[sdiy] Jupiter 8 HPF circuit weirdness

[Jack Jackson]

Hi Rob,

What test signal/output monitoring were you using?  I managed to get it working rather nicely once I stopped needlessy using the onboard LM13700 before the FET. (In fact I'm wondering if you could just use the onboard buffer and omit the FET entirely)

Best Regards,
Jack 

----------------------------------------
> CC: synth-diy at dropmix.xs4all.nl
> From: rob.keeble at amsynths.co.uk
> Subject: Re: [sdiy] Jupiter 8 HPF circuit weirdness
> Date: Thu, 4 Sep 2014 18:58:12 +0100
> To: jackdamery at hotmail.co.uk
>
> Hi
> I have built this circuit with BA6110 and found it to be rather unreliable, sometimes working ok other times it doesn't cut off or has a less than smooth response as you are getting. I put a log slider in rather than linear. I presume some hand selection of the OTA and FET is needed. A similar circuit from the SH5 with a ca3080 seems far more consistent. I use the GR FET too.
>
> Ideas from the list would be very useful!
>
> Best Regards
> Rob Keeble
> AMSynths
> www.amsynths.co.uk
>
>> On 3 Sep 2014, at 17:52, Jack Jackson <jackdamery at hotmail.co.uk> wrote:
>>
>> 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
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