Thursday, March 23, 2017

Luxman PD-121 Plattenspieler Upgrades

Luxman PD-121 Plattenspieler
Today were highlighting some upgrades performed to the  extremely popular Luxman PD-121 Turntable. The PD-121 is a two speed, DC direct-drive with a motor suspension, heavy mass platter (2.4Kg), touting a modifiable Bayonet mount which was commonly paired with a SME 3009 or better.  Below is the OEM arm supplied mounted. 

One of the common failures on these or the black-light strobe due to a failing 4.7MFD capacitor. Instead of replacing with another cathode strobe we elected to perform the LED modification. Using the 23Vac source we are able to tie in a series of diode emitters and mount appropriately for a clean, long last illumination of the speed tracking. 

The black-light drive circuit can be removed, as I did, as the buss is no longer needed nor the circuit behind the 33/45rpm adjustable speed tune controls. At this time  the two phenolic rotary pots were cleaned and lubricated with Caig Lab products. 

The Power supply PCB had the electrolytic replaced as well with low impedance, high temp (105C) Nichicon PW capacitors with an increase in operating voltages, new UF (Ultra-Fast) Diodes installed and new thermal compound for the voltage regulator. 13.5Vdc rails were confirmed.

 Regulated 13.5V supply Vpk

Wednesday, March 22, 2017

Brians Adcom GFA-555 Driver Rebuild & Upgrade

Adcom GFA-555

Today were highlighting another GFA-555 driver rebuild we got in locally. The GFA-555 Adcom is one of the most well known and popular Adcom Power Amplifier available, released also with a GFA-555 MKII which has a different design approach.

You can read another GFA-555 we’ve restored below;

One of the biggest issues are the original electrolytic and metal film capacitors utilized in the original build quality.  These silver films have a fairly higher failure rate.

The electrolytic capacitors are all replaced with a high temp (105C) low impedance type Nichicon PW with an increase in operating voltages. As well as the original metal film/mylar films to high grade MKP type polypropylene film capacitors.  Another major benefit are new 1% matched BETA differential pair transistors, now thermally coupled together for better tracking. 

The Driver board design is rotated out for easier access and to clean the mono/stereo operational switch.  Along with new passive components new thermal compound and MICA insulators were installed. The larger format polypropylene films are located now on the foil side of the PCB with appropriate leg shielding.

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Sunday, March 19, 2017

Brad's Marantz 2215B & Pioneer SX-1050 Repair Highlight

Today were showcasing a few special repairs we had come in from a customer who stayed in the area over night from out of state. 

Pioneer SX-1050

The Pioneer SX-1050 is a fantastic receiver, though has some typical SX series heat issues on the driver assembly as well as the original 1439 devices which have a high failure rate. This unit came in with an intermittent loud static after use that would pop in the outputs.

Further diagnostics revealed a failing BJT  (2SA750 w/ leakage RFdV) within the driver network and a stressed electrolytic tied in. Because of the heat issues and populated 1439 devices both channel were symmetrically rebuilt.

All of the electrolytics were replaced with a KT audio grade and low impedance high temp (105C) PW Nichicon capacitors with an increase in operating voltages, also the input .68 films were upgraded to high grade WIMA polypropylene films. The bias potentiometers were replaced due to the caustic glue near the molex and several heat battered resistors replaced (18K near the current limiting resistors. 
New matched differential pair TO-92 low noise fairchild and new Fairchild TO-126 modern transistors were installed up to the 3rd order driver pairs. 


New LED's to finish her off

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Marantz 2215B

The Marantz 2215B is one of the smallest entry levels Marantz receivers produced, this being the latter B version. The 2215 is a fantastic small wattage output receiver with the prototypical warm Marantz tone and presentation.

This unit came in from a  failed repair attempt by another. The driver assembly had suffered significant damage shorting several output devices.  As the unit came in major re-work was necessary to repair the repair attempts and then the assembly.  One of the outputs was still shorted along with the thermally coupled bias transistors and the right pre-drivers had evident leakage current.

As a precaution the board was limited-re worked. 100MFD to 10MFd electrolytic were replaced with KT audio grade and low impedance high temp (105C) PW Nichicon capacitors with an increase in operating voltages. 1MFD electrolytic were replaced with high grade WIMA polypropylene film capacitors.   A new MJ On Semi PNP TO-220 output device installed, new bias transistors and pre-driver transistors with modern low noise Fairchild TO-92 transistors.  New shorted resistors were replaced with KOA 1/2 carbon film type. 


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Wednesday, March 15, 2017

Greg's Pioneer SX-424 Repair Highlight & Report

Pioneer SX-424 Receiver 

Today were highlighting a small Pioneer SX-424 Receiver that came in for a quick repair.  The SX-424  was produced during 1972-74 as the predessor to the SX-434 which came out after the SX-525.  The SX-424 is a great solid unit, stabile and modest output with a good distortion factor.

The issue with this SX-424 was severe oscillation occurring in the left channel only noted after about 6dBW output. This was due to several poor electrolytic’s that some half-twit tech had incorrectly installed which stress the driver stage devices and caused some reverse voltage issues or premature breakdown.  

Due to the single PCB topology the front end AF stage/Driver was rebuilt as high heat from the TO-220 output heatsinks position.   All of the electrolytic capacitors were replaced with low impedance and audio grade PW/KT Nichicon capacitors with an increase in operating voltages.  The input and coupling values were upgraded to a high grade WIMA polypropylene film capacitors as well.

The AF state front end BJT’s were replaced with low noise TO-92 Fairchild devices. The differential stage NPN, driver and pre driver BJT’s were all updated to TO-92/ TO-92L Fairchild low noise devices.  This circuit utilizes a fixed bias idle. 



All of the controls, contact were cleaned as well as new SMD Custom LED’s installed.

Audio Notizen

Sunday, March 12, 2017

Steve's Marantz 2270 Restoration

Marantz 2270 Receiver
(New Customer Provided Black Faceplate *above)

Today were featuring a very prized Marantz 2270 receiver. The 2270 is certainly one of the more popular Marantz receivers available out there today.  The 2270 was produced from 1972 to 1975 with the optional wood case.  This particular unit came in with massive damage to the front end chassis. A new front chassis sub-frame, new Black faceplate (on the way), new tuning hardware components and re-stringing were all required adding an exuberant amount of time to the restoration process. The final product turned out phenomenal!  One of the issues I cover in this restoration is the expansion on the Bias stabilizer modifications. 

Power Supply P800 & Filters
The power supply on the 2270 requires a large amount of caustic glue to be removed used for mounting the large vertical capacitors. All of the capacitors were replaced with high temp (105C) long life Panasonic FC and Nichicon PW capacitors with an increase in operating voltages. New UF (ultra-fast) diodes were installed and general 4148 type diodes.  A new low noise Omron MY2 relay was installed and re-wired. Part of the 35V regulator circuit was replaced with TO-92L Fairchild low noise BJT devices. 



The original 9000MFD capacitors were replaced with 12,000MFD 80V high grade/reliability Panasonic THA capacitors.

P750 Drivers
Like many of the upper end 22XX series Marantz, the 2270 utlizes two separated driver assemblies which is always ideal. 
Sadly, in its original form the 2270 is incredibly unstable in its bias circuit and prone to failures. This is due simply to a piss poor design by Marantz. These issues were later acknowledged in the 2275 design where we can see them address this issue in hard form.  The issue is the way the thermal tracking bias transistor and diode is mounted to the output stage heatsink, where as it should be located at the driver stage of the design to better compensate for changes in output demands. 

All of the electrolytics and tantalums were replaced with audio  grade Nichicon KT capacitors with an increase in operating voltages. All the original films were replaced with high grade polypropylene MKP film capacitors as well. As I mention in other Marantz writeup if these large heavy frame pots clean and track well keep them! They are far better than even new Bourns. In this case I was happy with at least two of the 2.2K pots and new precision Bourns pots were added for the Dc deviation adjustment.  New 4148 general diodes and flyback diodes at the output installed. 



Each of the thermally tracking H761/760 diode and BJT were replaced (MJE OnSemi TO-126 devices) and heatshrinked with leads added. Each device was then relocated under the driver stage devices and the Vbias multiplier changed to compensate for a change in potentiometer values.  The final results is a rock solid 10mV bias at idle with an appropriate slope to peak to peak output and down, along with the bias modification new differential pair TO-92 low noise Fairchild devices were installed, having been matched with a 1% BETA and thermally coupled together.



In the 2270 AF Stages we start to see why the 2270 sounds so damn great….its a 2230 and 2245. The AF stage is essentially the same in each of these series, Marantz pretty much used the same damn design for each one with differences occurring the FM/AM functions, driver output and Power Supply topology. 

The P700 has some inherent issues though, such as the use of 2SC458 transistors and VD1212 epoxy diodes. The 2SC458 devices were replaced with matched 1% KSC TO-92 low noise Fairchild devices. The original VD/IS diodes were all replaced with 4148 general type (series.) The tantalum and electrolytic capacitors were replaced with audio grade KT Nichicon capacitors with an increase in operating voltages along with high grade MKP polypropylenes at both input and output stages. 


P400 Pre-Amplifier
As above this is the same topology and board used in the afore mentioned models. A very simply gain stage and driver.  The front end NPN/PNP devices along with the remaining devices were all replaced here with low noise TO-92 KSA/KSC Fairchild devices.  The original input films were replaced with high grade MKP polypropylene films as well. All 1MFD electrolytic were replaced with high grade WIMA polypropylene film capacitors and remaining with audio grade KT Nichicon capacitors with an increase in operating voltages.




New Vellum and LED’s were installed on both Dial Display and Meter Assemblies. During the break down the tuning section we re-strung as well and front end AM/FM alignment completed. 



Due to damage when the owner bought the unit, the Bass Potentiometer had to be replaced and cleaned and reinstalled. Along with a New EG1018 Power Switch

As noted earlier the sub-chassis had received some damage when the customer first bought the unit from jack ass off ebay to lazy to properly package the unit. Below is the new front sub-chassis being installed

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