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Jumped in BIG....found a Marantz 2500.

This isn't a transistor problem...this is almost certainly a problem with corroded ground connections.
 
I've been following along as you complete this project- nice work. But did you say (or did I miss it)- what speakers you are going to drive with this monster? My "main" unit is a 2325, and it is complete overkill for my Klipsch Forte II's. Just wondering if you had speaks that NEEDED this kind of power, or if its a case of 'you can never have too much' LOL. Anyway, very nice unit! :thmbsp:
 
EW.....if the hum originates from the pre-amp and is a corroded ground connection...where could this be? AFAIK, there is only one ground connection to that board....and it looks clean...............would you maybe have a suggestion where to look? Thanks.

sssmokin99......at the moment(test fase), I am using Bose 201's....eventually I will hook up JBL L50 and/or Bose 901............I also have modern Def Tech 900's that I will try with the amp.
 
It has been years since I had one apart. All I could suggest is to measure the AC and DC voltages from a ground foil trace on the preamp boards back to the power supply ground. Anything other than zero is an issue.
 
That is one very nice looking Marantz.
I have a 2218 & 2245 - I think I should add the 2500 now on my "watch" list.
 
Separates may be better but receivers are my favorites. But for surround, I went separates.
 
EW......I took out the pre-amp/filter boards......changed the sk30a's....cleaned all the connectors again.....put the board back in.....still that very slight hum......I also tested voltages a couple of 'ground' places...all were '0'................ Could it be near the pre-out/main in connectors? There is a small cap there connected to ground.......could it be this cap?
Anyway...I may have to live with it......when I play music, I don't hear the hum at all.

I have been playing around with the unit all day...this may be a more precise description of the problem.....when the pre-amp and amp are connected, there is a slight buzzing AND low humming. When I disconnect the amp from the pre-amp......the buzzing disappears, but the slight hum is still there(although lower).......seems like am I so close to solving this....I just don't know where it can be..............

What do big leaky caps sound like? My big caps look fine on the outside/underside.............

Are there any 2500 owners out there that can turn on thier units to see if they have any kid of hum? Thanks...........
 
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Ok forum'ers......been working with unit again...........please see above post too.

Today I found out , that, when I insert the IC into the R main-in FIRST, the buzz almost disappears. Would this indicate a problem with the R channel's grounding in the pre-amp section?

I also assembled the whole unit to see if the top/bottom covers had a 'shielding' effect.......the buzz was still there........................

Any info or advice is good....thanks.
 
Now a little more info.......I feel a bit dumb after this one......see, I had the speakers stacked on top of each other near my workbench....this made identifying the 'buzzing/humming speaker difficult(duh).......

Anyway......I figured out that the most buzzing/humming comes from the R channel. When I insert IC's into the main-in jacks.......buzzing disappears from both speakers, but the slightly lower humming remains ONLY on the R channel.......the L channel seems nice and silent.........now we are getting somewhere......OR............
 
anderslober said:
When I disconnect the amp from the pre-amp......the buzzing disappears, but the slight hum is still there(although lower).......
Click to expand...

This indicates to me that you have two separate issues. The "lower" hum you're hearing with the preamp disconnected is most likely a small amount of ripple being introduced into the main power supply by your big filters. Not much you can do about this without major surgery, so I'd ignore it for the time being.

The buzz you're hearing with the preamp connected is a grounding/shielding issue. Just for the hell of it, you might try reversing the power plug - this trick works more often to mitigate buzz/hum in tube equipment, but I've seen it make a difference in SS gear as well.

You mention that the buzz "almost disappears" when you connect the right preamp first. This points to a problem in the LEFT channel preamp circuitry. When you connect both preamp channels, do you get buzz in both channels, or just in the left?
 
skibjr.......I dis-connect the amp from the pre-amp , when I insert the IC into the main=in ONLY.

When there is no IC in either main-in......buzzing/humming is mainly in the R channel. When I insert the IC in main-in(L/R) ONLY(disconnecting the amp and pre-amp).....I get only a slight, very low humming from the R channel. Buzzing is gone from both channels..............
 
Okay, I get it now. I thought you were connecting/disconnecting the amps internally, using the connectors on the driver boards. So, when you connect an "IC" for a given channel, you're effectively breaking the connection to that channel.

So, you appear to have a weak filter can on the right side, and possibly a grounding/shielding issue in the right preamp channel, or in the connection between the preamp and the amp. If you connect right pre-out to left main-in and vice-versa, does your buzz move to the left side? If so, it confirms that the buzz is originating in the preamp circuitry and not in the wiring from the preamp through the rear jacks to the amp.

You did completely recap your PS board (P800), right?
 
skibjr......sounds good. I will fiddle with it a bit more.......

Yes...the unit is totally recapped(Panasonic FC/FM).....except the big dual caps. See post #45. The resistor I changed was completely corroded through....this could have a knock-on effect of other components........I am thinking zeners/diodes down the line.

I read in a thread somewhere, that a zener on the PS could cause the buzzing....as a precaution all the 14v zeners get changed today. I will also check the solder points.....

The slight, remaining hum will have to wait....as I think(like you), it is caused by a leaking big cap. Later on, I will try to build a couple of dual caps.....there is an excellent thread somewhere in the forum about this.....'DIY dual caps'...........

I think we may be getting close...............

EDIT: I just tried swapping/crossing around the main-in/pre-out IC's.....R to L and L to R........the buzz/hum remained on the same speaker(R). This would indicate an amp buzz....would it not?

When I put one IC from the L main in to either L/R pre-out.........no buzzing.
When I put one IC from the R main in to either L/R pre-out........buzzing in the same speaker.

Clear as mud.....;-)?
 
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This is a funny problem.......when the IC's are in the main-in jacks ONLY.....(amp and pre-am separated)...there is no buzzing. Just a very slight hum.

When I connect up the IC's to the pre-outs......buzzing starts again, mainly in the right speaker....crossing the IC's still causes buzz in the same speaker.....go figure.

'conundrummed'!
 
Well, it seems obvious that the issue is in the right channel, after the main-in jack - either in the amp itself, or the wiring to it. Carefully inspect the shielded connector from the main-in jack to the plastic input plug on the amp itself. Make sure that shield is zero Ohms to ground, and jumper it if you're not sure. If the connector is solid, then perhaps the right channel amp has a problem when connected to an input load. Not too many possibilities left...
 
skibjr...EW.....another odd thing......when the loudness is engaged..and the volume increased..the R channel starts bottoming out(at least thats what it sounds like) the speaker....to verify this , I switched speaker...and sure enough...the 'flapping' sound followed to the other speaker.........the left channel could easily take the 'loudness'. It didn't 'flap' at all......so, there is a problem with the R channel...voltages(dc-offset, idle current) are all spec.........I will take the 'pig' out and inspect everything...................bummer...I thought this was going to be easy!!;-))) thanks to Mr. marantz!

Edit: Just for sake of being sure.....I checked my voltages again.........L channel was fine at 25mV idle current........on the other hand, the R channel could not go below 70mV........and, I could easily hear the humming go up and down with the adjustment.......

I think I will have to look closer at the the R channel.......................skibjr, would you know which tr's drive the bias? Please confirm....thanks.
 
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Hey Forum'ers.......a wee spot of GOOD news!!!!!!!! Before taking the 'pig' out once again, I wiggled all the connectors to the amps..........LOW and FRIGGIN behold....R channel J701 connector was loose!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! The BUZZ is gone!

There is still a very low hum.......which you only can hear if you are standing less than 1m away from the speakers........I will put his down to the main caps rippling.

Otherwise, now there is GLORIOUS stereophonic sound WITH ultra-cool S-C-O-P-E!

Regarding the idle current on the R channel......after I let the amp warm up for 15-20 min.....somehow it was again possible to set the the idle current to 0.025v(25mV),,,,so now both channels are set within spec again......boy'o'boy...I feel kinda lucky!
 
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