Monday, February 23, 2015

Marantz 2330 European

Marantz 2330 Euro Restoration

Heres another great 2330 that came in for just a basic restoration. This particular unit is a European variant which basically means it lacks the P600 Dolby integration along with the voltage conversion. 

As far as the 2300 I love to work on these units, the modular molex connections make for a fairly quick tear-down. The 2325 and 2330 are similar in the fact that the regulated supply (P800 is the same in both units, on occasion I have seen different relays though such as a my4 vs a dual throw. 

P800 Power Supply
The design of the relay circuit is interesting to say the least, one caveat is that the thermal breakers attached to the P700 assemblies are actually in series with the coils at J814/815 via the collectors of H806/807.

All the caps were replaced with long life, high temp Panasonic FR/FC's, the diodes and zeners I added are a little more robust with a ultra fast 4005 diode. Because of the extent of the glue, most BJT's and resistors along with the film were replaced as well, in the factory they really made a mess of this assembly. The common rectifiers were replaced with TO-220 packaged MUR1620 series and a new Omron MY2 relay added. the sinked transistors had the mica replaced with new compound added as well.

P400 Phono
The lyrics here were replaced with Elna Silmics and an axial packaged TVX Nichicon, as I usually do with smaller capacitance  values, WIMA MKS2 were used.  The smooth red films Im not a fan of were replaced with Panasonic polypropylene ECW films.  As a precursor the potentially problematic 405/406 transistors were replaced with ksc1845s and the rest of the glass diodes replaced with 4148's in series or singled. 

P700 Power Amplifier Assemblies
Per my usual all the lower value capacitance lyrics were replaced with Wima MKS2 and a Panasonic ECW PP films and Elna Silmic II's for the rest. I did use a nice MKP PP to replaced the film at 706 with excellent results I thought. I've tried a few other PP's in this application but I keep returning to MKP's. The differentials were replaced with new thermal compound sandwiched and heat-shrinked together. I really like these more robust heavy duty potentiometers for the dc and Bias personally. I think they beat the modern smaller Bourns unless they tend to drift or don't stabilize during adjustments I keep these type. 

PE01 Tone / Pre-Amp
All the BJT's here tend to be okay, but as a precusor while I was in I like to update them to some more reliable, in this case matched 992'1845's BJT's. All the tantalums were replaced with either Silmics or WIMA MKS2's. CE37/38 are a pair of bi-polar, I used some nice MUSE but any film would be great as well. The small gray films at CE05/06 were replaced with nice Panasonic ECW polypropylenes, I would like to try the MKP's here sometime.  I've tried Mundorfs in the same location in a 2325, but it wasn't anything to write home about. 

PH01 Buffer had the lyrics replaced with all Panasonic FR/FCs. And new 18K 100V Nichicon main filter capacitors were added. These were an exact drop in with the Z-bracket lining up perfect. A new switch with a Vishay X1Y2 and the unit was buttoned up. Should add, probably from removing the euro jack, but a power cord had been spliced with tape. Needless to say a new power cord and tap were added for safety reasons. Like the 2325, P700 as easy access BIAS test points added which makes it straight forward.

Again, the 2300 class has to be my favorite variant to work on and they sound phenomenal, plenty of headroom, great extension and aesthetics to match.

Saturday, February 14, 2015

Kenwood 600 Supreme Integrated Amplifier

Kenwood Model 600/650 Supreme Integrated Amplifier 

I was very excited to get a chance to finally work on one of these, one of Kenwoods TOTL integrated amplifiers, the 600 Supreme. Certainly has an interesting export history. 

The unit came in with an issue of going into protection, , as well as a restoration. The protection circuit and power supply/protection had been properly redone a while back so I skipped that after giving a run through.  I'll say this, the 600 is not for the faint of heart. To do any front panel pcb assemblies I had to completely remove all the switches/pots etc, and remove the chassis section. Same goes for removing the filter caps. Contrary to a few posts i've read, if the unit was put together correctly at the factory you must undo each power transformer to undo the cap mounting bracket. One thing to note is the amazing Alps pot, its a HUGE enclosed stepped attenuator design, extremely solid construction and action, it would costs high dollar to do better IMHO.

Pre-Amp 08-1560-10
This particular board was slightly different than the documented one in the service manual vs the standard X08-1470-01 PCB. All the lyrics were replaced with Silmic II's and lower rated  caps with WIMA MKS2's. This is an interesting pre-amp compared to a lot of Marantz I've seen consisting of 6 FET's for the 4-stage eq phase.  This particular board is a bear because of the tight shielded wiring thats rampant here.

Tone Control X11-1310-00
I used a lot of nice MKS2 films and Silmic II's and MUSE KZ, its a little tighter in here as well. The design is a class A ,FET based Peter Baxandall circuit.  Again it was easiest to remove the chassis mounts and panel hardware on this board than wrestle inside and potential break something. I much prefer to work outside the chassis anyhow.

Filter Assembly - X12-1130-10

When doing the tone control it was easiest to do the Filter Assembly  recap at that time, the boards sandwich each other. Again Silmic II's were used for any lytic. 

Power Amp X07-1440-00
The design is a direct-coupled design, it also incorporates the constant current type dual FET stage i've seen in other Kenwoods such as KA-8100, what is interesting is that it does not utilize an initial input coupling cap. The big issue on these boards are the differential pairs (2sa810) and, again, the constant current regulating (2sc1452). If you do your research you note that these heatsinked to-18 type transistors tend to be failure prone. I had one of the 2sc1452 failing not this unit, causing an intermitted protection issue.   Remember to match the hfe of the  KSA1381's used in the differentials.  Not a whole lot of lyrics on this board either, they were replaced with some nice Silmic II's and a single Panasonic ECW PP film  along with the main course and BIAS pots were replaced with multi turn Bourns. 



Mind the different pin-outs of the new transistors (pictured below)

All four filter caps (18Kuf 75VDC) Chems were used, these are an exact drop in dimension wise, the screw terminal makes for fairly quick work after you add rungs. This is the first time I've tried these particular caps and they seem very solid, one of the filter caps I pulled had a nice big soft spot like a over ripened fruit on it.