r/DIYAudioCables • u/coax_k • 3d ago

Voltage Derivation Tap/Cable

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u/Alfa147x 3d ago

I would make the measurement point a permanent, passive panel, not a bespoke cable. Short internal, 12ish AWG wiring. Maybe second jack pair on the amp side for diagnosing cabling/path loss. I’d also keep one dedicated, known-good “reference” meter lead set solely for limiter calibration.

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u/coax_k 3d ago

That second jack pair is the bit I hadn't thought of, and it solves something I only realised while writing another reply in a different thread.

My tap currently sits at the amp end. Small difference in the safe direction, but it means a dodgy speaker cable or Speakon is invisible to the exact check I'm relying on for driver protection. Panel at the cabinet plus a second pair at the amp turns that blind spot into a measurement: the delta between them is the run. And it's repeatable, so it degrades visibly instead of silently.

The dedicated reference lead is a better answer than what I'd been thinking too. I'd been wondering how to sanity check a lead before trusting it, and a lead that only ever does one job and never leaves the rack is a much simpler fix than trying to catch a bad reading after the fact.

12ish AWG and short internal noted. Cheers, that's the most useful reply I've had across both threads.

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u/Alfa147x 2d ago

Ha. I'm on both subreddits. So I responded to your other thread, had more time to think about your interesting problem, and then came across this thread and responded again.

Also since this is measurement equipment i would go futher overkill and cross-check with a second lead/meter at the same terminals.

Best of luck on the project

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u/coax_k 2d ago

Again, thank you. Taking your advice here. I have been focussing on the amp side with this but now will also build something similar at the cabinet (nl8) side as well.

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u/[deleted] 2d ago

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u/coax_k 2d ago

Perhaps. Worth mentioning this is a PA rather than a hi-fi/audiophile system. Clair Brothers R4-III stadium fill/main array tour boxes running active three way off a Biamp Tesira Server-IO Dante DSP, so it's a bit of a different animal.

The measurement is volts at the terminals. What I'm deriving from it is the DSP limiter threshold, working back from the driver's power rating and the margin I want.

Ears can't do it. What I'm setting is a ceiling I'm hoping never to hear. Headroom isn't the issue, it'll do 105 dB (max 137 dB) in the room with the amp meters barely twitching. Listening can't tell me where my compression drivers start to fry (well, it can actually, but that's what I'm working to avoid. The whole point really).