Marantz MA500 thread

Bratwurst7s

Bratwurst7s

In The Frying Pan
Subscriber
I recently bought 4 of these little MA500 monoblocks. This thread is to share what information I can about them and my journey with them so far.

I have been wanting to move from my 2-channel Yamaha MX-1 power amp for some time. The MX-1 is actually a great amp but I have this hunger to try out monoblocks.
At the same time I have completely rebuilt my home theater system and made a new stand for the combined 2-channel and 9.2-channel systems.

So I actually started with buying 3 Denon POA-6600 amps, 2 that were supposedly good and one that was defective from the start. And as it turns out both of the "good" Denons have problems and are eating up all of my time and bench space.

I looked around at some alternative solutions that would fit in my rack and move me forward and let me take a more leisurely pace with getting the 6600's working. And that is when I came across these amps.

So, as I said, I bought 4 of them. They arrived very well packed and in very good optical condition.

Cheers,
James

edit 20 Jan 2024: Note that as I moved forward in the thread I noticed several points where I wrote something that was incorrect. One of the advantages of being a Subscriber is being able to edit post regardless of how old they are. I am making use of this to edit and correct the posts. Not to protect me from looking stupid but rather to avoid spreading false information.

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All 4 amps passed the dim bulb tester so I took them out front to test them in my system. And that is when the fun started.

2 of the amps had a partially stripped Plus speaker binding post. I was just barely able to get some threads engaged to tighten up on some speaker wire. So much for the seller's "tested and in good working condition".

But they did make music when hooked up.

As you can see my new stand was built around using monoblocks on the bottom shelf and there is no room for a wide 2-channel power amp.

Cheers,
JamesIMG_20231116_121921_369a.jpgIMG_20231116_121934_784a.jpg
 
 
After reading the above referenced threads it was clear that I would be needing to do some recapping, and if I am going to do it then do them all.
So I placed a Mouser order on the same day that I bought the amps. And it got here in Munich in about 44 hours, the day before the amps.

A few thoughts on caps.

My prefered choice for main PSU filter caps is no longer in production, (United Chemicon KMH 105°c), and choices for caps have in general become more limited.
I found no 30mm diameter caps at all, similar to those that proceded me, only 35mm diameter. UCC SMH are still available, and they are good caps, even if they are only 85° rated.
The SMH 10000µF/80v are 50mm tall but backordered until May of 2024. However, 12000µF/80v were in stock, so that was what I ordered.
https://www.mouser.de/ProductDetail/Chemi-Con/ESMH800VSN103MA50S?qs=sGAEpiMZZMvwFf0viD3Y3Wd4FpOoUsJZD%2BqsIOXmEUA=
https://www.mouser.de/ProductDetail/Chemi-Con/ESMH800VNN123MA63U?qs=sGAEpiMZZMvwFf0viD3Y3a3yb5D6sPUgk7/d8JbnaS1qtDFzPVNFmA==

For all other caps I used Panasonic FC and FM, as well as Wima MKS2, depending on what I had on hand or could order, with 2 exceptions.

There are several 4.7µF electrolytic coupling caps in the signal path. I ordered 2 different choices for these.
Some Wima MKS2, and taking the chance that I would be able to find room and make them fit, some Panasonic ECW film. If I have to have a cap in the signal path then I prefer these but they are large. And while these caps are not "audio" caps these particular ones have tinned solid copper leads, unlike others that have steel leads.
https://www.mouser.de/ProductDetail/Panasonic/ECW-F2475JA?qs=GoZnPdyRfjbTFkwsw7ZE%2Bg==

The 2nd exception was a ceramic cap, C702, a 1000pF that I would need to reposition to make some room. I replaced it with a TDK FA series C0G (NPO) ceramic.
https://www.mouser.de/ProductDetail/TDK/FA28C0G1H102JNU00?qs=zFwFjAF3uahjVpvv1P8ZLw==

Cheers,
James

edit 20 Jan 2024: I had stated above that I used Panasonic ECQ caps. That was incorrect. In fact ECW series were used.
 
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I have a large selection of Vishay Dale metal film resistors on hand and replaced several carbon film resistors, I'll explain that along the way.

2 other items.
If I am in there then replacing the relay is also on the list. For this I used a Finder 24v relay, part number 40.52.9.024.0000. As I bought these a long time ago from Conrad I do not have a link. I have used them in a number of amps with good results. Note that even though this is a single channel amp the original relay is a dual pole item. This makes good sense as the signal path is doubled and the load per contact is halved. The Finder part is DPDT but you just jave to snip off the pair of leads toward the center of the part and it is a drop in fit.

Speaker binding posts. The ones that I used are sold under several names, in this case Dynavox, and they are ones that I bought to use for my MX-1 and found that they were too long. So they were sitting for a few years just waiting for this project.

Also, I have actually finished repairing and servicing all 4 of these amps and they have now been in daily use for about a week and a half. So this thread is actually history.

Here is everything ready to go.

IMG_20231119_172234_001a.jpg

edit 12 Jan 2024: A note concerning replacement relays, please see post # 54.
 
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A few other general comments before we get to the actual work.

I had 2 concerns when buying these amps. One was that sound quality might actually take a drop compared to my MX-1 power amp. It is actually kinda dumb to replace it because it is a very good amp, but I just want to see what the channel separation brings to the table. My end goal is still the Denon POA-6600's, but these will work to clean up my rack so that I don't have the MX-1 perched on top of it, and bridge the time that it takes to get the Denon's working.

The second concern is that in theory I should not be using bridged pairs of these with my 4 ohm Speakerlab 7s. So I was taking a risk. But the amps have current protection, so I took that risk.

I will relate what happened later.

Also, after reading the above mentioned threads I was expecting to see a bunch of badly degraded caps. I measured each and every cap as I removed it and in all 4 amps the only caps that were degraded were the 2 470µF/35v C805, C806, filter caps for the 15v voltage regulators. They all read below 400µF, one was down to around 380µF. In retrospect I would probably replace them with an FC 560µF or 680µF part.
The main PSU filter caps were all different, but that will be better explained later. The worst, and oldest, were down to 9000µF, not that bad really considering their age.

As best as I know these amps were produced from 1993 to 1999, then they were replaced with the MA6100. Going by the date codes on the caps my amps were made in 1995 (1), 1997 (2), and late 1999 (1). And there were differences between them, as well as differences from the schematics. I will explain that as I go into the amps.

Cheers,
James

edit: after reviewing my notes I saw that C705 and C707, 100µF/16v were also badly degraded in the oldest amp and measured 66.5µF and 62.5µF.
 
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One more post for today and then I think that it will be time to go out front and listen to some music.

Amusingly, by cosmic chance, I managed to actually go through the amps in chronological order, '95, '97 and '99.

I started with grabbing one of them that had a damaged speaker post.

IMG_20231119_172220_715a.jpg
 
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OK, one more post.

Removing the combined heat sink and circuit board is fairly easy. Top cover off, remove all of the screws on the rear panel, snip the cable ties on the wires running along the top of the assy, remove the 2 plugs on the forward end of the board.

Then you just need a long screwdriver to remove the 2 screws holding the heat sink to the base and the assembly can be lifted out of the case.

When I did that on the first amp I got a shock. Not only was the speaker post damaged, the entire block was damaged, and apparently someone had either dropped, or kicked, or dropkicked the amp. Because the board had a vertical crack through about 1/2 of it, starting at the bottom. Many traces had been broken and sloppily jumpered. So There was more work ahead of me than hoped for.

Surprise surprise.

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i've been running 5 in the surround system for about 5 years.

good reliable amps. easy to work on. i recapped mine as well.

i've never put them in protect and i beat on them pretty good.

years back i used 1 for a sub that had a blown plate amp. i beat on that thing hard @4 ohms for 10 years, never had a problem. those caps were in bad shape when i recapped it.

only complaint is that they run hot. i generally don't use them much in the summer even tho the ac is running and it's cool in the basement. 5 of them are like space heaters.
 
painttoad said:
i've been running 5 in the surround system for about 5 years.

good reliable amps. easy to work on. i recapped mine as well.

i've never put them in protect and i beat on them pretty good.

years back i used 1 for a sub that had a blown plate amp. i beat on that thing hard @4 ohms for 10 years, never had a problem. those caps were in bad shape when i recapped it.

only complaint is that they run hot. i generally don't use them much in the summer even tho the ac is running and it's cool in the basement. 5 of them are like space heaters.
Click to expand...
I will be working on some active cooling for the stand soon. All the parts are on hand, just need to do the work.

Good to know what your experience with them is. Spoiler alert! (I like them a lot)
 
LOL, one more post as the system warms up.

Some more shots of the damage. And if you look close it is a wonder that the sloppy solder splash didn't cause a short.

DSC01861.JPGDSC01863.JPG
 
It seems like somewhere I read that to lower the chance of inductive crosstalk repair jumpers should be run exactly along the traces to be repaired. Perhaps I am wrong but that is what I tried to do.

IMG_20231118_161053_999a.jpgIMG_20231118_161108_362a.jpg

While less than perfect the results were at least better than what I started with and had the extra bonus of working.
I used tinned 0.8mm solid core wire.
Also, the relay was installed poorly, with the coil leads bent underneath the body and pressing down on the board. That was corrected with the new relay.
 
Going forward I think that I will deal with things so:

1) General recapping, resistors, and other small stuff,
2) The main PSU filter caps, a major issue,
3) The speaker binding posts,
4) The results,
5) Thoughts for the future.

Might take a few days.

Cheers,
James
 
All caps 4.7µF and smaller were replaced with film caps. For most positions Wima MKS2 in 63v. There is a recommendation in the diyaudio thread to use a 100v cap for CN05, 2.2µF/50v. That value is backordered at Mouser until sometime next year. So I used 63v and ordered 100v. When they get here I will decide if I want to change that cap again.

All 10µF, 16v and 50v, caps were replaced with Panasonic FC 50v.
All other 16v caps were replaced with FC 35v in most positions, a few with FM/35v where that is what had in my parts bins.
The 33µF/100v (C706, 710) were replaced with FC in 100v.

Most manufacturers of electrolytic caps have been cheating and producing caps in the lower end of the +/-20% tolerance. Nichicon is terrible in that regard and that is why I have mostly stopped using them, they are usually at -10% of the rated value right out of the bag. Panasonic seems to be in general better in this regard and delivers caps that are mostly near nominal.
I test all new caps that I buy and sort them. Anything that is too low gets tossed. I buy in large enough quantities that doing that doesn't hurt that bad.

DSC01905.JPGDSC01906.JPGDSC01907.JPGDSC01908.JPG
 
Lets talk about caps and resistors in the signal path.

I thought about this before ordering parts, but I didn't think it completely through.

Basicly, any of these amps that is being used stand-alone, or is the second amp in a bridged pair, is not using the signal inverting section and has one cap and 5 resistors in the signal path. And 4 of those resistors (R710, 711, 720, 721) appear to be metal film, at least they have a blue/green body and those are usually metal film.
So C701 and R701 are of interest. 4.7µF and 560 ohms respectively.

Since I didn't have the amps before I ordered parts I hedged my bet and ordered both Wima MKS2 and Panasonic ECW in 4.7µF. And because of their cost I only ordered 12 of the ECW. That is too many or too few, depending on how one looks at things.

Because there are 3 caps in the signal path in the signal inverting section. CS01, CS02, and CS03. If the amp is the first one in a bridged pair then these caps are important. There are also 5 resistors in that path, RS02, RS04, RS14, RS06 and RS07. More on them below.

The schematic shows CS01 as 0.1µF and CS02 & CS03 as 4.7µF. In the '95 amp that is what was installed. In the other 3 there was a 3rd 4.7µF in the CS01 position. Here is where I made my thinking mistake when ordering, I didn't have any reserve if I wanted to replace all 4 of the above caps with ECQ in all 4 amps. But later the coin dropped and I realized that I only needed to fully use the ECW in 2 amps. Yeah!

The schematic shows RS04 as 10k ohms. in the '95 and '97 amps there was a 3.3k resistor in that position, the ’99 amp had a 10k part.
The schematic shows RS14 as 5.6k ohms. All 4 amps had a 2.2k part installed in that position.

In all 4 amps I replaced all of these resistors with Vishay-Dale SFR series 400mw metal film, using the values of the part on the board rather than the schematic. If I had it to do again I would use a 10k part in the RS04 position. Note that I did not replace R710 to 721. These are noted as fusible 1/4w. (edit 20 Jan 2024: No, the parts list does not show R710, 711, 720 and 721 as fusible, only a safety flag and noted as 1/4W)

Cheers,
James

edit 20 Jan 2024: I had previously stated above that I used Panasonic ECQ caps. That was incorrect. In fact ECW series were used.
edit 17 Feb 2024: See post #115 for a complete list of discovered discrepancies concerning the schematic and what was installed in 5 different amps spanning 1993 to 1999.
 
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There was sufficient room to install the ECW film caps as long as I was creative when bending the leads. The risk in mounting the caps high up on long leads is that theoretically the leads can act as antennas and pick up noise. Balanced against that is the cleaner sound when using a poly cap in the signal path. I took the risk and used them.

C701 was a bit of a challenge. There is a ceramic cap, C702 (1000pF) that would have to be bent over in order to mount C701 as low as possible. I went ahead and replaced it with a TDK C0G (NPO) 50v type cap. If I continue to work on these amps I will replace all of the ceramic caps in the amps with this type.

The ECW caps are rated at 250v and 105°C.

DSC01910.JPGDSC01911.JPG

Cheers,
James

edit 20 Jan 2024: I had previously stated above that I used Panasonic ECQ caps. That was incorrect. In fact ECW series were used.
 
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I realize now that I did not take and photos of CS01 with an ECW installed. It went in right next to the main input/output jacks.

Here are the other 2.

DSC01912.JPGDSC01913.JPG


edit 20 Jan 2024: I had previously stated above that I used Panasonic ECQ caps. That was incorrect. In fact ECW series were used.
 
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