New Release Sansui BA312 IC to Op-Amp W/ Adaptive Circuit Modification
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Sansui QRX-9001 Quad
I am are very excited and proud to announce the release of my first modular product upgrades, and a first for the vintage audio community! The BA312-OPASIP7; an adaptive module for high performance, single ended operational amplifiers into existing BA312 designed pre-amplifier and phono stages!
Over about 8 months this last year I have been working on perfecting a concept I saw early on with talks on upgrading these original pre-amplifiers integrated circuits with modern operational amplifiers. After working with several companies I found Colorado based Sparkos Labs who specialize in designing and producing high-end discrete operational amplifier and voltage regulators. Through this partnership I was able to have my design cleaned and perfected and a production process for boards. The universal configuration was designed with their proprietary SS33601 high performance operational amplifier in mind in conjunction with my circuit adaptive module.
A brief introduction on Pre-Amplifier IC’s and Operational Amplifiers
Our focus will be on the original BA312integrated-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.
Frequency Response Plotting
**note a significant improvement in overal 20Hz-20Khz sweep response from -.5/+ to -.3/0+ 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 as well as an increase in gain output by +2.38Vpp**
As we can see from the reports the original frequency response of the Sansui 9090DB whihc is rated to a -1dB deviation reaches to about -.89 @ 20Hz original stock form and about -.6dB at the 20Khz peak stock which is fairly poor. With the BA312 we are able to tighten the frequency response to a crips -.1 @ 20Hz and -.3 @ 20Khz sweep which creates a far more accurate pre-amp stage The BA312 in most respective circuit has a limited 5V Peak to peak output which lends to a somewhat flat presentation without sufficient clean gain, 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 F-2544 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 and distinct Sansui sound. In addition we see a major improvement in RIAA Curve response versus Standardize RIAA output with a tighter subsonic 31.5Hz and 15Khz response with additional gain output for the AF front!
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.
Remaining PCB assemblies that house the module are rebuilt using low noise, modern TO-92 NPN/PNP discrete Fairchild transistors, Audio Grade Nichicon KT and low impedance PW Nichicon capacitors. The DC Filtering capacitors are increased (470MFD for PE01’s from 220MFD) and all input/output/bypass and ceramic pathway capacitors are replaced using high grade WIMA polypropylene film capacitors.
High-End Vintage Audio Restorations & Analysis (N. Schumacher)
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