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 Forum index » DIY Hardware and Software
"Okita" Vocoder (Roland SVC-350) - Adding more channels?
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AndyR1960



Joined: Feb 16, 2007
Posts: 299
Location: Manchester UK
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PostPosted: Thu Apr 09, 2015 9:00 am    Post subject: "Okita" Vocoder (Roland SVC-350) - Adding more channels? Reply with quote  Mark this post and the followings unread

I've just found the details for building N. Okita's 10 channel vocoder, based on the Roland SVC-350.

I'd like to double up on the channels, but I'm not quite sure if what I have in mind is the right way to go about it.
I should be able to add them simply by changing the value of the caps - as it stands, Ch1 uses 0.05 (0.047), Ch 2 uses 0.033 etc.

If I replace Ch 2's caps with 0.039 and put the 0.033 in Ch 3, then 0.027 in Ch 4 etc. then this would "fill in" the gaps of the current 10 bands, up to the desired 20.

BUT, should I also change the basic 4 pole BPF's shown, to 8 pole which would help create "space" for the extra channels... or is it just a case of changing the value of the resistors (which ones???) to narrow the bandwidth of each channel by 50%-ish.

I'm not sure where I should go from here. Any help/advice would be grateful.

Either way, I'm probably having one of my mad moments and maybe all this is bunkum Wink


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isak



Joined: Dec 13, 2009
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PostPosted: Wed Apr 15, 2015 9:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Andy.

My non pro advice would be to search another vocoder project with more Channs then 10, and see how they handle things over there.
Maybe it will give you direction or an idea.
Hope it helps in some way Rolling Eyes

Cheers,
Isak E.

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AndyR1960



Joined: Feb 16, 2007
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PostPosted: Yesterday, at 1:10 am    Post subject: Reply with quote  Mark this post and the followings unread

I've taken a look at other designs, particularly Senheisser & Syntovox. They both add the extra filter cells on the analysis side.

Luckily, Okita's board layout makes it easy to insert them via an add-on PCB Wink

I'll build the basic version, then tinker with it to see what happens.
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isak



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PostPosted: Yesterday, at 1:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool!
Waiting to see your progress Smile
Good luck with the project!

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StephenGiles



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PostPosted: Yesterday, at 11:14 am    Post subject: Reply with quote  Mark this post and the followings unread

EH Vocoder page 1


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StephenGiles



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PostPosted: Yesterday, at 11:14 am    Post subject: Reply with quote  Mark this post and the followings unread

EH Vocoder page 2


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StephenGiles



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PostPosted: Yesterday, at 11:16 am    Post subject: Reply with quote  Mark this post and the followings unread

EH Vocoder page 3


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AlanP



Joined: Mar 11, 2014
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PostPosted: Yesterday, at 11:23 am    Post subject: Reply with quote  Mark this post and the followings unread

The NE570 has me worried. It adds clarity, from what I understand, but with one for each channel...

Smallbear lists the V571 (a NE571 clone from CoolAudio) at $3.25, for 10-24 each. The original NE570 is $5.95, and the next price break is $4 at 100 each.
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AndyR1960



Joined: Feb 16, 2007
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PostPosted: Yesterday, at 9:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

AlanP wrote:
The NE570 has me worried. It adds clarity, from what I understand, but with one for each channel...

Smallbear lists the V571 (a NE571 clone from CoolAudio) at $3.25, for 10-24 each. The original NE570 is $5.95, and the next price break is $4 at 100 each.


I'm using the NE571 (same as the 570 but slightly different temperature specs) I got 12 of them from Futurlec $2.80 each Wink

They're used as the Envelope Follower/VCA for each channel, and compressor on the input board.

@StevenGiles - Many thanks for the EH schems, they will definitely come in handy. Okita's BPF's use different value caps, but the resistors are the same value, EH's version use the same 1% caps, but vary the resistor (but only one filter cell?)... I'll think I'll go a similar route, but keep the 4 cell idea. At least I don't need to source odd value 1% caps now, and calculating the resistor values for the extra bands will be far simpler. Looks like another order for Futurlec is on the cards - they stock all the resistors needed Wink

Much appreciated.
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