True peak programme meter

[GK.]

This is amazingly cool and impressive (professional) DIY project, indeed!

If possible, I believe it will never be possible though, I really would like to have six (6) of your True Peak Programme Meter in addition to my DIY-built IEC_16028-17_ballistic-behavior-compatible large-glass-face 12-VU Meter Array monitoring SP-high-level output of multiple amplifiers in my PC-DSP-based multichannel multi-SP-driver multi-amplifier fully active audio setup (ref. my post here #535 and #931on my project thread).

Spoiler

Please visit post #535 on my project thread for the details...
View attachment 424391

Very nice! I think every respectable power amplifier has to have a nice pair of vintage VU meters on the front panel.
The most vintage movement I've got, attached to a HAM shack speaker, is from the 40s or 50s, I'm guessing.

 

[GK.]

Really interesting old school design.

Is there a reason you chose this approach rather than a microcontroller + ADC system? (Other than just the for fun "because it's there" )

Yes, there is that and also the considerations mentioned earlier. This project has actually been a long time in the making. I originally come up with the scheme maybe 20 years ago or more, but the high-gain signal amplifier which is DC-coupled by necessity wasn't practically realisable. There just weren't any op-amps available with the necessary input offset drift performance that also had adequately low noise and high enough bandwidth. Traditional chopper techniques were out of the question because the gain stages are overdriven.

 

[GK.]

So, any CNC router enthusiasts here?
Model recommendations?

Currently considering one of these with a spindle motor upgrade for the panel engraving.

 

[MCH]

Just in case: jlcpcb also offers CNC services:

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And they have 60$ coupons for new customers. I guess shipping won't be super cheap but maybe worth checking it out...

 

[HaveMeterWillTravel]

Here is my initial prototype build of a LED level meter design, with a few fudges made to the PCB which have since been included into the second board iteration.

I wanted to make a meter that is not in anyway average or quasi-peak responding to audio-frequency signals and that has a dynamic range sufficient to indicate the noise floor of a signal source.

As far as audio frequency signals are concerned, the unit has practically zero attack or integration time. It will accurately indicate the peak amplitude of one single half-cycle of a 20kHz sine wave of either polarity.

Cool project, mind a few question it?

Have you given consideration to (possible) generated EMI (radiated or conducted) from all the comparitor/NAND gate transitions running wide open, and the larger current pulses when the 4520 transitions? I'm also curious on the 4520 selection. I assume that's the binary counter 4520?

I would think the effective fastest recovery time would be limited by the time response of the LEDs. But there may be a nice range of the decay rate clock frequencies where the observed brightness of a particular LED may be an indicator of how many cycles are over it per unit of time. Essentially acting like a dimmable LED.

 

[GK.]

These aren't ECL comparators driving TTL. Slow 4000-series CMOS is probably the least EMI-generating logic out there and the LM339s with the high value open-collector pull-up resistors (which I have since revised from 10k to 47k to draw less total current from the negative rail) are pretty benign too.

You can see that I put a steel shield between my closely stacked stereo pair. That's only because it only took 5 minutes to gullotine and drill. I don't get any cross talk between the boards and I probably still wouldn't if the shield as removed.

 

[GK.]

Currently considering one of these with a spindle motor upgrade for the panel engraving.

Not exactly sure where I am going to permanently set this up yet, but that is always a secondary consideration when it comes to toy acquisition.
For the spindle upgrade I bought the 700W 30,000 rpm 1/4" Makita router. The 300W 12,000rpm 1/8" motor that comes with the unit is a bit lacking for metalwork.

Just playing around with a demo engraving G-code file that came with the software bundled with the machine so far on some scrap aluminum. I am currently using a 1/4"-shank tapered bull-nose end mill and the results are fairly decent at 30,000 rpm with a slow feed rate. I also have some 1/4" 90 degree engraving bits to try out.

Now I just have to familiarise myself with software to convert my .dxf CAD files to G-code. I have an Autodesk license for Fusion 360 courtesy of my employer so I think I'll start there. Oh yeah, and I still have to order the engravers wax sticks.

So the process for a front panel will be:
1) Get the panels cut out of supplied stock of 3mm-thick 5052 aluminum flat plate at the local CNC water jet shop.
2) Drill and engrave at home
3) deliver panels to anodizing shop.
4) Wax fill engravings at home.

By the time I've finished my retro stereo HiFi system the Genmitsu CNC will have payed itself off.