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Marantz MA500 thread

Bratwurst7s said:
As of last night I have first hand experience that the overcurrent protection functions.

I was listening to some John Mellencamp, first Scarecrow and then The Lonesome Jubilee. But I forgot to turn down the volume between disks and TLJ has a lot more gain than Scarecrow.

After the first half second of very loud the amps went straight into protection. A jog down on volume and they came right back on.

So I know now that works, and I also know that as much as I like these amps they are not a long term solution for me with my 4 ohm speakers. As soon as I finish with the work on them I need to get busy getting the Denon POA 6600 amps working.

Cheers,
James
Click to expand...
i ran a stock ma500 on a 4ohm sub(ported, dual 10s) for 10+ years and never once hit protection and i was constantly getting downright stupid with the bass for hours and hours on end. amp was powered on 24/7 for years too.

i might concerned about that if it happens again. i'd like to see it on an audio analyzer and scope and see at what power/thd it tripped protect.

they should be fine running 4 ohm speakers all day with reserve power.
 
painttoad said:
i ran a stock ma500 on a 4ohm sub(ported, dual 10s) for 10+ years and never once hit protection and i was constantly getting downright stupid with the bass for hours and hours on end. amp was powered on 24/7 for years too.

i might concerned about that if it happens again. i'd like to see it on an audio analyzer and scope and see at what power/thd it tripped protect.

they should be fine running 4 ohm speakers all day with reserve power.
Click to expand...

Were you running bridged pairs? I'm thinking that in reality I am putting quite a load on them ohm wise with them bridged.

I have a scope and signal generator but am just starting to learn how to use them. No audio analyzer.

James
 
Bratwurst7s said:
Were you running bridged pairs? I'm thinking that in reality I am putting quite a load on them ohm wise with them bridged.

I have a scope and signal generator but am just starting to learn how to use them. No audio analyzer.

James
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oh, no i was not. pretty sure that's a no-no with (most) any bridged home audio amp.

but like you said, at least now you know protect works. ;)
 
painttoad said:
oh, no i was not. pretty sure that's a no-no with (most) any bridged home audio amp.

but like you said, at least now you know protect works. ;)
Click to expand...
:biggrin:

Yeah, I knew from the outset that I am treading on dangerous ground. Like, 2 ohm ground.

But since the current protection is working, and the amps are not baking, I think that as long as I keep them under the tripping point I am OK. The sound quality that I am getting is quite remarkable. I am very curious if this round of mods improves it any.

I noticed earlier with the aluminum heat sink on the UPC1342V module that it was getting fairly hot just sitting there with nothing connected. By the time an amp was warm enough to set the idle current they were quite hot to the touch.

With the copper heat sink it was only "very warm" at that point. Which is good since they are NLA. Other than those fine parts that one finds on ebay that are coming from China.

Wife and I are going for a walk, then, in about 90 minutes I will be sitting in front of warm amps.

Cheers,
James
 
JediDude said:
It's too easy to make that mistake.... ;-})>
Click to expand...

Oh yeah. And then the head goes into overdrive sorting through the problem scenarios, along with the punch in the gut feeling. It was such a relief to see the end of the power plug sitting there saying "Hello James".

I installed the 5th amp as the master in the left channel of the system yesterday, paired with the amp that has the repaired board as slave.

First off, no problems of any kind. Listened to 3 cd's and everything is sounding great. I want to say that the left channel sounds a bit more clear than the right now, but that can easily be wishful thinking. At the very worst I did a lot of work for nothing, but I think that once I get 4 amps brought up to the same level of work it will pay off.

I am already deep into the amp that was removed and am thinking that it should be ready to swap back in in 2 days. Then I will rotate them until 4 are the same. The one with the repaired board will be the last one out. It will then wait until I get the 6th one over here and make one good amp out of the 2 of them.

Cheers,
James
 
Finally getting the rest of the RCA jacks ready for the rest of the amps.

DSC02162.JPG

A 32mm length of wire seems to be just right.
DSC02163.JPGDSC02164.JPG
I discarded the slip on ground rings supplied with the jacks and soldered the minus leads directly to the bodies. There is a small notch in the hex portion for this.

Cheers,
James
 
I have been taking my X-acto knife and very carefully opening the through holes a bit. Not much, perhaps 0.2mm, I don't want to remove much of the solder pads. The leads are pre-tinned with just enough solder to hold the wire strands together.

Then I take some smooth duckbill pliers and squeeze the wire ends a bit flat and they are then fairly easy to pass through the holes. Too much solder on the leads and they are too fat, can not be flattened enough and will not go through the holes, it has to be very minimal.
The original holes are roughly 1mmx0.5mm.

DSC02167.JPGDSC02169.JPG
These isolation rings both have a flange that fits into the rear case panel. But two of them is too much, the jam nuts can't pull the post tight in the panel. So I cut one washer fairly flat.

The second completely upgraded amp went into the system yesterday as the right channel master. Doing all of this second round of work did not make a huge difference in sound, but did tighten it up a bit, cleaner and clearer. Bass is very tight. I am now half way through the next amp.

Cheers,
James
 
Found another schematic discrepancy or engineering change.

C703, a ceramic cap in the driver IC section.
Schematic shows 10pF, and that is what is installed in the oldest 1993 amp. All of the other amps have a 100pF cap installed, code 101 (tested at 95pF).

Cheers,
James
 
Today will be the 3rd day that I will be listening to the system with all 4 amps brought up to the full, dare I say it, Bratwurst Mod.

I am almost shocked. With all 4 amps now exactly the same I am getting wonderful clean and clear sound, very balanced, just wow. With what is effectively a very basic set of mods the sound quality that the amps deliver is greatly improved from what was good to what is very good. To say that I am happy with the results would be a massive understatement.

At this point I am just Chillaxing with the system and enjoying it but in the next day or 2 will post a combined list of the schematic discrepancies and then some final thoughts. In the meantime this project has been a complete success.

Cheers,
James
 
OK, a unified list of all of the schematic/parts list discrepancies that I found.

Caps:
C703: 10pF in schematic. 10pF installed in 1993, 100pF installed in 1995 to 1999.
CN05: Not shown in schematic or parts list. 1200pF ceramic cap installed in all years.
CS01: 0.1µF in schematic. 0.1µF installed in 1993/1995. 4.7µF installed in 1997/1999.

Resistors:
RS04: 10k ohms schematic. 3.3k ohm installed in 1993/1999. 10k ohm installed 1995/1997.
RS07: 10k ohms schematic. 10k ohm installed in 1993/1999. 3.3k ohm installed in 1995/1997.
(With these 2 resistors it seems to be an either/or situation, with one always being 10k and the other always being 3.3k.)
RS12: 10k ohm schematic. 100k ohm installed in all years.
RS14: 5.6k ohm schematic. 5.6k ohm installed in 1993. 2.2k ohm installed all other years.

That is all that I found. Note that I did not replace the carbon film resistors in the protection (RNxx) and standby/buss (RUxx) sections so there may be more undiscovered discrepancies.

Cheers,
James
 
So that is pretty much it. I think that I am finished here now.

It has been a lot of fun and also rewarding.

One thing that I will carefully note. My experience with Marantz products is limited to these amps and the Cinema 40 AV amp. I realize that there is an extensive Marantz fan base and a known Marantz "house sound". I have nothing bad to say about that, I get it that a lot of people like that. :thumbsup:
However. My impression with these amps so far is that they are quite neutral, more so after restomodding them. Nice and clean and balanced. I feel that I am listening to the music and not the amps, which is exactly what I want.

Hopefully this thread will be useful to somebody someday.

Enjoy the music,
James
 
A small addition.

1) As all of the new parts get to know each other better with use things are smoothing out more and more and the sound just gets better.

2) Something that I forgot to mention. With all 5 of the amps there was only a very small amount of dried out thermal paste on the driver IC. Very little. So it would be a good idea for a person to pull the heat sink, clean and apply some new thermal paste.

Cheers,
James
 
Bratwurst7s said:
So it would be a good idea for a person to pull the heat sink, clean and apply some new thermal paste.
Click to expand...
i think that you have understated the importance of this.

my suggestion would be to pull the chip because it runs so hot, it needs the solder reflowed anyway.

either way, it needs regreased and reflowed.

a couple weeks ago i could have brought home an ma700 but he only had 1 and i did not want to go on a search for a 2nd....and i definately do not need anymore gear.

but in retrospect, i should have just bought it. maybe i will when i go back :dunno:
 
painttoad said:
i think that you have understated the importance of this.

my suggestion would be to pull the chip because it runs so hot, it needs the solder reflowed anyway.

either way, it needs regreased and reflowed.

a couple weeks ago i could have brought home an ma700 but he only had 1 and i did not want to go on a search for a 2nd....and i definately do not need anymore gear.

but in retrospect, i should have just bought it. maybe i will when i go back :dunno:
Click to expand...

I agree, I should have better advocated re-soldering the entire board actually.

But I never reflow.
De-solder, clean and re-solder. Every. Single. Point.
I see reflowing only part of a 30 year old board as nothing more than preparing the next point of failure. Do it all right and have peace of mind.

So far I have not seen any MA700 at all over here. If I do see one for a reasonable price I might be tempted.

Cheers,
James
 
A small update.

Back in 2017 or 2018 I bought a few LME49720 op-amps.
DSC02522.JPG
A few minutes ago I swapped out the NJM2068DD for some LME49720.
Just because.

I'll report in a few days if it makes any change in sound.

Cheers,
James
 
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