Ok, after much ado, here are some photos of my mixer. Been working on this for the last two years and absolutely could not have done this without the people here, this is to date my most ambitious project and am beaming now that its working.
It's an 8x2 mixer with a passive mix buss, the chasis is 3 RU. I drilled the chasis myself, turned out pretty good. Each input channel has a 312 type circuit, the makeup amplifiers are closer to a 325 type circuit. The buss is fed from one of the 2503 windings and each channel also has a direct 2503 output.
Each channel has an input impedance selector, buss mute, polarity invert, -20dB t pad, phantom power, pannner and input gain. The polarity, pad and input transformer impedance logic circuit are all relay controlled. The input relay board layout was done by justin at roll music. The board is set up to accomodate both the early 2622 input and the later 70's reichenbach input transformer used on the api consoles.
In addition to the input transformer selection, all the input channels are set up in pairs with diffferent cap selections for different tones. I built the box with tracking, not really mixing in mind, so there is a pretty wide pallette of tones availale across the 8 input channnels.
All the hookup wire is silver teflon and the balanced hookup is mogami. The panner pots, gain pots, knobs, transformers and opamps were all taken from an api console, all the other components on the cards were restuffed to taste. The amps are all held in there with a screw down bracket I had made which mounts to the transformer, redco did the fabrication for the brackets. The dual concentric knob below the meters is the output fader.
NYDave designed for me a meter buffer circuit for use with the very old 500 ohm meters. They arent VU's, closer to PPM ballistis, very fast and very very cool. The meters are fed from the mix buss only, cant meter each individual input channel, but for what I designed this for, no biggie. The meter circuit is %100 isolated from the audio path.
Overall, Im totally psyched with the different tones I was able to tweak out of each of the amplifiers. Im also super happy about the sound of the makeup amps, the buss doesnt sound any different from the channel amps, its not noisy and doesnt feel like its working hard at all to makeup the 8 channels hanging on the buss. With the channels muted (and a loading resistor slugged) or feeding the buss actively, the tone and level of the buss doesnt change. My only complaint if I had to create one, is the crosstalk. If I was mixing a record solely on this, the crosstalk would be no good, but for how I intend to use it, its no problem for me right now at all.
What is the deal with cross talk? On a passive mix buss, is that a by product of a poor physical layout, or can cross talk be adjusted by changing the value of the resistor feeding the buss?
Im so happy this is finally done, all total with research and thinking, this took over two years to do, I absolutely cant wait to use it on my next session.
Big thank you to everyone who was patient and giving enough to help me along through my learning curve on this one!!!
dave
It's an 8x2 mixer with a passive mix buss, the chasis is 3 RU. I drilled the chasis myself, turned out pretty good. Each input channel has a 312 type circuit, the makeup amplifiers are closer to a 325 type circuit. The buss is fed from one of the 2503 windings and each channel also has a direct 2503 output.
Each channel has an input impedance selector, buss mute, polarity invert, -20dB t pad, phantom power, pannner and input gain. The polarity, pad and input transformer impedance logic circuit are all relay controlled. The input relay board layout was done by justin at roll music. The board is set up to accomodate both the early 2622 input and the later 70's reichenbach input transformer used on the api consoles.
In addition to the input transformer selection, all the input channels are set up in pairs with diffferent cap selections for different tones. I built the box with tracking, not really mixing in mind, so there is a pretty wide pallette of tones availale across the 8 input channnels.
All the hookup wire is silver teflon and the balanced hookup is mogami. The panner pots, gain pots, knobs, transformers and opamps were all taken from an api console, all the other components on the cards were restuffed to taste. The amps are all held in there with a screw down bracket I had made which mounts to the transformer, redco did the fabrication for the brackets. The dual concentric knob below the meters is the output fader.
NYDave designed for me a meter buffer circuit for use with the very old 500 ohm meters. They arent VU's, closer to PPM ballistis, very fast and very very cool. The meters are fed from the mix buss only, cant meter each individual input channel, but for what I designed this for, no biggie. The meter circuit is %100 isolated from the audio path.
Overall, Im totally psyched with the different tones I was able to tweak out of each of the amplifiers. Im also super happy about the sound of the makeup amps, the buss doesnt sound any different from the channel amps, its not noisy and doesnt feel like its working hard at all to makeup the 8 channels hanging on the buss. With the channels muted (and a loading resistor slugged) or feeding the buss actively, the tone and level of the buss doesnt change. My only complaint if I had to create one, is the crosstalk. If I was mixing a record solely on this, the crosstalk would be no good, but for how I intend to use it, its no problem for me right now at all.
What is the deal with cross talk? On a passive mix buss, is that a by product of a poor physical layout, or can cross talk be adjusted by changing the value of the resistor feeding the buss?
Im so happy this is finally done, all total with research and thinking, this took over two years to do, I absolutely cant wait to use it on my next session.
Big thank you to everyone who was patient and giving enough to help me along through my learning curve on this one!!!
dave
