I have a DIY mini mixer built on perfboard that I'd like to add a DI output to send the mixed signal to a PA. I'm not much more than an electronics hobbyist, so I could use some help with a couple details.
The mini mixer is built from on RG Keen's design:
mini mixer
There's no room in my box for a transformer, so I plan on using a simple dual op-amp balancer. The one I chose is from my bass amp that seems to work well:
![Bass DI.jpg Bass DI.jpg](https://cdn.imagearchive.com/groupdiy/data/attachments/84/84887-007139ceb54dd65a8ba77c6db9999499.jpg)
The Keen mixer works off a single rail power supply while the DI uses a bipolar power supply. Since I already have the mixer built into a pedal, I'd like to run the DI off the same power supply. My questions are:
The mini mixer is built from on RG Keen's design:
mini mixer
There's no room in my box for a transformer, so I plan on using a simple dual op-amp balancer. The one I chose is from my bass amp that seems to work well:
![Bass DI.jpg Bass DI.jpg](https://cdn.imagearchive.com/groupdiy/data/attachments/84/84887-007139ceb54dd65a8ba77c6db9999499.jpg)
The Keen mixer works off a single rail power supply while the DI uses a bipolar power supply. Since I already have the mixer built into a pedal, I'd like to run the DI off the same power supply. My questions are:
- How do I bias the positive op-amp inputs for the DI circuit? I sometimes see bias voltages applied through resistors and sometimes directly from VBias (1/2Vcc). I'm also confused where to inject it in reference to the voltage divider at the input to pin 3. Since the output of the final op-amp in the mini mixer should be at bias voltage, can I just take the input to R95 from just before the coupling cap at the mixer's output?
- Am I correct to assume that I will need to add capacitors with reverse polarity before C63 and C68 to render them effectively non-polar due to bias voltage showing up at the op-amp outputs?
- C63 and C68 are rated at 25V. Is this enough in the event that phantom power is applied to the XLR?