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Old 1st March 2003, 12:37 PM   #1
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Default AD797 op amp in active xover

I have an active xover of my own deisgn using TL07x op amps. This was just a cheap test to get the citcuit right etc and now Im ready to rebuild the whole shebang using higer quality op amps. I should be expecting to receive my ad797's shortly and was wondering if anything special needs to be done to use them well. I've read the other post on op amps and the spec sheet on the Analog Devices web site and as far as I can tell that the actual active xover bit should have no problem as its buffered before hand by two more op amps to give a low source impedance. However the buffers input come off a 50k pot fed directly from the DAC of my CD player. Now according to all the literature ive browsed this could be a bit of a problem reagarding the AD's need for a source impedance of under 1k. Will this be a problem or not?? So to finish off a run thru of the actual circuit. Output of DAC feeds 50k pot (volume control) which feeds op amps for buffer stage which feeds active xover circuit which feeds power amp.

Cheers for any input (aslong as its under 1k )

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Old 1st March 2003, 01:31 PM   #2
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Did you go through the AD797 datasheet? The input resistance of the AD797 seems very low. This might be a problem when it affects the corssover point of your filters?

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Old 1st March 2003, 01:37 PM   #3
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according to all the bumf ive got on active xovers as long as there is sufficient gain then the xover filter should maintain its profile and as a buffer supplies a low input impedence i would guess this be OK. Also the xover freq is lowish at 300hz and again I think this reduces the negative effects of high input impedence. If the input needs to be buffered by an alternative op amp what would be recommended?? OPA627??

Cheers again matt
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Old 1st March 2003, 02:32 PM   #4
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AD797 is a typical low level opamp, MC phono amp, mic amp etc. I would say this opamp is rather unsuitable.

Check out for example, OPA134, OPA2134, OPA627, AD8610, AD8620 and so on....

Extremely low noise opamps with bipolar input are suitable for low impedance signal sources and feedback network
/Per-Anders (my first name) or P-A as my friends call me
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