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 Forum index » DIY Hardware and Software » Developers' Corner
Moog type ladder filter with FETs?
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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Jan 15, 2018 2:26 am    Post subject: Moog type ladder filter with FETs?
Subject description: is this possible?
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While cleaning out old component boxes I have found 8pcs dual FET's K146GR.
Very little info on the net, only THIS where it says :
Quote:
the K146 is a silicon N - FET dual transistor, Uds=40V, Idss=5 - 30mA, applications: audio frequency stage, low noise, if OEM from japan see 2SK146

I wonder if these can be used in a Moog type ladder filter since my guess is that they are well matched?

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mrand



Joined: Mar 30, 2014
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Location: Yukon and London Ontario

PostPosted: Mon Jan 22, 2018 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Do you mean in place of the BJTs in the transistor ladder itself? I think that is not really possible, but I'm not an expert. But perhaps you could use them as buffers in an OTA type filter? Look at the roland system100 vcf, for example, which works best with 4 matched FETs.
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Grumble



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PostPosted: Tue Jan 23, 2018 3:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes I was hoping to build the Moog ladder filter with these FET's, because they are very nicely matched because they are with 2 in one housing.
I was under the impression that the Moog ladder filter was just a number of current mirrors with a capacitance in between them.
And making current mirrors with FET's isn't that hard, is it?

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mrand



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PostPosted: Tue Jan 23, 2018 5:49 am    Post subject: Reply with quote  Mark this post and the followings unread

ah, you see I told you i was no expert Wink
I'm interested to hear if you develop this further.
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Parkchemiker



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PostPosted: Wed May 23, 2018 1:32 pm    Post subject: Moog ladder filter with FETs instead of BJTs Reply with quote  Mark this post and the followings unread

Hello Grumble

FETS don't have the same I (collector) - U (base) behaviour as the transistor. But one should test this FET-ladder-filter with LTspice.

Parkchemiker

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varice



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PostPosted: Wed May 23, 2018 6:43 pm    Post subject: Re: Moog type ladder filter with FETs?
Subject description: is this possible?
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Grumble wrote:
While cleaning out old component boxes I have found 8pcs dual FET's K146GR.
Very little info on the net, only THIS where it says :
Quote:
the K146 is a silicon N - FET dual transistor, Uds=40V, Idss=5 - 30mA, applications: audio frequency stage, low noise, if OEM from japan see 2SK146

I wonder if these can be used in a Moog type ladder filter since my guess is that they are well matched?

Hmmm… a very intriguing idea. thinking

But, I think that it is worth noting that the good Dr Bob Moog only used silicon trannys in the multiple ladder designs that I have seen, such as even his more recent design of the moogerfooger MF-101.

BTW, it is Bob's birthday today party!

Still, I would be interested if anyone comes up with any Moog ladder alternative designs. Cool

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