Wanted WTB - VU Buffer / Driver PCB

[thomasdf]

Bumping this thread because I have a pcb layout for this type of thing (like the JLM and DIY-Tubes units, plus several other similar ones) that I need to finish up. Can probably get to it in a week or two and then I'll just upload the gerbers as a .zip that anyone can use to place an order on their own from PCB fab of choice.

Very kind of you !

 

[nielsk]

The TL072 version is so incredibly simple I have built many on proto board (I can fit 4 easily on the Radio Shack 276-150). Works great.
Takes about the same time as building it with a purpose made PCB.

 

[thomasdf]

Bumping this thread because I have a pcb layout for this type of thing (like the JLM and DIY-Tubes units, plus several other similar ones) that I need to finish up. Can probably get to it in a week or two and then I'll just upload the gerbers as a .zip that anyone can use to place an order on their own from PCB fab of choice.

Can you run it off 24VDC ?

 

[Disco Volante]

I'd be down for (at least) 4 of those handy little pcb, in case there's a group buy/order.
Cheers, V!

 

[zzzzz]

Okay, dug up my old VU driver layout and did some quick cleanup. My original board layout of this circuit from several years ago worked fine, and although these boards haven't been verified I'm sure they will work fine, too, but feel free to give it a once-over and please let me know if you see any errors that I didn't catch.

Because people in the thread have mentioned doing a group buy, I have made a pre-order page here on my site and here is some “ORDERING" INFO (available until 9/25/23):

I am planning on placing an order with my PCB fab for some other things and will order a set number of these boards as well around September 25th, 2023, so I will close this pre-order page at that point in time. Based on previous orders, I should have the boards in-hand by early to mid October and will ship them out to you shortly after that. Will ship cheapest possible option via USPS with tracking.

edit: group buy is now closed and all orders have been shipped as of October 2023. Feel free to download Gerbers and use as you wish!

edit 2: I found out you can share projects directly on PCBWay for direct ordering anywhere in the world. I don't use PCBWay (but have in the past), but it is affordable. I put links to the shared project order pages in the "info" section below


FULL DISCLOSURE: I am not a White Market seller and this will probably be a one-time-only situation, considering I am providing the gerber files for free for anyone to use. If someone else would like to take over the production of these boards in the future and put them on a White Market thread, feel free to do so but please just credit me for the layout and sell them for dirt cheap / not-for-profit!

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INFO / HOW-TO / BACKGROUND ON THE BOARD/CIRCUIT: ​

I have laid out two different versions of the board. Download the respective zip of gerber files, upload to your fab of choice, and it should work just fine. That being said, I should note that the gerber files attached were exported from EAGLE using JLCPCB's design rules & CAM specifications.

• v1.0a: VU Buffer / Driver with AC/DC Input Voltage Regulator scheme (hookups via 5.08mm LS terminal blocks). Board size: 48mm x 46mm

• order v1.0a on PCBWay
  
• v1.0b: VU Buffer / Driver w./ AC/DC Input Voltage Reg. scheme w./ pads to solder directly to meter tabs similar to JLM units. This isn’t really something I would usually use, but figured someone might like it and was easy enough to implement the pads. Board size: 48mm x 48mm
• order v1.0b on PCBWay

I made a version of this board in 2018 and the circuit I used is originally from an Audio Technology article by Rob Squire. Some part values were adjusted based on what components I typically stock. This is (I think) the same circuit as many other VU meter driver boards including the ones available from JLM, Aliexpress, and elsewhere -- you can change component values based on your application, as well.

Build is very similar to the info found in this JLM thread and there are some helpful notes in here on substitutions / omissions / jumpers based on your ideal application. Not trying to step on their toes by any means. VU BUFFER KIT BUILD THREAD - JLM AUDIO (and mirror link for backup)

You can use whatever Schottky type diodes you want for D1 through D6 (1N400X, 1N5819, etc), but D7 and D8 should be BAT85 because they have a low forward voltage like a germanium. Some VU meters have diodes built in, in which case follow the notes on the schematic on what to omit.

My layout uses one side of a TL072 or other dual opamp rather than a single on the original scheme just because I always stock duals.

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​

REGULATOR NOTES: ​

The regulator is a standard LM317 adjustable scheme so you can use DC or AC voltage input up to 40v. You could also use a LM317HV, which handle 60v max input voltage. The footprint is on the edge of the board so you can attach a heatsink or bolt to your chassis (with an insulator) if you’re worried about dropping a lot of power (or LM338 if you need more current for whatever reason…)

If you know your exact meter voltage and don’t want to use the "V+ADJ" trimmer, use a handy calculator to come up with a fixed resistor value and solder that in place of the trimmer. 

If you don’t want to use the regulator scheme at all, jump D5 and omit the following components:

• - C7 and C8
• - D6

• - IC2
• - R16
• - V+ADJ trimmer


edit: Also, if you’re just using a simple positive VDC rail to power it (like a wall-wart or something) you can ignore some components in the rectifier bridge: populate D3 for polarity protection, omit D1 and D4, and then jump D2. Run your positive VDC to the “V+ Unreg” input on the terminal block (pin 1) and then common to “V- Unreg” (pin 2).

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FUTURE NOTES: ​

When I have some time / upon request, I’ll adapt it to another board layout without the regulator scheme. Also since I'm already using a dual opamp, it would likely be easy to fit a "peak" indicator LED if that was of interest. Not something I really care about, though.

Here is a link to the schematic with part values:

aaaannndd bill of materials / partslist here but all components are very, very, very easy to source from Mouser / Digikey / Tayda / etc. (be wary of ICs from Tayda, though) and you probably already have a lot of them on-hand:

 

[zzzzz]

^ hate double posting, but just wanted to bump my previous post as it's getting closer to my September 25th "deadline" for the group buy -- shoutout to those of you who have grabbed some so far as mentioned, I am not selling these to make a profit and this will be a one-time-only "made to order" situation. Boards are $1.25 USD each and come in black or green.

also:

Can you run it off 24VDC ?

yes, can run off of whatever input voltage an LM317 or compatible will take.

 

[thomasdf]

Sorry I hadn't seen it ! Amazing ! Thanks a ton for sharing your work...!

 

[Disco Volante]

^ hate double posting, but just wanted to bump my previous post as it's getting closer to my September 20th "deadline" for the group buy -- shoutout to those of you who have grabbed some so far as mentioned, I am not selling these to make a profit and this will be a one-time-only "made to order" situation. Boards are $1.25 USD each and come in black or green.

also:

yes, can run off of whatever input voltage an LM317 or compatible will take.

I've ordered 6 pcs...
Thanks a bunch!
V!

 

[TimG]

I got 2 a’s and 2 b’s!

 

[innercityman]

Just ordered 4 pcbs. Thanks dude !

 

[zzzzz]

Boards came in last night — assembled and verified



Anyone who went in on my group buy — all orders were dropped off at the post office this morning and you should have received an email with tracking information.



Built a tester on the v1.0b board with a nice old DC mA meter without any rectification built in. Fully populated board with the bridge rectifier to test full functionality and powered with an 18VAC source. Set regulated DC voltage out of the LM317 to 12vdc because that's where the trimpot landed lol. Used a TL072 and BAT41 diodes for D7 and D8 because I didn’t have any BAT85 handy. The heatsink is on the LM317 because I just pulled a used one from my parts drawer to put this board together. It didn’t get very hot, but doesn’t hurt to have.



Sent 1khz tone at +4dbm (1.23vac) from my function generator over unbalanced 1/4” TS to “calibrate” and then tested with a 1/8” to 1/4” mono adaptor coming out of our workshop iMac headphone jack and moves as it should. Floating LED in the pic is just there as proof of functionality.



Also tested with a regular ol’ laptop power supply 12vdc SMPS - left the bridge rectifier and regulator still on the board (although unnecessary and dropped the voltage down after the bridge). Adjusted voltage trimmer for the LM317 accordingly. No issues at all and as mentioned, can ditch a LOT of the psu circuit if you plan to power it with something like this.



Other photo shows v1.0b board hastily soldered onto the tabs of a different meter just as a proof of concept. Not my cup of tea, but works as it should.

 

[zzzzz]

Looping back around -- I made this tiny utility board to go along with the meter driver. This allows you to mount multi-turn trimmers to your front (or back) panel for VU calibration of two different reference levels without needing to open up your enclosure. This replaces the on-board VU meter cal. trimmer on the meter driver PCB. I did this for a project so that I could switch between +4 dBu for 0VU alignment and then something else (-10 dBV or whatever)

Gerbers and drill templates can be found in this Google Drive folder.

It uses a through-hole DPDT on-on mini toggle switch and mounts to your panel with that, and then I have included three separate screw holes where you can put additional (optional) standoffs for support. It uses 3296W top-adjust trimmers.

You would then solder a JST XH style 2-pin terminal on the back and use that to run two wires to "VU.TRIM" Pins 1 and Pins 3 (there is a trace jumping 1 and 2) on the Meter Driver PCB. Or, just run bare wire if you don't care for JST headers.

With the DPDT switch in the the "UP" position, the calibration level set by the trimmer on the left of the switch is enabled. The "DOWN" position engages the trimmer on the right.

The switch is the commonly available mini toggle (such as Dailywell 1M series) available from all sorts of vendors all over the world. I have tons of these around because I use them in guitar FX pedals.

BUILD GUIDE:

The body of a 3296W trimmer is around 10.03mm according to the data sheet. The adjustment screw is around 1.52mm tall.

Most mini-toggle switches have a body that is 9 to 10~ish mm tall. Depending on how far recessed you want the 3296W trim screw to be, you can use a second nut or spacer for adjusting the length of the switch shaft, and then choose what length standoff you want to use for your additional mounting bolts.

1. Print drill template at 100% and drill accordingly.
   
   
2. Solder "TR.UP" (the trimmer on the left) before any other component. The JST header on the bottom side comes pretty close to those solder pads.
   
   
3. Solder the JST header (or wires to run to the VU Driver PCB) second to the BOTTOM SIDE of the PCB. Similarly, getting to those two little pads on the opposite side will be tricky once the other components are in.
   
   
4. Solder in "TR.DOWN"
   
   
5. Mount your DPDT in your freshly drilled hole. Depending on the body height, you might have to use one of the two nuts usually included with these types of switches as a "spacer" to make the overall switch height taller than the 3296W trimmers.

I also made a "stereo" version using a single 4PDT on-on switch and four trimmers if you have two VU meter project, but it is a bit clunkier (2 inches wide).