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 Forum index » DIY Hardware and Software » YuSynth
Arp 4072 self osc clipping
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gdavis



Joined: Feb 27, 2013
Posts: 359
Location: San Diego
Audio files: 1

PostPosted: Sat Jun 22, 2013 3:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Now that I think about, I think the P10x thing only affects the automatic voltage measurements which you're not using, but not the waveform on the screen. The cal thing is important for reading voltage of waveform off the screen accurately though.

I don't really have anything else to offer except that almost all my problems with boards I've etched have been the result of accidental solder bridges or gaps in traces (which can be very small and hard to see with the naked eye). I tracked them down by testing continuity with my multimeter on anything that didn't look perfect. A magnifying lamp or microscope is a great thing to have too.

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isak



Joined: Dec 13, 2009
Posts: 847
Location: Israel
Audio files: 18

PostPosted: Sat Jun 22, 2013 11:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks man, youve been very helpful Smile

i took some pics outdoors this morning, hope they are better.


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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Sun Jun 23, 2013 1:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Well I checked the board and it looks all good.
So as you asked, it might be a problem either due to a defective LM3900 or a bad matching of the BC557 pairs.

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Yves
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isak



Joined: Dec 13, 2009
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PostPosted: Sun Jun 23, 2013 1:24 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks Yves.

to tell you the truth, as long as it sound how it suppose to sound i really dont care how the self osc looks or sound at above 14khz.
i dont reach those freqs when playing.
i'll upload few sound clips later on today, hope you will have the time to listen to them.

thank you for your help Yves.
much appreciated.

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isak



Joined: Dec 13, 2009
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Audio files: 18

PostPosted: Sun Jun 30, 2013 1:16 am    Post subject: Reply with quote  Mark this post and the followings unread

sorry it took me long time to upload the audio clips.
but hey i made them Smile
the first is saw wave on C2.
reso all the down, reso at 1/4, reso at 1/2, reso at 3/4 and reso on full.
the second is square on C2.
reso all the down, reso at 1/4, reso at 1/2, reso at 3/4 and reso on full.

only VCO and the Arp VCF, are involve, no VCA.

so, are they good?


arp 2600 demo saw.wav
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arp 2600 demo square.wav
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yusynth



Joined: Nov 24, 2005
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PostPosted: Sun Jun 30, 2013 1:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks mostly correct. For the auto-oscillation there is a problem of aliasing with the recording. Otherwise it sounds saturated at high frequencies.
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isak



Joined: Dec 13, 2009
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PostPosted: Sun Jun 30, 2013 1:47 am    Post subject: Reply with quote  Mark this post and the followings unread

so only the self osc if a bit problematic cause of the high gain?
is this correct?

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yusynth



Joined: Nov 24, 2005
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PostPosted: Sun Jun 30, 2013 1:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Probably if you set the resonance at the beginning of auto-oscillation it will sound more as expected.
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isak



Joined: Dec 13, 2009
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PostPosted: Sun Jun 30, 2013 2:20 am    Post subject: Reply with quote  Mark this post and the followings unread

ok, is there any way to lower the maximum reso a bit?

another thing..
sounds weird but i have some strange sound at the begining of the opening of the cutoff, sounds like not all the vco is going through the filter?
like an buzzy highpass sounds that i hear at the beginning, hope that sounds reasonable.

sound clip are attached.

have any idea what is it and why?

EDIT:
it seems to happened after doing the mod with the dual gang pot for the bleed through.
if you hear the first sound clip ive uploaded (saw wave) you will hear that there non, no buzzy noise at all.
maybe it got something to do with rising left side of R43 (10k)?
maybe ill connect the R43 to the PCB along with the wire of the gual gang pot?


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isak



Joined: Dec 13, 2009
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PostPosted: Sun Jun 30, 2013 11:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, i found the problem after tracing the audio path.
it was a "bad" TL074!
i tell you... those Chinese ebay sellers Evil or Very Mad
now its not buzzy any more.

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isak



Joined: Dec 13, 2009
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PostPosted: Sat Jul 06, 2013 11:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves.

just wanted to let you and the guys that the weird non symmetric sine wave was coming from the same TL074.
its TI chip and i upload a pic for you and the guys just to see and not use them!
when replaced the TL074 to other brand (ST) the sine wave was perfect!
thank you for your help.


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yusynth



Joined: Nov 24, 2005
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PostPosted: Sun Jul 07, 2013 12:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info
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