Saturday, July 30, 2016

Marantz 2325 A Trio of Restorations

Marantz 2325 Receiver’s 

Today we’re detailing the restoration of three Marantz 2325’s in various states. All three units were approached using our protocol for the 2325.  

As I’ve mentioned before, next to the 2270 and 2385 these are one of the most popular units we get in for restorations for Marantz. The 2325 is a extremely well built. using dual symmetric driver topology and a plethora of RF shielding, modular pcb’s and well rated within specs at 125W .15% THD!


P800 Power Supplies
The 2325 power supply is located in an oddball area in the rear next to an exposed driver PCB.  Integrated with the protection, the 2325 enables a soft start delay, dc deviation and current draw protection.  A large transformer coupled with x2 15K MFD filter capacitors and dual output balanced rails (B+/-)

Rebuilding these boards first requires remove the Omron LY2 type and dousing the board in a lab grade 99.9% anhydrous solution to break up the glue for the large vertically mounted PCB’s.

  Next the common cathode rectifies at H808/809 were replaced with heavy duty MUR1620 TO-220 devices along with the 2373 type diode to a 4148. The regulating 2SD331 were removed with new mica and thermal compound applied and reflowed after buffing the heatsink. All of the small signal protection transistors H803-807 were updated to a NPN TO-92 2383 device. All the electrolytics were replaced with high temp (105C) long life Panasonic FC capacitors.

PH01 Buffer and PE01 Tone Control/Pre Amp
Viewed as a block the AF path goes through the voltage buffer stage PH01 being converted to low output impedances. The tone control of the 2325 consists of 3 way low/mid/hi stepped 11 detent dual attenuators along with the volume potentiometers. The 2325 tone uses two bipolar BA312 pre-amp IC’s which consists of a NPN gain stage configuration. This stage is similar in the 2275, 2250B as well

All of the electrolytic on the PH01 tone assembly were updated to low impedance Nichicon PW and the VD glass pack at HH11 updated (above).

All of the AF path films for the input/coupling at CE05/06 and Ce03/04 were updated to high grade WIMA polypropylene and Solen polypropylene film capacitors after trying the stage with ECW Panasonics, as I often find the MKP's do better in some passes vs the ECW and vice versa. WIMA MK’s also replaced the 1MFD tantalum capacitors. The remaining electrolytic and tantalums were replaced to low impedance Nichicon PW and KA audio grade electolytics. 
Small signal transistors 2sc1327/2sa721 were updated to groupings of 1845/992 NPN/PNP TO-92 transistors. 

P400 Phono Stage’s PCB
The phono stage of the 2325, again like the 50B/75 are an excellent design and prized by many of our customers.  A simple 3 stage NPN gain stage and is input coupling comprises the phono.  

The phono stage in many vintage units and even pre-amp stages used a common fault transistor label the 2SC458 TO-92 type, this transistor breaks down with age and causes significant noise. These are replaced to 1% pairs with 1845 TO-92 transistors, also the 2473 diodes updated to 4148 and the VD glass pack diodes to a series of 4148 type. The axial electrolytic was replaced with a axial TVX Nichicon capacitor along with the tantalum and electrolytic to Nichicon audio grade KA’s.

Driver Stages P700
The 2325 like many 22XX series used a full complimentary symmetry output section with a direct coupled design to ensure its .15% THD rating. 

The differential pair transistors were replaced with 1% matched 992 TO-92 transistors thermally coupled with compound and heats inked, along with the differential constant current transistors H703 to a 992 deivice. The  driver pair H708/709 to heavy duty MJE15032/33 TO-220 transistors. 
One of the units still contained the VD glass pack diodes at H718/719 diodes, which were replaced with 4148 in series.   

All of the electrolytic and tantalum capacitors were replaced with audio grade KA capacitors.  The 1MFD input film was upgraded to a high grade Solen polypropylene film capacitor, the remaining .01 and .1 film capacitors were all replaced with high grade WIMA and MKP polypropylene film capacitors. 

RF Stages
Like the 2275, the 2325 uses a compliment of FET RF amp IC’s and a 5-gang tuning capacitor including the standard phase-lock-loop (PLL) circuit. The remaining stage were recapped using all low impedance high temp variant Nichicon PW’s.

Filtering/Switches and Lamps

Each units large 15,000MFD filter capacitors were updated to 18,000MFD filter for a total of 36,000 microfarads to new high grade Nippon Chem-Con capacitors with the each rectifier .1 film upgraded to a Solen polypropylene film capacitor. At this team new power switches with new Vishay X1Y2 safety capacitors and a full LED conversion installed. Two of units that arrive came with broken push-function switches were were replaced with new dpdt-push pin type.



Audio Notizen

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