deveng
Well-known member
Gents,
I just finished this upgrade to my Soundcraft 400B console. The pcb sits inside what was once an empty space in the console meter bridge. The board replaces the master section's summing amp, fader buffer amp and monitor drive amp circuitry. The wiring was quite tedious as it all had to fit in the small space available. The wiring harness snakes down through a hole where the meter wires were originally run so no console frame cutting was required. It uses my custom opamps with sockets so I can quickly replace or try other discrete opamp options. Since there was not much room in the back of the console I mounted the output transformers at the back of the console. There are 2 Jensen transformers for the summing output and 2 Reichenbach transformers for the monitor. It all tested fine using RMAA. The original sum amp was a NE5532 and was not bad sounding at all but I wanted some Mojo. The addition of the discrete opamps and Jensens does just that. I tested the sum bus prior to and after the mod. The new summing amp stands up nicely with respect to distortion and frequency response tests and so far I'm very pleased. The original circuit used a TL072 to drive the monitors unbalanced. The mod should improve the monitoring to closely match the sound quality of the summing bus outputs. I've not done any critical listening tests as yet but so far its sounds good. I recently finished the ground bus mod, the full console upgrade (caps, ICs, mic pre transistors, power supply, etc) and found a bit of extra 60Hz. I just fixed that today and now have a S/N on the stereo bus at -101dB. With some additional grounding improvements I hope to improve on that and reach -104dB or a bit better. As it is now I can crank the monitor volume to maximum and there is only a nice clean hiss. Next up will be some critical listening.
regards,
Jeff
I just finished this upgrade to my Soundcraft 400B console. The pcb sits inside what was once an empty space in the console meter bridge. The board replaces the master section's summing amp, fader buffer amp and monitor drive amp circuitry. The wiring was quite tedious as it all had to fit in the small space available. The wiring harness snakes down through a hole where the meter wires were originally run so no console frame cutting was required. It uses my custom opamps with sockets so I can quickly replace or try other discrete opamp options. Since there was not much room in the back of the console I mounted the output transformers at the back of the console. There are 2 Jensen transformers for the summing output and 2 Reichenbach transformers for the monitor. It all tested fine using RMAA. The original sum amp was a NE5532 and was not bad sounding at all but I wanted some Mojo. The addition of the discrete opamps and Jensens does just that. I tested the sum bus prior to and after the mod. The new summing amp stands up nicely with respect to distortion and frequency response tests and so far I'm very pleased. The original circuit used a TL072 to drive the monitors unbalanced. The mod should improve the monitoring to closely match the sound quality of the summing bus outputs. I've not done any critical listening tests as yet but so far its sounds good. I recently finished the ground bus mod, the full console upgrade (caps, ICs, mic pre transistors, power supply, etc) and found a bit of extra 60Hz. I just fixed that today and now have a S/N on the stereo bus at -101dB. With some additional grounding improvements I hope to improve on that and reach -104dB or a bit better. As it is now I can crank the monitor volume to maximum and there is only a nice clean hiss. Next up will be some critical listening.
regards,
Jeff
