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

Friday, July 22, 2016

Pioneer SX-1250 Receiver Restoration

Pioneer SX-1250 Receiver 

Today were showcasing a customers Pioneer SX-1250 Receiver restoration.  The 1250 was one of the last few TOTL receivers made along with the SX-1980. Manufactured from 77-79“.  The 1250 features some impressive points such as a total of 88,000M Microfarads of filtering capacity and a massive toroidal transformer.  Each Driver is symmetrically isolated along with the power and protection assemblies. The front RF stages each have their own potted shield assembly as well.  Similar to the other 1250's we've done we featured this unit with the multi-facet SMD warm white custom LED's.

Power Supply AWR-107 and AWR-106 Stabilizer PS
The large toroidal is preferred due to the winding characteristics which is touted to display almost negligible inductance slew.  A large 20W 3.3OHM current limiting resistor is used, thermally coupled to a thermistor diode.  Each 44,000MFD filter section is dedicated to the independent rectification.
The AWR-107 uses large 470MFD axial’s which were replaced with Nichicon TVX 470/100 axial capacitors, along with the smaller 35V 470MFD to Panasonic FC high temp (105C) capacitors.

The AWR-106 Stabilizer assembly controls the rail points and driver stability.  As above the 1000MFD axial was replaced with a Nichicon TVX variant. The remaining electrolytic were replaced with a high temp (105C) Nichicon PW and Panasonic FC capacitors.  All the regulated TO-220’s were updated with high quality robust MJE150/32/33 BJT’s and 869/945 type TO-92’s to 2383/2690 BJT devices.  1S2473/and s10B type didoes were all replaced with 4148 standard and ultra-fast 4007 type diodes. 

The four original 22,000MFD 80V Nichicon capacitors were replaced with high grade Nippon Chem-Con 22K/100V filter capacitors and new .1MFD polypropylene rectification bypass films. 

Protection AWM-091
The protection circuit of the 1250 is comprised of a multi facet identifier; DC Deviations, DC Overload saturation and a Soft Start Relay. The overload consists of a resistor array and the relay driver circuit which shunts excessive current flow through Q1-D3. The Original was replaced with a 48V Omron.  A new MY2-24V relay was also installed not he AWM-091 PCB.  All of the electrolytics were replaced with the same above high temp (105C) PW and Panasonic FC type capacitors. Driver transistors Q5/ were updated to TO-220 2690 BJT“s and the the 945 to a 2383 type.

The AWF-021 circuit uses a tied emitter differential transistor group for 1st order gain while employing a SEPP )(single ended pp) complimentary circuit for voltage gain drive, high grade polystyrene and precision 1>% resistors results in incredible noise reduction and almost no discernible deviation (>.2dB) The larger filtering input capacitors were replaced with 470/220MFD Panasonic FC type capacitors and low impedance, audio grade PW/KA’s for the AF path.  The original input films were upgraded to a polypropylene Solen (1MFD).  Initial PNP Gain pairs were replaced with 1% matched 992’ TO-92 BJT’s and the original 2473 diodes to modern 4148 type.

The Flat amp assembly is comprised of a complimentary FET transistors in a direct coupled stage, the control assembly which features a stepped multi frequency attenuators in a two stage NFB circuit.  Dont forget the 3 electrolytics on the switching assembly PCB's either, this is the time to clean each switch and contact using Caig Labs D4/F5.

The original tone and flat assemblies were comprised of a large assortment of tantalum type capacitors which were replaced with audio grade Nichicon KA capacitors, remaining electrolytics were replaced with Nichicon PW low impedance capacitors.  Original AF path mylars and polypropylenes were updated to WIMA and Panasonic ECW polypropylene dielectric capacitors. 

Drivers AWH-048-A
 Designed around a classic a/b configuration the x1250 encompasses a 1st order differential pair gain stage tied to a constant current mirror design which mutually phases signal for a more stabile drive via Q3-4 und Q5/6 through a/b biasing resulting in a PP bias scheme.  3rd order drive is comprised of a tiered complimentary  darlington arrangement via BJT’s through to outputs. 

The differential pair transistors (TO-92) were repalced with 1% matched 992fbu transistors along with he Q11 to a 1845 device.  Pre-drivers were updated to TO-220 2690/1220 BJT and the final driver to a high grade robust MJE15032/33 TO-220’s with new thermal compound and insulators.  All of the 2473/and 1886 diodes were updated to 4148/ and ultra-fast 4007 type diodes.  The original bias/offset potentiometers were upgraded to multi-precision Bourns trimmers.  All of the electrlotics were upgrade to low impedance, high temp (105C) PW’s and remaining input film to a WIMA PP film capacitors. Remaining AF films were upgrade to high quality Panasonic ECW polypropylenes. 

Tuner Assembly AWE-068

The SX-1250 has an incredible FM/AM sectional, with a highly sensitive 5-gang FM tuning capacitor and 3 gang AM, the fm is driven from a dual stage gain circuit while employing an array of MOS/FET and AM IC gain stages (HA1138). Both tuning capacitors were carefully cleaned and treated.

Audio Notizen

Monday, July 11, 2016

Sansui 9090DB Receiver Restoration

Sansui 9090DB Receiver

Today were detailing a Sansui 9090DB Restoration.  Similar aesthetics to the 9090 and Black 990(E.)  The 9090DB differs from the latter with the feature of the Dolby Noise Reduction circuit and a rated 125W rms output compared to 100W. Topographies of the driver, tuner and power supply assemblies exists as while such as the use of complimentary outputs vs a quasi-complimentary stage in the 9090.  Manufactured in the late 70’s through 1979 the 9090DB features a dedicated MM phono, triple tone controls and direct output meters with  integrated output protection.

Power Supply F2656 & 12KMFD Filters
The power supply mounted int he rear center of the chassis is also the inboard connector point for the Driver assembly, all of the associated output emitter resistors also populate this assembly.
All of the electrolytic were replaced with high temp (105C) Panasonic FC and PW Nichicon capacitors.  Nichicon VP were used for the 4.7MFD bipolar capacitors.  The common-cathode-anode diodes were replaced with MUR1620 TO-220 type diodes.   BP-Transistors 2SD438/2SD3# and 1211 were all replaced with MPS TO-92  transistors along with the 1OHM fusible transistor.

In relation the two 12,000MFD filter capacitors were updated with new high quality Panasonic THA 12KMFD/80V capacitors.

Protection F2657
The protection assembly is located in a very odd angle considering the mounting hardware, this installation was obviously down with a reverse tear down in mind!  The Omron MY3 type relay was replaced along with the associated .01/1MFD electrolytic/ceramic capacitors to ECQ polypropylene film type.  The remaining electrolytic were replaced with Bipolar VP and low impedance PW Nichicons and FC Panasonics. The fusible resistor was replaced with a 1/2 carbon film KOA. 

F2544 Tone & F2653 RIAA & F2617
The tone PCB houses the three dual gang tone controls mounted to the front chassis plate. The front end gains take is comprised of a BA312 pre-amplifier IC and Baxandall negative feedback circuit. Larger filter capacitors were replaced with Panasonic FC’s and AF Audio grade Nichicon KA capacitors.  Small signal 2SC1313 to 1845 type TO-92. 100PF ceramics were replaced with stacked ECW films.

The Micamp PCB  had the .47 electrolytic replaced with a WIMA film capacitors and audio grade Nichicon KA’s and a PW installed.

The MM RIAA stage has several capacitors housed under the shaft mount, with a good pair of angled magell’s you can access these.  Electrolytics again like above with Panasonic FC’s and af Nichicon KA capacitors also replacing tantalums with KA’s. Also like the above its comprised of a BA312 IC three stage direct coupled SEPP topography.

F2624 Driver
The driver topography differs greatly from the 9090, comprised of a complimentary output stage vs quasi on a symmetric single PCB.  The electrolytic on the driver stage were replaced with high temp (105C) Panasonic FC and PW Nichicons.  The bias and offset potentiometers were replaced with Bourns precision trimmers and all fusible resistors replaced with carbon film 1/2W KOA’s.

NPN differentials were replaced with match 1% TO-92 ZTX transistors.  Bias and Pre-driver transistors were replaced with 2690/733 and 1220 TO-92/TO-220 transistors. Driver pairs were updated to MJE15033/32 pairs.  All 1588 and VD1212 diodes were replaced with 4148 and 4148 series pairs. 

F2549 AM/FM  F2619 & F2655 DB Assemblies
The tuner is quite different on the 9090DB, incorporating a 4-gang tuning capacitor and Phase-Loop Lock PLL circuit with matched MOS FET /AM High-IC devices!
The electrolytic and tantalum capacitors were replaced with low impedance Nichicon PW capacitors and tuning gang cleaned. 

Associated F2619 Front end power supply had the electrolytic replaced with high temp (105C) FC capacitors along with updated the 2SD313 to the MJE TO-220 transistor. 

The Dolby F2655 had minimal interaction with electrolytic and tantalums replaced to low impedance PW capacitors.

Audio Notizen