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Marantz Integrated Amp PM-68 Crackling Left Only (Both Channels)

A

ariwo

New Member
My 18 year old Marantz PM-68 recently started giving off a crackling distorting noise. By swapping and disconnecting speakers I isolated it to the Left side on both Channels (i.e. Systems 1 and 2). If I turn the balance all the way to the right or/and disconnect the left speakers then the crackling stops.

I am taking it into a shop ($80 diagnostics) but also wanted to see if the forum has any thoughts or if this is a known issue. Thanks.

Setup:
CD: Marantz CC38
Tuner: Marantz ST 6000
Integ. Amp: Marantz PM68
Speakers:
Monitor Audio PMC 702 Gold Reference x2
Monitor Audio Bronze BX2 x2
 
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I had the PM-64 and the PM-35 models, both had broken/cold solder joints due mainly to heat. (1)
Plus the relay contacts in both units were consumed/tarnished. (2) But you can first clean switches and pots with a contact cleaner like DeoxIt. (3)
 
Karl vd Berg said:
I had the PM-64 and the PM-35 models, both had broken/cold solder joints due mainly to heat. (1)
Plus the relay contacts in both units were consumed/tarnished. (2) But you can first clean switches and pots with a contact cleaner like DeoxIt. (3)
Click to expand...
Thank you. Will try Deoxit first.
 
In my experience, crackling in one channel is usually do to an intermittent driver or pre driver transistor in that channel. In my adventures, I have not seen or found an output device that would do this. It's usually downstream of the output transistors.

You might be able to listen to it sometimes without any pops or crackles, but it will eventually fail and throw your device into protection.
 
cademan said:
In my experience, crackling in one channel is usually do to an intermittent driver or pre driver transistor in that channel. In my adventures, I have not seen or found an output device that would do this. It's usually downstream of the output transistors.

You might be able to listen to it sometimes without any pops or crackles, but it will eventually fail and throw your device into protection.
Click to expand...

Then why does the balance control silence it?
 
OP: One additional piece of information that may be helpful: this amp has a Source Direct button which disables the tone control circuits, tape select, record selector and bypasses balance and sends the input signal to volume control (this for better signal quality).

When I activate Source Direct the crackling takes over the signal (as expected, balance then has no effect). Deactivating Source Direct again allows me to silence the crackling by turning balance all the way to the right.
 
Ok... so it's more epic distortion... you'd have to check transistors in power amp section - differential to outputs
 
I reckon you need to find the schematic and post a screenshot of the relevant pre-section here for others to comment on
 
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