Friday, August 17, 2018

J.Martens Marantz ESOTEC SC-6 Pre-Amplifier Restoration


Marantz ESOTEC Series SC-6 Pre-Amplifier



Released during the early 80s the SC-6 was part of Marantz’s high end ESOTEC series production in response to the newer flashy components being released at the time. The RIAA stage is incredibly accurate along with the line-stage frequency response due to their complex FET front end and cascade design.


P800 Power Supply
The SC-6 power plant consists of a single 1amp full wave bridge rectifier 44V supply knocked down and regulated to a 32-/+ dual rail supply for the AF front end and phono stages.

The initial rectification stage was replaced with a state of the art MUR series TO-220 Ultra-Fast, Soft Recovery diodes in an array with Nichicon polypropylene film bypass capacitors replacing the ceramic. The TO-220 regulators were replaced with modern, robust MJ OnSemi series devices coupled with Wakefield synthetic thermal compound. Remaining devices were replaced with better dissipation TO92L Fairchild devices, new 6.1V zener avail diodes were also installed.


The capacitors were increased in the original coupling from 1000 to 2200MFD and the output coupling from 470MFD to 1000MFD for better filtering and remaining capacitors with a low impedance high temp (105C) Nichicon PW with an increase in operating voltage. The small value and bypass capacitors were replaced with a high grade WIMA film capacitors. 



BEFORE 

AFTER




-/+32Vdc Rail Confirmation

CL Line Amp
The input stage of the line amp is a push-pull design utilizing a pair of Jfet M47 series devices for a low impedance amplifier with a tethered NPN differential pair and buffer stage, the output employs wide bandwidth power transistors in a 2 stage darlington circuit for a Class A output. The design of the physical board is separate into a front end and rear output via the chassis layout. The front-end is rather difficult to work with.

The initial differential NPN stage was beta mapped and matched, replacing the original single form factor device, associated devices in the front end were replaced with low noise, small signal Fairchild devices. Regulators were replaced with modern, robust MJ Series OnSemi TO-220 devices thermally coupled with Wakefield synthetic thermal compound. Electrolytic capacitors here were replaced with audio grade KT/KA and low impedance PW Nichicon with an increase in operating voltage.



Line Amp Differential Beta Mapping
in the output stage electrolytic capacitors were replaced with audio grade MUSE Bipolar and low impedance PW Nichicon with an increase in operating voltage. Bypass and small value capacitors were replaced with high grade WIMA polypropylene film capacitors. The idle current adjustments were located to the foil-side of the PCB for easier access with the new sealed precision Bourns potentiometers installed. 




BEFORE 


AFTER






Line Amp Idle Current Confirmation

PE00 Tone Amp (L/R Assemblies)
The tone amplifier is a push-pull gain stage driving the attenuation of separate left/right Treble/Bass parameters with stepped attenuators for precision control.  Each channel is subdivided per PCB assembly. 

All of the small signal devices here were replaced with low noise modern TO-92/TO-126 devices for better dissipation using Fairchild devices. The small value capacitors and coupling were replaced with high grade WIMA film capacitors. Audio grade KT/KA and MUSE Bipolar capacitors, as well as low impedance PW’s Nichicon capacitors installed with an increase in operating voltage. 



BEFORE 

AFTER



P400 MM Amp/ RIAA EQ
The 2.5mV input MM and RIAA circuit is a complex and VERY accurate design. The front end like the line amp employs a Jfet front end and current mirror and buffer push-pull design, the SEPP output comprises the output segment. 

The SEPP output power transistors here were replaced by robust, modern MJ Series OnSemi device. The capacitors were replaced with a audio grade MUSE Bipolar and low impedance PW Nichicon with an increase in operating voltage. 1MFD coupling and bypass films were replaced with high end WIMA polypropylene film capacitors.


BEFORE 

AFTER




RIAA Curve Response

CM MC Amp
The low input MC Cart Amplifier stage is a complex parallel input for a push-pull differential with a SEPP output gain stage. 

The secondary gain and output gain stage devices were all replaced with a low noise modern, TO92/TO-126 devices for better dissipation with Fairchild devices. All of the electrolytic capacitors were replaced with a audio grade KT/KA and MUSE/VP Bipolar capacitors, as well as low impedance PW’s Nichicon capacitors were installed with an increase in operating voltage. 



BEFORE 

AFTER




AUDIO NOTIZEN