[sdiy] Circuit Boards / kits

[mark verbos]

The VCA in the Buchla 410 looks a lot like that. It uses a 741. There  
are trims on the top and bottom of the transistor pair and he used a  
fancy pants matched pair as well. It probably wouldn't need all that  
if he had used 1% resistors.

The Buchla 110 is also a VCA based on a single matched pair, but it  
has transistors for the output stage as well.

Mark





On Sep 25, 2008, at 12:37 PM, harrybissell at wowway.com wrote:

> ARP usually used the LM301 opamp. They would look similar. In many
> cases the LM301 is feedfoward compensated (makes it faster).
>
> The 748 is a decompensated 741, its faster but not unity gian stable
> unless you add the right compensation cap (like PAiA did)
>
> H^) harry
>
>
>
> On Thu, 25 Sep 2008 11:38:40 -0400, David Moylan wrote
>> Roy J. Tellason wrote:
>>> On Thursday 25 September 2008 08:33, harrybissell at wowway.com wrote:
>>>> On Wed, 24 Sep 2008 18:22:38 -0400, Roy J. Tellason wrote
>>>>
>>>>> So what do they use for a VCA?
>>>> A differential pair, a transistor to sink current through the  
>>>> emitters,
>>>> and an opamp to revover the signal.  I added 1% resistors and it  
>>>> works
>>>> very well.  I think its a 741 (or 748)
>>>
>>> I have a vague recollection of seeing something of the sort  
>>> before.  I
> think I
>>> had a TI book that featured a circuit like that.  I haven't seen  
>>> it lately so
>>> I don't recall what particular amplifier it used or whether it  
>>> used 1%
>>> resistors though.
>>>
>>>> schematics are online (somewhere)
>>>
>>> Hmm.
>>>
>> Didn't Arp use this configuration too?  I know there are some of
>> this type in the Omni2.
>>
>> Dave
>
>
> Harry Bissell & Nora Abdullah 4eva
>
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