Very recently I acquired closed back headphones that revealed a problem with my 11-12 year old amp, a Marantz PM-15S2.
Day one of the new headphones revealed nothing out of the ordinary.
Day two I noticed faint hiss in the right channel.
Day three, the hiss had changed into a continous crackle of which I made a recording and attached the result here. The following days, the crackle has remained unchanged.
I have done some eliminating already, but will leave the results of that for a later post. First I'd like to present you the sound I am hearing.
There was quite some processing needed to present you with something you would be able to hear without straining your ears. So please note that this sound is very faint in reality, but once you know about it, it will be very noticeable during low and silent parts in the music.
Any feedback and insights are welcome!
Day one of the new headphones revealed nothing out of the ordinary.
Day two I noticed faint hiss in the right channel.
Day three, the hiss had changed into a continous crackle of which I made a recording and attached the result here. The following days, the crackle has remained unchanged.
I have done some eliminating already, but will leave the results of that for a later post. First I'd like to present you the sound I am hearing.
There was quite some processing needed to present you with something you would be able to hear without straining your ears. So please note that this sound is very faint in reality, but once you know about it, it will be very noticeable during low and silent parts in the music.
Any feedback and insights are welcome!
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Your recording is good. Right channel indeed clearly has the crackle in it.
Solder joints and output relay would get my first attention.
Tapping the boards gently with the back of a screwdriver could help locate the problem.
Hugo
Solder joints and output relay would get my first attention.
Tapping the boards gently with the back of a screwdriver could help locate the problem.
Hugo
Thanks for your response. Ever since day one I owned this amp I dreaded the moment I would need to go in there and trace some fault. It doesn't look like it's been designed with servicing in mind.
Without having taken the lid off (the photo is from 2012) I have already eliminated some circuits.
The PM-15S2 is an integrated amp but it does have some options that lets you more or less separate pre-amp and power amp sections. It also has an option for bi-amping.
There's only one mode of operation that gets rid of the crackle, and that is power-amp operation. This disables the pre-amp functions taking only the signal from the dedicated 'p.direct in' input. This leads me to believe the power amp sections are fine, including the speaker relay.
In all other modes of operation the crackle is present in the right channel. This is independent from volume setting, balance control, tone control or selected source. The crackle is also present on the preamp output, but not on the rec outputs. That seems to point me in the direction of that long board in the left of the photo packed with components and HDAM modules.
I have a digital copy of the service manual of the PM-15S1, but it looks like the PM-15S2 is only similar at first glance, so I ordered a service manual for the PM-15S2 and am waiting for it to arrive. In the mean time I might begin my search at that input/preamp board.
Without having taken the lid off (the photo is from 2012) I have already eliminated some circuits.
The PM-15S2 is an integrated amp but it does have some options that lets you more or less separate pre-amp and power amp sections. It also has an option for bi-amping.
There's only one mode of operation that gets rid of the crackle, and that is power-amp operation. This disables the pre-amp functions taking only the signal from the dedicated 'p.direct in' input. This leads me to believe the power amp sections are fine, including the speaker relay.
In all other modes of operation the crackle is present in the right channel. This is independent from volume setting, balance control, tone control or selected source. The crackle is also present on the preamp output, but not on the rec outputs. That seems to point me in the direction of that long board in the left of the photo packed with components and HDAM modules.
I have a digital copy of the service manual of the PM-15S1, but it looks like the PM-15S2 is only similar at first glance, so I ordered a service manual for the PM-15S2 and am waiting for it to arrive. In the mean time I might begin my search at that input/preamp board.
Hopefully there's only a buffer stage between REC OUT and the PRE OUT, which narrows it right down. Is there a mute function? That might be right at the end of the preamp...
Doesn't look like I might be that lucky. The REC OUT buffer is fed straight from the inputs while the pre out signal also passes through volume control, I/V conversion and tone controls. The latter can be bypassed, but that doesn't have any effect on the crackling noise.
I was looking some more at the photos I took almost 12 years ago and I noticed something I really don't like to see. Those heavy 4700 uF caps are just hanging there, presumably held in by just the solder.
There is a mute function on the amp albeit not user operated. By that I mean that (e.g.) while changing the input source, the amp will mute for a moment, including PRE OUT. The user can only use the ATT button which lowers the volume quite a bit but doesn't mute it..
This should be no problem as they are snap-ins.
The leads are bent and act as a clamp in the holes.
Hugo
Of course! I should have noticed by the way the leads are pointing that these are snap-ins.
Interestingly, but also annoyingly, the crackle has disappeared... for now. I checked the pre-out with a headphone amp cranked all the way up, but right now it's gone...🤔
Interestingly, but also annoyingly, the crackle has disappeared... for now. I checked the pre-out with a headphone amp cranked all the way up, but right now it's gone...🤔
Still, gently tapping the board could make the crackle return.
As for the solution, it most probably will require quite some disassembling and not easy to track the culprit.
Enjoy while it lasts.
Hugo
As for the solution, it most probably will require quite some disassembling and not easy to track the culprit.
Enjoy while it lasts.
Hugo
Tapping did not result in the problem recurring, so I started to disassemble the amp for inspection.
It's not as hard as it looked at first. On this amp you can take the sides off to gain better access.
I just started a visual inspection, and I already found something you don't want to see.
It's not as hard as it looked at first. On this amp you can take the sides off to gain better access.
I just started a visual inspection, and I already found something you don't want to see.
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Thanks...but this couldn't have been the cause of the crackle. It's on an unused input.
I had a good look over both input pcbs and found no other cracked solder joints. I did reflow the joints close to the inputs and some of the heavier components for peace of mind.
The amp is now reassembled and playing on the "test-bench" using my very firsty CD-player that I bought way back in 1991, a JVC XL-V231. It's still playing fine only ever having needed resoldering of the power switch. I'm not surprised I chose this one back in the day, it still sounds pretty good for a player that in today's money would cost about €470.
I had a good look over both input pcbs and found no other cracked solder joints. I did reflow the joints close to the inputs and some of the heavier components for peace of mind.
The amp is now reassembled and playing on the "test-bench" using my very firsty CD-player that I bought way back in 1991, a JVC XL-V231. It's still playing fine only ever having needed resoldering of the power switch. I'm not surprised I chose this one back in the day, it still sounds pretty good for a player that in today's money would cost about €470.
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After reassembly and testing, the crackle seems gone, for now. I made another recording the same way as the first.
This timeI switched on the DIY headphone amp first and at normal listening volume for a reference (noise of this amp + that of the external soundcard). I cut the power-on-thump from the recording, this thing has no muting or DC-protection whatsoever.
A few seconds later (@ 5 seconds) I switch on the PM-15S2 which can be heard as a short fading hum in the right channel. Then I fully open the volume control of the headphone amp at around 20 seconds.
This does show that the right channel is still somewhat noisier, but keep in mind that the signal has been heavily amplified (and notch fiiltered for 50 Hz and up to and including its 5th harmonic) and in reality is at or below my hearing threshold.
For now I see no reason to try and hunt for something that isn't there right now. Time wil tell...
This timeI switched on the DIY headphone amp first and at normal listening volume for a reference (noise of this amp + that of the external soundcard). I cut the power-on-thump from the recording, this thing has no muting or DC-protection whatsoever.
A few seconds later (@ 5 seconds) I switch on the PM-15S2 which can be heard as a short fading hum in the right channel. Then I fully open the volume control of the headphone amp at around 20 seconds.
This does show that the right channel is still somewhat noisier, but keep in mind that the signal has been heavily amplified (and notch fiiltered for 50 Hz and up to and including its 5th harmonic) and in reality is at or below my hearing threshold.
For now I see no reason to try and hunt for something that isn't there right now. Time wil tell...