hi guys,

i have available some SSM2142 balanced line driver IC's

these are what Rane use in their microphone preamps to provide balanced outputs,

i want to use them in some of my preamps to provide balanced output for connecting straight into a PA system.

I have connected the chip up as per the rane schematic, and it works fine on my pc (using the microphone input) however when i connected it to the PA system, i got no signal,

any ideas of whats wrong here?

cheers
Blair

What pins did you use when you connected it to the PC? The ground and the (+) signal?

If so, you could try it again with the ground and the (-) signal just to make sure it's working.

If so, are you sure the 2 signals are out of phase (the + and - pins)?

Because that's what you use in the PA if you use the balanced input.

Gilles

well there is definatly signal along both pins 2 and 3,

they seem to be out of phase, as far as i can tell using the cool edit phase analysis.

i guess i'll have to have another play with the mixer when i get the chance

cheers
Blair

well thanks to the software that you posted, i have discovered that the signals are infact in phase,

now i just have to work out how to get them out of phase,

anybody used this chip before?

cheers
Blair

from datasheet;



is that the same as the Rane schematic?

the rane schemtic had a 100r resistor between the two outputs and has a coupling cap between the linked pins (ie pin 7-8 and pin 1-2)

I have removed the 100r resistor and the phasing is now correct except that the -phase is now 10x lower in signal strength

what is going on here?

cheers
Blair

Are you sure it's a 100r resistor, not a higher value like a 100K?

Or maybe it's not connected between the outputs, but another way.

I didn't find the schematic you're mentionning.

what value are the coupling caps? Try removing them, one might be faulty... To be honest, I haven't the time to go reading the datasheet, but that gif I posted is the recommended "standard" circuit... so I would start there.

Seems like you always had the -ve phase, but it was swamped by the +ve signal via that 100ohm resistor. Double check that it is only 100ohms and not some multiple of 100.

BTW, schematic diagrams are notoriously full of errors. If you can, check the device itself, the schematic may be wrong.

www.muziek-gg.com/koerier/koerier%203%2001.pdf
here I find a schematics of a dibox with that ssm.

I will build a mic pre with that chip so please report  how goes

The caps between the output and sense pins should be bipolar, generally 10uF bipolar electrolytic. Check the datasheet. We use a circuit similar to Fig 7 in the datasheet in several products and have no problems, using it for balanced or unbalanced output.

well I pulled the caps out and stuck links between the pins where the caps were

everything is sweet now,

i had 22uf bipolar electros in there, but i find it strange that on two identical boards that i have made of this circuit that both had faulty caps on the -phase side,

should i go out and get some 10uf's or will the circuit be fine without them,

everything is in the correct phases and at equal strength,


now just to think about some protecting incase someone plugs it into a phantom powered channel...    anyone got any ideas?

cheers
Blair

the datasheet is all knowing and all powerful, obey it.

Quote from: from datasheetIn applications encountering a large dc offset on the cable or those wishing to ensure optimal rejection performance by avoiding differential offset error sources, dc blocking capacitors may be employed at the sense outputs of the SSM2142. As shown in the test circuit, these components should present as little impedance as possible to minimize low-frequency errors, such as 10 mF NP (or tantalum if the polarity of the offset is known).

Incidentally, 10mF in this case means 10µF. (Non-polarised.)