BA312 Adaptive Module + SS3601 OP-Amp


A brief introduction on Pre-Amplifier IC’s and Operational Amplifiers

Our focus will be on the original BA312  integrated-circuits (IC) but first lets take a step back to the first Operational Amplifiers (OP-Amp). The earliest true version of the OP-Amp was a vacuum tube used during the 1940’s in RF equipment developed by Bell Labs as general purpose feed-back amplifier. With the advent of the transistor, IC and Jean Hoerni’s Planar Process of manufacturing came the release of what we know as monolithic IC OP-Amps. The early innovations came from supplies like GAP/R and Arizona based Burr-Brown which was finally absorbed by Texas Instrument in the year 2000 to combine their product series.

 The BA312 we are focusing on is a SIP7 pin, high voltage (20-40Vdc) linear, monolithic device manufactured then by ROHM Semiconductor and Toshiba of Japan. Featuring at the time low distortion and high gain-loop qualities with relatively low noise, these early pre-amplifier IC’s. These were implemented as differential gain stages in many pre-amplifier and RIAA EQ (phono) circuit in audio equipment from the greater 1970’s and heavily in several specific Marantz, Sansui and Pioneer receivers, amplifiers, pre-amplifiers and integrated amplifiers.

Benefits of the Adaptive Circuit Modification & Sparkos Labs SS3601 OP-Amp

The original BA312  have long been out of production...for decades. This means the only reliable replacement for your classic vintage units is to find a donor unit and salvage parts!With the release of the BA312-OPASIP7, we now have a extremely high quality, high performance  replacement option for failed BA312  components or owners looking for a significant sound improvement. 

Marantz PE01 Performance Analysis
Frequency Response Plotting
**note a significant improvement in overal 20Hz-20Khz sweep response from -.29/+ to -.08/0+ with  smooth Pvv transitions**
 Frequency Response Comparative 
Intermodulation Distortion & S/N Ratio's
**note a good decrease in overall IMD  w/ (4:1 7khz/60hz) and overall noise reduction**
Vpp Output Plotting
**note a significant decrease in overall Total Harmonic Distortion + Noise**
Musical Notes
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.