Thanks y’all (@corpusjonsey, @rvense, @bcfrench9, @bmoren)! I have done a decent amount of electronics assembly, and designed some simple circuits with microcontrollers, but I haven’t done much of anything with audio.
I’m looking at adding a stereo send and return to the Befaco Hexmix. You can peep the full schematic here.
The signal runs through a mess of op amps to do most everything the mixer does. Ultimately I know I need to boost the singal to 5v and then bring it back down the expected level. I’m planning to pull the resistors at the end of each of the channel inputs (R22, R27, …), add stereo switches to determine whether they continue on their extant circuit path or get sent to a summed stereo send and return. There’s an unused channel 7 on an expander connecter that I would use for the returns (B_MIX_7_L/R). It’s also worth noting the jumpers on the schematic aren’t on the actual final module.
I’ve done enough research to understand loosely how op amps work, but they do so much it can be hard to really wrap my head around. If my reading informed me correctly, the following “Return” circuit from the Hexpander is using the op amps in an “integrator” configuration where the capacitor limits gain? Essentially the feedback on the negative line of the opamp allows the level of the signal to change.
The stereo switch determines whether the return signal is line level or modular level, and then the op amp brings the signal down to 800mVp.
So my first questions:
- In the realm of audio, what determines the voltage the signal should be at for any given process? On looking over the Hexmix schematic it seems it goes up and down a few times depending on which part of the chain we’re looking at.
- The math for this circuit confuses me. I feel the need to hard blink when considering what resistor and capacitor values are the correct choice for bringing the singal to the correct voltage?
- When looking at the middle of a circuit, is there a good way to understand the current level of the signal? Either viewing the schematic in a tool or otherwise.
Please assume I have little idea what I am talking about (true!). I’m sure I’m using incorrect terminology to describe things. Corrections welcome!
Next bit: The power supply!
I know that if I add op amps, I need to manage the power. I was proud of myself for figuring out the 4/8 lines were referring to the power lines for the op amps while I was in the shower yesterday. On the other hand, I have no idea what the network of capacitors and resistors are doing in this diagram. I’m not sure what this is called, so I can’t look it up. Any pointers would be welcome!
Thanks in advance!