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Humming sound from my audio system

Rosenild

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Dear all.


I have recently installed a phono amplifier (Pro-Ject Tube Box S2) using my new MC cartridge (Denon 103R). I use a Garrard 401 turntable with a SME 3012. It is amplified by a Sansui AU9500 integrated amplifier. Using the Pro-Ject manual and searching on the internet, I have installed the phono amplifier with 60 gain and 470 ohms.

The sound is great, but I think there are a few problems that needs to be raised.

First of all it seems after playing a record, a humming sound begins to appear. I tried to find the problem, but I am no technical expert. Therefore I would be delighted if you could please comment on the situation.

- There are no humming sounds when I play digitally, that is without the turntable.
- There are no humming sounds when I play the records without the phono amplifier, however I need to turn the volume up dramatically.
- If I turn off my turntable and my phono amplifier is connected, the humming is present but more discreet.
- If I turn off my turntable and my phono amplifier, the humming sound is not present at all.

Additonal actions/thoughts:

- I have installed the phono amplifier at 100 ohms, but after a while the humming reappear.
- I have tried to reconnect the ground wire. It is an old ground wire and the copper seems teared and fragile. Perhaps that is the problem?
- I have a simple power rail. Not sure if that has anything to do with this specific situation. Would it be better to invest in a good power rail?
- If I turn on "LOUDNESS" on my Sansui and turn up the volume I will immediately get feedback so I have to turn the volume down. Speakers are approximately 1-3 meter from the turntable. The turntable is approximately 1 meter from the amplifier.

Thank you very much in advance for your time and considerations.

Best regards.
 

DVDdoug

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I have installed the phono amplifier with 60 gain and 470 ohms...

...I have installed the phono amplifier at 100 ohms, but after a while the humming reappear.
Standard moving magnet or moving iron phono cartridges expect a 47k (47,000) Ohm load (and some small capacitance, some of which comes from the cables).

The combination of high impedance and high gain makes it prone to hum. (Welcome to the analog world. :rolleyes:)

Moving coil cartridges (usually more expensive) are lower impedance, but they are also lower output so they need more gain (a special preamp or a preamp with switchable gain & impedance) so it's a bit of a trade-off.

The Gerrard turntable may be poorly shielded, but I'm NOT going to suggest upgrading the turntable because that may not be the problem.

- I have tried to reconnect the ground wire. It is an old ground wire and the copper seems teared and fragile. Perhaps that is the problem.
That could be it. A good ground wouldn't hurt.

It could also be a broken ground in the RCA connections between the turntable and preamp.

There are no humming sounds when I play the records without the phono amplifier, however I need to turn the volume up dramatically.
You need a preamp because you need about 40dB of gain with a MM cartridge (at mid-frequencies) and RiAA playback equalization.

BUT, your integrated amplifier has one built-in (the "phono inputs"). If you are using an external preamp you have to use a line input (maybe "tape" or "aux"). Don't use both preamps! The RIAA EQ reverses the recording EQ by boosting the bass and cutting the highs. Without it you'll get all highs and no bass (and without the amplification, a weak-useless signal.)

If you go through two preamps you'll get the opposite problem... Too much bass and no highs, so any low frequency hum will also be over-amplified. Plus you'll probably get distortion from too-hot of a signal. And with all of that low-frequency gain you are more likely to get low-frequency feedback.

- I have a simple power rail. Not sure if that has anything to do with this specific situation. Would it be better to invest in a good power rail?
Although it's probably power line hum, that's very unlikely to help. Power is 50Hz AC in Europe, and 60Hz AC in the U.S., and you can't filter
THAT out (although it is converted to DC and filtered inside the equipment).

- If I turn on "LOUDNESS" on my Sansui and turn up the volume I will immediately get feedback so I have to turn the volume down. Speakers are approximately 1-3 meter from the turntable. The turntable is approximately 1 meter from the amplifier.
The loudness switch is supposed to boost bass at low volumes to compensate for the ear's "equal loudness curves"... When you turn-down the volume it sounds like you've turned-down the bass even more and the loudness switch compensates for that. It shouldn't have any effect at high volume settings. (It's the rotation of the volume control, not the loudness of the signal.)

Anyway... The feedback comes from the speakers and back into the turntable. (Welcome to analog again. :rolleyes:) It's acoustic/mechanical, not electrical. Moving the turntable farther from the speakers should help, or maybe some foam or something under the turntable. Sometimes the vibrations can feed-back through a wood floor. And of course, don't put the turntable on top of the speaker. Again, it MAY be related to the "cheap turntable".
 
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Rosenild

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Standard moving magnet or moving iron phono cartridges expect a 47k (47,000) Ohm load (and some small capacitance, some of which comes from the cables).

The combination of high impedance and high gain makes it prone to hum. (Welcome to the analog world. :rolleyes:)

Moving coil cartridges (usually more expensive) are lower impedance, but they are also lower output so they need more gain (a special preamp or a preamp with switchable gain & impedance) so it's a bit of a trade-off.

The Gerrard turntable may be poorly shielded, but I'm NOT going to suggest upgrading the turntable because that may not be the problem.


That could be it. A good ground wouldn't hurt.

It could also be a broken ground in the RCA connections between the turntable and preamp.


You need a preamp because you need about 40dB of gain with a MM cartridge (at mid-frequencies) and RiAA playback equalization.

BUT, your integrated amplifier has one built-in (the "phono inputs"). If you are using an external preamp you have to use a line input (maybe "tape" or "aux"). Don't use both preamps! The RIAA EQ reverses the recording EQ by boosting the bass and cutting the highs. Without it you'll get all highs and no bass (and without the amplification, a weak-useless signal.)

If you go through two preamps you'll get the opposite problem... Too much bass and no highs, so any low frequency hum will also be over-amplified. Plus you'll probably get distortion from too-hot of a signal. And with all of that low-frequency gain you are more likely to get low-frequency feedback.


Although it's probably power line hum, that's very unlikely to help. Power is 50Hz AC in Europe, and 60Hz AC in the U.S., and you can't filter
THAT out (although it is converted to DC and filtered inside the equipment).


The loudness switch is supposed to boost bass at low volumes to compensate for the ear's "equal loudness curves"... When you turn-down the volume it sounds like you've turned-down the bass even more and the loudness switch compensates for that. It shouldn't have any effect at high volume settings. (It's the rotation of the volume control, not the loudness of the signal.)

Anyway... The feedback comes from the speakers and back into the turntable. (Welcome to analog again. :rolleyes:) It's acoustic/mechanical, not electrical. Moving the turntable farther from the speakers should help, or maybe some foam or something under the turntable. Sometimes the vibrations can feed-back through a wood floor. And of course, don't put the turntable on top of the speaker. Again, it MAY be related to the "cheap turntable".

Hello and thank you for your answer.

I'm using the "Tuner"-line in. Is that a good choice of line in or will it interfere with the built-in preamp?

I will be getting a new turntable soon. I think it's the ground wire that is the problem, but I'm not sure. Can the cables from an old Garrard 401 be the potential cause of general poor sound and humming?
 

MaxwellsEq

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Unfortunately, the first and only rule of hum in your system is it is unique to you and your circumstances! Every situation is different, so there are no "just do this" fixes.

But there are some common things to work through. Hum generally comes from one of two sources - a) mains noise being induced inside a device with poor or faulty circuitry and b) differences between "grounds" allowing signals to travel via routes you don't intend. If we assume none of your kit is poor(ly), then b) is most likely.

Hum is often worse when you have lots of gain, which you do with cartridge outputs: MM needs a lot of gain, MC needs huge amounts of gain.

If you have the kit widely dispersed or plugged into lots of different mains sockets, try plugging everything into one distribution board.

Does the hum change when the platter is turning?

Power off and disconnect everything from the integrated amp (except the speakers). Is there any hum?

Plug the turntable into the integrated amp phono socket and connect the arm's ground wire to the integrated amp. It will be quieter but is there hum? There should only be the turntable and Integrated amp powered.
 

AnalogSteph

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- I have tried to reconnect the ground wire. It is an old ground wire and the copper seems teared and fragile. Perhaps that is the problem?
Quite possibly. That is the tonearm ground. Without it being properly connected, some hum is expected, and probably more so when the platter motor is operating (a synchronous AC job). If it's a bare wire, you could try stripping a bit more of the insulation and cutting off the tired old end. Twist and optionally tin the new end with some solder to prevent oxidation.
 
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Rosenild

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Unfortunately, the first and only rule of hum in your system is it is unique to you and your circumstances! Every situation is different, so there are no "just do this" fixes.

But there are some common things to work through. Hum generally comes from one of two sources - a) mains noise being induced inside a device with poor or faulty circuitry and b) differences between "grounds" allowing signals to travel via routes you don't intend. If we assume none of your kit is poor(ly), then b) is most likely.

Hum is often worse when you have lots of gain, which you do with cartridge outputs: MM needs a lot of gain, MC needs huge amounts of gain.

If you have the kit widely dispersed or plugged into lots of different mains sockets, try plugging everything into one distribution board.

Does the hum change when the platter is turning?

Power off and disconnect everything from the integrated amp (except the speakers). Is there any hum?

Plug the turntable into the integrated amp phono socket and connect the arm's ground wire to the integrated amp. It will be quieter but is there hum? There should only be the turntable and Integrated amp powered.

Thank you for your answer.

It is very certain that it's only when the preamp is turned on. Otherwise there are only a light hum which I would consider a part of the "analogue experience".
 

MaxwellsEq

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It is very certain that it's only when the preamp is turned on. Otherwise there are only a light hum which I would consider a part of the "analogue experience".
It seems to be a grounding issue. Can you confirm:
a) that there are no other connectors plugged into the integrated amp (including antenna). I.e. there are only two RCA cables coming into the tuner socket and two speaker wires leaving
b) what happens if you turn on the phono preamp when there are no wires plugged into it from the turntable (as above with nothing else plugged into the integrated amp)
 

LTig

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Hello and thank you for your answer.

I'm using the "Tuner"-line in. Is that a good choice of line in or will it interfere with the built-in preamp?
Yes
I will be getting a new turntable soon.
You should solve the hum problem first. As I see it it comes either from the phono preamp, the turntable or the wiring.

Disconnect the turntable completely. If there is no hum then the preamp and its wiring to the amplifier is fine.

Then connect the preamp without the extra ground wire. Listen to the hum. Connect the ground wire. Does the hum stays as loud as it was before? If yes then the ground wire is broken.
 
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Rosenild

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It seems to be a grounding issue. Can you confirm:
a) that there are no other connectors plugged into the integrated amp (including antenna). I.e. there are only two RCA cables coming into the tuner socket and two speaker wires leaving
b) what happens if you turn on the phono preamp when there are no wires plugged into it from the turntable (as above with nothing else plugged into the integrated amp)
a) I have an Apple Airplay connected to AUX input.
b) Nothing.

The humming is not appearing to begin with, but after playing a few records, the hum appears.
 
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Rosenild

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Hello everyone.

I have been testing and trying everything. Thank you for all your advice.

The old SME 3012 tonearm has not yet been rewired. I will receive components and cables in a short while and make an appointment with a relevant technician. I hope this is can fix some of it.
 
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Rosenild

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Maybe the sound is more of a swishing, "whoosh" sound like a mellow wind or breeze through a microphone.
 

MaxwellsEq

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Maybe the sound is more of a swishing, "whoosh" sound like a mellow wind or breeze through a microphone.
A wooshing noise? Not a hum? It comes on after a while?

This no longer sounds like an earth problem but something faulty.
 

Apesbrain

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Maybe the sound is more of a swishing, "whoosh" sound like a mellow wind or breeze through a microphone.
Sorry, I missed this comment. Your Pro-ject phono pre-amp is rated to deliver an SNR of 75 dB at 60 dB gain which is what your 103R needs, but it's not likely that it meets that specification. As tested in this ASR review, the unit could not hit 75 dB of dynamic range when set to 40 dB gain. At 60 dB gain, it will be as much as 20 dB noisier. You are going to hear that as a constant, white noise "whoosh" sound at all but the lowest playback volume.
 
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Rosenild

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I have tried to make a recording of the sound. Hopefully it is easier to know what is at play.
 

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somebodyelse

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That doesn't sound like a ground problem, which would be more like a constant tone. Inherent noise is usually more constant. This seems more like a poor contact or fault somewhere, whether inside the phono amp or in one of the connections to it. Does it change as you move any of the cables?
 

LTig

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I agree. Definitely no hum. I once bought a mixer where one channel did sound the same right from the start. It got repaired on warranty so I don' t know the exact cause.
 

Cwopete5

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Does the hum get worse when the volume is turned up? Reason I am asking is because it could be caused by feedback via your speakers. Have you tried moving your speakers further away from your turntable? Also note that turntables are very susceptible to any vibration. I had a similar hum issue with an older turntable that I resolved by using Vibrapods under the feet of the turntable. http://www.vibrapod.com/
 
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Rosenild

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Does the hum get worse when the volume is turned up? Reason I am asking is because it could be caused by feedback via your speakers. Have you tried moving your speakers further away from your turntable? Also note that turntables are very susceptible to any vibration. I had a similar hum issue with an older turntable that I resolved by using Vibrapods under the feet of the turntable. http://www.vibrapod.com/

Indeed it does.

Perhaps it is feedback. I will try and get back to you asap.

If I play digital through the speakers it doesn't present the noise though.
 
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