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 Forum index » DIY Hardware and Software
gate length
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zipzap



Joined: Nov 22, 2005
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PostPosted: Tue Nov 22, 2005 12:51 pm    Post subject: gate length
Subject description: with sequencer
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Hi there
I have been wondering and searching about this for some time:
How can i change the gate length comming from my sequencer?
The sequencer is the classic cmos4017 based type, and right now the gate length it produces is directly related to the pulsewidth of the clock.
Now what happens if i use a midi to clock device at slow speed: my ADSR starts right with the release part because the gate is so short.
What could one do to change the gate length with the turn of a pot?
thanks alot!
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Blue Hell
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PostPosted: Tue Nov 22, 2005 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Welcome zipzap to electro-music.com

Some things could be tried. Like pulse stretching by using a mono flop or something cooked up with resistor/capacitor/diode.

Both have the drawback that the pulse times you set with 'm are not related to the clock speed, resulting into no gate pulses at all at higher speed.

Maybe the clock oscillator could be changed to have PWM control, but that's hard to tell without knowing how it's built.

Any schematics avaialble ?

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Macaba



Joined: Jul 13, 2005
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PostPosted: Tue Nov 22, 2005 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

You could use an RC ramp capacitor circuit, with a comparator. adds a bit of complexity, you need another comparator to discharge the cap, and the first comparator will need hysteresis.

Does this sound like a sensible option?
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zipzap



Joined: Nov 22, 2005
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PostPosted: Wed Nov 23, 2005 6:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the replies!
Internet Comunity is a great thing!
Well, right now I am using a simple transistor multivibrator as internal clock. PW controll is easy to realise, but the problem is that i´m normaly using the sequencer synced to midi. The midi clock converter does not have PW...
In the meantime I found this page
http://www.analog-synth.de/synths/trigsequ/trigsequ.htm
It shows an cv controlled Gate Length control very similar to what you, marcaba suggested. I Attached the shemaic. Many thanks to JS!
The clock signal is first transformed into a short pulse that triggers an ar envelope. Atack is 0, release can be modified. A comperator gives +12v or -12V.
the question that remaines is a bit silly, since i managed to build half a modular synth and don´t know the answer myself:
How do i get -12V to be 0V and +12v to be 5V?


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vc gate length
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Blue Hell
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PostPosted: Wed Nov 23, 2005 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

zipzap wrote:

the question that remaines is a bit silly, since i managed to build half a modular synth and don´t know the answer myself:
How do i get -12V to be 0V and +12v to be 5V?


For the output circuit you mean ?

If so :

The circuit bit marked (3) already sort of does that for 12 Volt supply. For another supply voltage you might want to change the resistors a bit, or you could put in a 5v1 zener instead of the 8k2 resistor.

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zipzap



Joined: Nov 22, 2005
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PostPosted: Wed Nov 23, 2005 2:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

that seems clear for the positiv voltage. the output resistor makes 12 v become something like 5v. logic! Since I´m using +-15v power I will need higher resistor values.
but what happens to the negative voltage? would´nt it be turned down to -5v instead of 0v?
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zipzap



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PostPosted: Wed Nov 23, 2005 2:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

I guess thats what the diode at the output of the last opamp is for...is it?
pure logic.
I´ll have to try it. Hope i can manage this weekand, i´ll post if it worked.
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Blue Hell
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PostPosted: Wed Nov 23, 2005 3:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

zipzap wrote:
I guess thats what the diode at the output of the last opamp is for...is it?


Indeed.

Now lets label the existing 10k resistor as R1 and the 8k2 resistor as R2.

Assume a voltage drop of about .7 V over the diode, then for a 15 Volt supply you can calculate the ratio of the R1 and R2 values from

5 / 14.3 = R2 / (R1 + R2) or

R1 = 1.9 * R2

when you keep R1 at 10k R2 would be 5k26.

In the E12 range the nearest value would be 5k6 giving an actual output value of 5.6 * 14.3 / (5.6 + 10) = 5.1 This is about the same as the current circuit gives for a 12 V supply.

To be on the safer side, from the E24 series you could obtain 5k1 instead, giving about 4.8 Volt.


http://www.electronics-tutorials.com/basics/resistor-color-code.htm has the values for the E12 and E24 series.

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seraph
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PostPosted: Wed Nov 23, 2005 5:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:

http://www.electronics-tutorials.com/basics/resistor-color-code.htm .

I added it on the Links page Very Happy (under DIY resources)
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zipzap



Joined: Nov 22, 2005
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PostPosted: Mon Nov 28, 2005 1:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

it works and its fun! I had to add an amplifier to the input to get this react to my clock (tock more time to figure out than building).
You have to adjust it to the clock speed, than you have good controll over the gatelength with the release pot. the range goes from no gate till permanent gate.
cv controlling with an lfo or second sequencer line gives intresting rhythmic effects.
to get pathetic: this would not have been possible without the people at electro-music.com.....
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