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 Forum index » DIY Hardware and Software » YuSynth
Mod to YUSYNTH VCO
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yusynth



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

PostPosted: Fri Aug 17, 2007 6:26 am    Post subject: Mod to YUSYNTH VCO Reply with quote  Mark this post and the followings unread

Hi

For those of you building the YUSYNTH VCO I have changed the values of two resistors R36 and R51
(were 27K) which are now 4K7 in order to incease the range of the PW potentiometer.
I also corrected the value of R8 which was labelled 50K in the schematics but is actually 470K.

At the end of the page you'll find also a PDF file of Mods by Mariano for adding an octave range switch as well as how to use a NTC tempco resistor as a substitute to the PTC one.

Regards

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AndyR1960



Joined: Feb 16, 2007
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PostPosted: Fri Aug 17, 2007 7:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info Yves,

I had to change the value of the two resistors anyway, as I only had 100k pots...

Regarding your VCO, what type of sync is it? I'm after the conventional hard sync that you find on an Odyssey, but I find the sync on your VCO very different.

Regards,

Andy.
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yusynth



Joined: Nov 24, 2005
Posts: 1224
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PostPosted: Fri Aug 17, 2007 7:30 am    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
Regarding your VCO, what type of sync is it? I'm after the conventional hard sync that you find on an Odyssey, but I find the sync on your VCO very different.

I suppose that it also depends a lot on what signal (waveshape and amplitude) you are using to sync the VCO...

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yusynth



Joined: Nov 24, 2005
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PostPosted: Fri Aug 17, 2007 8:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Also, depending on component tolerances, the adjustment of the Hi-Tracking may be at the maximum limit of the trimmer T3, in such a case use a 10K trimmer instead of the 4.7K. It solves the problem nicely

Yves

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funkyfarm



Joined: Jan 21, 2007
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PostPosted: Fri Aug 17, 2007 8:38 am    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
Thanks for the info Yves,

I had to change the value of the two resistors anyway, as I only had 100k pots...

Regarding your VCO, what type of sync is it? I'm after the conventional hard sync that you find on an Odyssey, but I find the sync on your VCO very different.

Regards,

Andy.


Maybe the synchronization starts at high level, not zero, as on the VC-LFO ?
No "reset" but a "synchroniszation" ? Wink
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AndyR1960



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Posts: 284
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PostPosted: Fri Aug 17, 2007 12:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusson wrote:

I suppose that it also depends a lot on what signal (waveshape and amplitude) you are using to sync the VCO...


I'm using the square wave out from Ray Wilson's VCO (it's the only other type of VCO I have). The output is 10V PP (-5 to +5V).

I don't know why, but I changed the 47pf input cap to 0.01uf and I'm getting much closer to the sync sound I'm after, it seems that the higher the cap value the "harder" the sync, although I'm still locking onto certain harmonics as I sweep up and down - not quite as smooth as I want, but the only other value I have to hand is 0.1, which is way too much Grrr...

What exactly is the function of this input cap? Sorry, but I really have no technical knowledge of electronics... I just follow instructions and keep my fingers crossed Shocked

Thanks,

Andy.
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yusynth



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

PostPosted: Fri Aug 17, 2007 1:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
I don't know why, but I changed the 47pf input cap to 0.01uf and I'm getting much closer to the sync sound I'm after, it seems that the higher the cap value the "harder" the sync, although I'm still locking onto certain harmonics as I sweep up and down - not quite as smooth as I want, but the only other value I have to hand is 0.1, which is way too much Grrr...

What exactly is the function of this input cap?

The aim of that cap is to differentiate the input sync such that if the sync signal is a square the cap creates a brief positive spike on the rising edge of the square signal and a brief negative spike on the falling edge. This way the sync is transformed to a brief reset pulse that triggers the comparator (U5) which discharges the main capacitor C8. By increasing the value of C9 you broaden the reset pulse. In fact that might be the difference between what's called hard and smooth sync.

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yusynth



Joined: Nov 24, 2005
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PostPosted: Fri Aug 17, 2007 1:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
I don't know why, but I changed the 47pf input cap to 0.01uf and I'm getting much closer to the sync sound I'm after, it seems that the higher the cap value the "harder" the sync, although I'm still locking onto certain harmonics as I sweep up and down - not quite as smooth as I want, but the only other value I have to hand is 0.1, which is way too much Grrr...

What exactly is the function of this input cap?

The aim of that cap is to differentiate the input sync such that if the sync signal is a square the cap creates a brief positive spike on the rising edge of the square signal and a brief negative spike on the falling edge. This way the sync is transformed to a brief reset pulse that triggers the comparator (U5) which discharges the main capacitor C8. By increasing the value of C9 you broaden the reset pulse. In fact that might be the difference between what's called hard and smooth sync.

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Yves
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AndyR1960



Joined: Feb 16, 2007
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PostPosted: Fri Aug 17, 2007 1:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

yusson wrote:
In fact that might be the difference between what's called hard and smooth sync.


Thanks for the reply, much appreciated.

After some messing around, I've found that using the narrowest pulse from the master VCO (not a pure square wave) gives me much better results Smile

I can't seem to get the pulse wave narrow enough (no less than 5%) to get, what I think may be, the result I'm after.

Is there a simple circuit (maybe some sort of transistor/fet switch) which will convert a square wave input, and output the required very short reset pulse?

Andy.
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yusynth



Joined: Nov 24, 2005
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PostPosted: Fri Aug 17, 2007 1:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

AndyR1960 wrote:
After some messing around, I've found that using the narrowest pulse from the master VCO (not a pure square wave) gives me much better results Smile


Well try to use a smaller value for C9, say 10pF instead of 47pF, this should differentiate to a narrower pulse.

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yusynth



Joined: Nov 24, 2005
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PostPosted: Wed Aug 29, 2007 1:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have made some important modifications to my yusynth VCO in order to improve the HI-TRACK linearity and the PWM circuit.
This is a major update : new value for the core capacitor C8 which is now 220pF 1% stiroflex or silver mica (was 1nf before), suppression of the HI-Track trimmer and addition of a diode and 1M resistor in the expo circuit.

In order to facilitate these changes and addition I designed new PCBs. For those of you who have built the circuit with the old version (prior to august 29th) and don't want to etch a new PCB I have included photos that show how to modify the old PCB to integrate these changes.

Cheers

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Sebo



Joined: Apr 27, 2007
Posts: 539
Location: Argentina

PostPosted: Thu Aug 30, 2007 9:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you Yves, your modules are great !!!
I have some questions about the VCO
1 - The polyestirene caps: I can find 1% ones here in
Argentina, actually I only find a few values in 10%, could I buy a bunch
of 10% and meter them (with my cheap multimeter) to get the closest
value to 220pfui or I have to order the at Farnell or something?
2 - Also, I can't find the J112 or J111 FETs, what other FET could I use?
3 - I bought some 1K 3500ppm tempcos, could I use them instead of the
3000ppm one?
4 - C3,C4,C5,C6 I think are bypass caps, you list them as yellow LLC, I
don't know what kind of caps those are, but I think I can use poliester MKT
or multilayer ceramics.
5 - Finally, how I match diodes?

Thank you.

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yusynth



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PostPosted: Thu Aug 30, 2007 10:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Sebo wrote:
Thank you Yves, your modules are great !!!

You're welcome !

Sebo wrote:
1 - The polyestirene caps: I can find 1% ones here in
Argentina, actually I only find a few values in 10%, could I buy a bunch
of 10% and meter them (with my cheap multimeter) to get the closest
value to 220pfui or I have to order the at Farnell or something?

Well it is not the value accuracy that is important for this cap and you could take 10% caps and select one close to 220pF. However, this would not garantee a good stability of the VCO. It is very important that this cap has a low temperature drift, and mostly the caps that warrant a small drift are either styroflex or Silver mica. Personnally I bought mine at farnell.

Sebo wrote:
2 - Also, I can't find the J112 or J111 FETs, what other FET could I use?

You need a N-FET with a low Drain-Source resistance in conductive mode, typical value for this resistance should not exceed 60 ohms.

Sebo wrote:
3 - I bought some 1K 3500ppm tempcos, could I use them instead of the
3000ppm one?

It should do...

Sebo wrote:
4 - C3,C4,C5,C6 I think are bypass caps, you list them as yellow LLC, I
don't know what kind of caps those are, but I think I can use poliester MKT
or multilayer ceramics.

Yes you may use multilayer ceramic for these.

Sebo wrote:
5 - Finally, how I match diodes?

Well either you have this function in your DVM or not. If you haven't this function here is how to proceed :
    you need a stabilized voltage source (or a battery), a resistor and a voltmeter.
    Now considering, that the forward voltage drop through a silicon diode is nearly 0.7V, choose a resistor that provides a voltage drop equal to (voltage source - 0.7) under a current of 0.1mA. For instance if you have a 4.5V battery the resistor value should be 38K (that is a 33K and 4.7K in series),
    now to match the diodes, connect the resistors in series with a diode, power the cicruit with the battery and measure the voltage drop for this diode.
    Write this voltage down and proceed the same way for the other diodes
    Select the diodes whose voltage drops do not differ from more than 2mV .

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Sebo



Joined: Apr 27, 2007
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PostPosted: Thu Aug 30, 2007 1:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi again:
In point 1 I was refering to styroflex (that's the ones I can get at 10%).
But I think 1% will be better.
Thanks a lot for you answers !!!!

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www.myspace.com/cosaquitosenglobo
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yusynth



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PostPosted: Fri Aug 31, 2007 7:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Sebo wrote:

In point 1 I was refering to styroflex (that's the ones I can get at 10%)


That's fine then, just check that the temperature drift does not exceed 70ppm/°C

Cheers

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yusynth



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PostPosted: Tue Dec 04, 2007 10:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi all

GOOD NEWS. For those who were considering to build the third version of the YUSYNTH VCO based on a hand-matched pair of transistor for the expo convertor, I am glad to announce that it has been built successfully and with stable results by Csaba Zvekan of Basel, Switzerland who was kind enough to give me some return on this version ! Therefore, I have removed the mention "untested" from my VCO page !

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Last edited by yusynth on Wed Feb 06, 2008 3:48 am; edited 1 time in total
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Sebo



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PostPosted: Tue Dec 04, 2007 12:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's great.
Thank you again Yves.

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www.myspace.com/cosaquitosenglobo
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