<p dir="ltr" style="margin-top:0; margin-bottom:0;">TA7505 is much slower than TL072, and even then that cannot affect tuning range. There must be something shorted in connections between the boards probably. Or maybe the fault was there before you made SSK replacement.</p>
<p dir="ltr" style="margin-top:0; margin-bottom:0;">As long as your replcement provides proper tuning voltage, it's good.</p>
<br>
<p dir="ltr" style="margin-top:0; margin-bottom:0;">Roman </p><br><br>---- Użytkownik Pete Hartman via Synth-diy napisał ----<br><br><div dir="ltr"><div dir="auto">In the absence of the datasheet, I'd consider trying a "better" op amp than the TL072, maybe an LT1013 or OPA2134, if I had them on hand (I personally do :) ). Obviously the datasheet to get the actual details would be preferable....</div></div><div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Jan 4, 2025 at 9:31 AM Florian Anwander <<a href="mailto:fanwander@mnet-online.de" target="_blank">fanwander@mnet-online.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
Hello,<br>
<br>
I built a replacement for the SSK board in a Yamaha CS15,
essentially using Old Crow's approach. My schematic is here:<br>
<a href="https://florian-anwander.de/yamaha_cs15/CS15_SSK_FA__Nano_2_sch.png" target="_blank">https://florian-anwander.de/yamaha_cs15/CS15_SSK_FA__Nano_2_sch.png</a><br>
The original schematic is here:<br>
<a href="https://florian-anwander.de/yamaha_cs15/Yamaha_CS-15_Servicemanual.pdf" target="_blank">https://florian-anwander.de/yamaha_cs15/Yamaha_CS-15_Servicemanual.pdf</a><br>
<br>
Everything works perfectly. Only after switching on, VCO2 plays in
an extremely wide range, while VCO1 only plays over one octave
across the entire keyboard. I can "cure" this by briefly
interrupting the CV connection to VCO1.<br>
<br>
The difference between the two VCOs is that the TA7505M OpAmp, which
provides the buffering for the portamento circuit, is connected
directly to the IG00153 of VCO1; while for VCO2 there is an
additional OpAmp stage before the IG00153 that provides the detune
voltage. In my circuit I use a TL072 instead of the Toshiba TA7505M.<br>
<br>
Now I am looking for the datasheet of the TA7505M to find out what
could cause the problem. There doesn't seem to be the datasheet on
the web.<br>
<br>
Do any of you have a Toshiba Databook from the late 70s? Or does
anyone have an idea how I could solve the problem in a simple way
without having to make a new board (it is clear that I could also
put a buffer in front of the IG00153).<br>
<br>
<br>
Best regards</div><div><br>
Florian<br>
<pre cols="72" style="font-family:monospace">--
<a href="http://www.florian-anwander.de/" style="font-family:monospace" target="_blank">http://www.florian-anwander.de/</a></pre>
</div>
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