[sdiy] Spare op-amp useful in gain stage?

[rsdio at audiobanshee.com]

On Jan 28, 2016, at 3:57 PM, Mattias Rickardsson <mr at analogue.org> wrote:
> On 28 January 2016 at 23:17, Richie Burnett
> <rburnett at richieburnett.co.uk> wrote:
>> Putting multiple amplifiers in parallel lowers the noise level.
> 
> The "multipath amplifiers" approached mentioned. :-)
> 
> The question is if it's alright to tie their outputs together even if
> the op-amps can reach their clip level?

Two things:

First, the outputs are not tied together directly, but with series 10-Ohm resistors, as suggested in the opening message of this thread. This low resistance allows for imperfections where the op-amps might be driving different voltages, without attempting to break the laws of physics.

Second, some op-amps can actually withstand an output short-circuit, although such protection may cause excessive heating. The TL084, as one example, depicts an internal 200-Ohm output impedance in its equivalent circuit, which probably accounts for the output short-circuit protection - but up to 90 mA in the worst case still seems like a lot of current.

Brian