<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">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,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d" lang="EN-CA"><u></u> <u></u></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<u></u><u></u></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" target="_blank" rel="noreferrer">https://www.elby-designs.com/webtek/asm-1/vco/vco-asm1-cct.pdf</a><u></u><u></u></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)<u></u><u></u></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.<u></u><u></u></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<u></u><u></u></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.<u></u><u></u></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).<u></u><u></u></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. <u></u><u></u></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<u></u><u></u></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.<u></u><u></u></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..<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d" lang="EN-CA"><u></u> <u></u></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:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d" lang="EN-CA"><u></u> <u></u></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<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">158.0mV
=> 0.050sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">176.0mV
=> 0.100sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">193.8mV
=> 0.200sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">212.0mV
=> 0.400sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">229.8mV
=> 0.800sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">247.5mV
=> 1.6sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">265.5mV
=> 3.2sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">283.2mV
=> 6.4sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">301.7mV
=> 12.8sec<u></u><u></u></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<u></u><u></u></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!)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d" lang="EN-CA"><u></u> <u></u></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:<u></u><u></u></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<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">157.0mV
=> 0.050sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">175.0mV
=> 0.100sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">193.0mV
=> 0.200sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">211.0mV
=> 0.400sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">229.0mV
=> 0.800sec<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">247.0mV
=> 1.6sec<u></u><u></u></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<u></u><u></u></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<u></u><u></u></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 !!!<u></u><u></u></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. <u></u><u></u></span></b></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d" lang="EN-CA"><u></u> <u></u></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<u></u><u></u></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.<u></u><u></u></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..<u></u><u></u></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 (???)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d" lang="EN-CA"><u></u> <u></u></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 ??<u></u><u></u></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<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">(TL082,
MAT-02, CA3140, LM311).<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">JP<u></u><u></u></span></p>
</div>
<br>
<fieldset></fieldset>
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