As we can see from the reports a significant improvement in the sub sonic response 20Hz to 750Hz was noted (see frequency response reports) with a linear response 50Hz to 5Khz with the upgrade which is a HUGE improvement over the original BA312 IC. The BA312 does tend to lead to a somewhat lacking bass which is one of the reasons it was a prime candidate for the concept, the lower end definition is overall improve with transient peaks becoming more dynamic than fuzzy. The mid-range and high end response had a distinct clarity to upper crossover points while auditioning everything from Blues, Folk, Rock, Jazz even some Electronica so far I suspect from a cleaner,linear gain stage employed. Overall the upgrade brings the PE01 to the next level of performance with a distinct improvement in overall dynamic presentation and frequency response across the audible spectrum while retaining yet that smooth Marantz sound.
The choice of using Sparkos Labs SS3601 as an OP-Amp with my adaptive module was a no brainer..the acclaimed single-ended discrete, proprietary designed SS3601/3602 is fully discrete 8DIP family of OP-Amps. Touting features such as; high open loop gain 140dB, (2.9nV√HZ) Noise to 20KHZ, fully Class A biased with matched encapsulated transistors for the input stage and internal current mirrors. Comparatively outranking even the popular high-end OPA627 ( Gain @ 116dB & (4.5nV√HZ) Noise to 20KHZ) Texas Instrument OP-Amp. Wide bandwidth operation (5Mhz) 75° of phase margin, and 10dB of gain margin.
Comparatively many enthusiasts have found an affinity over the sound presentation of discrete components versus monolithic IC’s such as run of mill TI/AD chips used in the bulk of consumer and high-end audio components today.
SS3601 Circuit Description Excerpt from Sparko's Labs:
"...The SS3601 / SS3602 discrete op amp is based on Lin 3 Stage topology consisting of an input stage differential pair, a gain (VAS) stage, and an output stage all biased in class A mode with two pole compensation. All active devices are Bipolar Junction Transistors (BJTs) for the greatest linearity and agility that any silicon device has to offer. The device is fully protected from over current conditions by active current limit circuitry in the output and gain stages, as well as being protected from large differential input voltages by back to back high speed schottky diodes across the inputs. Figure x reveals a simplified schematic, and in reality, the device consists of 17 BJTs, 20 resistors, 3 Capacitors, and a smattering of diodes and precision shunt references...."
Construction of the BA312-OPASIP7 Adaptive Module
The BA312-OPASIP7 is fully discrete adaptive circuit module fitted with a high-end DIP8 discrete OPA device. Each module is hand built at my shop here and tested for use in each application and unit. Starting with high quality 65mil thick FR4 (glass-reinforced epoxy ) dual copper layer PCB for a solid, clean and reliable substrate.
Discrete components include; Panasonic ERA series thin-film chip resistors which feature a very high reliability, high accuracy-low TCR with .1-.25% tolerances, and leading edge Samsung Electro-Mechanics multiplayer NPO ceramic smd capacitors with a very low ESR. Hardware includes all gold plated SIP-7 headers and gold plated 8DIP socket adapters.