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<div class="moz-cite-prefix">Hello and Welcome to synth diy!</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">What you have here is a non-steady
power consumer paired with a "soft" power supply. <br>
</div>
<div class="moz-cite-prefix">Your devices see a variation in voltage
due to internal resistances: Composed of the finite output
resistance of your PSU and the wiring and connectors.</div>
<div class="moz-cite-prefix">As the current varies, there is a
voltage drop at this parasitic resistance. This changes the
effective supply voltage and/or ground potential seen by each
individual module. <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">If the consumption of your LFO were
independent of the signal then no modulation would occur. (Well a
fixed one, but you won't notice that...)<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">
<div class="moz-cite-prefix">The advice to add bypassing is not
bad per se. But it is not a panacea. <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">At LFO frequencies even 10uF does
next to nothing. <br>
</div>
<div class="moz-cite-prefix">When working into 10ohms the corner
frequency is 1.59kHz. <br>
</div>
<div class="moz-cite-prefix">It might remove clicks due to the
higher frequency content but will still move your VCO up and
down a little. <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I'd suggest to also look at the other
factor of the root cause, and that is the varying current flow:
<br>
</div>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">First, I'd be looking at temporary
disconnecting the LED from your LFO. Maybe that makes a difference
already? <br>
</div>
<div class="moz-cite-prefix">To me this is the most promising
candidate, how the LFO signal could affect the PSU (likely both
GND and +12). <br>
</div>
<div class="moz-cite-prefix">You run several mA between +12 and GND
there. <br>
</div>
<div class="moz-cite-prefix">If confirmed, go for a high efficiency
LED, and raise the 330 to something much larger. <br>
</div>
<div class="moz-cite-prefix">Depends on the LED of course. But less
current will result into less modulation of your PSU. <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Second: Why not use the triangle signal
for indication instead. That makes for less abrupt signal to begin
with. <br>
</div>
<div class="moz-cite-prefix">And hopefully this is then less
noticeable. I've been there, and had several situations where the
square wave created problems with LEDs, due to the higher dV/dT.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Third, your Opamp U1C might not like it
that it is run open loop for half of the cycle. A 1N4148 in
reverse (or a second LED) will easily fix that. <br>
</div>
<div class="moz-cite-prefix">This will then create a more continuous
current flow, which is less noticeable. <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<br>
<div class="moz-cite-prefix">And finally:</div>
<div class="moz-cite-prefix">Also look into your VCO design, it
seems it has sensitivity to the power supply voltage. I would look
into ways to reduce that. (Voltage references for pots etc.) <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Best,</div>
<div class="moz-cite-prefix"> René<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 19.02.2023 17:21, A.M. Barrio via
Synth-diy wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CABLLCo=nzXmHNjzmjoO8fmF8qbyw5orhFCMGnTnWeZZeoMMwPQ@mail.gmail.com">
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<div dir="ltr">
<div>This is the complete email I wanted to send. There's
another thread where the attached files and additional info is
missing. My bad, pressed CTRL + Enter by mistake whoops.
Please ignore that one! <a href="mailto:pata@ieee.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">pata@ieee.org</a> and <a
href="mailto:mbryant@futurehorizons.com" target="_blank"
moz-do-not-send="true" class="moz-txt-link-freetext">mbryant@futurehorizons.com</a>,
thank you for your replies, I have taken them into account :-)<br>
<div>
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<div>------------------------------------<br>
</div>
<div><br>
</div>
<div>Hello,<br>
</div>
<div>I'm having an issue where the frequency of my VCO is being
affected by the operation of other modules. I'll give a
broader explanation:</div>
<div><br>
</div>
<div>I'm a beginner on synth DIY, right now I have my home made
case, a PSU, two VCOs, an LFO, a clock module and an
amplifier/speaker (built in the case, not externally).
Everything has been arranged by me, I haven't purchased any
module yet. The clock and the LFO are the latest modules I
have built (pretty much both at the same time), and when I
tested them on their own, they worked just fine. However I
noticed that when they are powered, the frequency of the VCO
would stutter following the operation of the clock and the
LFO. <br>
</div>
<div><br>
</div>
<div>That would be: <b>without connecting the clock or the LFO
anywhere</b>, just having them powered up, whenever the
clock is up or down, or the waves generated by the LFO reset,
the frequency of the VCO varies a tiny bit. It gets more
noticeable the higher the pitch of the VCO.</div>
<div><br>
</div>
<div>After some head scratching I've realised that the signals
generated by any of the modules I have (both VCOs, the clock
and the LFO) are somehow leaking into the +12 and -12 rails of
my PSU. Measuring any of the rails on my scope (on AC mode, so
only the noise is shown), I can see that the waves generated
by the modules I mentioned above are there as well in the form
of noise (around 20mVpp each of them). That explains the
little variations in frequency of the VCO. However I have no
idea why this is happening or how to fix it. I have tried with
different PSUs I have around:</div>
<div><br>
</div>
<div>
<ul>
<li>11V 0.750A SMPS into DCDC to get +12 and -12</li>
<li>Two 12V 1A SMPS together to get +12 and -12</li>
<li>Linear PSU with 7812 and 7912</li>
</ul>
<div>I have the same problem<span id="goog_1466379976"></span><span
id="goog_1466379977"></span> with all of them. I'm
positive there's an issue somewhere with a lack of
filtering, but I don't know where, or why.</div>
<div><br>
</div>
<div>I'm attaching a sample of the VCO output where the
stutter can be heard and the schematic of the LFO. The way
the LFO is set up in terms of caps and isolation can be
extrapolated to every other circuit I have made, I always
place those 100nF caps between each rail and ground.</div>
<div><br>
</div>
<div><br>
<div class="gmail_chip gmail_drive_chip"
style="width:396px;height:18px;max-height:18px;background-color:#f5f5f5;padding:5px;color:#222;font-family:arial;font-style:normal;font-weight:bold;font-size:13px;border:1px
solid #ddd;line-height:1"><a
href="https://drive.google.com/file/d/1ts1WGcyl2y1Ypp5eP79Ptb5fHXawetZh/view?usp=drive_web"
target="_blank"
style="display:inline-block;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;text-decoration:none;padding:1px
0px;border:medium none;width:100%" aria-label="LFO
(square).jpg" moz-do-not-send="true"><img
style="vertical-align: bottom; border: none;"
src="https://drive-thirdparty.googleusercontent.com/16/type/image/png"
moz-do-not-send="true"> <span dir="ltr"
style="color:#15c;text-decoration:none;vertical-align:bottom">LFO
(square).jpg</span></a></div>
<br>
<div class="gmail_chip gmail_drive_chip"
style="width:396px;height:18px;max-height:18px;background-color:#f5f5f5;padding:5px;color:#222;font-family:arial;font-style:normal;font-weight:bold;font-size:13px;border:1px
solid #ddd;line-height:1"><a
href="https://drive.google.com/file/d/1RrUNX_Of_RGLAwn2CyV7I5fxRrlHvfHL/view?usp=drive_web"
target="_blank"
style="display:inline-block;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;text-decoration:none;padding:1px
0px;border:medium none;width:100%" aria-label="VCO
stutter.mp3" moz-do-not-send="true"><img
style="vertical-align: bottom; border: none;"
src="https://ssl.gstatic.com/docs/doclist/images/icon_10_generic_list.png"
moz-do-not-send="true"> <span dir="ltr"
style="color:#15c;text-decoration:none;vertical-align:bottom">VCO
stutter.mp3</span></a></div>
<br>
</div>
<div><br>
</div>
<div>In case you have any idea what could be wrong, your reply
will be greatly appreciated. Thanks beforehand!</div>
<div><br>
</div>
<div>Kind regards,</div>
<div><br>
</div>
<div>A.M. Barrio.<br>
</div>
<div><br>
</div>
<div>
------------------------------------
</div>
<div><br>
</div>
<div>In response to pata and Mike Bryant: <br>
</div>
<div>
<ul>
<li>Yes, the current PSU I'm using can provide 8W in
total. I'm only powering one VCO and one LFO with some
LEDs, power shouldn't be the issue in this case. </li>
<li>I always place 100nF caps between each rail and GND on
every circuit/board. However I hadn't heard of placing
caps on each IC. I suppose it should be between their
power pins and GND? I will have a look at capacitance
multipliers as well as I haven't heard about them
before.</li>
</ul>
</div>
</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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<pre class="moz-signature" cols="72">--
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