pad / piezo interface env/vca/trig (help plz) SOLVED

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fg
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pad / piezo interface env/vca/trig (help plz) SOLVED

Post by fg » Thu Feb 06, 2020 4:43 pm

hello I developed this very simple interface in order to use it with pads or piezo.
the detection, envelope and vca part works very well, however the trig out part is not perfect, it works but it is not very stable.
would someone have a very simple idea to stabilize it a bit ? thanks

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Last edited by fg on Sat Feb 08, 2020 10:49 am, edited 1 time in total.

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Re: pad / piezo interface env/vca/trig (help plz)

Post by guest » Thu Feb 06, 2020 4:54 pm

the trig out has a lot of resistance, so its going to be a weak pulse. you could either get rid of that 120k, or maybe put a buffer of some sort in there. also, it would be good to put a 10k in series with the piezo input to protect the opamp. piezos can produce hundreds of volts.
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Re: pad / piezo interface env/vca/trig (help plz)

Post by fg » Thu Feb 06, 2020 5:33 pm

ok, thanks i will protect op with 10k ;
but for the clean pulse the problem is strange because when rené is ok, my doefper is not ok...
i look for something compatible for all
i tried a lot of schem with transistors.. but nothing very clean
thanks again

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Re: pad / piezo interface env/vca/trig (help plz)

Post by guest » Thu Feb 06, 2020 5:42 pm

its possible the input impedance or thresholds are different between the two. with 120k in series, you are losing a lot of voltage on the pulses.
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Re: pad / piezo interface env/vca/trig (help plz)

Post by fg » Thu Feb 06, 2020 5:55 pm

i know but if i reduce it, its more chaotic

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Re: pad / piezo interface env/vca/trig (help plz)

Post by guest » Thu Feb 06, 2020 6:07 pm

what do you mean by chaotic? does it double trigger? or does it trigger sometimes, but not others?
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Re: pad / piezo interface env/vca/trig (help plz)

Post by fg » Fri Feb 07, 2020 2:39 am

chaotic in the sense that the sequencer forgets steps or goes too fast, a bit like a random number.
not clean

this version is more reactive but not very stable yet

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Re: pad / piezo interface env/vca/trig (help plz)

Post by guest » Fri Feb 07, 2020 12:13 pm

a couple of things to try:

1. put a diode from the piezo input jack to the 1M resistor, and then put 22pF across the 1M resistor.
2. use a similar circuit at the output of the opamp: 100ohm resistor to diode to 1uF cap with 10k across the cap.
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Re: pad / piezo interface env/vca/trig (help plz)

Post by fg » Fri Feb 07, 2020 2:59 pm

thanks for your answer but not sure to understand
may be there s no need 10k to protect op now ?
like this ?

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Re: pad / piezo interface env/vca/trig (help plz)

Post by guest » Fri Feb 07, 2020 6:40 pm

yeah, that looks good. the 10k is still required for protection, as the diode only goes in one direction. im also thinking that maybe there needs to be another 1M on the other side of the diode, to make sure no charge builds up on the piezo itself.
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Re: pad / piezo interface env/vca/trig (help plz)

Post by fg » Sat Feb 08, 2020 10:32 am

you're a great genius! it's perfect now
thank you so much.
the diagram below is so cool (for me)

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the whole project with pcb is here ---> http://pjmnc.free.fr/archives/drumVCA.zip

thanks again

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Re: pad / piezo interface env/vca/trig (help plz) SOLVED

Post by guest » Sat Feb 08, 2020 12:18 pm

awesome! happy to hear it works.
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Re: pad / piezo interface env/vca/trig (help plz) SOLVED

Post by fg » Sun Feb 09, 2020 5:54 am

version with a pot to adjust release

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Re: pad / piezo interface env/vca/trig (help plz) SOLVED

Post by fg » Mon Feb 10, 2020 6:18 am

thanks again

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Re: pad / piezo interface env/vca/trig (help plz) SOLVED

Post by guest » Mon Feb 10, 2020 12:37 pm

looks like theyre ready to party!
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