[sdiy] Buchla 259 timbre circuit and op amp compensation

[mark verbos]

Aaron,

I have seen the insides of several actual 259s. More often than not,  
they actually had 3130s in them! The caps were still 47p and the  
circuit seemed to work just fine.


Mark




On May 1, 2008, at 3:25 AM, Aaron Lanterman wrote:

> 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
>
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