AUDIO SERVICES

Monday, August 20, 2018

G. Widners Marantz 2270 Stereophonic Receiver Restoration


Marantz 2270 Stereophonic Receiver W/ Jupiter Condensers


The 2270 as I’ve highlighted in the past remains one of the most sought-after vintage receivers to date, fetching astronomical prices for a 70W receiver. The 2270 shares consistent design attributes as with similar 22XX series 2230/45 receivers with differences occurring in the PP amplifier design. 


In this particular restoration we employed Jupiter Condenser’s extremely high quality (and priced) esoteric grade Red Astron and Vintage Tone series film capacitors.


P800 Power Supply
The 2270 power plant revolves around a 4A Full Wave Bridge Rectifier and two 9KMFD filter capacitors for the -/+48Vdc reserve. The P800 assembly employs a 1A full wave rectification array with a regulator derived 35V and 13 supplies for the RF and AF Front end stages. The P800 also contains the output protection network for DC deviation and excess current consumption actions. 

The small signal devices here were all replaced with modern TO92L devices for better dissipation with low noise Fairchild type. The original rectifier diode array was replaced with a Ultra-Fast, Soft Recovery axial Vishay diodes. The bypass ceramics were also replaced with polypropylene high grade film Nichicon’s. The voltage adjustment was replaced to a sealed, precision Bourns potentiometer. The relay was replaced with a MY series Omron relay. Lastly the TO-66 regulator transistor was replaced with a modern, robust TO-220 equivalent.


The capacitors were replaced with a high temp (105C) low impedance Nichicon with an increase in operating voltage. The initial DC decoupling capacitor was increased to 1000MFD for better DC filtering.



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Regulated Confirmation35/13Vdc 

Filter Capacitors
The original schematic indicates two 6800MFD filters, with most manufactured models touting 9000 filters. These were both replaced with a Computer Grade Panasonic and increased to 12000MFD for a total of 24,000MFD for better filtering and sub sonic reserve at higher output.


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Rail Confirmation -/+48Vdc

P400 Pre-Amplifier
The 2270 uses in my opinion one of the most popular Marantz designs outside of the PE01 (BA312) based design. The 2270/30/45 have a cap coupled input out, with a NPN differential voltage gain stage and push-pull output design. In this particular rebuild we focused on special esoteric film capacitors by Jupiter Condenser and their Red Astron style films.

All of the small signal devices here were replaced with a low noise, modern TO92 Fairchild devices, replacing the noise prone devices. All of the electrolytic capacitors to 3.3MFD were replaced with a audio grade KT/KA and the DC filter capacitor increased from 100MFD to 330MFD for better filtering with a low impedance PW type. The 1MFD capacitors were replaced with a high grade WIMA polypropylene type and the input .22MFD mylar replaced with a esoteric grade Jupiter Red Astron AM film capacitors.   


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P700 RIAA/EQ (PHONO)
Like the above pre-amp stage, the phono stage concept was used in a half dozen 22XX series designs and a version of in the 1060 integrated. A very reliable and stable design with a warm cap coupled input out, push pull design and NPN voltage gain stage. 

All of the small signal devices here were replaced with a low noise, modern TO92 Fairchild devices, replacing the noise prone devices including the notorious 458 type NPN devices. The VD varistor and other diodes were replaced with modern axial 4148 general type. The clipping adjustments were replaced with sealed, precision Bourns potentiometers.  The DC filter capacitor was increased to 330MFD for better filtering with a low impedance PW capacitor, along with the remaining capacitors to a audio grade KT/KA Nichicon all with an increase in operating voltage. The input/output films were selected to use WIMA polypropylene in this restore for a specific, defined tone for the Astron capacitors in the pre-amp stage.

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RIAA Curve Response

P750 Amplifier Channels
The 2270 has a significant issue in the amplifier stages over the dozens of 2270’s I’ve done over the years, I consistently note skewed bias from factory and issues with proportional tracking. One of the solutions I employ for the 2270 is re-routing the thermal servo bias H760 to thermally track the 4th order driver dissipation versus the output stage heatsink dissipation with causes discrepancies in idle current consistency, along with choosing a device of higher beta range and wide Ft bandwidth.  

New differential pairs were replaced with modern low noise Fairchild devices, Beta matched and thermally coupled with Wakefield synthetic thermal compound. Remaining devices were replaced with low noise, modern Fairchild devices and Vishay axial diodes. As noted above the bias modification was employed with a MJE series NPN TO-126 device. The bias and idle adjustments were replaced with seal, precision Bourns potentiometers. 

Bias Modification


Differential Beta Mapping

All of the capacitors here including the tantalum were replaced with a audio grade KT/KA Nichicon with an increase in operating voltage. In conjunction with the pre-amp selection, films in the driver were complimented with esoteric grade Jupiter Condenser Vintage Tone film capacitors and high grade WIMA polypropylene compliments. 



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Bias Confirmation


LEDS
New 8V LED SMD lamps were used for the display and meters with new heavy weighted Vellum paper installed.



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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 

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-/+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. 




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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 

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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.


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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 

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