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 Forum index » DIY Hardware and Software » Thomas Henry designs
The VCO-555
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wackelpeter



Joined: May 05, 2013
Posts: 52
Location: germany
Audio files: 6

PostPosted: Sat Jul 19, 2014 7:30 am    Post subject: Re: sine wave Reply with quote  Mark this post and the followings unread

messerschmitt twin wrote:
hi, I built the TH 555 vco on stripboard, from the circuit diagram,everything works except the sine wave, I just get a triangle wave, so I bread boarded the LM13700 sine shaper and fed the triangle from pin 14 of IC3, but my breadboarded layout just produces a triangle output as well? Any ideas would be most wellcomed.


the Output of the sine is set via trimmer R24... which rounds it up as a sine the more you turn it in the one direction it goes more into a sine wave including a reducing of the Amplitude and in the other direction the amplitude rises and the waveform turns more into a triangle...
Trimmer R38 Centers the sine around Zero Volts/ground...

try playing with the values of R27 and the trimmer R24...
maybe the total of those both resistors is a bit to low or to high to achieve the best result...
also check the values of R3, R26 and R34
either the Input on Pin13 or the Input bias at pin1 seem to be to high i guess

if your Amplitude is a bit weaker than the 3 others try reducing R34 .
i have used 56K insetad of 100K so my sine is at the same Level as the triangle and 1,5VP/P above the square and ramp...

i also had to Change the values of some other resistors to get all signals at same Levels... for pulse i changed R8 from 1K8 to 2K7 and for the ramp i changed R33 from 100K to 120K...


hope this helps a bit.. otherwise just wait until one of the "wise men" of this Forum answers... Very Happy

P.S. nice to know i'm not the only one still drilling holes in stripboards... Wink

P.P.S. just forgot maybe your triangle signal at pin 14 of IC3 from which the sine is generated is maybe to high... what amplitude do you get there?

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messerschmitt twin



Joined: Jul 19, 2014
Posts: 6
Location: leicester, england

PostPosted: Sat Jul 19, 2014 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks for your help, i double checked the values, my other waveforms are fine, as is the triangle coming out of the sine wave shaper lol, maybe i'm not adjusting it properly if R27 and R34 can produce a triangle output. I have managed to blow a few LM13700's in the past messing with the inputs on pins 1 and 16, i'll have another try later, thanks again.
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wackelpeter



Joined: May 05, 2013
Posts: 52
Location: germany
Audio files: 6

PostPosted: Sat Jul 19, 2014 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

no Problem at all normally i'm the the one crying for help... but just finished 2 of them last week...

did a mistake in my previous post
i meant not pin 1 of the lm13700 i meant pin 16 of course...
to me it Looks like one of These just get to much Input so that the sine is folded into a triangle...

Matthias/Fonik pointed me on the value of R27 he suggested to lower R27 A bit think it was 33K or 27K and instead Exchange trimmer R24 with an 47 or 50K one...

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messerschmitt twin



Joined: Jul 19, 2014
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Location: leicester, england

PostPosted: Sat Jul 19, 2014 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

just had another look, using a 50K preset and adjusting it makes no difference to the triangle, also its about 15V peak to peak, yes knew you meant pin 16, i'll try lowering the 39k resistor, thanks again.
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wackelpeter



Joined: May 05, 2013
Posts: 52
Location: germany
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PostPosted: Sat Jul 19, 2014 8:30 am    Post subject: Reply with quote  Mark this post and the followings unread

15V PP seems to be too much... don't remember really but i think it was supposed to be 6-8 V PP at each signal Output...

do you measure these 15V PP at the sine or at the real/destinated triangle Output?

Maybe also have a look at this thread beginning on page 3 there Thomas gave some hints concerning the sine wave

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messerschmitt twin



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PostPosted: Sat Jul 19, 2014 8:37 am    Post subject: Reply with quote  Mark this post and the followings unread

lowered it to 27K still no change, swapped LM13700 and its now a perfect sine, just tweaking it now with the presets, so was down to a partially working LM13700, thanks for your help.
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wackelpeter



Joined: May 05, 2013
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Location: germany
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PostPosted: Sat Jul 19, 2014 8:47 am    Post subject: Reply with quote  Mark this post and the followings unread

nice to hear that it works now... great VCO you simply can't live wtihout one and when you have one you want more... Laughing

i think i will go for 2 more as i now have my stripboard layout as a "master" the second one got finished much more faster so will be the next ones...

if you just ahev one half of that LM13700 working maybe include that in an VCA i've finished yesterday...
http://hem.bredband.net/bersyn/VCA/lm13600%20vca%201.htm

goes quick and easy... the only negative Point is that it didn't mute the signal totally with 0V at CV Input... reduced to about 50% but for some Needs that is okay...

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messerschmitt twin



Joined: Jul 19, 2014
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Location: leicester, england

PostPosted: Sat Jul 19, 2014 8:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes I'll build some more now i know the layout is ok, im probably going to build eight cos the stripboard is so cheap and I got most of the other parts to hand, just need to buy a few more LM13700 and op amps, can use them for LFOS as well by switching in a bigger timing cap. Thanks for the VCA tip.
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messerschmitt twin



Joined: Jul 19, 2014
Posts: 6
Location: leicester, england

PostPosted: Mon Aug 04, 2014 3:22 am    Post subject: new question on sync? Reply with quote  Mark this post and the followings unread

Hi, does anyone know how the value of 470pf for the dc blocking capacitor in the sync part of the circuit gets its value and how critical is it?
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Janvier



Joined: Aug 12, 2014
Posts: 10
Location: Montréal

PostPosted: Fri Aug 15, 2014 9:29 pm    Post subject: LM13700 Black Magic
Subject description: Trying to calculate Iout according to Icon, without linearization diode
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Arfff still trying to understang that LM13700. I have a bunch of formula to be able to calculate Iout according to Iabc (control current) and I completely blind.

Formulas in the datasheet are including the linearization diode and according to this schematic they are not connected.

Someone can help me on this ???? HELP PLEASE !!

I just want to be able to calculate Iout which is supposed to be a relation between Vin and Iabc (according to what I think I understand) so I will be able to calculate the integration rate.
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Blue Hell
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PostPosted: Wed Aug 20, 2014 7:21 am    Post subject: Reply with quote  Mark this post and the followings unread

The linearization diodes should not matter ... its just:

Iout = Uin * Gm

with

Gm = 19.2 * Iabc

so .. not sure what the issue is ...

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Janvier



Joined: Aug 12, 2014
Posts: 10
Location: Montréal

PostPosted: Wed Aug 20, 2014 4:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Awesome.

I don't where you get this. But I know that 19.2 constant is telling me something.

Im now confident with the expo converter, with any type of scale. The only thing I was missing is the Iout of an OTA from the variation of its input vs. Ibias.

Since many OTA have the same kind of architecture (this is the number of current mirror which is different most of the time), is it a generic equation or it only applies for LM13700 ?

MUCH APPRECIATE !!
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Blue Hell
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PostPosted: Wed Aug 20, 2014 5:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

the 19.2 comes from a data sheet I found ... well . i had it in my head actually and verified it. It is the same for the CA3080 (where I remembered it from) .. it depends on temperature BTW.

Ah, found it ... qaIc/2KT ... page 2 from http://www.intersil.com/content/dam/Intersil/documents/an66/an6668.pdf - so yes, it is the same for all OTAs (based on that design at least).

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Blue Hell
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PostPosted: Wed Aug 20, 2014 5:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, and that also explains the 3300 ppm/K temperature compensation resistor needed to make it work properly :-)
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Janvier



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PostPosted: Wed Aug 20, 2014 5:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Awesome thanks for the application notes ! Very Happy
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