I have a low level hum/buzz with the above amps that I am trying to get rid of.
With both inputs on the power amp shorted or one channel connected to my CD player (other shorted) though the ID1P pre,it is near silent.Its only when both channels are connected that I get the hum which sounds to me like there is a ground loop somewhere.
Lifting the ground on the right channel of the interconnect to the power amp made the left channel slightly better but not by much,so I tried disconnecting the shield to each channel on the pcb and running a wire direct from 0v between the caps to the RCA's but this made it much worse.A 10 ohm resistor in ground of one or both channels interconnects made no difference
All the electrolytic caps have recently been replaced except the two on the soft start board/new bridge rectifier(I would guess the amps are around 20 years old)
I was thinking that there could be a fault with the pre-amp but my other ID power amp is fine with very little noise at all !
Any suggestions ?
Cheers............
ID1P
ID75
Other power amp
Paul.
With both inputs on the power amp shorted or one channel connected to my CD player (other shorted) though the ID1P pre,it is near silent.Its only when both channels are connected that I get the hum which sounds to me like there is a ground loop somewhere.
Lifting the ground on the right channel of the interconnect to the power amp made the left channel slightly better but not by much,so I tried disconnecting the shield to each channel on the pcb and running a wire direct from 0v between the caps to the RCA's but this made it much worse.A 10 ohm resistor in ground of one or both channels interconnects made no difference
All the electrolytic caps have recently been replaced except the two on the soft start board/new bridge rectifier(I would guess the amps are around 20 years old)
I was thinking that there could be a fault with the pre-amp but my other ID power amp is fine with very little noise at all !
Any suggestions ?
Cheers............
ID1P
An externally hosted image should be here but it was not working when we last tested it.
ID75
An externally hosted image should be here but it was not working when we last tested it.
Other power amp
An externally hosted image should be here but it was not working when we last tested it.
Paul.
Hi,
See no one has replied
With the usual warning of just trying this for purposes of elimination have you tried isolating mains lead grounds. Perhaps try first the CD player and then the preamp, possibly both together.
Also read,
http://www.diyaudio.com/forums/showthread.php?s=&threadid=129160
See no one has replied
With the usual warning of just trying this for purposes of elimination have you tried isolating mains lead grounds. Perhaps try first the CD player and then the preamp, possibly both together.
Also read,
http://www.diyaudio.com/forums/showthread.php?s=&threadid=129160
Hi Mooly,
I've just read through the thread on the link you provided and it doesn't really sound like a deep pure mains frequency hum,there is definitely harmonics/buzzing as well.
Lifting the mains earth on either the cd/pre or both at the same time doesn't change it.
If I turn off the cd player it says the same.Switching off the pre/or connecting just the power amp with inputs open results in more off a hum sound (buzz the same)
Touching just the grounds of the interconnects to the power amp with system connected up as normal=no change.
Disconnecting the power amp from the wall socket as well when the caps are discharging (it runs for a couple of mins after turning off) and now the hum is slightly louder again......don't know if this means anything.
I hope the above makes some sense !
Paul.
I've just read through the thread on the link you provided and it doesn't really sound like a deep pure mains frequency hum,there is definitely harmonics/buzzing as well.
Lifting the mains earth on either the cd/pre or both at the same time doesn't change it.
If I turn off the cd player it says the same.Switching off the pre/or connecting just the power amp with inputs open results in more off a hum sound (buzz the same)
Touching just the grounds of the interconnects to the power amp with system connected up as normal=no change.
Disconnecting the power amp from the wall socket as well when the caps are discharging (it runs for a couple of mins after turning off) and now the hum is slightly louder again......don't know if this means anything.
I hope the above makes some sense !
Paul.
You will know from the other thread how difficult hum problems can be to eradicate, particularly without actually being able to see how it's all wired up. Harmonics usually are introduced through wiring problems within the item. A buzz at 100 hz (twice mains frequency) points to the ripple on the PSU somehow getting into the signal line, either directly or through the grounds within the amp.
Paul,
I will look in again tomorrow, I'll have a think
When you pull the mains plug on the power amp, if it still buzzes it has to be coming in via the inputs. What is very odd is you say your other power amp is OK. These things can really have you chasing your tail.
Go over everything slowly -- recheck from the start.
If the power amp is OK with shorting plugs and buzzes with a passive preamp -- dunno really will have to think on that one.
I will look in again tomorrow, I'll have a think
When you pull the mains plug on the power amp, if it still buzzes it has to be coming in via the inputs. What is very odd is you say your other power amp is OK. These things can really have you chasing your tail.
Go over everything slowly -- recheck from the start.
If the power amp is OK with shorting plugs and buzzes with a passive preamp -- dunno
really will have to think on that one.Mooly said:
Yes it does.When I switched the power amp off at the wall earlier after I had killed the power with the front switch (with the pre-amp switched off as well) I noticed the buzz got a little louder.
I have never done this before as I usually leave the pre-amp powered up.
The buzz is there from when you switch the power amp on,but gets louder after the soft start has kicked in (approx 5 seconds)
Paul.
Really have to go but do try this. You say your switching off at the wall. That's not the same as pulling the plug as the earth pins are still connected. Switch off at the front then quickly remove the wall plugs. Does it still buzz. Try it a few times with preamp on and off, mains lead plugged in and not.
Is it any trouble to go back to the passive preamp to test. That can't buzz ? No posiblo
See how you have got on tommorrow.
Is it any trouble to go back to the passive preamp to test. That can't buzz ? No posiblo
See how you have got on tommorrow.
Mooly said:Paul,
I will look in again tomorrow, I'll have a think
When you pull the mains plug on the power amp, if it still buzzes it has to be coming in via the inputs. What is very odd is you say your other power amp is OK
Many thanks........its appreachiated.
When you switch off/pull the plug the buzz is reduced quite a bit but still not to what I would call a reasonable level and no where near to what it is when the inputs are shorted or on the other amp when connected up..........
Paul.
Mooly said:Really have to go but do try this. You say your switching off at the wall. That's not the same as pulling the plug as the earth pins are still connected. Switch off at the front then quickly remove the wall plugs. Does it still buzz. Try it a few times with preamp on and off, mains lead plugged in and not.
Is it any trouble to go back to the passive preamp to test. That can't buzz ? No posiblo
See how you have got on tommorrow.
Ah right.......with you.Will have another play tomorrow and let you know.
Paul.
............another dollar.
I've connected up the power amp to my passive pre (not really a pre,just a 22k pot with in/out phonos)
Compared to the power amp running on its own with inputs open, there is a bit more buzz/slightly less hum.
Switching off at the front or pulling the plug from the wall results in total silence.
Doing the above with out the passive connected results in a bit of hiss until the caps discharge,but no buzz/hum.
Paul.
I've connected up the power amp to my passive pre (not really a pre,just a 22k pot with in/out phonos)
An externally hosted image should be here but it was not working when we last tested it.
Compared to the power amp running on its own with inputs open, there is a bit more buzz/slightly less hum.
Switching off at the front or pulling the plug from the wall results in total silence.
Doing the above with out the passive connected results in a bit of hiss until the caps discharge,but no buzz/hum.
Paul.
Right then,
Lets try and get this, at least so we understand whats going on Your going to think I'm trying to find fault here, I know how it sounds. Just trying to cover all bases.
A few thoughts then,
Is that passive preamp in a plastic or a metal diecast box ? It's kind of 50/50 in the picture could be either.
With shielded leads a passive can't hum or buzz BUT it can still be prone to picking up hum from the magnetic field from the transformers in the amp inducing a current in any wiring.
Now then, with shorting plugs in the power amp you say it's silent. One more thing on this, with shorting plugs in the amp is it still silent if you connect the two grounds of the phono outers together ? An internal amp problem could cause it to be silent until the two input grounds actually connect together.
Back to the passive being in circuit. When you switch off you say it's silent. Depending on the test with the shorting plugs that points to induced hum. Does it go worse or better if you move the preamp near the amp etc.
Lets try and get this, at least so we understand whats going on
Your going to think I'm trying to find fault here, I know how it sounds. Just trying to cover all bases.A few thoughts then,
Is that passive preamp in a plastic or a metal diecast box ? It's kind of 50/50 in the picture
could be either.With shielded leads a passive can't hum or buzz BUT it can still be prone to picking up hum from the magnetic field from the transformers in the amp inducing a current in any wiring.
Now then, with shorting plugs in the power amp you say it's silent. One more thing on this, with shorting plugs in the amp is it still silent if you connect the two grounds of the phono outers together ? An internal amp problem could cause it to be silent until the two input grounds actually connect together.
Back to the passive being in circuit. When you switch off you say it's silent. Depending on the test with the shorting plugs that points to induced hum. Does it go worse or better if you move the preamp near the amp etc.
No worries........the passive is a plastic box.
Having it sat on top the amp or far away doesn't change the noise.
I've just connected the two grounds together with the inputs shorted and the buzz/hum comes back.
When doing this I also noticed a higher pitched buzz from inside the amp at the back which seemed to come from the relay for the switch.Switched off quickly and removed the link between the two shorting plugs and it gone now......must be just coincidence.....the things been switched on/off alot over the last two days !
The transformer (must be at least 1k va) does buzz quite a bit more in the ID75 then the other amp.I did think about rotating the transformer so the leadout wires were pointing away from the circuit boards...........clutching at straws ?
Paul.
Having it sat on top the amp or far away doesn't change the noise.
I've just connected the two grounds together with the inputs shorted and the buzz/hum comes back.
When doing this I also noticed a higher pitched buzz from inside the amp at the back which seemed to come from the relay for the switch.Switched off quickly and removed the link between the two shorting plugs and it gone now......must be just coincidence.....the things been switched on/off alot over the last two days !
The transformer (must be at least 1k va) does buzz quite a bit more in the ID75 then the other amp.I did think about rotating the transformer so the leadout wires were pointing away from the circuit boards...........clutching at straws ?
Paul.
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