How to upgrade a Bradshaw RSB-18


This is one project I have always had misgivings about. The reason? It's not the best way to solve a problem. I had a customer who wanted to make his RSB-18 sound better than it did. Well ahead of it's time in it's day, bulletproof in reliability, and with one of the best designed footcontrollers of any era, the RSB-18 is a remote switching unit which performs a somewhat similar function to the contemporary relay based units from CAE, Digital Music, Axess Electronics, and others. However the main difference between these current units and the RSB-18 is that the RSB-18 uses active buffers for every single switching section, while the modern units use relays. To be specific, 6 stages of active amplification were used per loop in the RSB-18. In order to get any type of fidelity that has come to be expected from the relay based units, it would take an over-engineered solution.

After reading the schematics, I projected that the best possible chance to make this unit sound better than it did would be to throw the highest quality electronics at it. To simply substitute the finest available dual and quad op-amps for the NE5532 and TL074 dual and quad op amps used in the unit, to replace the regulators with ones capable of higher continuous current delivery, and to use larger heat sinks on those regulators.

The upgrade consisted of substituting a Burr Brown OPA2132 for each NE5532 amplifier. It also consisted of Substituting a Burr Brown OPA 4132 for each TL074 op amp. To further complicate matters, the OPA4132 was no longer available in DIP format, and additional expense would have to made for the OPA4132's to be purchased in Surface Mount SOT form factor, soldered to SOT-DIP converters, and then the assemblies would replace each TL074

The customer agreed that he was willing to fund this work, and so it was performed. What surprised both of us was how dramatic the change was. The noise floor fell to levels I never imagined, and the overall signal degradation through all the loops was so small I would have never believed it.

Since then, based on word of mouth, I have done this upgrade more times than I have expected, and have kept the specifics quite secret. The typical customer would be one who had an RSB-18, did not want to change systems, had the money, and wanted to make it sound as good as possible. However I recently have stopped doing these upgrades as I feel it is better to 'move on' and convince customers that converting to a relay based system will always be a better solution, and in most cases, cheaper.