[sdiy] CEM3372 passband gain trick?

[Dave Manley]

The mini filter is discrete, so adding an opamp is easiest,  although it would interesting (perverse?) to keep it discrete.

-------- Original Message --------
 From: Tom Wiltshire <tom at electricdruid.net>
 Sent: Mon, Aug 13, 2012 11:06 AM
 To: Magnus Danielson <magnus at rubidium.dyndns.org>
 CC: Dave Manley <dlmanley at sonic.net>; synth-diy at dropmix.xs4all.nl
 Subject: Re: [sdiy] CEM3372 passband gain trick?

>
>On 13 Aug 2012, at 18:57, Magnus Danielson wrote:
>
>> Dave,
>> 
>> On 08/13/2012 05:15 PM, Dave Manley wrote:
>>> Is there a published mod to the minimoog filter to change this?
>> 
>> I haven't seen one, but given the hints in this thread, it should be trivial for you to do that. In fact, it would be fairly trivial to make the property switchable or even a separate pot to control how much pass-band suppression you should experience, as you would simply control how much of the input will be driven to the diff-amp inserted prior to the resonance pot. Full (1:1) amount gives no suppression, while no amount gives full suppression.
>> 
>> It should not involve more than an op-amp, a handful of resistors and a pot to pull this off.
>> 
>> Cheers,
>> Magnus
>
>If your Moog filter has voltage-controlled resonance using a CA3080 or LM13700 section, you could use the other input of the OTA for the input signal feed and not even need the op-amp. Just a thought.
>
>Tom
>