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 Forum index » DIY Hardware and Software » YuSynth
Yusynth Dual Gate Delay
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helix_modular



Joined: Aug 31, 2017
Posts: 22
Location: Germany

PostPosted: Sun Mar 18, 2018 2:34 pm    Post subject: Yusynth Dual Gate Delay
Subject description: Input impedance
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Dear Yusynth-adepts,

I've developed and tested a strip board version (which I'm happy to share, if that's OK with Yves) of the Dual Gate Delay module, it's tested and running.

However, I've experienced some undesired behavior: the impedance of the GATE IN is so low, it completely drains my gate source (e.g. the Yusynth LFO square out). Looking at the schematics I've noticed there is only 1k + 22k (with a reverse diode in parallel) resistors to ground. I think this is not exactly complying to electronote's standards, so I've simulated with 10k instead of 1k and implemented accordingly. That's still pretty low, but it works and doesn't cause blackout in the source!

I'm happy with the result -- but curios whether I'm missing something here...

Greetings,
helix
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LFLab



Joined: Dec 17, 2009
Posts: 488
Location: Rosmalen, Netherlands

PostPosted: Mon Mar 19, 2018 3:35 am    Post subject: Reply with quote  Mark this post and the followings unread

22k is not too bad as an input impedance, especially when driven from an opamp? Do you have the diode orientated correctly?
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g.gabba



Joined: Nov 29, 2008
Posts: 464
Location: berlin
Audio files: 23

PostPosted: Mon Mar 19, 2018 9:33 am    Post subject: Reply with quote  Mark this post and the followings unread

but the diode is shortening the negative half of the gate signal to gnd
the impendance is then only 1k

a solution could also be to put the diode in series with the 1k,
or try to leave the diode out, she is there to protect the transistor from negative Voltages but i never had horror experiences with when the transistors is not protected from them.
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LFLab



Joined: Dec 17, 2009
Posts: 488
Location: Rosmalen, Netherlands

PostPosted: Mon Mar 19, 2018 9:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah, yes, forgot the part where threadstarter mentioned using an LFO as an input. The circuit is aimed at gate signals, which do not go below zero.
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helix_modular



Joined: Aug 31, 2017
Posts: 22
Location: Germany

PostPosted: Mon Mar 19, 2018 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you guys for your replies so far!

LFLab wrote:
22k is not too bad as an input impedance, especially when driven from an opamp? Do you have the diode orientated correctly?


Confirmed.

g.gabba wrote:
but the diode is shortening the negative half of the gate signal to gnd
the impendance is then only 1k


Exactly. Still, even for positive voltages a fairly low impedance imho.

g.gabba wrote:
a solution could also be to put the diode in series with the 1k,
or try to leave the diode out, she is there to protect the transistor from negative Voltages but i never had horror experiences with when the transistors is not protected from them.


Something like this should do the trick. I don't have the module at hand but I've thrown it into LTSpice and apparently this doesn't. I assume you both have and used them -- and never any problems with the proposed values?

LFLab wrote:
Ah, yes, forgot the part where threadstarter mentioned using an LFO as an input. The circuit is aimed at gate signals, which do not go below zero.


Well. I admit I have somewhat of a paranoia when it comes to inputs; yet, it is my very understanding of 'modular' to be able to plug any output into any input without blowing something up or draining the signal source too much (even if 'it doesn't make sense' or has little effect). I've build quite a few Yusynth modules and found them very well designed in terms of safety, levels and simplicity -- that's why I asked, whether I'm missing something here. Hmmm...
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