hi:
I would be greatly appreciated if anyone here can help me. I have a vintage amplifier and it has hum noise from both speaker. I replaced all the electrolytic capacitors (including the power supply cap too). and there are still hum noise. anyone have any idea why that happen? my amp have pre-out/power-in jacks. and I tried the pre-out connected to another power amp. and it was fine. So I guess the pre-amplifier section is fine. So what generally cause the hum noise other than the electrolytic capacitors???
I would be greatly appreciated if anyone here can help me. I have a vintage amplifier and it has hum noise from both speaker. I replaced all the electrolytic capacitors (including the power supply cap too). and there are still hum noise. anyone have any idea why that happen? my amp have pre-out/power-in jacks. and I tried the pre-out connected to another power amp. and it was fine. So I guess the pre-amplifier section is fine. So what generally cause the hum noise other than the electrolytic capacitors???
I think it is ground issue. I check the recifier bridge and it looked ok. and there is a switch at the back of the amp that allow me to use pre-out and main-in for preamp out and power amp input. So I switch to pre-out and pwr-in. the level of hum/buzz change.
So how do I solve the ground issue?
Yes, the hum/buzz is loud enough that if I am a meter away from the speaker, I can hear it.
So how do I solve the ground issue?
Yes, the hum/buzz is loud enough that if I am a meter away from the speaker, I can hear it.
Just to narrow down possible causes:
(1) with NO inputs - i.e., NOTHING except he speakers - plugged into the amp, does it still hum?
(2) does it have an earth, either separate, or as part of the mains wiring (3 pin plug) ?
If it has no earth (2 pin plug) try reversing the plug in the socket & see if that makes any difference.
Also, try earthing it - it may have an earth connection on the back - usually close to the Phono input sockets. If not, the outter/screen connection of any of the input sockets is circuit ground, and will make a suitable earth point.
N.B.: Don't make or unmake connection with the amplifier ON, Always switch it off while you are changing the plug arrangements, or you may destroy a loudspeaker.
(1) with NO inputs - i.e., NOTHING except he speakers - plugged into the amp, does it still hum?
(2) does it have an earth, either separate, or as part of the mains wiring (3 pin plug) ?
If it has no earth (2 pin plug) try reversing the plug in the socket & see if that makes any difference.
Also, try earthing it - it may have an earth connection on the back - usually close to the Phono input sockets. If not, the outter/screen connection of any of the input sockets is circuit ground, and will make a suitable earth point.
N.B.: Don't make or unmake connection with the amplifier ON, Always switch it off while you are changing the plug arrangements, or you may destroy a loudspeaker.
I have already tried all the thing that you mentioned. I tried nothing is connected but the speaker only. still hum/buzz. I tried the pre-out to another power amp. it is fine. no hum, So I believe it is somewhere in the power amp circuit that generate the hum/buzz. For this amp, the pre amp and power amp have their own individual power supply circuit. well, anyway, I tried all the possible situation you said already and there are still hum/buzz.
there is a couple of things more
A) did you change may be also any rca input plugs ???? cause if you did there is a chance that the original was isolated from the box and yours are not.
B) when you changed the psu caps is there any chance that you made some mistake with the grounds ???? mistake can be :
1)forget to connect one of ground cables
2)connect some ground cable to the wrong place
3) adding some gound cable that wasnt there in the first place ( like for example from common of both capacitors to the box ground
C) did you maybe changed the power cord that goes to mains from existing 2pin cable to a new one three pin ???? if so ground will require other topology
D) Finally the only thing you need to find out is any of the input ground of your amp comes in contact with the ground of the box ...this will solve the problem
A) did you change may be also any rca input plugs ???? cause if you did there is a chance that the original was isolated from the box and yours are not.
B) when you changed the psu caps is there any chance that you made some mistake with the grounds ???? mistake can be :
1)forget to connect one of ground cables
2)connect some ground cable to the wrong place
3) adding some gound cable that wasnt there in the first place ( like for example from common of both capacitors to the box ground
C) did you maybe changed the power cord that goes to mains from existing 2pin cable to a new one three pin ???? if so ground will require other topology
D) Finally the only thing you need to find out is any of the input ground of your amp comes in contact with the ground of the box ...this will solve the problem
I did not change any RCA plugs/jacks. they are all original
I do not think I make mistake for the ground for the power supply unit. However, I will double check it in the next few day to verify that. actually, I think this is very good suggestion.
It is 2 pin cable. I did not change it at all
I will also try to find out if there are anywhere in the amp signal circuit ground to the chassis.
by the way, if I decide to buy a osillscope to help solving the problem. how do I do it??
I do not think I make mistake for the ground for the power supply unit. However, I will double check it in the next few day to verify that. actually, I think this is very good suggestion.
It is 2 pin cable. I did not change it at all
I will also try to find out if there are anywhere in the amp signal circuit ground to the chassis.
by the way, if I decide to buy a osillscope to help solving the problem. how do I do it??
someway somehow
people think that osciloscopes make miracles !!!!!!!!
A scope will never tell you what causes the problem .It might show you a grafic about this buzz but it will never tell or help you solving this out .
After you are done with the buzz a scope , a signal generator, and a dummy load will tell you a hell of a lot of things about your amp and may be others about performance ,frequency response , speed , power, distortion and others
regards sakis
people think that osciloscopes make miracles !!!!!!!!
A scope will never tell you what causes the problem .It might show you a grafic about this buzz but it will never tell or help you solving this out .
After you are done with the buzz a scope , a signal generator, and a dummy load will tell you a hell of a lot of things about your amp and may be others about performance ,frequency response , speed , power, distortion and others
regards sakis
>> A scope will never tell you what causes the problem
If you know how to use it, it certainly WILL help a great deal.
If you understand what you are looking at, you can tell a myriad of things about the cause and source of the noise.
It's just an expensive tool, and maybe not worth it for one or two diagnostic jobs.
If you know how to use it, it certainly WILL help a great deal.
If you understand what you are looking at, you can tell a myriad of things about the cause and source of the noise.
It's just an expensive tool, and maybe not worth it for one or two diagnostic jobs.
I guess I will buy a used scope at ebay. something less than $200. anyway, I have the circuit diagram for my amp. what I am going to do is trace the signal path from power amp input to the speaker output and check which stage introduce hum/buzz. then I will look in the diagram carefully and see if I can find where cause the hum. Is this sound like the right approach??
hi sakis:
I have not yet tried your tips. I was moving in the past two days. and thing are still in a mess. I will do it in the next few days. and then I will let you know. by the way, thanks a lot for your advice. I actually love my amp so much. especially, the physical appearance, and the sound of it. the sound is like each piece of air molecule standing in front of you and singing to you. but the hum sound make me feel bad
I have not yet tried your tips. I was moving in the past two days. and thing are still in a mess. I will do it in the next few days. and then I will let you know. by the way, thanks a lot for your advice. I actually love my amp so much. especially, the physical appearance, and the sound of it. the sound is like each piece of air molecule standing in front of you and singing to you. but the hum sound make me feel bad
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