Marantz MA500, only 50Hz output?

[sreten]

Hi,

An 8 ohm driver nearly always has dc resistance ~ 5.6R.

If the bass driver the speaker should be 8 ohms nominal.
(Unless the designer is a muppet ....)

The fact that 8 ohms impedance is not 8 ohms resistance is sort
of ignored to an extent for amplifier ratings. However it would
not make sense to build an amplifier that offered bridging but
it could not drive 8 ohm speakers, too many would blow up.

In fact it might not blow up bridged into 4 ohms with conservative
protection, it just would not produce a lot more power. Without
the protection details it is handwaving to a degree, but for most
japanese stuff you woud expect it to survive in some manner.

/sreten.

 

[RobertinMn]

Heh--

I like your response. So, it would be wise for me to limit what the speakers can draw, somehow.

Any recommendations?

BTW, most of what I use is American made:

An externally hosted image should be here but it was not working when we last tested it.

 

[hildebrau]

Cap list

Chris,

I have repaired a number of the Marantz MA500 mono block amplifiers. I have it to a point where I just go in and replace a number of capacitors and this keeps from having to open the amplifier up every 6 months to replace a capacitor in the protection circuit or in the signal path. The Marantz has a crappy circuit board made overseas so extreme care must be taken when working on it. When made the leads are bent over and hard to get out without damaging the foil on the PC board. If you are not capable of doing this I would suggest taking it to a repair facility and having them do it.

Replace C705,C701, C710, CN02, CN03, CN05 and that should take care of your problem. These caps effect gain and or the protection circuit. These are problems the MA500 is famous for.

Replacing these caps has taken care of the problems I have seen with respect to gain and to triggering the protection. Your looking at less than $10 worth of parts here and if you are capable of replacing them you will save yourself several trips to the repair shop in the future. The CN05 part is a 2mfd/50 volt cap. Replace this with a 2/100volt cap.

There is one that I forgot and that is CN01 and that is 22/16v.
Replace that one also.

I have 5 of these MA500's that I need to fix up. I'm terrible at soldering; but I've bought a new soldering iron and really don't have much to lose at this point. I pieced together the schematic drawings. Now I just need to know which caps to order. Can someone put together a suggest list of SKUs from mouser.com? I don't have much confidence in myself to order the most appropriate thing.

Thank you!