A Ghost Story (cont.)
What do we really want to do to this?
At one time the Ghost was used for mixing, but these days most things are done in the computer. However, there are a lot of people that I know, and have worked for that routinely run 16, 24, or more outputs from their DAWs (digital audio workstation)into their console line inputs, to take advantage of the character that the analog circuitry imparts on the mix.
The Ghost has an A Mix Bus and a B Mix Bus. In typical inline fashion, the A Bus is used for tracking, being fed from the mic pres and balanced line inputs. The B Mix is fed from the balanced tape return inputs. Both the A and B Mix Buses have their own summing amps and outputs, but the B Mix can also be fed into the A Mix if you need 64 channels on mixdown.
I still used the A Bus for tracking live bands, making use of the parametric EQ and flexible signal routing, but never had much use for the B Mix. So my plan was to use the B Mix Bus exclusively to provide 32 channels of analog summing for the DAW. This would involve upgrading all of capacitors and opamps in the tape return signal path of every channel.
The TL072 opamps were mostly replaced with OPA2134, and the 5532 opamps were replaced with 4562. For every opamp removed, a gold plated machined socket was soldered in place before installing the new opamp. All of the caps in the audio path were replaced with Nichicon Gold series audio caps, with larger values being used in many locations that would benefit from an improvement in low frequency distortion.
All of the summing amps in the console, including A Bus, B Bus, and Groups 1 thru 8, received OPA1612 opamp upgrades. These are surface-mount chips that need to be mounted on apdapter PCBs in order to plug into DIP sockets.
For the B Mix Bus, I installed a version of my summing bus gain mod that is used on several client consoles. There is an added 3-position switch in the master section labled B Bus -6dB in the up position, and B Bus -12dB in the down position. The B Bus is at unity gain in the middle position. These gain reduction settings come in handy when summing lots of channels in an active mix and things start to overload. Instead of turning down every fader or output, you can simply flip the switch for another 6dB of headroon without breaking the flow.
A mod was done to the group faders making use of the never used L+R switches. I always found the group faders to be in the way when working, being right in the middle of the console. They normally need to be set at the zero line, so I created a mod that when the L+R buttons are engaged, the group faders are bypassed and the gain is set to unity. This allows the faders to be pulled down and out of the way.
Notice the sockets added to the opamps and the oversized caps.
Group Summing Amp
Notice the surface mount chip (OPA1612) in the adapter. The wires are part of the Group Fader bypass mod. There are also a few visible bypassed caps that were deemed non-essential.