Today were showcasing another Marantz 1180DC Integrated Amplifier that came in for a restoration. The 1180DC, manufacturers from 1978 to 1980 was a good quality Marantz DC coupled/AC 90Watt output integrated unit with some favorable features such as defeating options, dubbing and precise logarithmic tone controls.
The 1180DC regulated power supply has a dual bridge rectification with a 1A in the P800 and separate filter array with a dual rail 45V supply and two 18,000MFD reservoir capacitors. The P800 located is shared with the PE01 tone stage and P400 RIAA circuit on a single assembly mounted inverted in the chassis and with Pin-Connectors.
All of the electrolytic capacitors were replaced with a low impedance, high temp (105C) Nichicon PW with an increase in operating voltages. The original 1A filtering capacitors were increased to 1000MFD for better noise/filtering properties. The original cathode/anode rectifiers were replaced with coupled Ultra-Fast, Soft Recovery axial Vishay diodes. The original NPN/PNP TO-220 rectifiers were replaced with modern, robust TO-220 OnSemi devices thermally coupled with performance synthetic Wakefield compound, remaining devices to Fairchild TO-92L for better dissipation. The 7.5Vzener and remaining diodes were replaced with axial Vishay type.
New computer-grade CDE Filter capacitors were installed for the -/+50V source rails.
The 1180DC has some notorious protection assembly heat issues stemming from the large dropping resistors and current limiters dissipating. Many of the resistors and solder pads had to be replaced/repaired in this stage.
New KOA/Vishay carbon film 1/2W resistors were installed replacing heat exasperated components. A new modern Omron MY4 relay installed as well as a new common cathode high performance Ultra-Fast, Soft Recovery TO-220 MUR type rectifier. New general 4148 and 7.5V zener axial Vishay diodes installed. All of the electrolytic were replaced with a low impedance, high temp (105C) Nichicon PW with an increase in operating voltages.
The 1180DC drivers are laid out on a single symmetric PCB with molex connectors which is convenient. The P700 does have a hosts of VD varistor issues on the foil side of this assembly that need to be addressed. As mentioned in prior posts the 1180DC uses a unique to Marantz 2SK109 dual Jfet for the initial differential stage so the bias is pre-determined by a constant current source.
All of the films were upgraded to a high-grade WIMA and MKP polypropylene film compliment including input coupling and IC bypass films. The electrolytic were upgrade to a low impedance PW and audio grade KA/KT Nichicon type with an increase in operating voltages. The offset adjustments were replaced with precision Bourns potentiometers.
IC current devices were matched as well as pre-driver current devices with modern, low noise TO-92 Fairchild devices and thermally coupled together with performance synthetic Wakefield compound. Pre-Driver, Drivers and QT devices were all replaced with TO-220 and TO-126 low noise, robust Fairchild/OnSemi devices.
PH00 Filter and PE01 Tone
The Tone stage in the 1180DC features a three-way logarithmic tone control and simple differential gain stages. All of the electrolytic capacitors here were replaced with a KA/KT Audio grade Nichicon and low impedance PW Nichicon capacitors with an increase in operating voltages, the decoupling capacitors here were increased from 100MFD to 220MFD for better noise filtering of the rail source. The input .47MFd films were upgrade to a high-grade MKP polypropylene film capacitor. The small signal devices were replaced with low noise, modern TO-92 Fairchild devices.
**Heavy attention must be paid to the AC/DC coupling switch on the rear of the panel as these open-frame slide switches can easily build up carbon and foreign matter. New Bipolar audio grade Nichicon Muse 10MFD capacitors were installed.
PH00 Filter stage film capacitors were all replaced all replaced with a high-grade MKP polypropylene film capacitors and electrolytic to a audio grade KA/KT Nichicon with an increase in operating voltages. The small signal devices were replaced with low noise, modern TO-92 Fairchild devices.
P400 RIAA (Phono)
Like the Tone stage, the P400 employees a simple staggered differential gain stage. As above, all of the electrolytic capacitors were replaced with a KA/KT Audio grade Nichicon and low impedance PW Nichicon capacitors with an increase in operating voltages, the decoupling capacitors were increased from 47MFD to 100MFD for better noise filtering of the rail source. New high grade WIMA polypropylene films were also installed at 680Pf. The small signal devices were replaced with low noise, modern TO-92 Fairchild devices.