BSM RPA California In 1974, right before the start of the "Burn" tour, Ritchie Blackmore changed his live setup. First and foremost, he wanted to play live with an echo effect and made the AIWA TP-1011 reel-to-reel tape recorder his first choice. This unit offered the typical 1/3 seconds echo repeat, perfectly matching Blackmores natural beat. Additionally, Ritchie Blackmore used the integrated microphone pre-amp as a booster, and with this his beloved Hornby-Skewes treblebooster he used for many years was not longer needed and was sent into retirement. The necessary trebleboost function (from a technical point of view a "highpass" function), was built into his heavily modified Marshall Major 200 amp. This first remarkable modification of the Major´s pre-amp stage was done in the Marshall factory, resulting in a raw and fat tone, you can hear on the "California Jam" recordings from April, 1974. Later on, a new mod was done, resulting in biting, piercing highs with a tight bass, the "Live in London" tone as well as for the rest of the Deep Purple Mk3 period. This two, totally different tones are integrated into the BSM "RPA California", and with the help of the "BITE" control pot, you can smoothly blend them, so the BSM "RPA California" is all you need to cover the complete sound-spectrum of Blackmore´s Deep Purple Mk3 time. The Major amp now received a cascaded pre-amp stage with a new, non-bridged cathode resistor at one of the triode stages to prevent to much overall gain. Further on, the 250Ohm screen-grid resistors of the four KT88 power tubes were changed to 1kOhm and the two 10uF electrolytic filter capacitors of the BIAS power supply were replaced by two 47uF (160volt minimum) caps. After 1975, Blackmores tech did several fine tunings over the years to Ritchies Major amp, because Ritchie experimented with several pickups in his guitars as well as with several new ideas of his trademark sound.
Not everybody owns such a heavily hot-rodded amp, and if so, for sure it will not have the correct highpass cutoff frequency ! So BSM had the idea, to not only rebuild the AIWA preamp stage, but to also integrate the important highpass function with the original cutoff frequency. The BSM RPA California emulates both typical soundshaping functions in only one stompbox - another BSM first ! The EQ control allows a tonal fine tuning for the use of the RPA California with different pickups, amps and speakers for an optimum in versatility. Depending on the pickups, the sweet spot of the EQ control is located between 12:00 and 03:00 o´ clock. As a soulmate for the RPA California, you can use any mild sounding amp with a good master control function. Plug it in front of the CLEAN or CRUNCH channel, but don´t use the high-gain or distortion channel ! Because of the EQ control, you can use all kinds of pickups, from the historical correct brilliant sounding low-gain Fender Custom Shop 69´ (aka "Abigail Ybarra" pickups) up to the thundering Seymour Duncan "Quarterpounds".
The RPA California Booster is inserted between guitar and amplifier, not into the FX loop. The magical tone is achieved by the interaction between guitar pickup, booster and amplifier. The unit is powered by a 9V battery with a current consumption of approx. 350 uA. The average output level is 9dBm, the maximum output voltage when the strings are struck really hard is 7V max. Because of the external DC jack, you can power the RPA Major with 9volts.
Note: The negative pole of the battery is ground !