XLR to TS grounding/shock concerns

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Re: XLR to TS grounding/shock concerns

Post by crochambeau »

Look forward to hearing the result!
When in doubt, add resistance.

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Re: XLR to TS grounding/shock concerns

Post by FAP »

Croch's circuit WORKED:
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I'm debating ordering more precise resistors for this; I just used 1kΩ because they're the lowest value I have that are 1% tolerance.
Still no idea why the transformer circuit didn't work.
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Re: XLR to TS grounding/shock concerns

Post by FAP »

So bad news/good news time: bad news is the XLR configuration doesn’t work well with the rotary switches. Because there’s 48v going through the lines, there’s this very harsh ‘pop’ every time a switch goes open. I think I know what the transformer in the original circuit was used now: it could theoretically prevent this harsh popping noise since one part of the circuit is isolated from the other. Still, I was never able to get the original circuit to work, so it’s back to the drawing board.

The good news is I might be able to bypass this issue entirely by making the handset powered as opposed to getting it from phantom power. This will obviously require a 9v battery at some point; if you guys have any idea of what else might need to go into such a circuit, I’m all ears.

EDIT: That original circuit is based one of two circuits put forward by none other than Godfried-Willem Raes; he’s an old school experimental artist who’s put out some neat stuff over the decades. Anyways, I’m thinking of trying his second circuit, one that omits the dc blocking cap entirely, as seen here:

https://www.logosfoundation.org/g_texts/ELQ-mike.html

Additionally, I found this video which shows powering the handset with a 9v battery is indeed possible, and could be as simple as tossing the battery on the other side of the transformer:

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Re: XLR to TS grounding/shock concerns

Post by NoiseWiki »

FAP wrote: Fri Aug 26, 2022 3:58 pm So bad news/good news time: bad news is the XLR configuration doesn’t work well with the rotary switches.
Rotary switches? I don't recall those being mentioned before?

Having said that.. in the passive audio switching devices I've built you'll get pops when switching between audio signals. I looked into using vactrols or some kind of solid state optocoupler IC to do the switching but ultimately decided for my purposes the pops where just part of the aesthetic
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Re: XLR to TS grounding/shock concerns

Post by FAP »

Oh no, I didn’t mean rotary switches: I meant the ten digits on the rotary phone part that act as momentary n.c. switches. Should’ve clarified.

As for the pops, no, these aren’t like standard audio pops: every time one of the rotar- er, momentary switches opens, the mixer levels PEAK. Like, imagine turning a mid-size practice amp on and off really fast ten times in a row: there’s a loud pop in the speaker each time, right? That’s sort of what I’m talking about. Like if you just laid an audio cable across a friggin’ car battery or something.
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Re: XLR to TS grounding/shock concerns

Post by crochambeau »

Did you disconnect ANY power from EVERYWHERE except feeding the cart?

OE wiring has those switch stacks doing interrupts on the power; which, as you say, causes massive signal spikes because that is how the phone informs the hub which is miles away of the number it is dialing.
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Re: XLR to TS grounding/shock concerns

Post by FAP »

The cart?
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Re: XLR to TS grounding/shock concerns

Post by crochambeau »

Cart = cartridge, microphone element
When in doubt, add resistance.

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Re: XLR to TS grounding/shock concerns

Post by FAP »

So a little update on this odyssey:

I’ve come to the conclusion [unless/until proven otherwise] the phantom power/XLR method in combination with the rotary phone switches just isn’t going to work, due to the aforementioned signal spikes. The only way to prevent these signal spikes is if the circuit powering the “cart” is isolated from the audio circuit: this simply isn’t possible if the power source comes after the rotary phone switch stage as it does here. I do intend to make XLR phone mics that use phantom power, they just won’t work with the base rotary phone; in other words, I can’t have my cake and eat it, too.

The good news is, I can have a power source come before the rotary phone switch stage, and do it with a much simpler circuit to boot:
BF8E1B6E-69AD-494A-B413-F5ACE8EDBB77.jpeg
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Please excuse the poor image quality, but I think it should be clear enough: all that really needs to be done is to add something to power the carbon mic—in this case, a 9v battery will suffice—while the rest of the circuit is isolated via the transformer (I know I’m probably using the term “isolated” here in a way that isn’t strictly correct, but just bear with me).

This also has the added benefit of freeing up the circuit to where I don’t have to use balanced audio cable, and in fact, shouldn’t use it: what this means, practically speaking, is I can build a handset mic with a 1/4” termination, then have it go through the rotary switches via 1/4” jacks. In this scenario, I can have my cake and eat it, too!

The only thing that sucks about this is there’s no real ideal way to mount a battery clip to the handset; these things have always been a PITA for me because I have yet to find screws to fit them that have a low enough profile to not scrape the battery to shit when loading/unloading one in the clip. The only solution I’ve come up with is to use wires to tie the clip down, though even then it elevates the battery a little higher in the clip than I’d like. If anyone could recommend some screws with low-profile heads to fit this POS then let me know:
B82A457A-4A10-481B-80AC-09FD39BAEB69.jpeg
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I have to admit, I sort of fear someone beating me to the punch with this idea now that I’ve done all the heavy lifting (i.e. research), even though this project is only synthesizing various bits of knowledge that’ve been known for decades… maybe I should’ve paid croch to collab with me on the hush-hush but I figure maybe someone else may find this info useful in the future.

TL;DR to get a handset mic, with a toggle between ear and mouth piece, going into a rotary phone set (essentially a bank of 10 momentary mutes) requires the use of battery power and unbalanced audio cable (e.g. 1/4” mono).
A handset mic can be balanced (e.g. XLR) to use phantom power, thereby eliminating the need for battery power, but it cannot use phantom power and go into a rotary phone set without signal spikes.
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Re: XLR to TS grounding/shock concerns

Post by NoiseWiki »

FAP wrote: Sun Aug 28, 2022 9:29 pm
The only thing that sucks about this is there’s no real ideal way to mount a battery clip to the handset; these things have always been a PITA for me because I have yet to find screws to fit them that have a low enough profile to not scrape the battery to shit when loading/unloading one in the clip. The only solution I’ve come up with is to use wires to tie the clip down, though even then it elevates the battery a little higher in the clip than I’d like. If anyone could recommend some screws with low-profile heads to fit this POS then let me know:
Image
What about using rivets?

As for people beating you to punch.. I feel like I've seen various incarnations of phone handset as microphone and rotary dial as noisemaker. It's not like there's a huge market for these kinda things but those who appreciate this kinda of stuff will like your efforts
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