Neve Ba 283/Discrete op amp input stage

[Tubetec]

Im working on an idea to combine a Neve Ba output stage with discrete mic pre from a yamaha Pm3000 series console .Ive cut away the pre from the large channel board ,works great directly from the Doa output with an unbalanced signal,
I also left  the next stage on the board in place ,its an ne5532 ,the first section is fed directly from the DOA ,the second section is fed in reverse polarity from the output of the first section. Originally these two outputs were fed to the phase switch ,Ive tried connecting them both to an xlr output , seems to work fine into a balanced line  ,but is that a valid circuit to drive a balanced send ?

The other thing I was hoping to find out was ,say I want to box this up with a Neve output driver  ,the neve requires the usual 24 volt + rail , is it possible to derive a supply from the 24volt rail to supply the DOA , it usually requires something in the order of +/- 15-18 volts ,maybe for the sake of simplicity I can take a hit on the supply voltages of the DOA  in any case the full voltage swing of the DOA wont be required at the neve BA input .

Just for the sake of simplicity ,suppose I have a 24 volt battery running the neve so + battery to 24 volt, battery neg to ground, would it be possible to connect the doa +/- rails directly across the terminals of the battery or will this cause some large voltage offset due to different ground potentials ? Is there any way to avoid this without interposing a transformer .


   

 

[Khron]

1) http://sound.whsites.net/articles/balanced-2.htm

2) The BA283 has an input DC-blocking capacitor, but for the output, instead of the transformer, you might need to use a load resistor, or a current-source (basically, just like the simpler class-A amplifiers do)

3) You're definitely gonna need some sort of rail-splitter for the mic preamp stage, in order to have a low-impedance path for the "half-rail" (mid-point between, in this case, the battery terminals).

 

[Tubetec]

Thanks Khron ,
thats a great article ,
I'll post up the schem of the yamaha pre later ,

 

[mjrippe]

2) The BA283 has an input DC-blocking capacitor, but for the output, instead of the transformer, you might need to use a load resistor, or a current-source (basically, just like the simpler class-A amplifiers do)

A BA-283 needs either an LO1166 transformer or T1310 inductor (or equivalents) on the output.

 

[Khron]

Because....?

A BA-283 needs either an LO1166 transformer or T1310 inductor (or equivalents) on the output.

 

[mjrippe]

Because....?

http://auroraaudio.net/forums/topic/test-jig-for-ba283

 

[abbey road d enfer]

the first section is fed directly from the DOA ,the second section is fed in reverse polarity from the output of the first section. Originally these two outputs were fed to the phase switch ,Ive tried connecting them both to an xlr output , seems to work fine into a balanced line  ,but is that a valid circuit to drive a balanced send ?

It works, but is one of the worst solutions in the real world. This was commonly known as the Tascam balanced output, and was famous for the "Tascam problem". Very simply, it cannot be connected to an unbalanced input like a floating output can, such as a transformer output or one of the Electronically Balanced Output Stages using cross-coupling to make it behave almost transformer-like.
You'd be much better off with a simple impedance-balanced stage.

 

[bluebird]

You'd be much better off with a simple impedance-balanced stage.

I second this. Its the simplest way and you get to take advantage of the drive capability of the existing DOA without adding any more active electronics. You don't get the +6db you would get with a true differential balanced circuit, but you still get noise cancellation.