newbie help for balanced I/O in an eq :shock:

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capnspoony

Well-known member
Joined
Apr 29, 2006
Messages
400
Location
brooklyn, NY
hi helpers,

this is my first time building not from specific directions and i'm looking for a good way to add a "good" balanced input/output stage using op amps...

http://www.ethanwiner.com/spect-3.jpg

I was looking at the calrec shemo on the gyraf page for help but I get confused with what is exactly necessary for the input stage and output stage

If i were to cascade this design to make a 3 band eq would i need the 150R resistor on the output or is that simply there for a buffer? do i need a buffer stage between stages to a parametric eq? and what purpose does the first opamp serve in this circuit im confused as to what the 100K log pot by the "input" does.

I just graduated college and am just getting started in electronics.. so far its been a headache .. but in a good way .. any help would be appreciated ..
best,
-richie :oops:
 
Ok, you raise a number of issues:

Balanced input and output. The simplest integrated circuit solution is to use the Analog Devices SSM2141 for the input and the SSM2142 for the output. The similar parts from Burr-Brown (TI) are INA134 and DRV134. Example circuits are given in the corresponding data sheets.

Cascading. You can leave out one gain buffer (the opamp after the level control in the schematic), and omit the level controls for the second and third stages and the 150R after the first and second stages. You need the x2 buffer at the input to buffer the level control. If you were to use only one other buffer, it may have to be x4 instead of x2, but positioned before the last stage. This avoids overload at the expense of signal-to-noise ratio. To get x4, use a 30K feedback resistor and 10K to ground in place of the 100Ks.
 
If you're talking about transformer input, just use a 1:1 line level transformer (not a mic transformer). Float the transformer primary and connect the secondary across the level control.

I don't recommend driving an output transfomer with this circuit.
 
Look for the eq Mr Barry Porter did design and gave it free on the internet , you find it by rogy with the name neteq or portereq somewere else.
Yust have a look in this forum and you will find enough of it.
 
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