[sdiy] Buchla 259 timbre circuit and op amp compensation

[anthony]

Hey this has cleared up a sticking point for me! Just try finding 3160's 
anywhere. What about 3140's? They aren't that much different from 3130's 
besides having different supply voltage limitations, right?

What about using a mix of what you have? I have a number of NTE7144's (a 
3140) and RCA 307-073's (a 3130) - seems like I could mix 'em together in 
the 259 timbre circuit. Haven't looked at that schematic in a while...

AA

> 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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