Hi,
recently recapped this entire amp + new output transistors (matched within tolerance of 10).
The amp still hisses in the speakers. It's only audible at max volume. It's very quiet from Tuner/CD outputs, but very loud from phono section (nothing connected).
I heard this could be caused by transistors before the main stage, there are couple of those in the preamp, they run rather toasty (60-70 degrees) and the board is discolored around them.
Anyone has any tips? The Pre-amp transistors are 2SA1124 + 2SC2632. I can replacement ones by On-semi for pretty cheap if needed.
Thanks!
recently recapped this entire amp + new output transistors (matched within tolerance of 10).
The amp still hisses in the speakers. It's only audible at max volume. It's very quiet from Tuner/CD outputs, but very loud from phono section (nothing connected).
I heard this could be caused by transistors before the main stage, there are couple of those in the preamp, they run rather toasty (60-70 degrees) and the board is discolored around them.
Anyone has any tips? The Pre-amp transistors are 2SA1124 + 2SC2632. I can replacement ones by On-semi for pretty cheap if needed.
Thanks!
Hi, I have the same amp HK 6650R, giving a loud pop in right channel during turn ON and OFF. Any suggestion will be highly appreciated. Thanks
This would be very normal you need to put shorting plugs on the phono inputs
You would never have the volume control at full on phono so you are not making a real world test.
Plug in a turntable with cartridge play a record at normal level then lift the pickup off the record what is the background noise like
Trev
You would never have the volume control at full on phono so you are not making a real world test.
Plug in a turntable with cartridge play a record at normal level then lift the pickup off the record what is the background noise like
Trev
ThatDavid , did you take latala,s advice ?
Well yes those active devices could be improved upon ( lower noise ) but only you can judge that its down to circuit design and whether you feel aggrieved enough by the noise.
The noise figures apply to an Ic of 1ma but you say they run hot ? ,again this is down to design philosophy but maximum is 1W not enough in my view to blacken the circuit board .
The heat would need to be transmitted through the legs of the BJT and would cause a softening of the soldered joints .
Are you sure its not a resistor that is causing the heat?
The plastic casing of the BJT would need to be in full contact with the PCB to cause a blackening.
Well yes those active devices could be improved upon ( lower noise ) but only you can judge that its down to circuit design and whether you feel aggrieved enough by the noise.
The noise figures apply to an Ic of 1ma but you say they run hot ? ,again this is down to design philosophy but maximum is 1W not enough in my view to blacken the circuit board .
The heat would need to be transmitted through the legs of the BJT and would cause a softening of the soldered joints .
Are you sure its not a resistor that is causing the heat?
The plastic casing of the BJT would need to be in full contact with the PCB to cause a blackening.
Dear Dancan2, Thanks you so much for your kind reply. As I am not much knowledgeable, but I can do a bit of soldering and so on, could you please advise me which one is the muting circuit. Really appreciated. Thanks
Hello Sam ,the muting circuit is on the output of the amp (some are on the input ) .
I am looking at the diagram after logging into hi-fi engine as it has a better quality reproduction of the service manual .
As is normal now FET,s are used in this position checkout-
Q805 and Q806 fets and Q803 and Q804 ( which are normal BJT,s ).
Now while you can test normal transistors using a digital meter normally FETS are tested using a digital active device tester which I have but I realise you might not so click on -
How to Check a MOSFET Using a Digital Multimeter | Homemade Circuit Projects
Hope this helps Sam .
I am looking at the diagram after logging into hi-fi engine as it has a better quality reproduction of the service manual .
As is normal now FET,s are used in this position checkout-
Q805 and Q806 fets and Q803 and Q804 ( which are normal BJT,s ).
Now while you can test normal transistors using a digital meter normally FETS are tested using a digital active device tester which I have but I realise you might not so click on -
How to Check a MOSFET Using a Digital Multimeter | Homemade Circuit Projects
Hope this helps Sam .
Sounds like a DC offset issue. This may require checking the signal path for sections with excessive DC, starting at the output (ideally compare L and R channels). Usually just a dead (excessively leaky) electrolytic coupling cap. Post where you find something unusual on the schematic and we may be able to say someting more specific.