crooner
Tube Marantzed
Hi there fellow AK'ers.
I was contacted recently by member Trucker1964 to restore his mint condition Marantz 7T. Having heard my Marantz 7 as restored in this thread:
http://audiokarma.org/forums/index.php?threads/ultimate-marantz-model-7-restoration-thread.727823/
He asked me if it was possible to do the same to the 7T.
His 7T is an early version (Serial number in the 11500 range) with a beautiful engraved front panel.
For this restoration, I kept the same philosophy as in my Model 7, with a few interesting twists along the way:
- Siemens film caps replaced with assorted West-Cap mil-spec PIO's. The West-Caps are paper/mylar and thus combine the warmth of the traditional PIO with the extended resolution offered by mylar. Paper caps in the tone control arrays were also replaced with West-Caps.
- Original tantalums replaced with Vishay 135D Wet Tantalum types. These were developed under partial sponsorship of the Marshall Space Flight Center and NASA. Extremely compact and high performance. At nearly $60 each, these are not your traditional tantalum. The Japanese are particularly fond of these for their vintage restorations.
- A state-of-the-art custom made Khozmo 48 step series attenuator with machined aluminum body, hardened gold contacts and Vishay SMD high performance resistors.
It is connected to a stepper motor for remote control.
- Original silicon rectifier bridge replaced with four C3D02060F CREE Silicon Carbide Schottky Diodes. The diodes are mounted on their own small PCB for neatness.
- Power supply also upgraded with modern low ESR electrolytic caps by Nichicon and Elna (Silmic II). Each bypassed by a West-Cap PIO cap.
- Small electrolytics in the signal path (15uF) replaced with Sprague/Vishay 109D Wet Tantalums. Also Mil-Spec and very expensive.
- CL-90 thermistor in the power transformer primary. It reduces the AC voltage from 120V to around 117V, the design center of the preamp. It also provides soft start.
The headphone jack was jumpered to prevent noise issues. Each transistor was removed and pins treated with Silclear silver contact enhancer.
In order to fit the new remote control attenuator, the recording output RAEF board was removed. It turns out this board is redundant in the unit. It is a unity gain buffer (0 dB gain). It was probably added to prevent signal loss when the scope outputs and the recording outputs were used at the same time. A rare occurrence in practice. The Model 7's recording output jacks are un-buffered and I have found this to have never been an issue.
The remote attenuator is powered by small wall-wart plugged into the back of the preamp.
Below is a YouTube video demonstrating the remote control feature:
Listening to it in place of my Marantz 7, I find the sound to be very lush and full bodied, with excellent retrieval of detail. With soundstage and midrange texture/purity rivaling the tubed unit. The output voltage seems higher too. I ended up setting the output switch to the "low" position for proper matching to my pair of Marantz 9's.
It will require a few hundred hours of burn-in to sound it's best. But so far, the results are spectacular!
I was contacted recently by member Trucker1964 to restore his mint condition Marantz 7T. Having heard my Marantz 7 as restored in this thread:
http://audiokarma.org/forums/index.php?threads/ultimate-marantz-model-7-restoration-thread.727823/
He asked me if it was possible to do the same to the 7T.
His 7T is an early version (Serial number in the 11500 range) with a beautiful engraved front panel.
For this restoration, I kept the same philosophy as in my Model 7, with a few interesting twists along the way:
- Siemens film caps replaced with assorted West-Cap mil-spec PIO's. The West-Caps are paper/mylar and thus combine the warmth of the traditional PIO with the extended resolution offered by mylar. Paper caps in the tone control arrays were also replaced with West-Caps.
- Original tantalums replaced with Vishay 135D Wet Tantalum types. These were developed under partial sponsorship of the Marshall Space Flight Center and NASA. Extremely compact and high performance. At nearly $60 each, these are not your traditional tantalum. The Japanese are particularly fond of these for their vintage restorations.
- A state-of-the-art custom made Khozmo 48 step series attenuator with machined aluminum body, hardened gold contacts and Vishay SMD high performance resistors.
It is connected to a stepper motor for remote control.
- Original silicon rectifier bridge replaced with four C3D02060F CREE Silicon Carbide Schottky Diodes. The diodes are mounted on their own small PCB for neatness.
- Power supply also upgraded with modern low ESR electrolytic caps by Nichicon and Elna (Silmic II). Each bypassed by a West-Cap PIO cap.
- Small electrolytics in the signal path (15uF) replaced with Sprague/Vishay 109D Wet Tantalums. Also Mil-Spec and very expensive.
- CL-90 thermistor in the power transformer primary. It reduces the AC voltage from 120V to around 117V, the design center of the preamp. It also provides soft start.
The headphone jack was jumpered to prevent noise issues. Each transistor was removed and pins treated with Silclear silver contact enhancer.
In order to fit the new remote control attenuator, the recording output RAEF board was removed. It turns out this board is redundant in the unit. It is a unity gain buffer (0 dB gain). It was probably added to prevent signal loss when the scope outputs and the recording outputs were used at the same time. A rare occurrence in practice. The Model 7's recording output jacks are un-buffered and I have found this to have never been an issue.
The remote attenuator is powered by small wall-wart plugged into the back of the preamp.
Below is a YouTube video demonstrating the remote control feature:
Listening to it in place of my Marantz 7, I find the sound to be very lush and full bodied, with excellent retrieval of detail. With soundstage and midrange texture/purity rivaling the tubed unit. The output voltage seems higher too. I ended up setting the output switch to the "low" position for proper matching to my pair of Marantz 9's.
It will require a few hundred hours of burn-in to sound it's best. But so far, the results are spectacular!
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