E. Leavell & J. Mendelsohn Marantz 2325 Restorations

Two Marantz 2325 Receiver Restorations with Pre-Amp Stage BA312 Upgrade

Here are another two Marantz 2325 that came on my bench for restorations, both include the new (Now available from Sparko’s Labs!) BA312 upgrade in the PE01 Pre-Amp stage.  The 2325 is a absolute legend in the Marantz arena, sought after by most and well regarded for its solid construction and warm phono stage presentation. 

P800

The 2325 P800 assembly regulated power supply establishes the single-ended 14 and 35V supply rails via a Full-Wave rectification array, a Full-Wave rectified supply also enables a onboard protection circuit responsible for DC deviation and over-current protection of the output stage. The 60V rails are established via a Full-Wave array and two 15Kmfd filter capacitors.

All of the electrolytic capacitors were replaced with a high temp (105C) low impedance Nichicon PW with an increase in operating voltages, the initial DC filtering capacitor was increase to 1000MFD, C804/806 to 330MFD and the protection DC filing to a 47MFD for bettering DC filtering. 

Common cathode diodes were replaced with Ultra-Fast, Soft Recovery MUR type  TO-220 devices. TO-220 regulators were updated to a modern, more robust TO-220 type TIP devices with new synthetic performance Wakefield compound applied. Remaining TO-92 devices were replaced with modern low noise Fairchild TO-92L devices with better dissipation. A precision Bourns adjustment potentiometer installed.

BEFORE 

AFTER

35VDC CONFIRMATION

Filter Capacitors

In both units the 60V -/+ DC full wave 15,000MFD filter capacitors were increased to 18,000MFD computer-grade Nippon Chem-Con capacitors for better filtering and sub-sonic response reserve.

-/+ RAIL VOLTAGE CONFIRMATION

PH01 & PL01 400Hz Oscillator (TONE)

The PH01 buffer assembly essentially processes input via the function and converted to a low output impedance source. 

PL01 400Hz Oscillator (TONE)

PL01 is the 400Hz test tone available at 580mV sinusoidal wave form generator.

The electrolytic on this assembly were replaced with low impedance Nichicon PW and audio-grade KT capacitors with an increase in operating voltages. The films in this stage were updated to a high-grade WIMA polypropylene film capacitors. The varistor was updated to modern 4148 type diodes in series. 

BEFORE 

AFTER

PE01 W/ BA312 AE UPGRADE

The original BA312 integrated-circuit (IC) is a old, early pre-amplifier IC device used as a gain stage in many of the PE01 pre-amp designs including Sansui variants. With great advances in todays high-end operational-amplifier (OP-Amps) we were able to design a circuit that allows for integration of a op-amp into the original BA312 location with no cutting or hacking…and no messy/noisey extra PS rails. The results are astronomical and frankly quite blatant!  You can now purchase the BA312 directly thru Sparko’s Labs available and their Ebay Store!

All of the electrolytic capacitors here were replaced with a audio-grade Nichicon KT/KA type., the decoupling capacitor was increased to a 470MFD low impedance PW for better dc filtering after testing, all with an increase in operating voltages. The output bipolar were replaced with a audio-grade Nichicon MUSE BiPolar type. Input and all coupling films including electrolytic at 1<MFD were all replaced with a high-grade WIMA polypropylene type film capacitors and a new favored compliment of ECW polypropylene input films. Lastly the original BA312 IC’s were both removed and replaced with the BA312 Upgrade kits.

BEFORE

 AFTER

P400 RIAA EQ

Like the PE01 pre-amp stage the P400 phono stage is another very popular design used in many of the 22/23XX series receiver.  The P400, with our proper upgrades has a very linear and accurate RIAA Curve response, the warm and smooth P400 I think is complimented from its coupled stages.

The DC filtering 100MFD filter capacitor was increase to a 220MFD in a more reliable radial package designed, low impedance Nichicon PW, remaining electrolytic were replaced with a audio-grade Nichicon KT all with an increase in operating voltages. The original tantalum/mylar/P films were replaced, along with the inputs and outputs to high-grade MKP polypropylene films. The varistor and associated diodes were replaced with modern fairchild 4148 type and all remaining 2473 types, the failure prone 2SC458 and all remaining small signal devices were replaced with low noise Fairchild TO-92 devices. Both clipping adjustments were replaced to precision Bourns potentiometers. 

BEFORE 

AFTER

P700 Drivers

The 2325 uses a differential gain stage and current stage which drives the eventual pre-drivers, the drivers are tied to the dynamic bias circuit. 

The differential pairs were matched within >5% and thermally coupled together with beta mapping notated below for confirmation. Remaining devices to pre-driver were updated with modern Fairchild TO-92 and TO-92L type devices. Diode service bulletins were also performed with a series of 4148 type axial.

MATCHED DIFFERENTIAL CONFIRMATION

The electrolytic capacitors were replace with a audio-grade Nichicon KT including replacing the 33MFD tantalum to KT, all with an increase in operating voltages.  All of the input and bypass films were upgraded to a high-grade WIMA and MKP  polypropylene type film capacitors, the input was replaced with a high-grade ECW polypropylene.

BEFORE 

AFTER

BIAS CONFIRMATION

Hardware

Both meters and dial displays had the vellum all replaced with new filters as well as 8V SMD Custom LED’s to mitigate the unfortunate heat damage caused by incandescent to the plastic shroud that occurs.  Both 33MFD decoupling capacitors across the meters were replaced with a low impedance PW Nichicon capacitor. 

AUDIO NOTIZEN