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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: 3
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: 929
Location: Northeastern shore of Toledo Bend
Audio files: 29
G2 patch files: 53

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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efm-7



Joined: Jan 27, 2016
Posts: 3
Location: Ontario, Canada

PostPosted: Tue Feb 09, 2016 7:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you Varice! - I noticed that this hadn't had a reply for days so I was horrified that might have asked a stupid question for my first post.

Now I will go source a 4-pos 2-pole multiswitch and give it a shot and report back. Still waiting on the 50k antilog pot from Tayda - man, are they ever taking forever to arrive.
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Flareless



Joined: Jan 16, 2016
Posts: 27
Location: Ontario, Canada

PostPosted: Wed Mar 02, 2016 2:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

efm-7 wrote:
Thank you Varice! - I noticed that this hadn't had a reply for days so I was horrified that might have asked a stupid question for my first post.

Now I will go source a 4-pos 2-pole multiswitch and give it a shot and report back. Still waiting on the 50k antilog pot from Tayda - man, are they ever taking forever to arrive.


Very interested to see how this works out. I'm building my second filter now and would like to try the mod you come up with if it's successful.

It's also nice to see another builder from Ontario.

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Rich
Lower West Side Studio
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efm-7



Joined: Jan 27, 2016
Posts: 3
Location: Ontario, Canada

PostPosted: Thu Mar 03, 2016 8:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Flareless wrote:

Very interested to see how this works out. I'm building my second filter now and would like to try the mod you come up with if it's successful.

It's also nice to see another builder from Ontario.


What I probably will do this weekend is break out the different parts of the ladder to a header and use jumpers to give it a test run.

It might be a while before I finish this, because I've yet to order a switch - which I will be ordering from Tayda and waiting 6 weeks, because I refuse to give DigiKey $8 for one, haha. I also don't have enough rack space left in my case, so I have to finish construction of a second one. I have 2 Yusynth VCOs and a second minimoog VCF and a few other modules for which parts are counted out and placed into jars.

Whereabouts in Ontario are you? I'm, from the NCR
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Flareless



Joined: Jan 16, 2016
Posts: 27
Location: Ontario, Canada

PostPosted: Thu Mar 03, 2016 9:18 am    Post subject: Reply with quote  Mark this post and the followings unread

efm-7 wrote:
Flareless wrote:

Very interested to see how this works out. I'm building my second filter now and would like to try the mod you come up with if it's successful.

It's also nice to see another builder from Ontario.


What I probably will do this weekend is break out the different parts of the ladder to a header and use jumpers to give it a test run.

It might be a while before I finish this, because I've yet to order a switch - which I will be ordering from Tayda and waiting 6 weeks, because I refuse to give DigiKey $8 for one, haha. I also don't have enough rack space left in my case, so I have to finish construction of a second one. I have 2 Yusynth VCOs and a second minimoog VCF and a few other modules for which parts are counted out and placed into jars.

Whereabouts in Ontario are you? I'm, from the NCR


I hear you on Digi-Key. The good thing is that if you do decide to pay their ransom you get the part the next day. Mouser is worse with their $20 shipping fee. I try to make larger orders in order to make them a better value.

I ran into the space constraint in early January. Fortunately I have a guy who does carpentry for me (I'm hopeless : ) and he built a beautiful 44 space walnut cabinet to match my Dotcom 22 space cabinet. The trouble is with all the new space I have to fill it! So far that's coming along well.

Still interested in how you make out with the VCF. I'm still an electronics rookie and don't get too deep into modifications but once they're available I can follow instructions pretty well. Please post your findings.

I live about half way between Collingwood and Owen Sound. It sounds like we may not be too far from each other. PM me if you're interested in getting together sometime, although not this week if you got as much snow as we did up here Very Happy

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Rich
Lower West Side Studio
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bassculture



Joined: Jan 23, 2011
Posts: 22
Location: france

PostPosted: Sun Jul 02, 2017 5:11 am    Post subject: Reply with quote  Mark this post and the followings unread

hello guys,

did you finally succeed with this mod ?
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