[sdiy] AC coupling caps on MS20 clone

[megaohm]

On Sat, Aug 7, 2010 at 12:57 AM, David G. Dixon
<dixon at interchange.ubc.ca> wrote:

>
>>  3) level pot with pull-switch, to select AC or DC coupling.
>
> Too complicated/expensive for my tastes (which are simple and cheap).
>


It's no more complicated than a pot and a toggle switch. If you use
quality toggles (NKK for example) then a P/P pot is less expensive
than a pot and toggle.



>
>> The pull-switch solution is my personal favourite, but it might
>> interfere a bit with another clever thing discussed here some weeks
>> ago when it came to "bipolar" level pots... where the true null point
>> can be hard to find, and a pull-switch could come in handy when the
>> signal is supposed to be totally off.
>

Another benefit is you get the full rotation of the pot for level
control instead of just half the travel.




>> I expected the plug tip to be connected to either the jack's tip
>> connector or the jack's ring connector, respectively, but I realized
>> that it wasn't true - at least not on my Switchcraft stereo jack.
>> - With mono plug half-in, BOTH jack tip and jack ring goes to plug tip.


The reason I don't like this idea/solution is because all patchcord
plugs are different. When half inserting into a stereo jack the tip of
the plug should make contact with the ring lug only, not the tip lug
of the jack, too. Switchcraft plugs have stubbier tips and will seat
properly. MANY other plug tips are slightly longer/more pointy and
will tend to make contact with both tip and ring (as was described by
the OP).



Have you thought of this solution:
Use just one cap and one toggle switch.
Connect all inputs (after the level pots) to one side of a cap. Other
side of cap connects to summing point of op amp. Use the toggle switch
to short the cap when you don't want AC coupling. This solution saves
you two toggles and two caps.

p.