Need line driver to 100 KHz

[Earl]

Hi Folks,

I need to drive a .004 mfd total capacitance line from 30 to 100 KHz. The
application is composite stereo to an FM transmitter, so I need flat
response upwards of 100 KHz, and good phase response. The cable is Belden
1800, 110 Ohms, I think, tho that probably doesn't apply much in these low
freqs. It's around 130 feet. It's actually two-cond shielded, though this
is unbalanced. Noise doesn't seem to be a problem. The signal level is
about 4V P-P.

I've tried an NE5532 op-ampwith some series resistance in the output, but
get a lot of hash around 1 Mhz. Non-inverting configuration -- unity gain.

What's a good chip for this app?

 

[Robert Baer]

Hi Folks,

I need to drive a .004 mfd total capacitance line from 30 to 100 KHz. The
application is composite stereo to an FM transmitter, so I need flat
response upwards of 100 KHz, and good phase response. The cable is Belden
1800, 110 Ohms, I think, tho that probably doesn't apply much in these low
freqs. It's around 130 feet. It's actually two-cond shielded, though this
is unbalanced. Noise doesn't seem to be a problem. The signal level is
about 4V P-P.

I've tried an NE5532 op-ampwith some series resistance in the output, but
get a lot of hash around 1 Mhz. Non-inverting configuration -- unity gain.

What's a good chip for this app?

I bet that "hash" is one or more local radio station.
If the level is well within the capabilities of the op-amp, then you
should see if the drive is OK or not.
Add some RC filteringto decrease that "hash".
Use an LH0002 current buffer (inside the loop) for extra current drive
capabilities.