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Discrete opamps vs IC's opamp for CV mix Moog 904x cloning..
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jpdesroc



Joined: Dec 05, 2007
Posts: 27
Location: Canada

PostPosted: Tue Jun 03, 2014 6:16 am    Post subject: Discrete opamps vs IC's opamp for CV mix Moog 904x cloning.. Reply with quote  Mark this post and the followings unread

I'm in the process of cloning a Moog 904B module
with its original circuitry.
The only thing I would change are the followings:

Both opamps for CV mixing and stages freq cutoff originaly made of discrete
parts and transistors..
I heard the MOS-LAB, in their 904B clones used
2 separate 741 opamps to replace the Q1,2,3,4,5 and Q6,7,8,9,10 amplifiers.
http://www.freeinfosociety.com/electronics/schemview.php?id=944

I think any single opamps could be used as far as I
use the same feedback resistors, trimmers and surrounding parts..
741 seam a bit old to use in new made designs..
I was thinking of using 2 x TL071, one TL072 or something like that.
What about it ?

Second question:
I'd also put buffers for both input and output of this filter
still using TL07x opamps. I'm hesitating in using 2 separate TL071
or only one TL072. I'm just curious about any
possibilities of 'crosstalk' between both opamp parts
that could cause oscillations easily..
Maybe 2 separate TL071 would be the best or it doesn't
matter in this type of design..(??)

Thanks.
JP
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EdisonRex
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Joined: Mar 07, 2007
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PostPosted: Tue Jun 03, 2014 2:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

It is debatable when cloning how "accurate" to the original design you want to be and whether or not it's going to affect the sound. Personally I think anything that improves voltage control is a good thing.

I wouldn't worry about using a TL071 for a 741, it's not complicated.

I can't comment on any interactions in the output stage though as I haven't got this schematic handy. But in general, control side benefits from modern ICs. Audio side, well, it depends.

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