Marantz MA500 thread

[Designguy]

Been a busy week but got around to testing these caps. My multimeter had a blown fuse and trying to find local proved too hard. Had to go to the amazon to find them. First round they sent the wrong ones but got the right ones today. I decided to order a cheap esr tester as well to play with as well... The 10k main caps tested at 8700 each and an esr of around .1 Im still learning about the esr stuff but that seems to be ok? The caps have lost some uf but were not that bad. The caps at c805 and c806 measured a higher esr at .24 and only 370uf (supposed to be 470uf) but again not sure if that is causing my issues of the sound cutting out. Was having a bit of trouble getting readings from the other smaller caps with these clip on style connectors.

 

[Bratwurst7s]

Been a busy week but got around to testing these caps. My multimeter had a blown fuse and trying to find local proved too hard. Had to go to the amazon to find them. First round they sent the wrong ones but got the right ones today. I decided to order a cheap esr tester as well to play with as well... The 10k main caps tested at 8700 each and an esr of around .1 Im still learning about the esr stuff but that seems to be ok? The caps have lost some uf but were not that bad. The caps at c805 and c806 measured a higher esr at .24 and only 370uf (supposed to be 470uf) but again not sure if that is causing my issues of the sound cutting out. Was having a bit of trouble getting readings from the other smaller caps with these clip on style connectors.

View attachment 3415918

I am not an expert on this but generally lower ESR is better concerning caps that are doing supply voltage filtering. The V-loss is showing leakage. Generally it seems that the smaller electrolytic caps are the higher their ESR and leakage will be even when new.

Those 470µF caps are shot, and 4% vloss is very high for a cap that size. At 8700µF the big caps are on their way out too and I would 100% replace them.

I am making the guess that your amp is shutting down under load because something is drawing too much current and the protection circuit is opening the relay until the load drops below acceptable limits.

,
James

 

[Bratwurst7s]

Oh, it is hard to get a reliable reading in circuit, you need to remove the caps to get a good test.

 

[Bratwurst7s]

C805/806 are providing local supply voltage filtering at the plus/minus 23v voltage regulators I think. Fairly important caps. In the end I replaced them with Panasonic FC 680µF/50v parts.

Post #133, second notes page. That shows what the caps in one of my amps tested at and is pretty representative of all of them. Capacitance/ESR/V-loss%. You can use it to compare with what you are seeing.

 

[dankik]

When you are measuring a capacitor's ESR a "good" value is dependent on not only the capacitance, but also the voltage rating.
Here is a typical chart (there are many online and they all vary a bit).
The larger the capacitance and voltage rating, the lower the expected ESR, the smaller the capacitance and voltage, the higher the ESR.
So, for example, if you are testing a 10,000uF/63V, the ESR should read about 0.01 Ohms. You are reading 0.11 Ohms.
It also needs to be tested out of circuit to get accurate readings.
One more thing, each ESR tester has a minimum and maximum capacitance that it can measure. You need to check to see what yours is.

Be sure to discharge the capacitor before testing, else you can damage your tester.


Hope this helps.

 

[Bratwurst7s]

When you are measuring a capacitor's ESR a "good" value is dependent on not only the capacitance, but also the voltage rating.
Here is a typical chart (there are many online and they all vary a bit).
The larger the capacitance and voltage rating, the lower the expected ESR, the smaller the capacitance and voltage, the higher the ESR.
So, for example, if you are testing a 10,000uF/63V, the ESR should read about 0.01 Ohms. You are reading 0.11 Ohms.
It also needs to be tested out of circuit to get accurate readings.
One more thing, each ESR tester has a minimum and maximum capacitance that it can measure. You need to check to see what yours is.
View attachment 3416726
Be sure to discharge the capacitor before testing, else you can damage your tester.

View attachment 3416710
Hope this helps.

All of this is part of why I almost always go up 1 or more steps in rated voltage when I can. Not only will ESR be lower but the ripple current rating will usually be higher, which is also good.

,
James

 

[Designguy]

Sounds good. I got a cart on Mouser Im working on filling. I was still trying to find caps that I didnt have to go through the effort of modification that @Bratwurst7s did for the main caps, but it seems options are really getting limited these days.

@dankik Thanks for the info! I did read that the advantage of reading esr values instead of just capacitance was that you can tell the health of the caps while in circuit, would you agree? The main caps(10k ones) were removed for those readings but the others were still in circuit.

 

[Bratwurst7s]

Sounds good. I got a cart on Mouser Im working on filling. I was still trying to find caps that I didnt have to go through the effort of modification that @Bratwurst7s did for the main caps, but it seems options are really getting limited these days.

@dankik Thanks for the info! I did read that the advantage of reading esr values instead of just capacitance was that you can tell the health of the caps while in circuit, would you agree? The main caps(10k ones) were removed for those readings but the others were still in circuit.

You really need to remove the caps to get good test results.
There are not all that many elcos in the amp and they are all equally old. You have it apart. Just replace them all.

,
James

 

[Designguy]

Anybody order from these guys before? Reputable source? Looks like I can get these Elna audio caps for about 8 bucks a piece and wouldnt have to notch the frame since the height is only 50mm, id still have to drill the board since they are 35mm in diameter. Says they are authentic...
The Audio Crafts

 

[Designguy]

Well after further investigation it seems like the payment options are a bit strange for that site

Found these guys too that take paypal...
LCSC.com

 

[dankik]

Are you located in the U.S.? Just order from Digikey or Mouser for genuine parts. I think they also service the EU also.
LCSC.com are located in China. I would be cautious about ordering from them.

 

[Designguy]

I am in the US, but Mouser and Digikey are super limited on options. Especially for the main caps. Cant seem to find a lot of audio grade caps from them. Bratwurst even had to up the Capacitance to 12000uf(80v) and in non audio grade Caps from Chemi-con to get something that was in stock(and required some significant modification to the amp cage to get them to clearance.) I discovered the same when I tried to order.

​

 

[Bratwurst7s]

Mouser is my first choice almost always. They are one of the most trusted sources that there are. I have ordered transistors from LCSC, KTA/KTC types. Never ordered caps from them.

I was not able to find 10,000µF caps in 30mm, only 35mm. Most caps these days are sold under-rated. So that 10,000µF cap that you buy may arrive at only 9,500µF. The 12,000µF that I bought tested at around 11,000µF. I upped the rating to 12,000µF because of this and to add a bit of future proofing. These amps run hot and your new caps will eventually degrade.

That brings up another point. Buy caps that are rated at 105° where you can. Unfortunately I was only able to find 85° for the big filter caps but for all of the others used 105°.

The frame mod takes about an hour of time.

,
James

 

[zinda]

Although I don't own these amps I really enjoyed reading through this thread. It's rare to see complete post from start to finish and then answering others questions. I've read so many long posts that ended up becoming abandoned at about the 25th page and never knowing if things ever worked or how they sounded.

Like most people I saw a few of these posted for sale locally and decided to check out if they are worth the cost and possibly time to get them back to good output levels. I've never been much of a diehard Marantz person or have much allegiance for any one company. I'll try anything before I judge it. My issue now is I'm clearly hooked on running electrostatic speakers and of course that has many challenges for amps.

The low impedance is hard on them but what's worse is I won't run an amp if it has fans which limits my choices to very few. I admired you're offsetting of leads since I've done that a few times myself and itwh's mostly been to use a lager size but needed to keep them centered which is very easy if the caps have long leads allowing them to be bent in any way you want.

I always get nervous when I solder a longer lead onto the short piece since it could end up coming loose while soldering and this leads me to a few questions of advice. What do you do when the board has traces on both sides and you are have to heat the top and bottom trace, typically this will require more heat to get the solder to flow and could destroy the connection you added.

The other is related in while trying to remove a large cap with traces on both sides and the use of new solder that seeams to be impervious to heat to a point that it just doesn't seem to let go on the other side no matter how long it's heated. I pulled acap off a board that had the leads bent sharply and heated it to where I could straighten them but as you know they still may offer a challenge to remove them.

While extracting them I always seem to end up with the hidden hole staying attached to the lead and even had a trace lift off the board a bit from so much heat. The same can be true on the visible side when too much heat is required and the trace just kinda disappears.

I've fixed some with bare solid core copper wire running way passed the lift off section and drilled out the holes so I could run the wire through to the other side and connect them through hole but I never considered the o-ring spacer but that gave me an idea that would help to ensure the cap case could never end up touching the extended top fix when it ends up extended past the caps can.

Not sure if that makes sense but there could be a notch cut in the o-ring to keep the clearance off the bare wire. It's just an idea that came to me when I saw the o-ring used because until I saw the picture I I visioned the o-rings to be smaller and one around each post of the lead and not on the outer rim of the cap! Basically as a spacer to keep the heat off the added solder joint not really to add support I can see now how the outer ring can do both and also add room for a corrected or fixed trace.

The problem with boards now is you never know if there's a trace thats hidden unless you're very familiar with the board or the maker. What's worse is trying to repair a bad trace when you don't know which one it is since it could be in between layers as many computer bistds are. I used to do repairs on computer video cards using a double magnifying glass using 2 old projector tv 10x lenses to fix those tiny surface mount components. The boards would get so hot during use the tiny chips would fall off the board or worse the chips would be scraped off the boards while laying around unused and take the trace mounting pad with it.

Those boards had multiple layers sandwiched together so pulling off a pad meant that there could be a lost connection to other layers as well

Now that I'm old and fixing things that make a needle tip soldering iron look like a telephone pole once it enters your view through a double 10x magnifying set up, is something my eyes can't do, I seem to find new ways to frustrate myself! I also enjoyed your sheet metal skills since I myself was a sheet metal mechanic who did tons of specialty parts and made my own tools to make tools to do things that were not possible and something as simple as bending a small piece of copper will have challenges itself when keeping the metal perfectly flat is important.

In that case I would have cut another piece that was flat and applied grease to both sides and then mounted that piece onto the bent piece with possibly a few pop rivets in the corners to ensure max heat transfer. One more thing, since I have worked with copper many times and understand it's heat convection , I would expect that the heatsink would actually become hotter than the standard piece since you have more transfer occuring unless the copper is not actually transferring properly.

When I welded copper I learned that you never place you hands on it at any point while welding because the heat at the weld pool will be about the same temp at any place on that sheet once it starts melting . You may start with your hands very nicely positioned for easy control with your face close to the metal but 1 inch into the weld, you find out that you're going to be as far from it as possible while your gloves are smoking from the intense heat given off . The transfer is unbelievable compared to anything else.

I used to make heatsinks for welding stainless steel hoods, the heatsinks had to cover the welding areas to keep the metal from turning blue and red from heat. That discoloration is impossible to remove when it's in a corner seam even when using acid cleaner. So id bend up strips of aluminum to fit over the welded areas and then id attach copper strips on top of the aluminum to act as heat spreaders .

We had a small punch like machine called a rivetless riveter than would join them together by drawing them through a die (like a punch that had too big of a relief in the bottom die which would not actually punch through). There were times where I had to leave a path for a purged weld . That required leaving a bit of offest to the copper strips so gas could flow behind the weld to keep out contamination.

If your amp is getting hot I'd rethink the way the heat is transfered at that brace and maybe use the original with a copper piece added to it. The coopper spreads the heat but it doesn't shed it well, t retains it, while the aluminum will disapate it and move it away from the source. My heat sinks also helped to keep the metal from warping but that's not the point I was making

 

[zinda]

I forgot to mention that that you said the denon amps were much better than the marantz, I have already looked into the demon and discounted them for my own use based on their lack of 2 or 1 ohm abilities. I have been using dual mono (stereo 2 channel) amps for quite some time so speration has never been an issue but I can tell instantly when a recording is not perfectly equal on both sides and I require a dual volume or a balance setting to be done at the start of anything I play to recenter the perfect image.

I can almost see the image shift from one album to another. Sometimes its huge and mostly it's very slight but with electrostatic speakers that shift destroys the overall enjoyment of what they can deliver. It's magical when you're in the sweet spot and there's nothing like it no matter what naysayers tell everyone. I listen alone 90% of the time so what do I care about off axis sound? It so happens that I have excellent off axis but I'll never get any use from it.. I'm a firm believer in bigger is better when it comes to audio. Thanks for a great rebuild post!

 

[pclissold]

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.

View attachment 3061772View attachment 3061773

I found this thread to be quite helpful during my repair and restoration of one of these amps. Thanks for taking the time to be so thorough. I have decided to keep the main filter capacitors for now as they measure within spec and show no outward signs of failure. Thanks, again.

 

[Bratwurst7s]

I should have updated this thread a long time ago, but today will have to do.

This last spring I rebuilt the amp with the cracked main PCB using the scavenged board that I bought in 2024.

Since the donor amp was sold as defective and I had no desire to try to test it I simply completely depopulated the board and then moved all of the parts from my working amp over one at a time. It's kind of like building a kit, I just had to be careful and make sure everything went where it was supposed to.

It powered right up and after warming up the idle current was even spot on.



Concerning using copper vs aluminum for the driver chip heat sink. Copper has a thermal conductivity of 231 BTU/hr, aluminum 136 BTU/hr. Obviously different alloys will behave a bit differently. Copper pulls the heat from the hot chip and spreads it over the entire surface much faster than aluminum.

Since aluminum has 1/3 the density of copper, an equal mass of aluminum can have 40~50% more surface area and offer better heat dissipation with heat sinks of equal mass.
Aluminum is both cheaper and lighter than copper, and that drives the economics of production.

Neither is a factor here. And by my rough calculation my new copper heat sink has about 20% more surface area than the original. I will stick with the copper one.


James

Copper vs. Aluminum Heatsinks: What You Need to Know
Aluminum vs Copper Heat Sink | The Definitive Practical Guide
Aluminum vs Copper Heatsinks: Key Differences | Heatscape
https://www.heatell.com/copper-vs-aluminium-heat-sinks/

Copper vs Aluminum Heatsink: Performance & Cost Guide

Compare copper vs aluminum heatsink. Discover thermal conductivity, weight, and cost differences to choose the right material.

walmatethermal.com