[sdiy] 281 - a tall order.

[Peter Grenader]

Buchla used the usual 741 - pins 2.3 as inputs, 6 as output. -V at 4, +V and
7, pin 8 n/c.

Words of warning:

1) the 281 schematic does not include all the circuit

2)  Some of the components were only required if it was to be optionally
driven by a computer (a la Buchla 300s and 500s)

3) The schematic has errors in it.

4)  If you're attempting to sub Q1 and Q4 with discrete trannies, they will
need to be matched.  Google this and you will find a test circuit.  I
believe Jim Patchell has one on his site if memory serves.

5)  Building a Buchla module such as this one, from scratch, is a tall
order.  Not impossible, but it's going to test anyone's troubleshooting
skills to the nines.  Remember, the 281 incorporates no less than three
stacked PCBAs interconnected via 26 pin flat cables.

My suggestion:

I believe Mark Verbos has an incarnation of the 281 on his simple-answer
site.  Slightly different, but Mark's gone to the trouble of specing easier
to find subs, plus he's worked the bugs out.

- P



>> From: J Alexander [mailto:diyid at hotmail.com]
>> -The schemo calls for a diode numbered uA741, where 'u' is
>> the micro symbol.
>> What is this part?  What to substitute?
> 
> The mu-A was a manufacturer identification that
> Fairchild used.  The part is just a garden-
> variety 741 op amp.  In a lot of applications,
> almost any other opamp will do, but you have
> to watch out for circuits that use external
> compensation to do tricky things.  You also
> have to watch out for pin compatibility if the
> packaging is unusual.
>