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Step 8Build the circuit
The circuit for this mixer is based almost entirely off an incredibly awesome schematic found here.
Build the circuit pictured below onto your mounting bracket.
Don't yet wire the audio jacks or any of the potentiometers. Add extra wires as necessary (such as for ground and audio in) keeping in mind that they will have to attach to components later.
Build the circuit pictured below onto your mounting bracket.
Don't yet wire the audio jacks or any of the potentiometers. Add extra wires as necessary (such as for ground and audio in) keeping in mind that they will have to attach to components later.
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PD: sorry for my english, i'm from Argentina
Firstly, will the original schematic work or do the miswirings completely ruin it?
And what are the values of these capacitors you have added?
I'm looking to make one of these, and am interested.
Thanks.
Full-resolution: http://www.instructables.com/files/orig/FJT/8F2A/FW39KSPG/FJT8F2AFW39KSPG.png
The capacitors in parallel with the resistors should be about 180 pF, depending on how much bandwidth you want. (180 pF gives you 88 kHz) No one can hear above 22 kHz, but we usually extend it out far beyond this so it's super-flat, without going up into the MHz where it will oscillate. Some op-amps might oscillate even with this, so you would have to increase the cap to decrease the bandwidth.
The capacitors on the power supply should actually be a large electrolytic (100 uF or so) in parallel with a small ceramic cap (104 = 100,000 pF), which I forgot to show.
You've done pleny already, its just that I need a concrete schematic to follow because the last time I had a ciruit which told me to 'experiment' it all went downhill from there :P
In this circuit, there are two op-amps inside the one chip. The first one is configured as an inverting summing amplifier, so it adds together all the inputs and inverts the polarity. The input resistors and feedback resistor are both 10k, so the gain is 0 dB for each input (no change in level). Then that feeds into a plain inverter that is also 0 dB of gain, which does nothing except reverse the polarity again so that it is correct at the outputs. So when the input faders are at maximum level, a signal will be passed through with no change.
Yeah, it's hard to experiment when you don't know how stuff works. It's best to get a working circuit first and then experiment from there.
Also, if this is meant to drive headphones directly, the headphone circuit needs to change. It can't go through a pot like that, and the capacitor needs to be larger for good low frequency response.