Thursday, April 30, 2015

Marantz 2270 Receiver

Marantz 2270 Receiver Serial# 3900<

So heres a Marantz 2270 receiver. These are certainly one of the more popular Marantz receivers for some reason. They share a similar pre-amp/phono as the 2230/45 variant. Its a great sounding unit, about the only thing I don't like is the amplifier section, i've never seen Marantz pull a trick like this before….

Power Supply
As typical I used Panasonic FR/FC high temp long life electrolytics here. Their are several diodes (801/802/811/813) that can benefit from a more robust UF4005 diode. A Omron MY2-24 relay was installed. This particular PCB was coated with some foreign material that had caked all over, the PCB was striped and buffed, this caused some of the lettering and shiny phenolic to be removed, its a better alternative that letting that goo eat at component leads or cause oxidization to them. 

New Cornell Dubilier CDE 10000uf capacitors were used for filter replacements, a very nice capacitor IMHO, I've used the CDE series a lot recently as the Panasonic THA is being phased out of production for the most part. A new EG1018 power switch and Vishay safety capacitor, 33uf PW meter capacitor and move on.

As I mentioned and you can see, the 2230/2270/45 pre amp sections are all basically the same. One thing I do like to use here are nice polypropylene film capacitors instead of the mylar's. I've tried Mundorf EVO Oils, SoniCaps, Jensens and keep coming back to the MPK Solen, I think its an excellent film, and the price is unbelievable.  Audio grade Elna Silmic II's were used for all the electrolytic and WIMA MKS2s for low capacitance lyrics. 

Heres a photo of my 2270 Pre-Amp PCB

And heres a photo of a Marantz 2230 I did a while back to compare

All the lyrics here replaced again with audio grade Elna Silmic II's, the original low capacitance and film capacitors were replaced with Panasonic ECW polypropylene  film capacitors.  There are several additional changes to be be performed as well. Updating the 2SC458 BJT's is a critical due to their failure rate/noise issues, with KSC1845 BJT's.  the varistor H709 should be replaced with two 1N4148 in series and the 1S1212 with singles.

Power Amplifier
Ah P750… That 2270 has a notorious bias issue. originally it was not stable, and frankly I think the hfe of the service bulletin BJT mod causes another issue as well. Lots of folks seem to have this same issue. The key is to replace that damned thermal BJT with a MJE243, replace the diode with a uf4005/4 and get rid of the junk bias/dc potentiometers, I used precision Bourns 3386 angled.  Note the MJE243 uses a different PCB pinout. 

All the lyrics were replaced with audio grade Elna Silmic II's and a nice polypropylene MPK's for the film.  I always recommend updating the differential pairs as well, heres KSA992's work well, all are hfe matched as well. .

Wednesday, April 29, 2015

Harman/Kardon 730 Receiver

Harman/Kardon 730 Dual Power Receiver 

I want to take a moment and show off a Harman/Kardon 730 receiver.  Again like the three-thirty from a while back, it has a nice green lighting hue to all the lighting with the black on dial plate. These look just amazing.  Another neat little caveat is that it utilizes a dual power supply/dual rectification stages along with dual outputs; two aux, two tape, two phono and pre-out/main in jumpers!

This particular unit came in for a general maintenance package including new lamps. I did however run across a needed Bias repair /modification outlined below.

The amplification stage is a easy to access in this unit, it uses molex snap connections and just the heat sink mounts.Doing some research I have found many 730 users complain that the Bias was finicky, sure enough I encountered the same issue. On occasion you can clean the bias potentiometers, but more than likely if thats necessary the pot should go. In this case a Bourns precision, multi-turn 3296 potentiometers were installed, the 3296 is preferred because of the 90 degree access on the PCB. 

Another issue to note on a large number of vintage Harman/Kardons, including this one, is the 1S1211 varistors. In the 730 they are located at D407/408, a standard 1N4148 should be replaced here for stability in the bias circuit. The actual bias procedure itself is relatively straight forward, measuring across the collector of the main TO-3 outputs for 35mV. 

Even for a mere 40W/CH rated output the 730 is a damn nice receiver if you can snag one!

Tuesday, April 21, 2015

Sansui 350A Receiver

Sansui 350A Receiver 

Just thought I'de share some photo's of a Sansui 350A receiver.  This unit came in for a good cleaning including switches and potentiometers, also noted some noise issues. Its a little guy rated at 20W/CH output and an impressive 4 gang tuning allotment. 

One thing thats kinda neat is the woodcase, its the older slid in style so it doesn't have a metal case, but it has its own built on pedestal to the case.   I have to say, for a little unit it really sounds nice. I've been running some Melody Gardot and live sessions of the Head and the Heart for a few hours, it has a real nice warmth to it that a lot of older Sansui receivers do, in my opinion. 

I do want to note, the 350A has some reported noise floor issues. The Pre-Amp/tone (F-1248 Assembly) utilizes X4 2SC458 transistors. The 458 is notorious for pre-mature failure and noise issues.  These were swapped out with close HFe set of KSC1845 NPN transistors.

Sunday, April 19, 2015

Another Marantz 2325 Receiver

Marantz 2325 Receiver

Here we've got another Marantz 2325 receiver coming in.  I've said this before, but short of the 2230, this is my favorite Marantz. Very accessible from a technical point of view, but it also has the crisp clean/yet slightly warm tone I associate with the 2230.

Power Supply
Not much in my procedure for this unit has change from the other 2325's I've done. The lyrics were replaced with a high temp, long life Panasonic FC/FR type. Along with the dual diode 131B packages updated to TO-220 MUR1620 type. The relay is a LY-2 Omron, which is still available for a drop in, the regulating BJT's were regreased and the voltage regulated at 35.Vdc. Unlike the 2330 variant, no thermal breakers are led through this supply like the 2330.

Phono Assembly P400
The biggy with the phono assembly is to update several diodes and the H405/406 BJ-Transistors. The 2SC458 BJT's are notorious for developing noise/pre mature failure issues, these are replaced with matched HFe pairs of KSC1845's. The VD1212 glass varistor is updated to two 1N4148 diodes in series. Tantalums and films were updated with Panasonic ECW polypropylene films. Electrolytics were replaced with a single  Nichicon TVX axial and audio grade Silmic II's by Elna. 

Pre-Amp PE01
I really like how easy it is to pull the Pre-amp tone/control sections, this allows you to work with no hassle but also allows you to fully clean and lubricate each potentiometer without fuss. 

The original gray films in this application were update to Panasonic ECW polypropylene films and the original orange films left.  The lyrics were replaced with Silmic II's again and tantalum/low value lyrics were replaced with PET WIMA MKS2 film capacitors, one thing to mind is the footprint, space gets tight with the MKS2's.  Nichicon MUSE BP's replaced the original Bi-Polar Elnas at CE37/38. If you look at my other 2325 posts you can see some photos of the assembly. 

Power Amplifier P700
The amplifier sectionals have a really nice setup here, it uses a molex type power connections and uses a RCA type hookup for the signal path.  The lyrics here were replaced again with audio grade Silmic II's by Elna, the coupling film at C701 was replaced with a nice MKP polypropylene capacitor. Its always a good idea to do a little preventive care and replace the differential pairs at H701/702 (2SA722) with matched HFe pairs of KSA992' transistors. When doing differential pair packages, apply a thin amount of thermal compound and enclose the BJT's together with some shrink-wrap. Note a service bulletin should also be performed if not already done on your series; Updating 718/719H diodes with a single 1N4148. New thermal compound and MICAs were applied as well.

AM/FM Sectionals
In this particular rebuild the customer opted to include all the AM/FM circuits as well. High reliability, low impedance Nichicon PW & Sprague were utilized in this application.  I should note, P600 the Dolby noise reduction circuit isn't applicable anymore. Dolby FM was introduced in the late 70's as unsuccessful noise reduction system, similar to the High Com FM predominate in Germany at the time. 

Extra Curricular 
The buffer stage's lyrics were swapped with audio grade Nichicon FG's and Silmic II's, I recommend updating HH11 to two 1N4148 in series. The PL01 400Hz Osc. PCB was recapped using again, high reliability, low impedance Nichicon PW's.

Last but not least I always recommend replacing the original power switch in these 22XX's series with a DPDT 7A< switch, I like the EG1018-ND and add a X1Y2 safety cap.  The large filters caps were replaced with Nichicon's 18Kuf/75Vdc type, which are a perfect drop in for the 2325/2330. New Vellum paper was applied, warm white LED's and new 33uf electrolytic caps across the meters finishes up the lighting. 

Thursday, April 9, 2015

Adcom GFA-555 Power Amplifier

GFA-555 Power Amplifier

I wanted to take a moment and look at a Adcom GFA-555 Power Amplifier. This unit came in from a customer who stated after playing for an hour or two at high volumes it started to emit a lot of white smoke...yep smoke.

 One thing in particular I like about the 555 is cosmetically its a knock-out. Which might give you ad idea on my spartan decor' but I really like the plain-jane clean look, the front has this nice extruded type plate that envelopes the chassis in a U shape. That makes disassembly pretty quick.  The 555 has some impressive performance specs as well, with reported stability in the 4 ohm variant; rated up to 325 Watts and 200 at 8ohms respectively, the 555 has an easy switch bridged mode as well. 

Driver Assembly

I really like seeing the use of silver-mica capacitors employed vs cheaper mylar variants you typically come across. The silver mica's really have a great track record for reliability and sonic attributes. The metal film was replaced with a better Polypropylene Panasonic ECW film capacitor. The electrolytics were replaced with audio grade Nichicon KZ Muse and Nichicon FG with voltages bumped to 100vdc. 

The differential pairs Q01/02 were replaced with matched KSC1845 transistors. The Biasing network utilizes an interesting array of associated resistors in conjecture with the driver transistors to create a constant voltage bias, removing driver abnormalities and thermal influences on the circuit. Also updated were the original diodes to Vishay standard 1N4148's.

One channels NPN bank of outputs has shorted every single emitter resistor at the TO-3's, along with a few shorted resistors in the driver assembly, these were replace with MOX flame proof KOA 2W resistors and thermal compound and new MICA insulators supplied. 

One thing to note is the filter cap PCB's seem to suffer from some high heat situations, all the 3.9K resistors were again replace with MOX flame-proof KOA 2W resistors, along with a .1uf  Polypropylene Panasonic ECW film capacitor. One impressive note though is the application of X4 15,000uf capacitors used in the rectification filtering. What I don't like is a lack of robust dc protection.  This particular model has a host of modifications published online in regards to the MKII GFA-555 as well.

Currently I've got the GFA-55 hooked up to the Adcom GTP-500 Pre-Amplifier Control, which frankly…isn't anything to write home about, in fact its about as bland as Mayonnaise…I prefer Miracle Whip.