Sunday, November 15, 2015

Aker's Marantz 2245 Receiver

Marantz 2245 

UPDATE 11/30/2015
Here is the 2245 back at the customers home, he has installed a new Black Faceplate, the attention to detail on these plates is amazing!

With all the press these are getting lately I wanted to go over a Marantz 2245 receiver that came in from an Audiokarma member. The 2245 was the little brother price quid for the 2270, sharing a very similar driver design (difference in rails and drive power basically) and a very similar pre-amplifier topography.  Built from 71-76' their fairly common units but built extremely well, besides the bias modification thats needed on many serials.

Power Supply P800
Per my usual all the electrolytic here were replaced with Panasonic FR/FC high temp (105C) long life capacitors and all general diodes updated to UF. Common cath/anode to220 packaged rectifiers are omitted from this design but because this particular unit is a European version it includes an extra fusing assemblage. The PCB is a tight fit in this section so cleaning the caustic glue is a major PITA on this model, it took several soakings and still had to chip away. The relay was removed and contact  operations tested and cleaned. 

Phono P700
The 2245 uses the same phono PCB design as the Marantz 2230, which is noted for its incredible phono stage.  Typically the films here would be replaced but in this case the original fat brown films known in Marantz were populated and left.  Original tantalums were replaced with 22 microfarad  Elna Silmics and C713 follows the upgrade from 100UF to 220UF. When working on these phono stages one needs to updated the original failure prone 458 transistors as in this case to a matched Hfe pair of 1845 transistors, also noted glass pack diodes were replaced with 41418 and H409 with two 4148 in series. 

Tone/ Preamplifier P400
The major difference in the 45 vs the 30 pre-amplifier is the use of a 1uf film at R418/419 vs omitted on the 2245, all microfarad values remain the same along with topography.  On this version I populated with all audio grade Nichicon KA and Elna Silmic II's, the coupling c414/415 was originally a mylar upgrade to a polypropylene .22 microfarad film capacitor. 

Drivers P750
This section takes the longest on the 2245 rebuild. Due to serials variations their are some noted modifications and upgrades that should be performed to ensure stabile, reliable operations. 

The biggest point is that most 2245 use an oddball transistor at H760 (circle body TO), this BJT's is fairly unreliable and lends itself to many biasing issues on the 2245 and 2270, if your experiencing biasing issues I recommend attacking this modification. The recommended replacement that works is 2SD669 transistor but this typically only available as NOS, I recommend MJE243 or KSC3503.  Though the ECB pinout is different than the original so leads are recommend and using the existing heat-sink mount. 

H760 acts as a output coupled thermal regulator compensating for thermal variances at H001/2 & H003/4. From an Aker's experiment he (excuser) noted that the driver stages (H758/759) current bias stability  is affected by thermal variations far more than H001/H002 thermal variations and thus elects bias runaway. He discusses compensating with a lower Vbe at the drivers and reducing source voltage  in comparison, to create a constant bias along with isolating thermal governance at  H001/02. Very interesting topics discussed and I recommend reading all the comments. 

I also recommend on the 2245/70 adding a protective device against excessive on/off voltage peaks in case of a catastrophic failure, add a 4004IN diode across the output (TO-3's) H001/2 & H003/4 according to the following; 

Audio Adjustments
Regulated PS P800
-J802 und Boden beim R809 für 35vdc
Bias P750
-punkten +J754 und -J760 beim R763 für 10mV

H001/03 PNP SJ2514 - Cathode zu Emitter und Anode zu Collector w/ 1N4004
H002/04 NPN SJ2513- Kathode zu Collector und Anode zu Emitter w/ 1N4004

Differential pairs at 701/702 were updated with matched Hfe 992's (2SA640) along with the electrolytics here replaced with audio grade Elna Silmic II's and the very large paper film replaced with a high quality Panasonic ECW polypropylene film capacitor. The original mylar film at C763 was also upgrade to a high grade Solen MKP polypropylene film capacitor New Micas and compound applied as well. 

As the right driver stage is pulled I always recommend replacing the filter at this time for more accessibility. The coupling capacitors were replaced with 10,000 microfarad Nichicon Fine Gold capacitors (40mm) which are a perfect drop-in replacement.  I also like to complete the new power switch (7a Eg1018) and Vishay X1Y2 safety cap at this time to complete hardware along with new LED compliment in the main and meters. 

RF Stages
The final boards attacked consists of the RF stages MPX/FM and AM. After the left drive is pulled I like to complete these stages as you have the most work room. The P300/P150 assemblies are stacked, I recommend pulling all the mounting hardware so you can open book the RF PCB modules.  \/

Depopulated capacitors...shit load

Bitte, notiz beim C183 polarity error!

For all RF stages I use  high reliability, low impedance Nichicon PW capacitors. 

Short of the inherent bias flaw the 2245 is an incredibly nice sounding Marantz, very similar IMHO to the 2230 (compare again pre-amp stages) with a solid construction. 

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