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MARANTZ PM-66SE KI Signature PSU Modifications
MARANTZ PM-66SE KI Signature PSU Modifications
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Old 15th June 2019, 04:37 PM   #1
Hamish119 is offline Hamish119  Europe
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Join Date: Sep 2014
Location: London, UK
Default MARANTZ PM-66SE KI Signature PSU Modifications

I recently purchased a Marantz PM-66SE KI Signature (the same circuit as the PM-40SE, PM-44SE and PM-66SE, but with a toroidal transformer, a sprinkling of 'boutique' capacitors and a copper-plated chassis.

N.B. The PM-66* variants have an extra transformer winding for the remote control features.

Whilst it appeared to be fully-functional (** I normally listen with the 'Source DIRECT' button engaged **), I was concerned by the amount of heat dissipated by Q801 & Q802.

I resolved to reduce the amount of heat dissipated by these transistors with the minimum amount of circuit modifications and parts.

I noted that R802 had been replaced. I also noted that Q801 was loose! Too much heat in a TO220 package.

Marantz_PM-66SE_KI_1_small.mp4
Marantz_PM-66SE_KI_2.mp4

N.B. I had a Marantz PM-44SE that used to intermittently drop-out the speaker relay, then re-engage a few seconds later. That amplifier 'disappeared' before I could investigate the cause (I now suspect Q801 as aove).

After measuring the voltage drops across R802 (47R / ~5V drop) and R804 (47R / ~3V drop), I determined that the +24V rail was supplying ~100mA (worst case - speaker + source direct relays engaged) and the -18V rails was supplying ~66mA (worst case - ALL LEDs illuminated).

It's not surprising that (according to 'the Internet') R802 is the most common failure with these amplifiers - it's severely underrated. It's a design oversight!.
R804, D804 & D805 also take a beating in the default configuration.

Marantz_PM-66SE_KI_PSU.jpg
Marantz_PM-66SE_KI_Resistor.jpg

** When I disengaged the 'Source Direct' relay, I lost the right channel (intermittently). Re-engaging the 'Source Direct' relay restored the right channel (always).

After replacing ALL the semiconductors and capacitors, the amplifier was completely destroyed.
The above sentence is completely untrue and is precisely what happens when you believe 'misinformation' on the Internet.

The right channel could be restored (temporarily) by moving the large ribbon cable (WV01), but would disappear minutes/hours later.
After chasing the intermittent problem, I discovered that the (never used) 'Balance' control had been 'whacked' by a previous (l)User.

Resoldering ALL the pins restored normal operation (but for how long?).

Balance_Control_Knob.jpg
Attached Images
File Type: jpg Marantz_PM-66SE_KI_PSU.jpg (104.3 KB, 119 views)
File Type: jpg Marantz_PM-66SE_KI_Resistor.jpg (112.3 KB, 114 views)
File Type: jpg Balance_Control_Knob.jpg (97.9 KB, 102 views)
Attached Files
File Type: mp4 Marantz_PM-66SE_KI_1_small.mp4 (5.73 MB, 16 views)
File Type: mp4 Marantz_PM-66SE_KI_2.mp4 (4.52 MB, 7 views)
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Old 15th June 2019, 04:46 PM   #2
Hamish119 is offline Hamish119  Europe
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Iteration 1

As I had a 5 pack of 150R/2W wirewound resistors, I replaced R804 with a 150R/2W wirewound and R802 with a 75R/4W (2 x 150R/2W in parallel) wirewound. I also removed the wire link adjacent to Q801 and installed a 75R/4W wirewound in R809 (which Marantz thought about, but didn't fit). This further reduces the strain on Q801.

Marantz_PM-66SE_KI_R809_link.jpg
Marantz_PM-66SE_KI_link.jpg

Heatsinks were attached to Q801 & Q802, power applied and measurements taken.
Although the transistors were cooler, I felt that further heat reductions could be made.

Marantz_PM-66SE_KI_Iteration_1_reduced.jpg

Iteration 2

Criteria: 5-10mA(max) through the Zeners/6-12V(max) across R805 & R806. Minimum heat dissipation in Q801 & Q802.

R802 120R/2W(min)
R804 330R/2W(min) (350R/3W preferred, but would be a 'boutique part)
R809 39R/2W
R810 68R/2W

Marantz_PM-66SE_KI_Iteration_2_reduced.jpg

R802_junction_R801.jpg
R802_junction_R805.jpg
Q801_Collector.jpg

R804_junction_R803.jpg
R804_junction_R806.jpg
Q802_Collector.jpg

Unfortunately, I didn't have a 330R/3W wirewound, so I used a 270R/2W wirewound.

Now that R802 & R804 are doing most of the 'heavy lifting', I can now keep my finger on Q801's heatsink!

C801, C802 and D801 were also replaced.

Parts were purchased from RS & Farnell.

Apart from the heatsinks, no audiophool 'boutique' parts were used.
Attached Images
File Type: jpg Marantz_PM-66SE_KI_R809_link.jpg (354.8 KB, 103 views)
File Type: jpg Marantz_PM-66SE_KI_link.jpg (244.9 KB, 103 views)
File Type: jpg Marantz_PM-66SE_KI_Iteration_1_reduced.jpg (138.2 KB, 44 views)
File Type: jpg Marantz_PM-66SE_KI_Iteration_2_reduced.jpg (134.6 KB, 41 views)
File Type: jpg R802_junction_R801.jpg (144.4 KB, 34 views)
File Type: jpg R802_junction_R805.jpg (148.7 KB, 24 views)
File Type: jpg Q801_Collector.jpg (147.4 KB, 18 views)
File Type: jpg R804_junction_R803.jpg (145.0 KB, 16 views)
File Type: jpg R804_junction_R806.jpg (146.4 KB, 17 views)
File Type: jpg Q802_Collector.jpg (150.9 KB, 18 views)
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Differential input (instrumentation) amplifiers - the correct method of amplifying the output from a phono cartridge!
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Old 15th June 2019, 05:30 PM   #3
Hamish119 is offline Hamish119  Europe
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I forgot to add the final PSU circuit diagram

Marantz_PM-66SE_KI_PSU_Final2.jpg
Attached Images
File Type: jpg Marantz_PM-66SE_KI_PSU_Final.jpg (145.9 KB, 48 views)
File Type: jpg Marantz_PM-66SE_KI_PSU_Final2.jpg (138.9 KB, 43 views)
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Differential input (instrumentation) amplifiers - the correct method of amplifying the output from a phono cartridge!

Last edited by Hamish119; 15th June 2019 at 05:55 PM.
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Old 15th June 2019, 08:21 PM   #4
Ian Finch is offline Ian Finch  Australia
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You've obviously thought hard about the problems there but there are plenty more to consider before signing off on your efforts. The design looks a bit "pieced together" to my way of thinking and seems to have had more than one person at the drawing board.

For example, C801 and 802 are under-rated. The black triangle mark for those electrolytic caps has me puzzled too. Of course, that's only what is shown in your posts, there are likely more "errors" such as that. Also, If you are planning on ignoring the significance of the fusible resistors, don't forget that they are a necessary part of the design, so think carefully about safety when using the amp or leaving it unattended when powered. Read up on them and learn a little about designs that include fusibles where specified (that's the black triangles and "!" marks.)
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Last edited by Ian Finch; 15th June 2019 at 08:32 PM.
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Old 15th June 2019, 08:36 PM   #5
Ian Greenhalgh is offline Ian Greenhalgh  United Kingdom
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I had a PM66SE as my main amp until just over a year ago when it died, dead, nothing, so probably a power supply issue like this.


I replaced it with a Cambridge Audio A5 and that was sonically, quite an improvement. I gave that A5 to a friend when I got my hands on some Linn kit dirt cheap and he is enjoying it to this day.


Point being, the PM-66SE isn't all that great sonically, yes, it's a good amp, but there are better ones that are common and cheap, so if yours is proving a PITA to get working, perhaps better to move it on and get something else.
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Old 16th June 2019, 04:20 AM   #6
Ian Finch is offline Ian Finch  Australia
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The original power transformer likely had an internal thermal fuse. If it failed due to overheating or any other reason, the transformer would wind up just as useless as it would be if burnt out due to overload.

It's not clear in your posts, but according to the voltages shown on your schematic snips, you or the previous owner must have replaced the power transformer with one that has some 4VAC higher output. If so, this would certainly be the reason for an overheating problem and failure of the fusible resistors. Is the original schematic shown in the OP with only +/-38VDC main output correct for your model? Importantly, if you persist with the transformer's higher voltage supplies, it will necessitate a re-design rather than just patching over the problem with larger dropping resistors for the auxiliary 24 and 18VDC supplies. It should also be obvious that higher voltage rail voltages to the power amplifier won't be without their problems either. Check the capacitor voltage ratings there and whether fusible resistors there are still functional too.

If the transformer is incorrect, I can't see any problem with fitting a standard dual 25VAC toroidal in place of what appears to be a stock dual 30VAC type toroidal. (if that was changed, it would have been an ill-conceived "upgrade") Then you can get back to safe operation with raw 34V rail voltages and replacing the fusible resistors with appropriate similar, original spec parts.
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Old 16th June 2019, 05:52 AM   #7
wiseoldtech is offline wiseoldtech  United States
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It's no surprise that quality, design, and cheapness has taken over once-great names like Marantz. (and many other brands too)

And all the while, these components have gone UP in price.
Sad state of affairs it is.
Thanks to greedy companies.
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