at the copper side of the power amp board,
L signal, a jumper J248 was used to connect CN52 to C301,
J248 is adjacent to the +40v and -40v power rail. ( very close )
it might cause the noise trouble.
try
lift up the +leg of C301,
lift up L wire on the CN52,
solder a jumper wire to connect C301 and L wire directly. ( not on the board )
just to narrow down the fault.
L signal, a jumper J248 was used to connect CN52 to C301,
J248 is adjacent to the +40v and -40v power rail. ( very close )
it might cause the noise trouble.
try
lift up the +leg of C301,
lift up L wire on the CN52,
solder a jumper wire to connect C301 and L wire directly. ( not on the board )
just to narrow down the fault.
I just found in some web photos,
glue was used to hold the capacitors in L channel,
if your amp also use glue,
suggest to clean the glue first.
sometimes glue become conductive.
glue was used to hold the capacitors in L channel,
if your amp also use glue,
suggest to clean the glue first.
sometimes glue become conductive.
Not very helpful post, but I bought one with exactly the same problem. The seller accepted the return and I got a Marantz equivalent instead. It is a pity, since I really like my PMA1500AE.
Yes, all inputs are noisy in the left channel, however I connect its always the left channel.
Even if I switch left and right channels in to the power section coming from the volume pot board, the noise stays on the left channel. So the noise cant have anything to do with the input section or the volume section. That's how I see it now.
Putting gnd at the left input of the power section makes it quiet. So perhaps its something close to the inputs of the power section, and when grounded the noise is shunted to the gnd?
The image shows the input of the power section. Could it be something going on here?
Even if I switch left and right channels in to the power section coming from the volume pot board, the noise stays on the left channel. So the noise cant have anything to do with the input section or the volume section. That's how I see it now.
Putting gnd at the left input of the power section makes it quiet. So perhaps its something close to the inputs of the power section, and when grounded the noise is shunted to the gnd?
The image shows the input of the power section. Could it be something going on here?
in page 17 of the schematic, copper side,
beside the two big caps,
the signal track from CN52 to C301
J248 is position in between C301 and C302,
with J248, the signal track is placed beside the +/- 40v rail, ( right next to it )
(I doubt it because I have a Digital speaker which suffering from leakage between signal tracks and power rail.)
the noise could be caused by a leakage of very tiny current between the tracks....
J248 is not seen in the schematic on page 37.
#21 might be of help.
pardon me if I am wrong.
beside the two big caps,
the signal track from CN52 to C301
J248 is position in between C301 and C302,
with J248, the signal track is placed beside the +/- 40v rail, ( right next to it )
(I doubt it because I have a Digital speaker which suffering from leakage between signal tracks and power rail.)
the noise could be caused by a leakage of very tiny current between the tracks....
J248 is not seen in the schematic on page 37.
#21 might be of help.
pardon me if I am wrong.
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FYI
if C301 can not be lift up,
try
on the copper side
cut open the signal track right next to C301 +leg joint,
cut open the signal track right next to CN52 L joint,
solder a wire from CN52 L joint to C301 +leg joint,
ground the empty signal track by soldering it to CN52 ground joint.
this will have no change on the component side
and L signal will be kept away from the power rail.
if C301 can not be lift up,
try
on the copper side
cut open the signal track right next to C301 +leg joint,
cut open the signal track right next to CN52 L joint,
solder a wire from CN52 L joint to C301 +leg joint,
ground the empty signal track by soldering it to CN52 ground joint.
this will have no change on the component side
and L signal will be kept away from the power rail.
Yes there is a lot white glue holding the capacitors. I scraped some off the worst without any improvement (from C301), I will try to remove it completly. And perhaps from the other caps as well.
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Progress! 🙂
After coming home from the summer vacation I had the chance to look at the amp again.
I tried Alexchoi suggestion with C301, nothing changed. Still thanks for that suggestion Alexchoi.
But I have suspected the Q301 for a while since it is the first active part in the signal chain and when grounding the signal input, the noise disappears. So I swapped places of Q303 & Q301 from the left channel with Q302 & Q304 from the right channel and guess what. The noise moved to the right channel!
So one or both of the transistors (originally at Q303 & Q301) is broken
The part name is TR KTC3200GR.
So I need to get me a good pair of those.
Question is: Do they need to be a matched pair? And are there any reliable source of those transistors?
I found this on ebay: 10pcs Transistor KTC3200GR 2SC3200 C3200GR KC3200GR TO-92 | eBay
Perhaps this one is better, Its In EU meaning faster shipping and less problems with customs.
C3200GR KTC3200GR KEC Tranzystor - north.pl
After coming home from the summer vacation I had the chance to look at the amp again.
I tried Alexchoi suggestion with C301, nothing changed. Still thanks for that suggestion Alexchoi.
But I have suspected the Q301 for a while since it is the first active part in the signal chain and when grounding the signal input, the noise disappears. So I swapped places of Q303 & Q301 from the left channel with Q302 & Q304 from the right channel and guess what. The noise moved to the right channel!
So one or both of the transistors (originally at Q303 & Q301) is broken
The part name is TR KTC3200GR.
So I need to get me a good pair of those.
Question is: Do they need to be a matched pair? And are there any reliable source of those transistors?
I found this on ebay: 10pcs Transistor KTC3200GR 2SC3200 C3200GR KC3200GR TO-92 | eBay
Perhaps this one is better, Its In EU meaning faster shipping and less problems with customs.
C3200GR KTC3200GR KEC Tranzystor - north.pl
It would be better is you bought a matched pair or bought a lot of them and tested for two near each other in gain.
Input long-tail pairs effect the output offset if there is no other means of stabilizing it.
I am not an eBay buyer so of the two I would chose the EU link.
Input long-tail pairs effect the output offset if there is no other means of stabilizing it.
I am not an eBay buyer so of the two I would chose the EU link.
Realized after i posted that the EU link wont ship outside Poland. To bad.. Guess I have to search around a bit more. 2SC2240-GR should also be compatible.
The "GR " tag signify,s the lower gain version 0f the 2SC2240 audio BJT ,other lettering would be a higher gain (usually ).
2240=200/700Hfe
2240GR=220/400Hfe
2240BL=350/700Hfe
But that's in my old original manufacturers book --goodness knows where they originate from now.
EU-
2SC2240 - Transistor: bipolar,NPN | 120V; 100mA; 300mW; TO92 | TME - Elektroniskas daļas (WFS)
As their specifications are identical otherwise , you could buy a pile of standard 2240
2240=200/700Hfe
2240GR=220/400Hfe
2240BL=350/700Hfe
But that's in my old original manufacturers book --goodness knows where they originate from now.
EU-
2SC2240 - Transistor: bipolar,NPN | 120V; 100mA; 300mW; TO92 | TME - Elektroniskas daļas (WFS)
As their specifications are identical otherwise , you could buy a pile of standard 2240
Yes its okay ,as I said the only difference in the end lettering is the amount of gain --all other specifications are identical.
