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 Forum index » DIY Hardware and Software » YuSynth
VCF tracking: no Tempcos?
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Jaba



Joined: Feb 27, 2009
Posts: 47
Location: Genova, Italy

PostPosted: Thu Mar 05, 2009 7:04 am    Post subject: VCF tracking: no Tempcos? Reply with quote  Mark this post and the followings unread

Hello,
I want to build some of the Yusynth filters (actually all of them), but now I notice that none of your those filters has tempcos; do they manage to track correctly when oscillating ? how is it ?
should I want to add tempcos, would you please give details about them, such as specific value, where to put it in the schematic, ... ?
thank you
Paolo
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yusynth



Joined: Nov 24, 2005
Posts: 1224
Location: France

PostPosted: Thu Mar 05, 2009 2:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nearly no VCF (Moog, ArP, EMS...) have tempcos in them.
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Yves
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Jaba



Joined: Feb 27, 2009
Posts: 47
Location: Genova, Italy

PostPosted: Fri Mar 06, 2009 4:02 am    Post subject: Reply with quote  Mark this post and the followings unread

thank you for your answer, but this sounds new to me

I am no expert, but all the schematics I have from ARP VCFs (4012, 4023, 4034, 4035, 4072, 4075) use a 1K87 3% 3500ppm Tempco resistor, and most transistor ladder based filters I have seen use a 1K Tempco 3000ppm, even the EFM VCF2f had it

maybe you just don't care about temperature compensation, or you found another way to make the tracking good enough, ... ?

but my point is: if I build your filters (trans. ladder and ARP4072) and make them oscillate, will I be able to play them in tune over at least three octaves ? (as if they were VCOs)

and if the answer is yes, then I would like to learn how you achieved it, if you would share your design criteria
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yusynth



Joined: Nov 24, 2005
Posts: 1224
Location: France

PostPosted: Fri Mar 06, 2009 6:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Jaba wrote:
maybe you just don't care about temperature compensation, or you found another way to make the tracking good enough, ... ?

but my point is: if I build your filters (trans. ladder and ARP4072) and make them oscillate, will I be able to play them in tune over at least three octaves ? (as if they were VCOs)


You are confusing goodness of tracking and temperature stability.
The tempco just compensate for frequency drift when ambient temperature is changing. The goodness of tracking over a given number of octaves depends mainly on the tracking of Icb versus Vbe of the transistor(s) involved in the exponential converter.

Therefore VCF in oscillation can achieved a good V/Oct over many octaves without having tempcos.
Concerning the various yusynth VCF : the moog and ARP clones track well over at least 5 octaves, the Steiner tracks well over three/four octaves and the diode EMS only tracks well over two/three octaves.

Now if you wish to use a tempco , then use a 1.8K 3000ppm PTC resistor, in the Moog clone substitute the tempco to R11 and in the ARP 4072 use a 1K tempco and substitute it to R46.

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Jaba



Joined: Feb 27, 2009
Posts: 47
Location: Genova, Italy

PostPosted: Fri Mar 06, 2009 8:37 am    Post subject: Reply with quote  Mark this post and the followings unread

great!
thank you a lot, this makes me very happy
No more excuses now, I'll have to build them all.

I'll order the kits from Bridechamber for diode ladderVCF, MiniMoog VCF and ARP4072 VCF, and buy 3096 and other components for a Steiner VCF

Any plan to do more ARP clones, such as the 4023 and 4034/4035 filters, or the Odysseys VCOs ?

thank you
PaoloV
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yusynth



Joined: Nov 24, 2005
Posts: 1224
Location: France

PostPosted: Fri Mar 06, 2009 10:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi

Have fun then Wink

I have no plan of making more ARP clones, I am really satisfied with the ARP4072 and my yusynth VCOs, I am not interested in making ARP VCOs.
But one must never say "never" Wink

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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
Audio files: 5

PostPosted: Fri Mar 06, 2009 10:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Jaba wrote:

Any plan to do more ARP clones, such as the 4023 and 4034/4035 filters, or the Odysseys VCOs ?


You might find this interesting - http://electro-music.com/forum/topic-28604.html - you'd have to etch your own board but I've built this circuit and it's great!
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Jaba



Joined: Feb 27, 2009
Posts: 47
Location: Genova, Italy

PostPosted: Mon Mar 09, 2009 7:13 am    Post subject: Reply with quote  Mark this post and the followings unread

yes, very interesting
thank you numbertalk, and thank you yusynth

btw, which circuit did you build, numbertalk ? is it the dual ODY osc/ringmod ? it is already on my "to do" list
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numbertalk



Joined: May 05, 2008
Posts: 980
Location: Austin, TX
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PostPosted: Mon Mar 09, 2009 7:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Jaba wrote:
btw, which circuit did you build, numbertalk ? is it the dual ODY osc/ringmod ? it is already on my "to do" list


Yep, that's the one.
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