Thursday, August 24, 2017

Greg's Two Marantz 2325 Receivers W/ BA312 MOD

Marantz 2325

Today were showcasing two Marantz 2325 Receivers  customers brought in for restoration with out exclusive BA312 to OP-Amp modification recently released to the public! The 2325 is a 125 Watt rated receiver, I like to single out the excellent construction on the 2325 compared to a lot of other similarly rated receivers. The 2325 features a healthy amount of RF shielding over each stage, the ever popular P400 phono RIAA EQ stage and now a high performance discrete OP-Amp tone stage.
P800 Power Supply
The 2325 power supply also houses the protection circuit which protects agains over current, dc deviation detection and initially inrush at power up.  The P800 is a regulated single end design using two full-wave centre taped rectifiers with a final regulated 35V and 14/19V+ SE rails.

The two initial rectifiers were replaced with state-of-the-art Ultra-Fast, Low Leakage TO-220 common cathode, MUR On-Semi devices with high grade Pansonic ECW polypropylene films capacitors. The initial 220 and 470 smoothing capacitors were increase to 330/1000MFD Nichicon PW low impedance capacitors for decreased ripple potential, along with remaining circuit capacitors to Nichiocn PW’s with an increase in operating voltages.  A new precision Bourns adjustment potentiometer installed. All new small signal TO-92L Fairchild devices for better dissipation installed as well as both TO-220 heatsink mounted regulators to a more robust, reliable TIP device with new performance Wakefield thermal compound applied. A new  low noise/indicator type Omron MY2 relays were installed.


(someone had soldered in two fuses instead of a relay on this beauty...)


Both bridge rectifier filter capacitors were increased from 15,000 to 18,000 computer grade Nippon filter capacitors were installed.

PE01 Tone W/ OP-Amp Adaptive Circuit Upgrade

Proceeding the the function switch the AF path is converted here to low output impedance sources

The PE01 assembly is mirrored in many Marantz models, all of which utilize the monolithic BA312 SIP7 pre-amplifier IC. The BA312 is a obsolete, out-of-production chip used for differential gain stages. We are proud to recently release the first solid, clean Op-Amp adaptive circuit module to replace the original BA312 ICs to a high performance, audiophile grade single end OP-Amp which has been installed on these two 2325’s. We are currently employing the Sparkos Labs SS3601 SE discrete OP-Amp, you can read additional details and performance reports at the link below to our upgrade;

Custom circuit installation is required for our adaptive circuit module which was designed as a SIP7 design (all hardware including pin seats/headers and DIP plated gold) that fits perfectly into the device foot print without the need for changes any traces or cutting any traces! Through changes required in the PE01 circuit some components are omitted.  The input coupling films were replaced with high-grade WIMA  polypropylene films as well as the 680PF and .1 to high grade WIMA PP films. The FB network and 1st stage coupling as well as the 2nd stage coupling/NFB capacitors all replaced with a audio grade KT and MUSE BiPolar Nichicon capacitors. The DC filtering Ce39 was increased to a 470MFD low impedance PW Nichicon for better results. Remaining small signal devices were replaced with low noise, modern TO-92 Fairchild devices. 



P400 RIAA EQ & PH01 Buffer
Through testing we see these P400 have an excellent curve response, as well as a massive following for their wonderful sound, why many initially purchase their first Marantz!  One flaw to the P400 stages is the implementation of the 2SC458 TO-92 NPN transistor which have a tendency to become noisy, their are often changes to initial coupling stage MFD value from 1-3.3MFD. These tantalums should be a polypropylene 1MFD installed. 

For these two models both input/output coupling capacitors were replaced with high grade MKP polypropylene film capacitors. The DC Filter axial capacitors was replaced with a preferred radial type audio grade KT Nichicon and increase to 220MFD for better filtering capacity, KT’s replaced the remaining electrolytic as well with an increase in operating voltages. The VD type epoxy diode was replaced with a series of general Vishay axial diodes and remaining diodes to axial Vishay type. The clipping adjustments were measured and replaced with fixed resistors rather than potentiometers for a more symmetric response. All the NPN devices including the 458 were replaced with low noise, modern TO-92 Fairchild devices. The resulting output is a 40dB gain stage. 



RIAA Curve Response

P700 Drivers
The 2325 uses a differential gain stage and current stage which drives the eventual pre-drivers, the drivers are tied to the dynamic bias circuit. 

The differential PNP pairs were matched and thermally coupled together (beta mapping see below Mirrored for X4 Channels.) The 714/715H bias transistors were updated to modern On-Semi TO-126 devices and current stage to modern TO-92L Fairchild devices for better dissipation. These large frame potentiometers tend to hold very well, I recommend a proper cleaning/lubricating as their as good as the Bourns available today. 

The electrolytic capacitors and tantalum 33MFD were all replaced with a audio grade KT Nichicon with an increase in operating voltages as well as all films including 1MFD input coupling to high grade MKP polypropylene and WIMA film capacitors. The SB was applied with new axial Vishay diodes.



New custom SMD LED indicators and fuse the lamps installed with fresh new Vellum filter paper

Audio Notizen

Tuesday, August 15, 2017

New Release Marantz & Sansui BA312 IC to Op-Amp Modification

New Release Marantz & Sansui BA312 IC to Hi-Fi Op-Amp Module

Applicable Models
Marantz 2250,2250B,2265,2275,2285,2325, 2330 PE01 X2
Sansui 8080DB/9090DB F2653 RIAA X2 — F-2544 Tone Control X2
Sansui 8080/9090 F2541 RIAA X2 — F2543 Tone Control(MST VOL.) X1 — F-2544 Tone Control X2
Sansui 7070 F2622 Tone Control X2 — F2620 RIAA
Sansui QRX-9001 Quad Tone Control X2 

Today I am very excited and proud to announce the release of my first modular product upgrade, 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/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 BA312 and TA7136 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 upgrade & Sparkos Labs SS3601 Operation Amplifier
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. 

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. 

Performance Report VS Original BA312 application 
(Marantz 2325 PE01 Tone Stage)
To get the best possible picture of whats going on, all tests were performed with the PE01 stage isolated from a full unit, with a constant source 35.09Vdc/1.5A SE rail source

Frequency Response
(Frequency Response measure the output level of a device at different frequencies. Showing changes in amplitude over frequency)


FFT Spectrum Analysis

Total Harmonic Distortion + Noise 
(THD+N, think of THD+N as the output produced other than the signal injected.)
Intermodulation Distortion
(IMD, the measurement of amplitude modulation of the injected signal compress in two or more frequencies caused by non-linear responses in a system design (7Khz/60Hz 4:1))

Signal/Noise Ratio
(S/N Ratio or SNR is a measurement the describes how much noise is in the output of a device, in relation to the injected signal amplitude.)
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 (N. Schumacher)
Sparkos Labs SS3601 High Performance Op-Amp