Vintage Synth Repair

You can look at the FET as a switch. It appears to be turned on very
briefly by the key gate into a decaying sample and hold which should
give a very fast rise to the AT level followed by a decay set by the
10M resistor & cap.

As far as the two different resistors goes they are probably balancing
the two filters and if you look at the resistors labled R6 & R7 with
no value they are probably for fine calibration.


--- In vintagesynthrepair@yahoogroups.com, "maxferfranc"
<faxiomas@...> wrote:
>
> Hi all, this is my first message here: I'm thrilled by analog circuits 
> although I'm not an expert, so I'm studying the Yamaha CS80 to try and 
> make some sort of virtual, as I'm not satisfied with the Arturia.
> 
> I would ask you some questions to the people here who knows more than 
> me about reading schematics
> 
> First question: if you look at the picture I posted there
> 
> http://f1.grp.yahoofs.com/v1/YIrqSApHmjS6cA3dqhZH-
> GmV76P2YcikZA_XszBHjYyz7poNC3SZztKSOwD4kC4LWbNppnry_1movZzpGN2mUqumJOKHG
> p_Ipg/CS80%20schems/tws.jpg
> 
> You will see the velocity generator in Yamaha CS80: I'd like to know 
> this: what is the FET doing here? And, what is the output of 
> the "Initial touch"? Is it a decay envelope? How does it link to a 
> supposed variable gate velocity?
> 
> Now look here
> 
> http://f1.grp.yahoofs.com/v1/YIrqSFqjXlS6cA3dBH1N34CSLYoZ5oUQzDqtOY18kaL
> q4napy2NIUcZliGnwlKUQlnbxNbPxLmA0pd3mVL77desKCsG_EsLsbQ/CS80%
> 20schems/41%2520-%2520M%2520Circuit%2520Diagram.bmp
> 
> You will see that I highlighted in red two resistors, one set at 100k 
> to the HPF and the other set at 47k : do these resistors act as CV 
> limiters? And what is more limited, the HPF or the LPF?
> 
> Hope these questions are not too hard, thx for any reply
>