the vio/gry output tx taps?
Sifam AL series datasheet
Sifam AL series datasheet
Here’s exactly how API did it off the spare winding on the 2503
Here are gerber files to make your own VU meter buffers for using DC mA meters among other things https://groupdiy.com/threads/wtb-vu-buffer-driver-pcb.82932/page-2#post-1107221
Here are gerber files to make your own VU meter buffers for using DC mA meters among other things https://groupdiy.com/threads/wtb-vu-buffer-driver-pcb.82932/page-2#post-1107221
Attachments
djmiggymigz
Well-known member
wowww okay sweet thank you!! I have that same schematic but mine doeesnt have the note on where the spare leads go! Okay so they go straight off of the transformer to a presumably "real" VU meter which doeesn't need a buffer circuit?
Can someone confirm that the linked Sifam meter is a "real" vu that wouldnt require the buffer?
Sifam AL series datasheet
Brian Roth
Well-known member
What Walrus mentioned in post #4 is that with two secondary windings in series for the program output the voltage produced by that last winding for the VU meter will be 6 dB low, hence the need for the buffer.
Bri
Bri
djmiggymigz
Well-known member
Yeahhh that's right, I guess I was hoping that the sifam VU could be calibrated to work with the quieter signal by altering the resistor value that's inline with it. I would likely use a 5-10k trimpot so that it would be easy to dial that in. Maybe that's not how it works though?
Regardless, getting the buffer involved doesnt seem to be too hard or that much different so maybe I can try without it first and if it's not working, short the resistor and opt for the buffer instead?
Edit: BUT if the buffer is gonna be needed either way, wouldn't it kind of make more sense to just get a cheap VU off ali or ebay? Rather than spending $70-80 on the quality VU that might end up just needed the buffer anyway. What would y'all do?
Regardless, getting the buffer involved doesnt seem to be too hard or that much different so maybe I can try without it first and if it's not working, short the resistor and opt for the buffer instead?
Edit: BUT if the buffer is gonna be needed either way, wouldn't it kind of make more sense to just get a cheap VU off ali or ebay? Rather than spending $70-80 on the quality VU that might end up just needed the buffer anyway. What would y'all do?
Brian Roth
Well-known member
This can be confusing to decide what route to take. A meter with "true" VU performance needs to meet industry standard specs that were published decades ago. I posted a few papers I've collected over the years (and have a few more as well on my hard drive) in the tech docs:
https://groupdiy.com/threads/vu-meter-articles-docs.85007/
One of the specs involves the physical action of the meter....rise and fall time, overshoot, etc. That is determined by the physical design of the meter movement.
In year 2024 some folks will argue that a mechanical VU meter is totally obsolete and should be consigned to the dustbin of history. I see a point there, but since I grew up in this biz with mechanical VU meters I find them still usable. My viewpoint will likely set off arguments here!
Yes, the VU spec is 80+ years old and comes from a different time in the audio industry compared to now. LED (or similar) meters have taken over the world. One reason...they are far less expensive. Also, the meter "ballistics" can be changed by tweaking the driving circuitry.
El cheapo mechanical "VU" (ahem) meters made by Mechowhung <g> are just eye candy compared to Ye Olde mechanical meters that met/meet the published industry specs. They flip and flop around when driven with a program signal.....I call them "wiggle needles".
Unlike a true mechanical VU meter the cheapos don't have the required internal diodes to convert the audio signal into a DC voltage to drive the meter's movement. No biggie with a card like the JLM which has that option.
I don't know what to suggest for any given project. Over the decades, I became used to a decent VU meter that also had a "peak winkie" LED that detected fast transients which could cause overload/clipping that wouldn't register on the associated mechanical meter.
One overlooked advantage of a CALIBRATED meter is adjusting a signal voltage to a fraction of a dB...useful when calibrating an analog tape machine. Ooops...another obsolete device! lol
Younger folks will scoff at me......shrug.
Bri
https://groupdiy.com/threads/vu-meter-articles-docs.85007/
One of the specs involves the physical action of the meter....rise and fall time, overshoot, etc. That is determined by the physical design of the meter movement.
In year 2024 some folks will argue that a mechanical VU meter is totally obsolete and should be consigned to the dustbin of history. I see a point there, but since I grew up in this biz with mechanical VU meters I find them still usable. My viewpoint will likely set off arguments here!
Yes, the VU spec is 80+ years old and comes from a different time in the audio industry compared to now. LED (or similar) meters have taken over the world. One reason...they are far less expensive. Also, the meter "ballistics" can be changed by tweaking the driving circuitry.
El cheapo mechanical "VU" (ahem) meters made by Mechowhung <g> are just eye candy compared to Ye Olde mechanical meters that met/meet the published industry specs. They flip and flop around when driven with a program signal.....I call them "wiggle needles".
Unlike a true mechanical VU meter the cheapos don't have the required internal diodes to convert the audio signal into a DC voltage to drive the meter's movement. No biggie with a card like the JLM which has that option.
I don't know what to suggest for any given project. Over the decades, I became used to a decent VU meter that also had a "peak winkie" LED that detected fast transients which could cause overload/clipping that wouldn't register on the associated mechanical meter.
One overlooked advantage of a CALIBRATED meter is adjusting a signal voltage to a fraction of a dB...useful when calibrating an analog tape machine. Ooops...another obsolete device! lol
Younger folks will scoff at me......shrug.
Bri
djmiggymigz
Well-known member
Sweet reply thank you!! I appreciate the confirmation of my suspicions re: the 3$ VU meters on aliexpress! So that being said, quality it is. That also brought to mind what my friend always advocates for which is to do something and do it RIGHT. Cutting corners usually ends up just disappointing. Deal. Gonna track down a good VU meter and go from there (likely with a buffer circuit).
Question: How would I go about identifying whether a VU has the rectifiers inside? There's an awesome store near me that has a PLETHORA of old and otherwise electronic things (the shop is called Surplus Gizmos for context). I have almost no doubt that I'll be able to find a meter there but would certainly have to identify whether its legit and has the internal components or if its a cheapo.
P.S. I'm making this pre for the studio that I work at, in which, I am very often using tape machines among other "vintage" gear! I'm all for the VU and consistent reference point (besides the fact that it's going to up the aesthetic of the pre enormously!) Also, the SSL desk that we have has VU's for the main outs/busses so the integration would surely be useful not just pretty.
Question: How would I go about identifying whether a VU has the rectifiers inside? There's an awesome store near me that has a PLETHORA of old and otherwise electronic things (the shop is called Surplus Gizmos for context). I have almost no doubt that I'll be able to find a meter there but would certainly have to identify whether its legit and has the internal components or if its a cheapo.
P.S. I'm making this pre for the studio that I work at, in which, I am very often using tape machines among other "vintage" gear! I'm all for the VU and consistent reference point (besides the fact that it's going to up the aesthetic of the pre enormously!) Also, the SSL desk that we have has VU's for the main outs/busses so the integration would surely be useful not just pretty.
Brian Roth
Well-known member
Another toughie. IMHO a super-duper real VU meter on a preamp might be more than you require for that application. You're not using typically using that meter for any ultra accurate measurements like you would lining up a desk with a tape machine. If only decent meters sold today weren't so #$&*^% pricey!
The internal diodes can be "detected" by applying a low DC voltage (like from a DVM on the Ohms range) through a series resistor. The resistor is there to limit the max current into the meter....depending on your meter, maybe 1000 Ohms. With internal diodes, the VU meter will deflect up the scale regardless of which way the red and black leads are connected to the meter's terminals.
The manufacturer of the meter can be useful info. True VUs were once made by Simpson, Triplett, Dixson, and Modutec. Sifam and Hoyt are the only old school brands I know of making VUs in current production (maybe also Modutec/Jewell??).
I looked at the JLM website and his driver PCB seems to be capable of handling meters with or without internal diodes. I couldn't find a schemo there to see what sort of features the board offered. Looks like some versions are sized to attach to the rear of the meter via the wiring studs/nuts.
To be honest, all you need for a real VU is a cheapo opamp (like a TL071, or even a LM741) , a few resistors and a trimmer pot. Oh yes...power supply bypass caps. This can be fed from suitable bipolar (+/- VDC) power rails.
As an Olde Phart I recall when light meters first began to appear on studio equipment. The original Kepex gate modules comes to mind, using Neon bulbs.
What I don't like are really low-end meters with only a small number of lights....steps are too coarse. At the other end are the old Burroughs bargraphs with 100 or 200 steps. They also looked really cool!
Bri
The internal diodes can be "detected" by applying a low DC voltage (like from a DVM on the Ohms range) through a series resistor. The resistor is there to limit the max current into the meter....depending on your meter, maybe 1000 Ohms. With internal diodes, the VU meter will deflect up the scale regardless of which way the red and black leads are connected to the meter's terminals.
The manufacturer of the meter can be useful info. True VUs were once made by Simpson, Triplett, Dixson, and Modutec. Sifam and Hoyt are the only old school brands I know of making VUs in current production (maybe also Modutec/Jewell??).
I looked at the JLM website and his driver PCB seems to be capable of handling meters with or without internal diodes. I couldn't find a schemo there to see what sort of features the board offered. Looks like some versions are sized to attach to the rear of the meter via the wiring studs/nuts.
To be honest, all you need for a real VU is a cheapo opamp (like a TL071, or even a LM741) , a few resistors and a trimmer pot. Oh yes...power supply bypass caps. This can be fed from suitable bipolar (+/- VDC) power rails.
As an Olde Phart I recall when light meters first began to appear on studio equipment. The original Kepex gate modules comes to mind, using Neon bulbs.
What I don't like are really low-end meters with only a small number of lights....steps are too coarse. At the other end are the old Burroughs bargraphs with 100 or 200 steps. They also looked really cool!
Bri
djmiggymigz
Well-known member
Hmmm yeah you're probably definitely right about that. Unfortunate thing is I can't seem to find any mid-range new meters! Only seeing super cheap $3 ones orrr THIS one! Found the same one elsewhere for a bit cheaper + cheaper shipping would only come out to around $70. What I'm really hoping for is to find one at the store I mentioned for something like $20.
Might also consider buying an old test meter of some sort (VTVM or something of the sort) and just pull the meter from it! However, end of the day if I get the Sifam that's not too bad. Definitely a cost I'm willing to eat.
Thank you for the info on testing them!! That super helpful to know. Wish me luck on my digging thru crates and dust for a meter!
One more question. In terms of providing power to the meter, would it be okay to just split a track off of the +-16v rails from the 500 card and routing that over to the meter? Most the meters I'm seeing seem to accept anything from like 9V-24Vdc. Only issue I see is if the meter/buffer circuit would draw too much current away from the 2520 of the pre. Tho, JLM says their buffer is very low on current draw.
Might also consider buying an old test meter of some sort (VTVM or something of the sort) and just pull the meter from it! However, end of the day if I get the Sifam that's not too bad. Definitely a cost I'm willing to eat.
Thank you for the info on testing them!! That super helpful to know. Wish me luck on my digging thru crates and dust for a meter!
One more question. In terms of providing power to the meter, would it be okay to just split a track off of the +-16v rails from the 500 card and routing that over to the meter? Most the meters I'm seeing seem to accept anything from like 9V-24Vdc. Only issue I see is if the meter/buffer circuit would draw too much current away from the 2520 of the pre. Tho, JLM says their buffer is very low on current draw.
