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 Forum index » DIY Hardware and Software » YuSynth
Yusynth LFO V2 output levels
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murmeklis



Joined: Oct 26, 2018
Posts: 4
Location: Lithuania

PostPosted: Fri Oct 26, 2018 9:51 am    Post subject: Yusynth LFO V2 output levels Reply with quote  Mark this post and the followings unread

Hello everyone! I have recently build Yusynth's LFO v1 and v2. While v1 worked as expected, I have a bit of a problem with v2. While waveforms are great, output levels of V2 are around 15-16 Vpp. Given I am running both modules from +-12V I find that quite high.

I have been debugging with the oscilloscope and found that IC2b non-inverting input (PIN5) already measures saw-wave of 8Vpp, which is surprising as looking at the oscillator design I would expect 1/3 * 12 ~ 4Vpp. (BTW, schematic is here: http://www.yusynth.net/Modular/Commun/LFO/new/VCLFO2-sch.gif). By comparing it to the schematic of V1 LFO I have decided to play around and removed C4 (next to PIN 2 of 7555) capacitor, as it was not present in V1 schematic. It indeed fixed my problem and the amplitude dropped to expected levels.

So my question is about that C4 capacitor - have I done something wrong and was lucky to observe what I have, if not, then what is the purpose of that whole RC bit next to PIN2 (and any other comments?). I am mainly interested to learn something here as I currently have no clue (with no success googling) and to know whether I can safely remove that capacitor.

Thanks in advance!
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gabbagabi



Joined: Nov 29, 2008
Posts: 540
Location: Berlin by n8
Audio files: 23

PostPosted: Fri Oct 26, 2018 10:45 am    Post subject: Reply with quote  Mark this post and the followings unread

hi,
we had the same problem here
http://electro-music.com/forum/topic-69587.html

the solution for 15V supply would be lower R17 from 200k to 100k, the one at IC2A (with the 120pF Cap) because there are two R17

you run on 12V, as far as i remember the 555 switches at 66% supply voltage, 66% of 12V would be 7,92V, that means to feed the waveshapers correctly R17 should be 127,8k

why it helped u to remove C4 makes no sense to me, something magical?


cheers,
gabi
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murmeklis



Joined: Oct 26, 2018
Posts: 4
Location: Lithuania

PostPosted: Sat Oct 27, 2018 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for your response.

I have read the thread, but come to conclusion that the amplification (using the first R17) in the circuit is correct. I have thought that 555 timer in that particular configuration should give 1/3 of Vcc range, not 2/3, but I might be wrong. I will post if I find anything else.

Regards,
Dominykas
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gabbagabi



Joined: Nov 29, 2008
Posts: 540
Location: Berlin by n8
Audio files: 23

PostPosted: Sat Oct 27, 2018 4:34 am    Post subject: Reply with quote  Mark this post and the followings unread

well you could measure at pin7 of ic2b,
if the signal is there 5Vpp or 10Vpp,
if its more 10Vpp it is to hot, cos ic2a wil double it,
if its more 5Vpp it is ok, and i was wrong Smile
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