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.


BEFORE

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

AFTER



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

PH01
Proceeding the the function switch the AF path is converted here to low output impedance sources
 (PH01—>Dolby—>PE01)

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. 


BEFORE

AFTER



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. 


BEFORE


AFTER

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.


BEFORE

AFTER





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

Audio Notizen










Monday, August 14, 2017

Paul's Sansui G-7700 Receiver

Sansui G-7700 Receiver



Today were showcasing a customers Sansui G-7700 Receiver. The G-Series had several variants released during the period with the G-X700 being the mid-way point. Touting a pure DC amplifier section, Peak LED and digital tuning display with their quartz-locking feature.



F-2980 Power Supply/Protection
The Sansui G-7700 and other G-series feature this similar layout, with a MAIN-PCB in the centre of the unit populated as the power supply and driver section F-2980.  Many of these G-series present the same faults here from an over heating power supply and caustic glue. The glue used to mount the large vertical capacitors in the power supply becomes oxidized over time and causes the exposed leads of components such as resistors to oxidize and break as well as excessive radiant heat from the nearby regulator devices (x3.)

One of the first issues to address as mentioned above was removing all the glue and replacing about half dozen or so resistors with new 1/2 carbon film KOA resistors and several diodes with axial modern Vishay/Fairchild diodes.   All three regulators were replaced with a robust ST, TO-220 modern regulators manufactured using their new construction standards along with new performance Wakefield thermal compound.


All of the electrolytic capacitors were replaced with a high temp (105C), low impedance Nichicon PW and VP Bipolar capacitors with an increase in operating voltage. New axial Vishay Ultra-Fast, Soft recovery diodes were installed as well.


BEFORE

AFTER


The protection network integrated into the F-2980 is similar to the recent SX-780 I did with a HA12002 monolithic IC used to monitor dc deviation, current consumption in conjunction with varistors for thermal run-away.  This also controls the front “Safe” operation mode indicator. A NOS relay was installed from a reputable retailed in the UK and new filter capacitors. 


F-2980 Driver Stage
Shared on the same MAIN-PCB as the PS the G-7700 has an interesting design. Using an initial Dual FET 2SK150 devices the differential stage, current mirror/differential, and a two-stage OCL Darlington design.

All of the electrolytic here were replaced with high temp (105C), low impedance Nichicon PW capacitors with an increase in operating voltages. 1MFD< capacitors and mylar were replaced with high grade WIMA polypropylene ilm capacitors. New precision Bourns potentiometers installed, new modern, low noise TO-92 Fairchild (see underside adaption for smoother action while biasing protocol) for a matched constant current stage (see BETA mapping below), new modern low noise, low distortion audio applicable On-Semi TO-126 type NPN/PNP pre-drivers/current devices were installed.  Original drivers were removed and tested with new performance Wakefield thermal compound applied. (high volt. broad spectrum drivers should be cross references VERY carefully if replaced to prevent oscillation issues..note the often reference MJE15032/33 are NOT good references @ 30Mz)


BEFORE

AFTER


BIAS Confirmation
(SM error, Correction at .66x5mA @ 3.3mV)

NPN BETA Matching
F-2855 Tone 
The tone control features a defeat option with dual Bass and Treble attenuations, a 41-stepped precision volume attenuator is used for gain control which is always nice to see, though not potted..
The tone is designed around an initial NPN differential gain stage.

All of the electrolytic capacitors here were replaced with audio KT and MUSE (Bipolar’s) along with VP Nichicons with an increase in operating voltages. All the small signal devices were replaced with modern TO-92 low noise Fairchild devices. 


BEFORE

AFTER

F-2857 MIC AMP
The G-7700 features a separate driver for microphone line level and dual dubbing options.

The small signal devices here were replaced with modern TO-92 low noise Fairchild devices. Electrolytic’s were replaced with audio grade KT and low impedance PW Nichicons with an increase in operating voltages, a new high grade WIMA polypropylene .47MFD film was installed as well.


BEFORE

AFTER

F-2865 EQ RIAA
The RIAA is placed under the main chassis carriage using a metal standoff as shielding. Built using an array of precision resistors for low noise (SN @ 78dB) comprised again of a PNP gain stage…..also the G-7700 has two phono inputs!

All of the small signal devices were replaced with low noise, modern TO-92 Fairchild devices. Electrolytic’s were replaced with low impedance and audio grade Nichicon KT capacitors and 470MFD VP Nichicon Bipolar with an increase in operating voltages.


BEFORE

AFTER

G-7700 TESTED RIAA CURVE RESPONSE
(EXTREMELY GOOD RESPONSE AFTER THE REBUILD!)
F-3060 Digital Display Power Supply
The digital display requires its own power supply source, with a 5/13V output for the display.  Their are several variations of the supply, all suffering the same issues from the large wire-wound resistors radiating enough heat to scour the PCB. Each resistor should be increase in watt rating as well as foil foot prints exposed and expanded for a good anchor over time.

New robust ST, TO-220 modern regulators manufactured using their new construction standards along with new performance Wakefield thermal compound were installed. All electrolytic capacitors were replaced as well with high temp (105C), low impedance PW Nichicon capacitors with an increase in operating voltages as well as emitter values and several carbon film 3.9K 1/2W resistors.


BEFORE

AFTER

F-3000 Digital Display
Using a FL type Tube display, it broadcast the FM/AM RF tuning indication and locking  features, it utilizes the MSM5540 monolithic IC with a advanced circuit NJM4558 OPs and BA658 monolithic devices.

All of the electrolytic capacitors here were replaced with a high temp (105C), low impedance PW and VP Bipolar Nichicon capacitors with an increase in operating voltages. The FL assembly was carefully dissembled and cleaned. 


BEFORE

AFTER


F-2988 RF Stages
The G-7700 features a very fine tuned RF stage, with a emphasis around their “Digital Quartz Locked Tuning System”.  The FM uses a 4-gang tuning capacitor with a dual MOS-FET front end. The AM features a “Frequency linear, double-ganged tuning capacitor, along with a high performance monolithic IC in the IF circuit”.

In both stage all of the electrolytic capacitors here were replaced with a high temp (105C), low impedance PW Nichicon capacitors with an increase in operating voltages.




New Custom 8V SMD Warm White LED’s installed for the highlight



AUDIO NOTIZEN