Topic: balanced to phantompower to unbalanced

[perik]

hi!

Im going to build a small and simple preamp. the only thing im thinking of is how to go between the balanced XLR output on the microphone to the unbalanced input in the preamp.

First I was thinking of:

XLR
Pin 1 (Shield)     --->    - (ground)
Pin 2 (Hot (+))   --->   + (signal)
Pin 3 (Cold (–))  --->    - (ground)

but then I was thinking that maybe Im in the future will connect Denecke ps2 or something similliar (or build one myself) phantompowersupply in between so that the setup will be like this:

condensermic ---> phantompower ---> unbalanced input in preamp

Ive heard that the mic will be damage if you would connect it as above (1 -> ground, 2 -> signal, 3 -> ground) into a phantompowered input. This make sense.

My question is:
Do I have to worry about this if I connect it like this: condensermic ---> phantompower ---> unbalanced input in preamp if I have got the cable with 1 -> ground, 2 -> signal, 3 -> ground beween the phantompower unit and the unbalanced input???

can I connect it like this instead on the unbalanced input on the preamp. with not connecting the shield into anything:
Pin 1 (Shield)     --->    without any connection
Pin 2 (Hot (+))   --->   + (signal)
Pin 3 (Cold (–))  --->    - (ground)

or will I have problem with noise?

or do I not have to worry about this because the phantompower is before the unbalanced input?


thanks for your help!

Perik

[Church-Audio]

You can use a opamp input and create a active balanced circuit with a dual opamp, or use a transformer to balance the input of your unbalanced preamp. Just remember transformers have insurtion loss of 1.5 db to as much as 6db. Its pretty simple if you can build a preamp its not a problem to create a balanced front end with an opamp and have it so its the first stage of your preamps input insurt a pad between the first stage and second stage and run the first stage at unity gain to keep the noise floor down. There are many schematics on line for mic pre's.


Chris Church

hi!

Im going to build a small and simple preamp. the only thing im thinking of is how to go between the balanced XLR output on the microphone to the unbalanced input in the preamp.

First I was thinking of:

XLR
Pin 1 (Shield)     --->    - (ground)
Pin 2 (Hot (+))   --->   + (signal)
Pin 3 (Cold (–))  --->    - (ground)

but then I was thinking that maybe Im in the future will connect Denecke ps2 or something similliar (or build one myself) phantompowersupply in between so that the setup will be like this:

condensermic ---> phantompower ---> unbalanced input in preamp

Ive heard that the mic will be damage if you would connect it as above (1 -> ground, 2 -> signal, 3 -> ground) into a phantompowered input. This make sense.

My question is:
Do I have to worry about this if I connect it like this: condensermic ---> phantompower ---> unbalanced input in preamp if I have got the cable with 1 -> ground, 2 -> signal, 3 -> ground beween the phantompower unit and the unbalanced input???

can I connect it like this instead on the unbalanced input on the preamp. with not connecting the shield into anything:
Pin 1 (Shield)     --->    without any connection
Pin 2 (Hot (+))   --->   + (signal)
Pin 3 (Cold (–))  --->    - (ground)

or will I have problem with noise?

or do I not have to worry about this because the phantompower is before the unbalanced input?


thanks for your help!

Perik

[perik]

ok. thanks for your reply.

what is an opamp then? im using a schedule to build this preamp. i know some about electronics but I would never be able to come up with one preamp myself.

is it possible to do it the way Im doing it as well?

XLR
Pin 1 (Shield)     --->    - (ground)
Pin 2 (Hot (+))   --->   + (signal)
Pin 3 (Cold (–))  --->    - (ground)

and also is it possible to put an phantompowerunit in between without taking the risk of destroying any mics?

thanks

P

[Church-Audio]

What kind of schedule are you on You mean to say schematic If you do not know about buffer amps and balancing circuits its pretty simple electronics this will be hard to understand. You need a dual op amp like a TLO72, or NE5532, you take the - input and use that for your pin3 and the possitive input and use that for pin 2. Then you have a balanced input then connect the output of that opamp to your unbalanced preamp input, there is a few bits and bobs that need to be put in like dc blocking caps for the inputs and a resistor in the feedback loop to make it run at unity. But this is beyond what I can explain via a text message. In short take a look at some designs that are out there, and build something similar what schematic are yoiu using? if I could see it I might be better able to help, also talk to guys like Poorlyconditioned and Sparke.

PS... make the phantom supply part of the circuit its much better that way then to have all these seperate boxes. By the way expect to spend atleast $100 to $150 in parts for a mono preamp when it is all said and done, if you want to use transformers expect to pay atleast $50-100 per channel.


Chris Church

ok. thanks for your reply.

what is an opamp then? im using a schedule to build this preamp. i know some about electronics but I would never be able to come up with one preamp myself.

is it possible to do it the way Im doing it as well?

XLR
Pin 1 (Shield)     --->    - (ground)
Pin 2 (Hot (+))   --->   + (signal)
Pin 3 (Cold (–))  --->    - (ground)

and also is it possible to put an phantompowerunit in between without taking the risk of destroying any mics?

thanks

P

[perik]

yes i mean schematic ...

ok. thanks a lot for your help.

can u just answer once more

Is it possible to do like this as well (the input in the preamp is already for miclevel)

Pin 1 (Shield) ---> without any connection
Pin 2 (Hot (+)) ---> + (signal)
Pin 3 (Cold (–)) ---> - (ground)


or like this if Im not are using the external phantompower:

Pin 1 (Shield) ---> - (ground)
Pin 2 (Hot (+)) ---> + (signal)
Pin 3 (Cold (–)) ---> - (ground)

are any of these wrong? in what case which one or is it possible to use both solutions?

/ p

[Church-Audio]

All of these solutions would work but the ground should be connected to the preamp ground because you never want to float the ground on your mic because then you lose the ability to drain inducted interference, and your XLR becomes a giant antenna.

Chris Church

yes i mean schematic ...

ok. thanks a lot for your help.

can u just answer once more

Is it possible to do like this as well (the input in the preamp is already for miclevel)

Pin 1 (Shield) ---> without any connection
Pin 2 (Hot (+)) ---> + (signal)
Pin 3 (Cold (–)) ---> - (ground)


or like this if Im not are using the external phantompower:

Pin 1 (Shield) ---> - (ground)
Pin 2 (Hot (+)) ---> + (signal)
Pin 3 (Cold (–)) ---> - (ground)

are any of these wrong? in what case which one or is it possible to use both solutions?

/ p

[perik]

ok. thanks!

so this solution would work with a "phantompowersupply unit" in between as well? Its only when the phantompower comes straight from the input where the "modified XLR cable" is connected i risk to destroy my mic?

would this work then:
condensermic --<XLR>--> phantompower --<modified XLR>--> unbalanced input in preamp

modified xlr:
Pin 1 (Shield) ---> - (ground)
Pin 2 (Hot (+)) ---> + (signal)
Pin 3 (Cold (–)) ---> - (ground)

thanks a lot for your help! very much apreciated!!!

/ p

[Church-Audio]

You can use an external phantom box. And you can connect the output any way you wish. It should not be a problem because the output should be coupled with dc blocking caps but just in case I suggest a 10uf poly cap with as small of a voltage as possible to keep the size down.
I would also watch out for input impedance you need a mic preamp to have about 1k for a 600ohm load from your condenser mic.

Chris Church

ok. thanks!

so this solution would work with a "phantompowersupply unit" in between as well? Its only when the phantompower comes straight from the input where the "modified XLR cable" is connected i risk to destroy my mic?

would this work then:
condensermic --<XLR>--> phantompower --<modified XLR>--> unbalanced input in preamp

modified xlr:
Pin 1 (Shield) ---> - (ground)
Pin 2 (Hot (+)) ---> + (signal)
Pin 3 (Cold (–)) ---> - (ground)

thanks a lot for your help! very much apreciated!!!

/ p