RickJ_2270
New Member
I just purchased this fully serviced and somewhat 'modded' Marantz 240 from that auction site. Some of you perhaps saw the listing. I'm guess I'm taking a bit of a chance on 'untried/untested' mods, but what the heck, how bad can it be? Different is good. Here's a summary of the work done. It should be arriving in several days. What do you think? Personally, I'm looking forward to the adventure, lol, and hopefully some 'warm tube-like sonics'.. Wish me luck.
Up for your consideration, is a one-of-a-kind Marantz Model 240 Stereo Power Amplifier. Conservately rated at 120 watts RMS per channel at 8 ohms. The Model 240 has been known to deliver more than the rated output. Already a classic, rare, vintage, Marantz model, this unit has been throughly serviced. All questionable parts were replaced. This includes new high frequency Panasonic electrolytic capacitors, polystyrene film capacitors, polyester film capacitors, silver mica capacitors and any questionable resistors. All transistors are either the original devices or Marantz approved OEM type replacements. Moreover, the often troublesome output relay was replaced with a new OEM type whose contacts are free from any corrosion. The relay provides solid contact for maximum signal transfer from the outputs. The RCA input connectors were replaced with high quality jacks, thus eliminating the troublesome original types that were prone to corrosion and poor signal transfer.
If all these serviced items weren't enough to greatly improve this vintage amp, this Model 240 has been modifed with the addition of an ultra high quality power supply modification that decouples the output power supply from the input stages by providing a separate, regulated, high performance, 18 volt D.C supply to the input stages. Originally, one power supply provided power for the entire amplifier, thus limiting it performance and sound quaility. Now, with the additional power supply, the sound quality has been transformed from comparative "transistor" like chacteristics, to a much darker, warmer sound more closely resembling tube sonics.
This change in sound quality is a result of a rear mounted, high-current, dual secondary toroidal power transformer supplying (2) 24V lines to (4) low noise, ultra high speed diodes to form the dual bridge rectifiers. The 24 volt lines are reduced to 18 V.D.C. via (4) ultra high quality, Linear Technology low dropout voltage regulators. Each channel has separate regulation stages for both positive and negative voltage supplies. This configuration greatly reduces noise and improves sound quality by eliminating the usual power transformer center tap direct connection to ground. Now, due to the dual secondaries, dual bridge rectifiers per channel and dual regulators per channel arrangement, the bridge rectifiers commons are D.C. in nature not A.C. as was before. This is a much cleaner arrangement, opening up the potential of the Model 240 that wasn't possible with the previous configuration.
The original input power supply was fed from the output stage supply line, through a dropping resistor, then zener diode regulated. While this arrangement was adequate in its day, it can't compare to a separate, low noise, dedicated, 2 channel, regulated power supply, that specifically feeds the input stages of the amp, while freeing the main power supply to drive the output sections.
All components are of first rate quailty and mounted on high quality fiberglass printed circuit boards. Separate fuses are used for the input power supply and main power supply. The bridge rectifiers are International Rectifier ultra high speed, low noise, high current devices. Linear Technology LT 1085 and LT 1033 low-noise, low drop-out devices are used for the positive and negative 18 volt regulators. Additionally, the original bridge rectifier diodes for the main supply were replaced (see pics) with low noise, ultra high speed, high current, International Rectifiers diodes to help reduce noise in the output stage supply. High quality Panasonic capacitors are used throughout, for filtering the A.C. and for long life. The high current, torodial, rear mounted power transformer is protected by an attractive, heavy gauge steel covering, ensuring protection and isolation. The A.C. power cord was replaced with a compatible OEM type style. The original (2) 20,000 mfd. main power supply capacitors are in excellent condition. They show no signs of leakage.
The cosmetic condition of the Model 240 is very good to excellent, as the pictures show. The faceplate is very good to excellent, with only minor flaws not easily seen. The unit is very clean.
Thanks and regards, -rick..
Up for your consideration, is a one-of-a-kind Marantz Model 240 Stereo Power Amplifier. Conservately rated at 120 watts RMS per channel at 8 ohms. The Model 240 has been known to deliver more than the rated output. Already a classic, rare, vintage, Marantz model, this unit has been throughly serviced. All questionable parts were replaced. This includes new high frequency Panasonic electrolytic capacitors, polystyrene film capacitors, polyester film capacitors, silver mica capacitors and any questionable resistors. All transistors are either the original devices or Marantz approved OEM type replacements. Moreover, the often troublesome output relay was replaced with a new OEM type whose contacts are free from any corrosion. The relay provides solid contact for maximum signal transfer from the outputs. The RCA input connectors were replaced with high quality jacks, thus eliminating the troublesome original types that were prone to corrosion and poor signal transfer.
If all these serviced items weren't enough to greatly improve this vintage amp, this Model 240 has been modifed with the addition of an ultra high quality power supply modification that decouples the output power supply from the input stages by providing a separate, regulated, high performance, 18 volt D.C supply to the input stages. Originally, one power supply provided power for the entire amplifier, thus limiting it performance and sound quaility. Now, with the additional power supply, the sound quality has been transformed from comparative "transistor" like chacteristics, to a much darker, warmer sound more closely resembling tube sonics.
This change in sound quality is a result of a rear mounted, high-current, dual secondary toroidal power transformer supplying (2) 24V lines to (4) low noise, ultra high speed diodes to form the dual bridge rectifiers. The 24 volt lines are reduced to 18 V.D.C. via (4) ultra high quality, Linear Technology low dropout voltage regulators. Each channel has separate regulation stages for both positive and negative voltage supplies. This configuration greatly reduces noise and improves sound quality by eliminating the usual power transformer center tap direct connection to ground. Now, due to the dual secondaries, dual bridge rectifiers per channel and dual regulators per channel arrangement, the bridge rectifiers commons are D.C. in nature not A.C. as was before. This is a much cleaner arrangement, opening up the potential of the Model 240 that wasn't possible with the previous configuration.
The original input power supply was fed from the output stage supply line, through a dropping resistor, then zener diode regulated. While this arrangement was adequate in its day, it can't compare to a separate, low noise, dedicated, 2 channel, regulated power supply, that specifically feeds the input stages of the amp, while freeing the main power supply to drive the output sections.
All components are of first rate quailty and mounted on high quality fiberglass printed circuit boards. Separate fuses are used for the input power supply and main power supply. The bridge rectifiers are International Rectifier ultra high speed, low noise, high current devices. Linear Technology LT 1085 and LT 1033 low-noise, low drop-out devices are used for the positive and negative 18 volt regulators. Additionally, the original bridge rectifier diodes for the main supply were replaced (see pics) with low noise, ultra high speed, high current, International Rectifiers diodes to help reduce noise in the output stage supply. High quality Panasonic capacitors are used throughout, for filtering the A.C. and for long life. The high current, torodial, rear mounted power transformer is protected by an attractive, heavy gauge steel covering, ensuring protection and isolation. The A.C. power cord was replaced with a compatible OEM type style. The original (2) 20,000 mfd. main power supply capacitors are in excellent condition. They show no signs of leakage.
The cosmetic condition of the Model 240 is very good to excellent, as the pictures show. The faceplate is very good to excellent, with only minor flaws not easily seen. The unit is very clean.
Thanks and regards, -rick..
