Need sum 1 2 look at my PCB Layout and tell me if it is OK??

[Minion]

Hi ,I am pretty new to electronics but I have been learning slowly but surely...I recently aquired some Burr Brown INA103 Op amps and while looking through the Data sheet i found a Schematic for Building a Basic Mic Pre amp (Unballanced) with Phantom power and a 20db Pad so I figured I would try building it but first I need to design my PCB which is something I have never done before and the Schematic didn"t show the Power input curcuitry so i came up with my own and the Schematic uses a OPA627 for the Output Offset Voltage controll loop and the OPA627 is one of the most expensive Opamps the is so I figured I would use a OPA134 or a OPA137 Instead as they have simular specs and are Both Fet Opamps, Do you think this will be a Problem??
I also added the CMR Trimmer....

Here is the PCB Layout I designed:

And here is the Schematic:

And here is a Link to the Datasheet:

http://www-s.ti.com/sc/ds/ina103.pdf

Can you see any Mistakes I made or problems with the design??


I was also trying to Figure out how to Make a Ballanced output without haveing to use an audio transformer and came accross some information on 'Impedance Ballancing" which is a way to get Semi Ballanced output from a Non ballanced source....

From what I read it says that you basicly Tie Pin 3 of the XLR to Star/Chassis Ground and then measure the Output Impedance of Pin 2 and then add a resistor of that Value to Pin 3 so that the Impedances of Pin 2 and 3 Match and then you will get an Impedance Ballanced output...

Am I totally wrong here?? If I am can you please Set me straight?? If I am on the Right track is the way I Implemented the Impedance Ballanceing Correct?? If not can you please Set me Straight......


ThanX a Lot Guys....


Cheers


PS: If my design is OK you have permision to use it.....

 

[Svart]

I wouldn't run the ground trace all the way around the circuit. You can get strange things to happen with a ground loop like that.

opa134 will work fine here but if you are planning to do more than one preamp I would lay them both out and share an opa2134 or opa2604.

You could easily make a balanced output with the 2142 IC or you could do it with a dual opamp. There are a lot of ways to do it, it depends on what you want to do with it!

 

[Boswell]

I wouldn't run the ground trace all the way around the circuit. You can get strange things to happen with a ground loop like that.

Running a grounded track all the way round the board is a common technique. The trick is to connect it to ground at only one point, usually the input connector. So the track from pin 7 of the INA103 and other nodes should have its own path to input ground.

The servo amp does not need to be an OPA727. Any FET-input device with a very low input offset voltage such as an OPA124 will do here. It needs to be FET-input to minimise the extra offset caused by the bias current flowing through the 100K resistor.

The BB circuit is balanced input. If you want transformerless balanced output as well, add a TI DRV134 or DRV135 on the end.

 

[Minion]

Thanx a Lot for the Tips guys.....

How could I use a Dual Opamp (NE5532 ??) to get a Ballanced output??

I see if I fed the Dual inputs the same audio signal I would get Two of the Same Signal comeing out of the Dual But How would that be ballanced cuz don"t both outputs have to be Out of Phaze with each other to be ballanced?? Or are they allready out of phaze with each other??

and If i used a Dual Opamps like the NE5532 what do i do about the Gain Controll?? Do I set the Dual to Unity gain or something and then just controll the Gain with the Gain adjust of the INA103??

Will the Impedance Ballancing I mentioned before work the way i Explained it or was I way off??

(Maybe I don"t really need Ballanced output as I usually use 1/4 TS connections anyways and I use short cables...)


Thanx a Lot Guys.....


PS: I wasn"t sure about the way the gain adjust on the INA103 was supposed to work as I had never seen that Schematic symbol before, can someone tell me if i Implememnted the gain adjust Properly in my PCB Layout??

Also If I run the Ground Trace all the way arround but do not Join them at both ends would it be OK Or would it be best to Give all Grounds a Direct Trace to the Main Ground??
:grin:

 

[Svart]

Running a grounded track all the way round the board is a common technique

yes but I have physically measured RF on ground traces that re of certain sizes. You are making a loop antenna if you do this. It's just best not to do it.

 

[peterc]

Double

 

[peterc]

How could I use a Dual Opamp (NE5532 ??) to get a Ballanced output??

I have a design for a balancing amp here:

http://1176neve.tripod.com/id6.html

Used it many times, works well.

Peter

 

[Minion]

ThanX a Lot Peter, So I can basicly connect the Output from my curcuit to the Input of your curcuit and Run the IC"s off of the Same Power rails and get a Ballanced output??

Does your Curcuit affect the Gain of My curcuit or introduce any Distortion?? (Meaning it won"t make it louder or quieter and I would adjust the gain the same way I do in my design)

Also can I use any Dual opamps of simular specs?(EG:OPA2107,OPA2277)
and are there any other things I should take into consideration when integrateing your Ballanceing design into my Preamp design??

ThanX a Million!!!

 

[CJ]

Hang an HS-66 or an A-20 on that thing and you will be one happy camper.
This not only gives you a balanced output, but also provides galvic isolation for maximum dependibility.
I always get nervous when I see an opamp output, easy to pop if you get a 120 ground loop or somethimg like that.

 

[Tryinmybest]

I'm an idiot, so forgive me for my questions but does one NEED a pre-designed pcb board? or can you just pick up a generic one from radio shack and start soldering?

 

[Minion]

No You don"t "need" a PCB Board But for me it is easier than useing a Breadboard or Vertaboard and Makeing your own PCB Board from a PCB design is Pretty easy to do and only takes a couple hours and when you are done you have a nice looking PCB that just needs to be stuffed.....


Cheers

 

[Tryinmybest]

makes sense..so how does one go about making their own pcb boards?

 

[kiira]

[quote author="Tryinmybest"]makes sense..so how does one go about making their own pcb boards?[/quote]

Tada.

http://www.fullnet.com/u/tomg/gooteepc.htm

http://www.electricstuff.co.uk/pcbs.html

http://headwize.com/projects/index.htm#diy

there's stuff all over the www but I like these.

Kiira