P800 Power Supply
The power plant of the 2270 revolves around a classic protection/regulated single assembly and the B-/+ 48V rails. The P800 assembly has a 35Vdc & 13.5Vdc output. The protection monitors excessive DC deviation occurring in the output stage congruently.
The initial 1A rectifiers were all replaced with a ultra-fast, soft recovery type axial Vishay diodes. All of the electrolytic capacitors were replaced with a low impedance, high temp (105C) Nichicon PW type, with several DC input/output stages increased in value for better noise filtering, with a noted increase in operating voltage as well. The original TO-66 style regulator was replaced with a modern, more robust OnSemi MJ series TO-220 type with new synthetic thermal Wakefield compound applied.
The remaining devices were all replaced with TO92L and TO-126 Fairchild devices for better dissipation handling. The adjustment hardware was replaced with a sealed, precision Bourns potentiometer. The original relay was replaced with a modern 24V Omron series.
BEFORE
AFTER
+35V Reg. Confirmation
Filter Capacitors
The 9KMFD filter capacitors were both increased in value for better subsonic reserve and filtering with new CDE type computer grade capacitors.
AFTER
-/+B Rail Confirmation
P750 Drivers
I’ve highlighted several aspects of the ASO and bias issues abound with the 2270 so I won’t cover them here redundantly but as documented before the original biasing scheme was replaced with a new TO-126 MJE series device thermally coupled to the driver array versus output dissipation.
New matched differential pairs were installed and thermally coupled together. As well as several remaining devices with modern TO92L Fairchild devices. Offset and Bias adjustment hardware was replaced with a sealed, precision Bourns potentiometers as well.
DIFFERENTIAL CONFIRMATION
All of the electrolytics including tantalum were replaced with a low impedance type Nichicon PW with an increase in operating voltage. Remaining films to precision/high grade MKP/CDE polypropylene films.
BEFORE
AFTER
BIAS CONFIRMATION
P700 RIAA (PHONO) & P400 Pre-Amplifier
The 2270 shares an indentical almost front end pre-amp and phono stage as i’ve highlighted many times, that I much prefer. The phono stage is accurate while the coupled pre-amp stage lends that warm Marantz tone. The P700 is cap coupled input/output stage with a NPN gain stage.
All the input/output films were replaced with high grade MKP WIMA polypropylene film capacitors. Remaining electrolytic were replaced with a audio grade KT/KA Nichicon type with an increase in operating voltage. The DC filtering capacitor was increased in value and replaced with a Nichicon PW, low impedance type capacitor. The general diodes and varistor were all replaced with modern axial 4148 type diodes and clipping adjustment hardware replaced with sealed, precision Bourns potentiometers. All of the small devices were replaced with a low noise, modern TO92 Fairchild type.
BEFORE
AFTER
RIAA CURVE RESPONSE
P400 PRE
As noted above I love the sound and simplified design of the 2270 front-end audio stage and its warm undertone. Like the P700 RIAA stage both are driven by a single-ended 35Vdc rail.
All of the electrolytics were replaced with a audio grade KT/KA Nichicon type with an increase in operating voltage. The DC filtering capacitor was increased in value and replaced with a Nichicon PW, low impedance type capacitor. 1MFD> capacitors were all replaced with a high grade MKP WIMA polypropylene film capacitors, inputs were replaced with precision CDE polypropylene films.
BEFORE
AFTER
RF Stages
Shielding was removed and RF assemblies accessed with new Nichicon PW low impedance type capacitors with an increase in operating voltages installed.
New Vellum with SMD Warm White 8V LEDs installed.
AUDIO NOTIZEN
No comments:
Post a Comment