[sdiy] Buchla 259 timbre circuit and op amp compensation

[Aaron Lanterman]

So, along the Buchla timbre theme, I have yet another student,  
Alfredo, working on the Buchla 259 version of the timbre generator.

This one uses CA3160s, which are capable of "rail to rail output." The  
CA3160 is a frequency compensated version of the CA3130. The CA3160  
datasheet says: "Miller Effect compensation (roll off) is accomplished  
by means of the 30 pF capacitor and 2Kohm resistor connected between  
the base and collector of transistor Q11. These internal components  
provide sufficient compensation for unity gain operation in most  
applications. However, additional compensation, if desired, may be  
used between Terminals 1 and 8." The data sheet does not suggest what  
additional compensation might be needed, or when, but it appears that  
Buchla decided to add some additional compensation, in the form of 47  
pF caps.

I don't have any CA3160s, but I do have some CA3130s I gave Alfredo to  
use. It appears the CA3130 is an uncompensated version of the CA3160.  
The CA3130 datasheet suggests using a 47 pF between terminals 1 and 8  
for compensation.

Since Buchla felt the need to add some compensation to the already  
compensated CA3160 op amp, should we use a higher value cap than the  
47 pF suggested by CA3130 datasheet? Say 100 pF?

We had lots of high-frequency goo in our deadband circuit outputs,  
especially when the output was near zero. Putting in the 47 pF  
compensation caps removed a lot of the goo, but the signals still  
appear pretty gooey.

- Aaron