<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Unfortunately, the problem happens on those, too. Vintage Buchla cabinets use Power One supplies and a lifetime ago I replaced all of mine and had exactly this problem. This list was able to provide me a mod to disable the sensing circuit to stop the latch up.<div class=""><br class=""></div><div class=""><br class=""></div><div class="">Mark</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Aug 27, 2020, at 6:47 AM, Oren Leavitt <<a href="mailto:obl64@ix.netcom.com" class="">obl64@ix.netcom.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div class=""><p class="">If you're doing a power supply for a whole synth cabinet, I'd
just spend a little extra for a good ready-made power supply like
the Power-One HAA, HBB or HCC series power supplies.</p><p class=""><br class="">
</p><p class="">The 3-terminal regulators are not the best choice where you're
going to have several modules and the cumulative inrush currents
they impose.<br class="">
</p><p class=""><br class="">
</p><p class="">- Oren<br class="">
</p><p class=""><br class="">
</p>
<div class="moz-cite-prefix">On 8/26/20 6:24 AM, ackolonges fds
wrote:<br class="">
</div>
<blockquote type="cite" cite="mid:SYCP282MB04807FB47876219D1D407A68D5540@SYCP282MB0480.AUSP282.PROD.OUTLOOK.COM" class="">
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<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">Hi All,</span></div>
<div style="" class=""><br class="">
</div>
<div style="" class=""><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">I've been
having issues with a very standard +/- 12V power supply design
for a modular synth. Every once in a while when powering up,
the positive rail doesn't rise, and it needs to be reset to
work. After some trial and error, and research, I found
mention of this issue in Douglas Self's 'Small Signal Audio
Design' book, where he shows a circuit almost identical to my
power supply. A screen grab of the related page can be found
here: </span><a href="https://pasteboard.co/Jo8PuIu.png" id="LPlnkOWALinkPreview_0" moz-do-not-send="true" class=""><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">https://pasteboard.co/Jo8PuIu.png</span></a><br class="">
</div>
<div style="" class=""><br class="">
</div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">This paragraph from
that page describes the issue I'm having perfectly :
<i class=""><br class="">
</i></span></div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""><i class=""><br class="">
</i></span></div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""><i class="">"</i></span><i class=""><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">D2, D4 will prevent
damage
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">in this
case, but leave the power supply vulnerable to start-up
problems; if its output is being
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">pulled
down by the
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""></span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">15 V regulator, the</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">15 V
regulator may refuse to start. This is actually
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">a very
dangerous situation, because it is quite easy to come up
with a circuit where start-up will</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""> only fail one time
in 20 or more, the incidence being apparently completely
random, but</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""> presumably controlled by the exact point in the AC
mains cycle where the supply is switched </span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">on, and other
variables such as temperature, the residual charge left on
the reservoir capacitors,
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">and the
phase of the moon. If even one start-up failure event is
overlooked or dismissed as</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""> unimportant. then there is likely to be
serious grief further down the line.</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""> Every power supply</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""> start-up failure
must be taken seriously.</span></i><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class=""><i class="">"</i></span></div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<br class="">
</div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
Unfortunately after stressing how important it is to fix such an
issue, no solutions are mentioned... I've tried removing all of
the protection diodes, increasing and decreasing the value of
the smoothing caps, tried many different makes of voltage
regulators, and also tried an NTC thermistor to slow the in-rush
current, all to no avail. <br class="">
</div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<br class="">
</div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
I'm starting to run out of ideas, so if anyone on the list has
come across a fix it would be great to hear about it.
<br class="">
</div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<br class="">
</div>
<div style="font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;" class="">
<br class="">
</div>
<br class="">
<br class="">
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