two miniature questions

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mercyofwolves
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two miniature questions

Post by mercyofwolves » Wed Oct 13, 2021 5:00 pm

rec'd my first 40106's from tayda last w/e, on about 5.5v ("spec'ed for a minimum 3v") they seemed to take a minute to warm up before oscillation half the time i power them up. wondering how abberant this is from teh norm.

i'm nescient regarding the selection of "delay in a chip" packages. do any of the options perform well enough for karplus-strong stuff, or should i think more in terms of adopting a microprocessor for performance approaching 2nd order hermite (allowing eg. sustain for over a minute at short intersample lengths)?

and thanks for all the answers folks, they've been tremendously helpful!

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devinw1
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Re: two miniature questions

Post by devinw1 » Wed Oct 13, 2021 6:05 pm

What is the circuit and what are you trying to accomplish? 40106 is a hex inverting schmitt trigger chip, it can be used for a lot of different things...

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EATyourGUITAR
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Re: two miniature questions

Post by EATyourGUITAR » Wed Oct 13, 2021 6:30 pm

PT2399 was designed for cheap mass produced karaoke machines. It will do karplus strong. The only disadvantage to a PT2399 is that it will not be as clean as a 24/96 AD DA delay.

I understand that the 40106 is being used with an RC low pass filter to create an oscillator. It should oscillate instantly when it is powered on. Maybe your power supply did not boot. Or maybe your power supply is overloaded and it went into protection mode. Maybe your caps are so big that the in rush current to charge the caps triggered over current protection on the power supply. So after the caps get fully charged then the 40106 was able to operate. This is most plausible because the power supply in over current protection mode will try to start then stop again as it detects over current. After 100 cycles the caps are charged and the power supply does not go into protection. You can fix this with a soft start that puts a current limiting resistor between the power supply and the load then removes the current limiting resistor with a relay or a MOSFET after the caps are fully charged.
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executiveBlaster
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Re: two miniature questions

Post by executiveBlaster » Wed Oct 13, 2021 6:46 pm

my understanding is that pt2399 will NOT do karplus strong, as it has a minimum delay of around 30ms.

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EATyourGUITAR
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Re: two miniature questions

Post by EATyourGUITAR » Wed Oct 13, 2021 7:38 pm

Ok so 66Hz then
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executiveBlaster
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Re: two miniature questions

Post by executiveBlaster » Wed Oct 13, 2021 7:53 pm

33Hz?

ashleym
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Re: two miniature questions

Post by ashleym » Thu Oct 14, 2021 4:42 am

Are any unused triggers grounded?

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EATyourGUITAR
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Re: two miniature questions

Post by EATyourGUITAR » Thu Oct 14, 2021 7:36 am

executiveBlaster wrote:
Wed Oct 13, 2021 7:53 pm
33Hz?
If you invert the phase you can exploit it to get 66Hz.
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executiveBlaster
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Re: two miniature questions

Post by executiveBlaster » Thu Oct 14, 2021 2:59 pm

sorry to hijack the thread! but, EYG, can you elaborate?! we can halve the effective delay time with some inversion trickery?

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EATyourGUITAR
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Re: two miniature questions

Post by EATyourGUITAR » Thu Oct 14, 2021 7:51 pm

If you'd did not invert the phase then any short transient or white noise excitation would have a natural period of 30ms or a frequency of 33Hz. There are other stable frequencies though. They are at 66Hz 99Hz 132Hz etc.. the problem is that you need a matching bandpass filter tuned to that frequency and the excitation to start oscillation should be a pure sine at the desired frequency. Basically talking about ideal conditions. We don't usually get ideal conditions because if we had a sine oscillator to start with we wouldn't need the karplus strong to get an oscillator. I just did the math again... I was wrong. It is actually 16.5Hz if you invert the phase. But but you can get stability at all the odd integer multiples of the resonant frequency. The half wave period for 16.5Hz is 30ms. The formula for the period with inverted phase is 60ms / n where n is a positive odd integer. So 16.666Hz, 50Hz, 83.333Hz, 116.666Hz etc..

In reality, you need some white noise and you need a tuned bandpass but you can probably hack a 2399 with enough gain. If the gain is high enough you don't even need the white noise because the noise floor will be enough. Oscillation happens when the total gain at some frequency is > 1.

There are some formulas you can use to find all the filter poles and zeros but that math is just a bit over my head. This is part of a control systems theory class or a signals and systems class. There are full courses for free on YouTube. I have two signals and systems books but I have not finished them and I am only half way through control systems on YouTube.
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Nightly Closures
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Re: two miniature questions

Post by Nightly Closures » Thu Oct 14, 2021 7:56 pm

Thanks for that explanation.

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