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 Forum index » DIY Hardware and Software » YuSynth
Minimoog filter - different slopes?
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efm-7



Joined: Jan 27, 2016
Posts: 1
Location: Ontario, Canada

PostPosted: Wed Jan 27, 2016 7:39 am    Post subject: Minimoog filter - different slopes? Reply with quote  Mark this post and the followings unread

Hi all, this is my first post here - and regarding my first Yusynth module build.

Is it possible to tap into different parts of the ladder to get different slopes?

I have a moog sub 37 with 6,12,18,24 dB/oct settings for the filter, and my favorite filter slope is actually the 6dB/oct!, and would love to be able to have something similar in my modular.
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varice



Joined: Dec 29, 2004
Posts: 810
Location: Northeastern shore of Toledo Bend
Audio files: 27
G2 patch files: 52

PostPosted: Mon Feb 01, 2016 8:26 am    Post subject: Re: Minimoog filter - different slopes? Reply with quote  Mark this post and the followings unread

efm-7 wrote:
Hi all, this is my first post here - and regarding my first Yusynth module build.

Is it possible to tap into different parts of the ladder to get different slopes?

I have a moog sub 37 with 6,12,18,24 dB/oct settings for the filter, and my favorite filter slope is actually the 6dB/oct!, and would love to be able to have something similar in my modular.

welcome to the electro-music forum efm-7 Exclamation

Yes it is possible to get different slopes from this filter. You just need to tap into different points down the transistor ladder. This is a four pole filter, and the most common configuration is to tap the top of the ladder for the 24dB slope. In this case, it is tapped at the collectors of transistors Q6 and Q7, across the capacitor C7. The next point down the ladder is across C6 for the third pole 18dB slope, then across C5 for 12dB, and then across C4 for 6dB.

I’m not sure exactly how the four different slopes are selected on the Moog Sub 37, but I have a moogerfooger MF-101 Low Pass Filter. It has two slopes that can be selected, 12dB and 24dB. I have traced the circuit and found that the 12dB selection is tapped from the second pole of the ladder. It has another differential amplifier connected there. So, the slope switch actually selects the output of one of the two differential amplifier circuits. The feedback circuit for the filter resonance (emphasis) remains connected to the differential amplifier connected at the top of the ladder and is not affected by the slope switch setting.

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