[sdiy] Jupiter 8 HPF circuit weirdness

[Jack Jackson]

I'm quite ill today so I built the JP8 HPF circuit using the correct FET (2SK30A-GR) and an LM13700 in place of the BA662 for the OTA. 

It seems to perform the high pass function but with a few seconds of delay until it 'climbs' up to start filtering but when I turn the feedback OTA down it stops the high pass filter instantly. If I change the frequency of the oscillator the high pass filter seems to stop working and has to 'climb' up again. Any ideas what could be causing this? Note I'm using decoupling capacitors on the circuit.

Best Regards,
Jack