DIY circuit issue

[aborgman]

So I recently built up a little box implementing a Linkwitz-Reiley 24dB high pass filter... and in testing I'm seeing something strange that I can't rightly explain.

Circuit is as follows:

1st order active highpass (7Hz) -> LR24 active highpass (60 Hz) -> 12dB gain stage -> variable attenuator

Everything looks great through the LR24 section - here is the signal at LR24 output:



That output is feeding a gain/variable attenuation circuit:



Inverting amplifier should provide ~12dB gain (more accurately 11.7dB), and the attentuator should provide ~12dB attenuation (more accurately 14dB). Output of the gain opamp should be identical to output of LR24 section, just amplified 12dB.

...but it isn't. It looks like this:



Op Amp is OP470 - 6MHz GBW, so it certainly is fast enough.

Test conditions are 50mV swept sine.

[Taylor Livingston]

This is a fairly advanced question for a non-technical forum. I think you'd get lots of in-depth answers at a dedicated DIY forum like DIYaudio or DIYstompboxes. Or even in the Amps section here at TB.

Are you simming it in Spice or just using that to draw the schematic?

[aborgman]

Originally Posted by conical johnson

This is a fairly advanced question for a non-technical forum. I think you'd get lots of in-depth answers at a dedicated DIY forum like DIYaudio or DIYstompboxes. Or even in the Amps section here at TB.

Are you simming it in Spice or just using that to draw the schematic?

It looks wonderful in Spice, but then everything always does... I've simulated all three sections in Spice - and the first two match up reasonably well, about as well as I'd expect.

The last one? Something is going on there - and I feel like it should be obvious, but it just isn't coming to me.

[PilbaraBass]

don't double post, please?

see my response in the effects section...

hint...starts with "cap" and ends with "acitor"

[moose23]

Originally Posted by PilbaraBass

don't double post, please?

see my response in the effects section...

hint...starts with "cap" and ends with "acitor"

Eh this is the effects section and he only double posted as someone here told him to post in in the amp section as he probably get a better response there which he did.