noisy marantz 1050

Depaj

Member
2015-08-05 5:31 pm
lyon
Hi!

Just finished recapping and cleaning (pots included) a marantz 1050 but I have some crackling on both channels, independent of any tone controls. I've been poking around with an oscilloscope and I can pick up this noise everywhere I touch, first I thought a noisy transistor in the power supply ( There are 2 2sc2390, 1 2sa1627 and 1 2sa817).
But then I decided to unplug some of the devices in the room and it came from a internet connection on the same power line as the one the amp was using.
This has always been there and I never had any problems with other amps. Is there anything obvious that could cause this particular amp to translate this into noise ?
 
Most of this behavior comes from

1) noisy transistors (most common )
2) Ground issues ( these machines are made with all around ground topology rather than a star ground and loose contacts can do this and many more )
3) AC mains switch ( monitor between contacts to see if there is voltage drop at the time the problem is presented ) rare but very possible ....

Kind regards
Sakis ...

@Welcome .... I cannot agree with that ..I understand that there is far more high pitch noises in mains today and in the area we have amplifiers but i expect that this can should could would be traced and fixed ....
usually YES one of our devices might produce more noise than expected but the amplifier should reject that ...

Imagine the most common mistake that people do ....Mains noise in one amplifier they try to solve it by removing the ground adding filters and so on and on ..Reality is that either the amplifier /circuit is at fault or a bad designed ground scheme ...Its not our Laptop producing Its our amplifier that has the problem and picking up noises ....Think ....
 

Depaj

Member
2015-08-05 5:31 pm
lyon
Hi Sakis,

It's definitely not a noisy transistor as the sole fact of unplugging that internet adapter stops the noise, also I checked all the different grounding wires across the amp and get good contact there. The power cord has a grounding wire that goes to the chassis so nothing to improve there either.

Anyway it works fine when that internet thing is plugged in somewhere else so.
 
DepaJ you get many advice from me most of the time free:D

But please spent some time on my writing .... I have been there one million times before you did we repair more than 1000 audio devices per year we have seen it all ....

---It's definitely not a noisy transistor as the sole fact of unplugging that internet adapter stops the noise,

That doesn't make the adapter faulty but it could be as well faulty Point is that in both cases amplifier should not pick it up

---I checked all the different grounding wires across the amp and get good contact there

All around ground is based and many mechanical parts screw and terminals in a logic that we don't know but probably the Japanese do ...check again

---The power cord has a grounding wire that goes to the chassis so nothing to improve there either This is a safety ground expect one with and one without to behave more or less the same in the specific problem

In general ground issues will pop up with a noise problem not with crackling ...

Check the mains switch isolate pre and main to understand which part of your amp is at fault /sensitive the specific behavior \

Regards
Sakis
 

Depaj

Member
2015-08-05 5:31 pm
lyon
I'm always very happy with advice and was just stating what had been done so far.

I checked all the different ground wires, the screws are tight and I resoldered all the boards because the joints were cracked and dry all over it. I used the diode mode to check the different groundings to the chassis and they all seem ok.

I seperated the preamp and power amp but I pick up the noise on both and even directly on the inputs.

What exatcly do You mean by "check the mains switch" ?
 

Depaj

Member
2015-08-05 5:31 pm
lyon
The Caps are red/orange panasonic suppression caps, still worth replacing ? Removing them doesn't change anything to the noise. How can I send you the video file (you have to turn the sound all the way up to here it on the video) ?

I don't think the transistors are at fault here Esgigt as the noise disappears when I unplug the internet adapter.
 
Last edited:

Depaj

Member
2015-08-05 5:31 pm
lyon
I think I understand what Jerluwoo means, the two caps I was talking about (the red panasonic caps) are on the switch so only to prevent arcing, for the noise problem I need to install one across the mains just before entering the transformer as I did on a previous restoration on a Luxman L31.
 
Οκ
Let me clear out things

There has been a few amplifiers presented random crackling noises that was related to poor contacts on the mains switch

That very often can and will be tricky to trace since the mains is related to psu circuits that have some capacitance as a back up and when AC is at any fault capacitors are already charged ...When caps are empty the AC demands are higher then the switch fails

That on its own makes the crackling noises random or periodic ...

So in case that this is the fault removing the ARK preventing capacitors will make the problem worst and point you out the problem just in case problem lays there

Akai AM series 2450 and other models suffer from this some Teac models 2 Onkyos and ALL Sanyo Plus 55 that we have repaired in the past ...

Kind regards
Sakis
 
Last edited:

Depaj

Member
2015-08-05 5:31 pm
lyon
This is good to know if I encounter this problem later on but on this particular amp the switch doesn't seem to be the problem as removing the ark preventing caps doesn't change anything, also when I don't use the internet adapter the noise disappears instantly. I will order a suppression cap to install across the mains and report back.