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<div class="moz-cite-prefix">On 10.06.2023 06:08, David G Dixon via
Synth-diy wrote:<br>
</div>
<blockquote type="cite"
cite="mid:EF3108BCCA9A42D0B44A47FDE778BEF4@david78c70950b">
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<div><span class="776105503-10062023">Hello SDIY Team,</span></div>
<div><span class="776105503-10062023"></span> </div>
<div><span class="776105503-10062023">I've built a ladder filter
on my own PCB layout from Yves Usson's Minimoog ladder filter
schematic, and I must confess that the results are less than
stellar. The filter works, but not terribly well, and it
sounds nothing like a Minimoog. I used 2N3904 and 2N3906
instead of BC547 and BC557, but I matched all of the
transistor pairs in the ladder, and matched the four
transistors at the top and bottom of the ladder as well as the
other four transistors, using Ian Fritz's transistor matching
circuit (which I also laid out and built on a PCB). I did not
try to match the one PNP to the current driving NPN below the
bottom of the ladder.</span></div>
<div><span class="776105503-10062023"></span> </div>
<div><span class="776105503-10062023">Does anyone here have any
experience with this schematic? Will it change anything if I
replace the 3904s with 547s, etc? Everything else was exactly
as specified in the schematic. This was my second attempt to
build from an Yves Usson ladder filter schematic. My "Raging
Bull" Taurus filter didn't work at all.</span></div>
<div><span class="776105503-10062023"></span> </div>
<div><span class="776105503-10062023">I just want to know if there
is some fundamental flaw in this schematic before I spend too
much more time with it. Any insights would be most
appreciated.</span></div>
<div><span class="776105503-10062023"></span> <br>
</div>
</blockquote>
<p>That minimoog sound comes partly from overdriving the filter.</p>
<p>To replicate the sound you need to create the same level
situation as in the minimoog. <br>
</p>
<p>Yves has a resistor in the design that is meant to be tuned for
that.</p>
<p><br>
</p>
<p>I built mine from BC547s too. <br>
</p>
<p>Overall I find that it hardly ever makes a difference which
transistors are used, as long as you use ones with similar beta. <br>
</p>
<p>(Transistor parameters stray anyway.... And the TIS97 was pretty
much a jellybean go-to part. )<br>
</p>
<p>The CA3046 might have much lower beta, compared to the original
TIS97. <br>
</p>
<p><br>
</p>
<p>The caps are are different. 68n vs 47n. <br>
</p>
<p><br>
</p>
<p>You might want to have a look at my version as well, much more
bare bones, a bit more faithful to the original. </p>
<p>(But mine has different caps, I used the 22n from the Prodigy
filter.)</p>
<p><br>
</p>
<p>One problem I had when I built mine, was that due to the
different collector voltages in the diffamp one side heated <br>
</p>
<p>up more than the other, imbalancing the diffamp. (And removing
much of the resonance gain.) <br>
</p>
<p>That could also happen in Yves version. (There run some 5-6mA
through there, with 15V thats 90mW... Original voltages were
lower.)<br>
</p>
<p>I placed a resistor in the other leg (the one with 22 / R25 in
Yves schematic), to balance it. <br>
</p>
<p><br>
</p>
<p><br>
</p>
<p>Best,</p>
<p> René<br>
</p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:EF3108BCCA9A42D0B44A47FDE778BEF4@david78c70950b">
<div><span class="776105503-10062023">Dave Dixon</span></div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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