[sdiy] Datasheet Toshiba TA7505M / modern replacement

[René Schmitz]

On 04.01.2025 16:27, Florian Anwander 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.
>

Can you state what you think your problem is? Is it that the IG00153 is 
loading the portamento cap?


> 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).
>

This opamp is likely similar to a 324 / 358 or 741. Sometimes a high 
impedance causes problems. Maybe the 072 is too modern. :)

Also try an LM358.


Best,

  René


>
> Best regards
> Florian
> -- 
> http://www.florian-anwander.de/
>
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