Two Wire Transmitter <--> Three wire mic

[Plantman]

Hi,

 

I look after a budget PA system for a group of folk who do demonstrations of crafts on a stage.

It uses a pair of KAM UHF Body pack transmitters with the supplied mics. Head and Lavalier.

Head mics are fine, but the lavalier tend to feedback at too low a level, so I'd like to change them for something better.

 

The existing mics are two wired, signal and screen. The open circuit voltage at the transmitter unit is 7.6volts and when mic is connected 4.7volts. Nominal resistance of a mic is 1.1kohms. (Quite interested how these high voltages are achieved with only three volt worth of battery cells....but I digress)

 

I was thinking about using something like a Sennheiser ME4 cardioid unit, but I see that 'proper' mics like these have three wire conections.

Could I have some advice on how to connect these two things together please?

 

Thanks

[Sound Man]

Sennheiser microphones are only connected to the Tip and Sleeve of the 3.5mm plug so it should be a straight swap.

 

David

[j_b]

Some bedtime reading for you http://en.wikipedia.org/wiki/Boost_converter :o

[paulears]

The maths in that article just shows me how long ago I was good at it!

[Plantman]

So simple, I'll get one on order.

Thanks.

 

Re the SMPS, then I see, if you create AC, you can step it up, or perhaps that an oversimplification from a machanical engineer. But you are correct, that level of maths was wee while ago.

 

Cheers

[Stan Hope-Streeter]

Hi,I look after a budget PA system for a group of folk who do demonstrations of crafts on a stage.

It uses a pair of KAM UHF Body pack transmitters with the supplied mics. Head and Lavalier.

Head mics are fine, but the lavalier tend to feedback at too low a level, so I'd like to change them for something better.

 

.... I was thinking about using something like a Sennheiser ME4 cardioid unit, ....

 

Whilst a better microphone may help, this might not be the answer to your problem.

 

Some specialised techniques are required for using personal mics effectively and there are serious limitations on what can be achieved on a small budget. People often have unreasonable expectations of what can be done.

 

I don't know your level of experience, so sorry if this is sucking eggs stuff, but:

 

Are you subgroupng the lav mics and inserting a graphic, parametric, or FBX on their group? Have you at least one sweepable, or parametric, EQ on each console channel? Are you ringing out the mics thoroughly before the show?

 

If you can't do any of the above, my advice is to just use head mics - they will work much better with a budget rig.

 

Opinions differ re cardioid or omni for lav mics. An omni is less prone to popping and will give a more consistent level when the performer turns her/his head, but will usually be more prone to feedback. A cardioid will be more prone to popping and the level will change a lot with head movement, and because it has to be carefully pointed there will be serious problems if it gets moved out of position. But if it can be positioned properly, it will be less prone to feedback. My own preference, after decades of experience, is omnis every time - but I don't have to do this with low budget systems.

 

HTH

[Plantman]

Ah, I may be found out here.

My expertise in this field is pretty minimal, Valve amp with 802's for a disco, when I were a lad... Year of engineering in another field, so for sure my expectations could be unreasonable. But, with this bit of kit over the last few years I've invested some time out of interest and pretty close to being happy with it.

I can say that the PA amp has a collection of sliders that might be termed a graphic equaliser, and I have managed to tune out a lot of the ringing to make it useable, but we are just on the edge of that.

The audience is about 50-100 folk sitting in rows and generally well behaved, and they use it simply to allow those at the back to clearly hear the presenter's speech. With the headmics, I can easily make it too loud for their comfort, so we are not after much power.

Prior to the system, the audience used to get restless if the pesenter couldn't be heard well.

The hall used is always the same, and so I guess the local acoustics won't change greatly. I am trying to make what I think is an incremental step so that the system can more or less be switched on and the levels set, without having to battle feedback.

So cardioid may be the wrong thing, ok point taken..Iguess that I'll have to let you know how we make out. Thanks

[Stan Hope-Streeter]

The hall used is always the same, and so I guess the local acoustics won't change greatly. I am trying to make what I think is an incremental step so that the system can more or less be switched on and the levels set, without having to battle feedback.

So cardioid may be the wrong thing, ok point taken..

 

If your mixer is able to subgroup the lav mics, and has an insert point on the subgroup, your money might be better invested in a secondhand Sabine FBX than in some new mics. You would need to spend some time learning how to use it (to ring out the mics automatically, a few frequencies for each lav mic in each of several locations on stage, then locking it - NOT leaving it to look for feedback during the show)

You wouild have to look for a mains powered unit, not the very early types with a separate power supply. Suitable older versions are the 1020+ and 2020+, later ones are 1200, 2400 and 2410, and current production (expensive) 1220 and 2420. The "1" types are single channel and the "2" types have two independent channels, all are 1U rack mounting.

[Plantman]

My education is gathering momentum, fantastic.

 

I can insert a device between the mic receivers and the PA

The original supplier suggested a feedback suppressor when I first questioned the issue, and I was very attracted to the idea, other than the price for an effective one seemed OTT when compared with the overall package. However, my research into it did give me the clue that made me play with some success with the existing equaliser on the PA.

 

So, plan is to try out this cardioid, as its almost with me, and if that's the backwards step then see about an FBX unit.

 

Excellent advice all round, great to be allowed to communicate with such in depth knowledge.

[Plantman]

Guys,

 

Well, I tried the ME4 cardioid, and it is less sensitive to feedback than the std Kam items, and does work on only two wires as told. (Required a Senhheiser socket from Canford to get properly connected)

Its not as directionally sensitive as I imagined eitherso works pretty well in our environment.

 

In fact it is in my opinion significantly better and should be the small improvement I needed.

 

Thanks for all the advice.

[Stan Hope-Streeter]

Guys,

Well, I tried the ME4 cardioid, and it is less sensitive to feedback than the std Kam items, and does work on only two wires as told. (Required a Senhheiser socket from Canford to get properly connected)

Its not as directionally sensitive as I imagined eitherso works pretty well in our environment.

In fact it is in my opinion significantly better and should be the small improvement I needed.

Thanks for all the advice.<br />

 

That's very good news.

 

When attaching this (or any cardioid) mic to the presenter, be very careful to clip it on in such a way that it can't move out of position and point sideways instead of upwards.

 

An extra clip, safety pin etc can be used on the cable, an inch or two from the capsule, to help with this.

[AndyL]

Hi,

 

I look after a budget PA system for a group of folk who do demonstrations of crafts on a stage.

It uses a pair of KAM UHF Body pack transmitters with the supplied mics. Head and Lavalier.

Head mics are fine, but the lavalier tend to feedback at too low a level, so I'd like to change them for something better.

 

The existing mics are two wired, signal and screen. The open circuit voltage at the transmitter unit is 7.6volts and when mic is connected 4.7volts. Nominal resistance of a mic is 1.1kohms. (Quite interested how these high voltages are achieved with only three volt worth of battery cells....but I digress)

 

I was thinking about using something like a Sennheiser ME4 cardioid unit, but I see that 'proper' mics like these have three wire conections.

Could I have some advice on how to connect these two things together please?

 

Thanks

 

See a previous thread on a similar subject: Here

Scroll down to the last post in the thread (#13, from me) and at the bottom is a useful link. With electret mics it is very easy to use 'three wire' mics on 'two wire' inputs, the other way round can be much more difficult however.