AUDIO SERVICES

Friday, November 30, 2018

D. Bennett's Pioneer SX-9000 Stereo Receiver Restoration

Pioneer SX-9000 Stereo Receiver



The SX-9000 was a very early released solid-state SX series from 1970-1972 and touted an impressive amount of features for a receiver of its time such as microphone dubbing (X2!), two phono stage inputs, a present tone feature for the audio front-end. The unique faceplate has a drop-drawer for the additional attenuators and control plane. 



W16-028 Power Supply
The regulated power supply on the SX9K employs two full-wave rectifier stages comprised of common mode diode devices as well as a 80V full wave bridge rectified output with the initial bridge cap coupled with a 2200MFD capacitor for the B-/+ rails. The handful of 2200MFD dc coupling capacitors are actually chassis mounted in this outlay. 

The initial full wave rectifiers were both replaced with a modern HexFred Ultra-Fast soft Recovery common cathode TO-220 devices with new high grade polypropylene bypass film capacitors. The failure prone TO-92 device was replaced with a more robust TO92L modern Fairchild device. All of the PCB mounted electrolytic were replaced with a low impedance, high temp (105C) Nichicon PW type with an increase in operating voltage with several coupling stage values increased for better noise suppression. Chassis mounted 2200MFD 50V< capacitors were all replaced with Nichicon PW type as well with an increase in operating voltages. 


BEFORE


AFTER


Regulated Vdc Confirmation

 Bridge Rectifier & Filter Capacitor
The large single B-/+ 2200MFD filter capacitor was replaced with a computer grade CDE type 2200MFD/100V capacitor.  All of the original 3A diodes were replaced with modern axial Vishay 3A 1KV rectifier diodes along with new high grade polypropylene bypass film capacitors. The two parallel 100MFD/100V axial capacitors were replaced with a single 220MFD/100V radial type Nichicon PW capacitor.


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W28-002 Reverb 
An oft-gimmick at the time for audio was the echo effect brought fourth with “Reverb” units and designs. The SX9K also uses a front display reverb indicator that would display potential crosstalk as the reverb is increased. 

The failure prone 800 series NPN devices were all replaced with a modern, low noise TO92 Fairchild devices in both input/output stages. All of the electrolytic capacitors were replaced with a audio grade KT/KA Nichicon with an increase in operating voltage. All remaining films were upgraded to a high quality MKP WIMA polypropylene type film capacitors. 


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W21-003 Mic Amp
The SX9K allows for multiple microphone inputs as well as separate input gain attenuation. With one microphone input uses the concept runs its signal monaurally through both left/right outputs.

The simplified gain stage devices were all replaced with a modern, low noise TO92 Fairchild devices. The DC coupling capacitors were replaced with a low impedance Nichicon PW type as well as audio grade KT/KA Nichicons all with an increase in operating voltages. Upgraded high quality MKP WIMA polypropylene film capacitors were installed. 


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W21-002 RIAA Phono (HeadAmp)
The W21-002 design I have spoken of on MANY SX series as this circuit concept was used in many of the SX8XX series employing a simple NPN gain stage and RIAA EQ output. 

All of the small signal devices were replaced with modern, low noise TO92 Fairchild devices. The DC coupling capacitor was increased for better filtering and replaced with a low impedance PW, remaining electrolytic were replaced with KT/KA audio grade Nichicons with an increase in operating voltages. Bypass mylar were replaced with a high grade WIMA MKP polypropylene film capacitors. 


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W15-052 Driver Stage (PA)
Designed in the same fashion as the single symmetric PCB’s perpendicular output layouts of several other SX series. With a quasi-complimentary output and single cascade differential stage. With the parallel output design, a soft output defeat "over-protection" is employed. 

All of the electrolytic capacitors here were again replaced with low impedance Nichicon PW type with an increase in operating voltages, two mylar were replaced with a high grade WIMA MKP polypropylene film capacitors.  The input NPN was replaced with a low noise, modern TO92 Fairchild devices. The symmetric clipping adjustments were relocated to the foil side PCB with sealed precision Bourns potentiometers for better access during testing. 


BEFORE


AFTER

BIAS Confirmation

W28-001 Tone Colour
Unique to this design is the use of preset tone filters. The SX9K has a “Flat, Soft, Bass and Vivid” 4-preset curve selector for signal attenuation that sets a specific response. 

All of the electrolytic capacitors were replace with a low impedance PW and audio grade KT/KA Nichicon type with an increase in operating voltages. High grade WIMA MKP polypropylene film capacitors replaced the original mylar films. All of the small signal devices were replaced with modern, low noise TO92 Fairchild devices.


BEFORE


AFTER


W22-002 Pre-Amp (ControlAmp)
The large amount of electrolytic capacitors here were replaced with low impedance PW and KT/KA audio grade Nichicon capacitors with an increase in operating voltages. New high grade WIMA MKP polypropylene film capacitors in stalled as well. All small signal NPN devices were replaced with modern, low noise TO92 Fairchild type. 


BEFORE

AFTER


RF Assemblies
Each of the chassis mounted RF assemblies had all electrolytic capacitors replaced with low impedance Nichicon PW type and high grade MKP WIMA polypropylene precision film capacitors. 





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Thursday, November 22, 2018

B. Villadiego's Marantz Model 19 Restoration


Marantz Model 19 {Fifty-Fifty} Custom~Calibrated Stereophonic Receiver



The Marantz Model 19 receiver is a legendary receiver sought by any Marantz collector and fanatic! Touted as a TOTL 50Watt receiver during the early 1970’s thru 1974 the Model 19 featured the early gyro tuning and coupled oscilloscope output display in the front with he series signature plastic capped black push-buttons. The Model 19 uses an appropriate amount of shielding for its build quality and employs a massive amounts of film capacitors in the cap coupled stages providing that warm lush Marantz tone.



A1 Power Supply & Time Delay
The Model 19 employs a regulated supply thats split for both high voltage 500/200V scope display and a full wave bridge rectified -/+36Vdc, -/+12Vdc & -36Vdc full wave rectified single and dual ended sources. The original design uses an array of 80 ohm wire-wound cement resistors which exhibit a fair amount of dissipation wear on the cement substrate. Careful and thoughtful placement of the new radials allows a perfect with the original cover and no pintout modification!

All of the original multi-cap capacitors were replaced with a better suited single radial, low impedance, high temp (105C) Nichicon PW type electrolytic capacitors with an increase in operating voltage and capacitance in serval DC input coupled stages for better filtering. The 3-5Watt zener’s were all replaced including the original full wave and bridge rectifier diodes with a ultra-fast, soft recovery type Vishay diodes. The original cement-wire wound resistors were all replaced with Vishay precision, silicone coated resistors. 



BEFORE


AFTER



REGULATED VDC CONFIRMATION

A14 Time Delay
The populated axial capacitors, which I am not a fan of due to a typically reduced quality in construction were all replaced with a low impedance, high temp (105C) Nichicon PW type electrolytic capacitors with an increase in operating voltage.

BEFORE


AFTER

Filter Capacitors
The large chassis mounted, full wave bridge rectified filter capacitors were replaced with computer-grade CDE 10KMFD filter capacitors with a reduced profile due to the proximity to the perpendicular mounted driver board.




-/+B CONFIRMATION

A8 RIAA EQ (PHONO)
The phono assembly uses a simple PNP gain stage with NFB and can coupled input/output in a very similar fashion to the P400/700 design with clipping adjustment. A -36Vdc source drives the phono stage. This PCB also mounts the separate volume and balance potentiometers. 

All of the small signal devices were replaced with a high gain ZTX DI Eline type devices. Clipping adjustments were replaced with precision, sealed Bourns potentiometers. The input/output compliment was updated with high grade precision CDE, MKP WIMA polypropylene film capacitors.


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RIAA CURVE RESPONSE MODEL NO.19

A10 Tone Front End & A11 Filter
The front end tone stage uses a large amount of yellow film capacitors, which tend to have a noted failure rate, these are used quite a bit thru out the Model 19. The audio stage is a more complex NPN/PNP gain stage/NFB design with a +12/-36V input  and cap coupled input/output.

All of the small signal devices were replaced with a high gain ZTX DI Eline type devices. All of the electrolytic capacitors were replaced with low impedance Nichicon PW type with an increase in operating voltage. All of the films were upgraded to a high quality WIMA MKP type polypropylene film capacitor. The chassis mounted C3 can cap was replaced with single radial low impedance Nichicon PW type with an increase in operating voltage and capacitance for better filtering. Input films on the filter assembly were updated with a high grade ECW polypropylene film capacitors.


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A12A/B Drivers A13A/B PA
The amplifiers are divided into a driver stage front end and a separate power/current gain stage output with a complimentary output pair. The feedback is routed via a integrated relay protection that can tend be problematic due to the poor relay construction and NFB design. One may consider bypassing the integrated relay. 

The input differential pairs which can often cause DV offset stability issues were replaced with matched high gain ZTX DI Eline type devices and original mounts removed for direct solder placement, these significant reduce DC drift in the design. The clipping and bias adjustments were all replaced with precision, sealed Bourns potentiometers. The original wire-wounds on the PA and driver stage were all replaced with new Wire-wounds and MOX type resistors. 


All of the electrolytic capacitors were replaced with a low impedance type Nichicon PW and the original axial replaced with a better quality radial MUSE BP Nichicon capacitor. All of the films were upgraded to a high quality MKP WIMA polypropylene films. 


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AFTER



DIFFERENTIAL MAPPING

BIAS CONFIRMATION

MPX Matrix & MPX Oscillator / RF &Scope
The MPX stages are uniquely mounted perpendicular to the chassis very simple brackets mounts on the rear of the unit top side with isolating material covering the foil side from the chassis cage. The RF Pcbs are shielded properly, especially around the scope display.

All of the films were updated on both assembly with high grade MKP WIMA polypropylene film capacitors, the 1MFD coupled axial on the scope assembly were both replaced with a robust high quality ECW polypropylene films. The original axial was also replaced with a TVX Nichicon 680MFD capacitors in the same form factor. 


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LAMPS
New SMD LED’ 8V warm white spectrum were installed replacing the original BAS9 type incandescents. 



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