Tim. How about an instrument input for the A12?

[Category 5]

We need to get your forums kicking!

How would I add an instrument level input to the A12? One of my favorite uses for the 312 was Bass DI and it would be great to use the A12 for that here. How bad is it if I just use a direct box? Any special type to use?

Is it easy to add an instrument input (aside from cutting a hole in the case)?

Shane

[tpryan]

Most racked preamp modules I've seen have had a DI added by inserting a switched 1/4" jack between the input transformer and the preamp input. You could do the same by breaking the trace between the input attenuator and non-inverting input of the op-amp. Run the signal from the jack tip through a .01uF cap, and add a 1M resistor from the non-inverting op-amp input to ground. This will certainly get the signal into the A12, but I don't think it's an ideal arrangement. Much of the character of the preamp gets bypassed this way, since you'd be taking the input transformer out of the picture. I'd prefer a single-ended JFET buffer that would provide enough current gain to drive the input transformer. That way you'll have a preamp circuit with a very high input impedance, a more guitar amp like topology, and the slight distortion from the input transformer. This is the idea behind the DI01, which is still a few months away. It's essentially a guitar amp front end which buffers and balances the instrument signal.