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PostPosted: 15 May 2017, 21:07 
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Joined: 06 May 2017, 18:49
Posts: 12
Location: Seixal. Portugal
I'm wondering if anyone can help me.

I'm a bass player and sometimes on stage I need to use a microphone :sing: for background vocals.
I need a circuit that turns my AKG C1000 microphone on and off when I want it, without the intervention of the FOH operator :lildevil: .
I prefer the connection to be made by footswitch, placed on the floor near the microphone stand.
The Noise Gate is not suitable for this service due to the sound pressure variations that appear on stage.
Moreover, there is a problem :bawling: : A condenser microphone takes a few seconds to be prepared to respond, if it is turned on for a particular moment. This makes the on/off operations via the microphone's own switch not suitable for the required speed.
Therefore, the powering circuit of the microphone itself must be PERMANENTLY in operation, and the circuit I need must act directly on the balanced audio output (mute).
I have researched this subject and i found this but the asked price is quite higher for something apparently simple.

http://www.alectrosystems.com/alectro/M ... witch.html

So, my question is:

Does anyone know of a simple, low-noise, transistorized cheap circuit that simply turns a condenser microphone (phantom power P48) IMMEDIATELY on and IMMEDIATELY off, for balanced microphones that are switched over and without making any noise at the FOH when switched?

Sorry for my poor english and thanks in advance

Macedo Pinto
Portugal


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PostPosted: 16 May 2017, 03:32 
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Hi,

While $150 may seem a lot for it's function, I build similar circuits for pro use and once the (mostly) cost of the case, XLR's and switch that can handle pro stage use is factored in, it's not that bad at all.

How I would approach it is leave the phantom power there all the time (cutting it on and off is most of the delay as the voltage balances settle) and just mute the audio output by "shorting" the AC signal.

The simplest way of doing this is attached.

There is other ways, using VACTROL's or signal relays, but they all need power to do so. This is a totally passive method.

Tie the ground (pin 1) to the metal case.

Cheers!

*edit*
Note that this is for true-balanced microphones. It won't work with the el-cheapo pseudo-balanced ones that are just unbalanced mic's tied to pins 1 and 2 and leave 3 floating. It WILL work with a pseudo-balanced elements if you tie the mic between 2 and 3.


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Last edited by Geek on 16 May 2017, 03:45, edited 2 times in total.

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PostPosted: 16 May 2017, 03:42 
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As for the switch, I see AES is no longer carrying the gold ones (at least they don't specify), so I'd go with a Digikey MB2085SS1G01-ND and just mount it in the box (poss. with a sub-bracket) to make overtravel impossible.

It's DPDT instead of SPST, so just tie the two sides together for more reliability.

Cheers!

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* Ratings are for transistors - tubes have guidelines*
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PostPosted: 17 May 2017, 00:02 
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Joined: 06 May 2017, 18:49
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Location: Seixal. Portugal
Thanks for the comments on the issue raised, Geek.
In fact, I am aware of the prices for manufacturing this type of assembly and I totally agree with your observation.
But I never miss an opportunity to make the circuits I need myself, like anyone who cares deeply about audio electronics.
Luckily I have a fair amount of components, including boxes.
I figured this type of circuit would be more complicated
As I understand it, this simple circuit can do exactly what I need.
The only question I get is whether the on / off switch is really silent.
Nothing like experiencing!
I'll take care of this at the weekend.
By the way, the fact that this circuit is purely passive, it pleases me immensely.
Not everything that is done within the scope of professional audio has to be active.
And I think my AKG C 1000 will do well with this assembly

Thanks again, Geek!


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PostPosted: 19 May 2017, 06:57 
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Joined: 26 Oct 2012, 21:00
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Location: ontario canada
so is the phantom power going to tolerate having pins 2 and 3 of the xlr shorted?
and the proposed arrangement is likely to make noise at "switch on" and that's not something any competent system operator is going to like.
better solution would be a stand alone phantom supply so the mic supply is constant and mute the audio after it's been put through a 1:1 isolation transformer much like the device you linked to.
no offense to Geek he's a knowledgeable guy but i think he neglected the phantom power considerations here.

as someone who has done sound reinforcement for years i prefer seeing an engineered solution rather than a homebrew solution or device on a professional stage.


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PostPosted: 19 May 2017, 09:12 
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turk 182 wrote:
... I prefer seeing an engineered solution rather than a homebrew solution or device on a professional stage.
I have a question about this statement. I will add up front that it is not my intent to offend so please don't take it that way. Where do you draw that line between "engineered solution" and "homebrew solution"?

I think we can all envision the ends of that spectrum; high quality units from reputable manufacturers on one end and poorly executed, hand soldered circuits, in cheap plastic boxes on the other. But in the middle, I think it gets much harder to distinguish. If an audio engineer working for Sure comes home and knocks out a design to perform a particular function, builds it in an aluminum Bud box, and runs it through testing in his den, is that an "engineered solution" or a "homebrew solution"? Now replace the Sure engineer with a self taught individual of high skill level, which then?

My only real point here is that all designs and builds rest on a continuum of function and quality. I think sometimes we (especially those of us who are engineers) can forget this and sometimes reject, out of had, solutions that are, or can be, very good simply because we have placed a label like "homebrew" on them. I know we all use terms like this as a shorthand to convey a message or idea. But we need to remember that these terms mean different things to different people and I for one never want to discourage a budding hobbyist, potential professional, or seasoned expert through my use of inexact language. Just my thoughts on the issue.

If I have offended, I apologize. I'll get off my soapbox now.

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PostPosted: 19 May 2017, 10:56 
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Location: ontario canada
no offense and valid point,i did state i "prefer" and as someone who frequents both sides of the fence both as a DIY'er and a sound tech nothing should raise more concerns and questions than something that involves power,grounding,and potential shock hazards.
that probably stems more from a liability standpoint, it's not meant to be a poke at DIY'ing but a commercially available product has to meet applicable standards and existing regulations(and there are exceptions to that too!) where as a DIY solution/homebrew device does not.
i've faced all sorts of interface, connection, and switching systems problems over the years and been of the other side of the equation with respect to providing evidence that implemented (homebrew)solutions will both work and be safe.
and over the years i've accumulated a nifty collection of of repeat coils/isolation transformers for those occasions where a performer/musician insists on using the DI line out of a questionable looking amp or some bizarre harmonica mic they found at a yard sale linked to an old amp with no ground....

i guess the OP has not encountered or had success with "soundmen" because i would have supplied him with VCA control of his mic channel but i'm spoiled to have such functionality with the equipment i routinely use.

and as to where to draw the line or set criteria of what constitutes acceptable, it is a slippery slope grey area indeed, i like most, would be more likely to accept using something in house fabricated or homebrew if it demonstrates good mechanical workmanship (no sloppy assemblies) it doesn't need a fancy finished appearance but it can't fall apart or cause spontaneous combustion or ventricular fibrillation in use....and with microphone circuits that sweaty musicians holding guitars that are plugged into amps that may or may not be properly grounded(pedal boards and effects pedals on bad wall warts to boot) i do try to exercise caution with what's allowed on stage.i guess being in the role of soundman/production manager it would be neglectful of me to allow safety to lapse just so a guy can mute his mic at will but as i've learnt over the years you can't tell an "artist /musician" he can't have something....or total control....or red M&M's.....what he wants already exists but hey, if he wants to put together his own i'd gladly help i am a diy'er to!


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PostPosted: 19 May 2017, 14:54 
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sorry further musings on the topic, with some of the features on many new digital mixers and the right interface one could do "far more" than just mute audio without the phantom supply switching issue.


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PostPosted: 19 May 2017, 15:16 
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Location: ontario canada
sorry one more sidebar and it's with respect to phantom powered mic's in general.
over the years if a vocalist insisted on using a phantom powered mic my concession was the mic must remain mounted on a stand! no hand holding or handling of any sort....nothing kills Pa compression drivers faster than the DC transients caused by an intermittent mic line connection, even with the cable taped to the mic if pulled (like singers do with a wired mic)that momentary change/loss of contact can produce nasty destructive noise!!(this is probably why at least in the live sound world there exists a cultural resistance to hand held condenser use!)


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PostPosted: 20 May 2017, 00:10 
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I fully agree with the comments made.
It often happens that I’m on stage and I can’t require the service soundman to know the particularities of the musical themes that are performed, using frequent microphone switching.
For that reason alone, I would prefer to turn my microphone on and off, which makes the task easier for the soundman.
I never handle microphones during the performance, whether dynamic or condenser. For me, all the microphones should be on stands. As a bass player, I need to use both hands on my electric bass and besides I only approach the microphone for short vocal lines.
For those who perform this type of work on stage, the use of a local On/Off selector operated by foot, would be the simplest things to accomplish.
The question of using condenser microphones is related to my preference and the working distance between myself and the microphone. I never liked the proximity effect and I usually sing at 10 cm/3.93 inches from the microphone.
On the other hand, as soundman, I also approach with some concern any situation that falls outside the scope of standardized audio engineering solutions and it has happened to me that sometimes I have to take special care with equipment that is apparently out of the norms.
Meanwhile, nothing has ever happened to me that would seriously endanger the equipment. So far, so good.
As a DIYer, I feel it my duty to inform me thoroughly of standards and good practices, particularly with regard to the safety of operation of everything that is put into professional or domestic service. For this reason, I try to proceed in accordance with what I know of other manufacturers and that it is accepted as a standard, not making it easy for the subjective quality of what I am producing. Both mechanical and electronically speaking.
It is clear that the issues raised here are important to everyone, thanking Turk 182 and Suncalc for referring them when it comes to making equipment that will be connected to standard audio systems and because they may interfere with the individual concepts of people directly involved in the professional audio industry
I have never done this kind of circuit/assembly and I have also never used any commercial solution for this purpose and so far I have only used Noise Gates in this condition, which is the first time that I think about it any further.
As for the manufacture of the aforementioned Mic Mute, since there is still no concrete solution for this in a DIY context, contrary to what I intended I am going to cancel for now what I was going to do, unless in the meantime someone shows a safe method to proceed accordingly .
As you can see, it is not a pressing matter.

Many thanks Geek, Turk 182 and Suncalc for the effort expended in an attempt to clarify all aspects related to this matter.

Macedo Pinto, from Portugal.


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