[sdiy] Datasheet Toshiba TA7505M / modern replacement

[Pete Hartman]

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....

On Sat, Jan 4, 2025 at 9:31 AM Florian Anwander <fanwander at mnet-online.de>
wrote:

> Hello,
>
> I built a replacement for the SSK board in a Yamaha CS15, essentially
> using Old Crow's approach. My schematic is here:
> https://florian-anwander.de/yamaha_cs15/CS15_SSK_FA__Nano_2_sch.png
> The original schematic is here:
> https://florian-anwander.de/yamaha_cs15/Yamaha_CS-15_Servicemanual.pdf
>
> 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.
>
> 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.
>
> 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.
>
> 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).
>
>
> Best regards
>
> Florian
>
> -- http://www.florian-anwander.de/
>
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