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 Forum index » DIY Hardware and Software » YuSynth
New module at yusynth.net : Quadrature VC-LFO
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oculus



Joined: Oct 30, 2011
Posts: 30
Location: Iceland, Reykjavik

PostPosted: Sat Aug 16, 2014 9:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey yves
first of all your site has been a great help and i love some of the circuits
that iv´e built from your page like the steiner filter.

im really interested in this module but would like to add sync input (retrigger)
ive used this circuit (attached) that tim parkhurst came up with for his 8k lfo for a few different lfos with success,
i was wondering would i only have to put the circuit on C6
or also on C7 on the quad lfo ?
thanks
Fridfinnur


Tim parkhurst 8k lfo retrigger.jpg
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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Sun Aug 17, 2014 5:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Synching this lFO is not easy indeed. To stop the oscillator it is sufficient to act on a single integrator only, since it's the chaining of both integrator that makes it possible to oscillate.

Still I am not sure that you won't have problem to restart the oscillation since in its normal configuration the circuit enters slowly into oscillation when the CV is low. I am afraid there will be lag with a synch circuit.

Well in my opinion (though I have never tried) is this VC-LFO is not suited for synching application.

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wackelpeter



Joined: May 05, 2013
Posts: 57
Location: germany
Audio files: 6

PostPosted: Thu Sep 25, 2014 7:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Folks,

i have just finished this my next yusynth module and finally got it working after some Trouble Shooting (as always i forgot a resistor on my stripboard and interchanged pin 8&9 on one of my tl074's

In the description it is mentioned that the filters slowest rate is 30 seconds per cycle.. mine won't do that... at slightly lower than 1Hz it stops oscillating and also the width of one Phase seems to be longer than the others... at least the led is longer on...
judging from the scope at higher rate everything seems fine and the width of each Phase Looks equal...
i must admit that i haven't matched both caps the resistors are in the 1% area... is this my fault?
and also i noticed that at higher rate the Output is +/-8Vpp and when the frequency get slower increases up to +/-12Vpp... can i reduce it simply with dropping other zener diodes in?

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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Thu Sep 25, 2014 8:15 am    Post subject: Reply with quote  Mark this post and the followings unread

In the BOM it is said C6,C7
10nF matched to 1%, polyester

A good match of these two caps is very important for the LFO to oscillate at very low rate. Those I built with matched caps can go down to 30s per cycle without difficulties.

I am also surprised by the output range you get, Z1 and Z2 are there to limit the range under +/-10V.

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wackelpeter



Joined: May 05, 2013
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Location: germany
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PostPosted: Thu Sep 25, 2014 8:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves,
thanks for your fast reply.

The caps i used are Wima MKS-2 63V 5% These are Polyester i think... right?
okay as mine are unmatched and you say it's very important for stability at low rates that makes it clearer for me...first i thought it would maybe only have an effect on the Beauty or symetry of the sine waves...


can i use this circuit to match them:
http://www.dartmouth.edu/~aurora/procedures/capacitor.matching.pdf

or is there any other simple way to match them?

regarding the voltage it is as you wrote on your website +/-8V when the oscillator is swinging faster... will check with my magnifier if i used the correct ones ... have taken them out of a bag with a dozen of fresh 5,1 Zeners i got 2 weeks ago from reichelt... the bag is labelled correct of course...

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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Thu Sep 25, 2014 9:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes its a good way to match caps unless you have a DVM with a good capacimeter function.

The oscillating capacity is insured by the fact that the outputs of the two integrator stages are shifted 90° from one to another. If the caps of the integrators are different then the poles of the integrator will be different introducing a phase shift greater or smaller than the ideal 90°.

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wackelpeter



Joined: May 05, 2013
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PostPosted: Fri Sep 26, 2014 10:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Back from work where i matched all my 10nF caps with a Benning MM3...

replaced the caps with those matched pairs (10,00 vs 10,02 or 10,16 vs 10,17) which are the closest ones... still not working properly have tried different pairs of those matched caps...
It's slightly better at the low range but still not going below 0,5 Hz...

At some point even in the range of circa 2Hz ist running a few cycles then the cosine Output stays for 1-2 secs longer high or frozen before it switches back to oscillation...
whenever it stops it stopped at between Sin+pi and cosine Output both remaining high...

Ahh have found one troublemaker and pushed him in the bin... it seems that the first tl074 had a Problem with it's first op stage... replaced it with an lf347 and know it goes much lower without stopping the cycle...

okay didn't reach 30secs yet... it runs stable until 12-14 secs per cycle...

any other suggestions or hints how to get it working a bit better in the lower frequency spectrum?

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yusynth



Joined: Nov 24, 2005
Posts: 1233
Location: France

PostPosted: Sat Sep 27, 2014 5:35 am    Post subject: Reply with quote  Mark this post and the followings unread

No not really more ideas, the quality of component is important (good FET AOPs) an improvement could be using LF444 instead of TL074 for U2. Yet again here at home it works with a plain TL074. What about Q1,Q2, are you using matched BC557C ?
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wackelpeter



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PostPosted: Tue Sep 30, 2014 9:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves, thanks again for your reply... until now i didn't take really much care about matched trannies as all things i've built so far worked really well so far... will give myself a kick and build ian's Transistor matching circuit now... guess that will also show some improvement on the circuits that i thought to be working well already... will also have a look für the lf444 when i order something online next time...
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wackelpeter



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PostPosted: Wed Oct 01, 2014 9:46 am    Post subject: Reply with quote  Mark this post and the followings unread

hi Yves,
it's me again... built the Transistor matching circuit following Ian's design and matched some trannies... are 1mv difference of Ube enough or must they be closer matched?

Looking at my scope the oscillator didn't stop at it's slowest frequency now ( that was the faulty lt074 chip) but the Level at the different stages sinks when the frequency is slowed down...

at full Speed it's +/- 10v now and the Level then shifts down to quite lower voltages from cycle to cycle... it goes so low that the led's aren't turned on...
when i had it all full Speed and then abruptly turn it to lowest Speed within a few minutes or so the Levels sink and reach only:
0 degree: amplitude swing between 2v to 1,5v
90 deg.: 0,8v to 0,6v
180 deg.: -1,6v to -1,8v
270 deg.: swing very slightly somewhere around -0,65v

also noticed that it Needs some attempts at some time to get over a Point sligthly lower than the Peak before the voltage would go in the direction of 0V/gnd...

can the Led's do cause this? i used red for all of them with the same resistor (the brightness differs a bit, especially at slower rates) i guess that's not the Problem as there is simply not enough voltage at the Input of the buffering Transistors...

hmmm... don't know where to look at besides your Suggestions with an lf444 for U2...
maybe the caps, the lm13700, some of the resistor values??? for the resistors i mostly used 2 resistors in series in lack of 1% tolerance resistors... choosed those that are as with my digital multimeter within that 1% tolerance... for example 67k9 for 68k and None of them more than 0,2k difference...
as i didn't used a etched pcb layout i can imagine that my positioning of my component on my stripboard may be not the best and some of the traces could be placed better... but i don't have a clue if they would affect each other... for some higher frequencies i could imagine some interferences or pops and plops caused by signals with higher level peaks and spikes or capaciator discharging

Anyone with some further suggestions where to look at? Otherwise i fear i must use it as a not so slow LFO... Smile

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