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<p>Because you steal from the high end what you gain in the low end.</p>
<p>Have a look at the VCO3 at my home page for an example of a
circuit that runs well below the LFO range even (1 cycle per 15
Minutes!) and still uses regularly sized cap, and has a decent
high range as well.<br>
</p>
<div class="moz-cite-prefix">Am 17.01.2020 um 15:43 schrieb Ben
Bradley:<br>
</div>
<blockquote type="cite"
cite="mid:CA+wjhVtZ1KH0bca6RjthR72WKsWjQHpyPUFXAL3RYJxV_9EH3w@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="auto">That's what I was thinking, why not increase the
timing capacitor by 100 or 1000 times.</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, Jan 17, 2020, 8:07 AM
Spiros Makris <<a href="mailto:spirosmakris92@gmail.com"
moz-do-not-send="true">spirosmakris92@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="auto">It is true that a low charge current will be
less ideal because then leakage currents etc become
significant. They usually cause a rise to the minimum
frequency the oscillator will still work at.
<div dir="auto">One can lower the frequency of any similar
oscillator by increasing the timing capacitor
appropriately and that should not impact the tuning range
etc (referring to caps with similar specs and different
nominal capacitance).</div>
<div dir="auto"><br>
</div>
<div dir="auto">Spiros</div>
<div dir="auto"><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, 17 Jan 2020, 14:49
Magnus Danielson, <<a href="mailto:magnus@rubidium.se"
target="_blank" rel="noreferrer" moz-do-not-send="true">magnus@rubidium.se</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<p>Hi,</p>
<p>Recall that as you go for very low frequencies, you
get very small currents, as you have a Volt to
exponential Current converter followed by a Current
Controlled Oscillator. For the low frequencies to
work, it needs to be very clean for instance. It's not
scaled to be a LFO, you could do that, but care must
be taken in such an effort.<br>
</p>
<p>I should dig up my ASM-1 board and measure this as I
once intended to do. I built the ASM-1, measured it
with a scope to span a large range. I then got a
rubidium clock, a counter and a couple of DMMs and
intended to measure this more carefully, learned more
and now have a excessive time and frequency lab, but
still have not returned to the original project of
measure the ASM-1 VCO. Also got to repair the original
rubidium clock.</p>
<p>Hmm, maybe I should resurrect the ASM-1 homepage I
maintained, just as a reference.<br>
</p>
<p>Cheers,<br>
Magnus<br>
</p>
<div>On 2020-01-16 17:48, Jean-Pierre Desrochers wrote:<br>
</div>
<blockquote type="cite">
<div>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">Hi list,</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">I'm working on the Elby-Design
ASM-1 VCO</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA"><a
href="https://www.elby-designs.com/webtek/asm-1/vco/vco-asm1-cct.pdf"
rel="noreferrer noreferrer" target="_blank"
moz-do-not-send="true">https://www.elby-designs.com/webtek/asm-1/vco/vco-asm1-cct.pdf</a></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">Im want to use it as a 1v/oct LFO
(.05hz to 20hz)</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">I first mounted the circuit on my
protoboard with success.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">at first I used a matched pair of
2N3904 for Q1A & Q1B</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">instead of the MAT02 shown in the
schematic.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">I could reach very low frequencies
(as low as .04hz).</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">But to do so I needed to replace
R9(56k) for a 33k temporarily. Fine. </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">This morning I replaced both 2N3904
with a genuine MAT-02</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">and started the same frequency
measurements as yesterday.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">I bumped into something weird..</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">Here are the actual measurements I
first did using 2x2N3904:</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">mVolt at 1k TEMPCO resistor vs
Sawtooth period</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">158.0mV
=> 0.050sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">176.0mV
=> 0.100sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">193.8mV
=> 0.200sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">212.0mV
=> 0.400sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">229.8mV
=> 0.800sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">247.5mV
=> 1.6sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">265.5mV
=> 3.2sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">283.2mV
=> 6.4sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">301.7mV
=> 12.8sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">319.7mV => 25.6sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">(18mV steps, nice exponential
response!)</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">Now here are the actual
measurements with a MAT-02:</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">mVolt at 1k TEMPCO resistor vs
Sawtooth period</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">157.0mV
=> 0.050sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">175.0mV
=> 0.100sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">193.0mV
=> 0.200sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">211.0mV
=> 0.400sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">229.0mV
=> 0.800sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">247.0mV
=> 1.6sec</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">271.0mV => 3.2sec</span></p>
<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">*** Now trying to go further
increasing the TEMPCO mVolts</span></b></p>
<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">*** the oscillator starts backing
up and re-increase its frequencies !!!</span></b></p>
<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">*** I could not go further
lowering the frequency. </span></b></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">I tried 3 different MAT-02's and
even LM394's</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">and they all behave the same.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">Using different matched pairs of
2N3904 worked perfectly..</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">I suspect MAT-02’s minimum base to
emitter current reached (???)</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">What am-I missing here ??</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"
lang="EN-CA">By the way, all the IC's I'm using
here are genuine one's</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">(TL082,
MAT-02, CA3140, LM311).</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">JP</span></p>
</div>
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