Audio/-9V ground question

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WestOfBen
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Audio/-9V ground question

Post by WestOfBen » 09 May 2019, 08:59

I am making a box that will receive a line/headphone feed from a metronome and it will have an LED indicator of some type.

Due to the limited pins on the cable I am intending to use, I am a bit stuck for how to ground this thing, so I have two questions.

1. Can I tie the LED negative and the audio negative to the same return? Isn't this what active basses do? I will be connecting a resistor inline with the LED to bring voltage down. 9V will be sent from my Voodoo Labs PP2. No dangers here, or here lay gremlins?

2. I plan on using a volume pot to allow some control of audio volume. What value of pot do you suggest? I have some spare 500K and 25K pots I think.

Thanks!
Rickenbacker 4003JG, Epiphone Ripper, Marina P/J fretless, Tanglewood ABG, 1960s Rose Music Tempo SS semi-hollow bass, an acoustic guitar, GK 700RB-II, SWR Henry 8x8, some pedals
My band is called Ascribe!

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noplanb
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Re: Audio/-9V ground question

Post by noplanb » 09 May 2019, 11:04

As always, a circuit diagram can explain and clarify a lot.
So, 'on the face of it' replies:
1. Yes. Led's may use hardly any power depending on its specs, and shouldn't interfere with anything.
Resistor size can be fine-tuned either to favour a bit more brightness, or bit less current (dimmer). Double or halve the resistor accordingly if you want to see.
2. The 25k pot should cause less (background) noise than the 500k - damping factor is better - and you've got the current covered.
I see..............basses!

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Bill Fitzmaurice
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Re: Audio/-9V ground question

Post by Bill Fitzmaurice » 09 May 2019, 11:52

WestOfBen wrote:
09 May 2019, 08:59
Can I tie the LED negative and the audio negative to the same return?
Yes. That same return would be tied to the chassis ground.

WestOfBen
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Re: Audio/-9V ground question

Post by WestOfBen » 09 May 2019, 13:25

Beautiful! Thanks guys!
Rickenbacker 4003JG, Epiphone Ripper, Marina P/J fretless, Tanglewood ABG, 1960s Rose Music Tempo SS semi-hollow bass, an acoustic guitar, GK 700RB-II, SWR Henry 8x8, some pedals
My band is called Ascribe!

WestOfBen
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Re: Audio/-9V ground question

Post by WestOfBen » 16 May 2019, 11:46

It all worked out well, thanks again! No ground loop issues. I am using a 5-PIN DIN (MIDI, but not, because your average MIDI cable only has 2, 3 and 4 active). No noise issues on audio. Everything works tied back to common ground.
Rickenbacker 4003JG, Epiphone Ripper, Marina P/J fretless, Tanglewood ABG, 1960s Rose Music Tempo SS semi-hollow bass, an acoustic guitar, GK 700RB-II, SWR Henry 8x8, some pedals
My band is called Ascribe!

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BigDaddy
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Re: Audio/-9V ground question

Post by BigDaddy » 16 May 2019, 14:05

Great idea! Can you post pics of the guts? I like this sort of innovation from folks - well done!
Basses: Sandberg, Fender, SUB & Squier
Amps & Cabs: Ashdown, Ampeg, Tecamp & Aguilar

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BazzBass
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Re: Audio/-9V ground question

Post by BazzBass » 16 May 2019, 16:24

:useless:
Loud things: Trace Elliot Elf and 10" cabs ,Markbass LittleMark 250, Hartke HA2500 amps, Hartke XL210 cabs
Pretty things: Fender MIA P, MIM P and J, Hofner B Bass, SX J, Takamine ABG
Bands: Los Mescalitos , Distorted Tarts

WestOfBen
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Re: Audio/-9V ground question

Post by WestOfBen » 17 May 2019, 14:29

Pics coming. In the meantime, enjoy a video of the setup. I have called it Roget's & Hammertime :D I hope you also like stories.



So the previous setup was painful on our first gig. For a while I had been running a momentary switch via a long lead, in a tiny box from Jaycar, for the start/stop - connected to the Start/Stop jack on the Boss DB-90. For the audio I ran direct from the DB-90 to a Behringer 8 channel mixer near the drummer. Setting up wasn't so complicated but it was three different leads and another device. Pack-down to get off stage for the next band was messy under the constraints - I ended up just throwing it all in a case and dealing with it at home.

This prompted the question; Surely there is a way I can come up with a single-cable means of...
1. Sending metronome (click-track) from Boss DB-90 to drummer for his ears - driven by song patches (see below)
2. A click start/stop button (expanding on previous experiment)

We are running some small sequenced and time-arpeggiated things, so at least a minimum level of time strictness is required. No full sequences or tracks though, no no no.

We have gone this path because we don't all have IEMs and venues can't necessarily provide channels for these things. If they do, we can actually work with that, since I have two Behringer DI-20s on board for 4 DI channels. AND I am not running any software solutions and didn't want to integrate them either. Not that I hate software, I already had most of my desirable pedals, so hardware begat hardware begat more hardware.

Straight away I could see that required minimum of three signals, start/stop (2) and audio (2) - if I could share the ground that would be three. I thought maybe I could use an XLR cable, but then I remembered we had another minor issue at the gig.

The drummer and I are a great unit, but a couple of times he wasn't sure when the click was at the new song tempo - because a couple of the songs were at very similar tempos. He was looking to me to nod head but singer/guitarist and I had some tuning stability issues through the gig, temperatures really wavered, so I didn't always look back to drummer. This resulted in some slight start issues for two songs, he started and then I switched to the next song and he heard click change tempo and adjusted almost seamlessly, such as the pro he is. My fault as much as anything.

So, for the sake of giggles, I thought... why can't I reuse a green LED from another disassembled project and indicate to the drummer that we are at the start of the next song? The LED would be ON for Intro patch and OFF for the rest. This might prompt us both to make contact, or whatever. In some cases he can start and I will catch up. It is "something" though, and more of a why not do it!

This meant another signal required, and that was the prompter for the question about combining audio and power grounds. This meant I would need 4 signal wires on a cable... but no such "common" thing exists. I couldn't help but want to use an industry standard cable... and I had two 5 pin DIN chassis plugs just sitting in spares... and a full 5-pin connected MIDI cable... hmmmm.

Yeah, but to switch the LED on and off I would need a control line as well as the voltage... ESPECIALLY if I was to reuse another piece of kit, in the form of an audio level meter I had leftover from another disassembled project. This was a Jaycar kit I had fun with. Why not provide a visual indicator of beat, if the major ticks light up to red and the minor ticks are slightly quieter and only light green. Why the heck not?!?!

The total was then 5 wires needed > 5-PIN DIN/MIDI it was then! These are the lines I ended up with:

1. Click start/stop > tied between common GND and the DB-90's start/stop jack
2. Green LED GND return > routed through a Boss ES-8 CTRL relay, switching to ground
3. +9V rail
4. -9V or common GND
5. Audio +

In the video, the yellow patch I am connecting/disconnecting to light the green LED is the one linked to ES-8 CTRL, so I can turn the LED on/off per patch. In this case I use a bank per song (100 banks available) and each of the 8 patches (footswitches) correspond to a song section - IN, V, PRE-CH, CH, BR, OUT and S1, S2 (for special sections).

The sender unit therefore has 9V DC pos-tip supply from VL PP2+, Start/Stop, LED CTRL, audio-in and audio-return/bypass I can send to one of the DI boxes if required, plus of course the DIN output. Nothing fancy inside, common GND and some patching between.

The receiver has DIN in, audio out, volume knob that may be adjusted by foot (10K pot), level meter sensitivity knob (1K pot). Internally the LED is protected by a 300ohm resistor. Aside from the audio meter circuit, nothing too fancy.

Does it work? Connected it up to ES-8 yesterday morning and it all works. First test with band will be a rehearsal next week. We use headphones in the studio from a SM Audio amp, so I can actually send the audio from the receiver to the second mix signal input on the headphone amp, so drummer can get a mix of master mix plus click - and he will be the only one getting the click.

I haven't figured yet which of the components is Roget's or Hammertime. Receiver = Roget's maybe would be easiest to remember.

This has been a very satisfying project. I have not so many skills nor electical circuit knowledge, but I am enjoying learning!
Rickenbacker 4003JG, Epiphone Ripper, Marina P/J fretless, Tanglewood ABG, 1960s Rose Music Tempo SS semi-hollow bass, an acoustic guitar, GK 700RB-II, SWR Henry 8x8, some pedals
My band is called Ascribe!

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